An-Najah National University  

Faculty of Graduate Studies 

 

 
Assessment of Milk Quality and Antibiotic 

Residues Detection in Milk Samples from 

Palestinian Market 

 
By 

Dalal Hamdan 

 

Supervisor 

Prof. Ansam Sawalha 

Dr. Amjad IzzEldein Hussein 

 
This Thesis is Submitted in Partial Fulfillment of the Requirements for 

the Degree of Master of Environmental Science, Faculty of Graduate 

Studies, An-Najah National University, Nablus, Palestine. 

2019 





iii 

Dedication 
 

First of all, my greatest gratitude to Allah 

To my patient and supportive husband Adnan 

To my lovely sons Mohammed, Ady and Laith 

To my mother and father 

To my sisters and brothers, especially lovely Saleem and his family 

for their encouragement and support during this study. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 



iv 

ACKNOWLEDGMENT 

 

    My special praises and thanks to Allah the almighty, most gracious 

and most merciful who gave me the health, strength, and patient to 

conduct this thesis.   

    I would like to express my deep thanks to my supervisor Prof. 

Ansam Sawalha and Dr. Amjad IzzEldein Hussein for their advice and 

continuous support throughout the study period. 

     Special thanks to all the technical stuff at An-Najah University for 

their help. 

     Last but not least, I am grateful and indebted to my precious family, 

my husband and sons, and for all my friends.  

 

 

 

 

 

 

 

 

 

 

 



v 

 اإلقزار

 الوٌقع أدناه هقذم الزسالة التي تحول عنٌاى:أنا 

Assessment of Milk Quality and Antibiotic residues 

Detection in Milk Samples from Palestinian Market 

ليو شارة إالخاص، باستثناء ها توت اإلنوا ىي نتاج جيذي إ الزسالة، هأقز بأى ها اشتولت عليو ىذ

أً بحث علوي أً  علوية،جزء هنيا لن يقذم لنيل أي درجة أي أً  ككل،ًأى ىذه الزسالة  ًرد،حيثوا 

 بحثي لذٍ أي هؤسسة تعليوية أً بحثية أخزٍ.

Declaration 

The work provided in this Thesis, unless otherwise referenced, is the 

researcher’s own work, and has not been submitted elsewhere for any other 

degree or qualification. 

   :Student's name                         اسن الطالب: 

  :Signature                         الخوقيع: 

 :Date                               الخاريخ: 

 

 

 

 



vi 

LIST OF ABBREVIATION 

ADI Acceptable Daily Intake 

AMRs Antibiotic Maximum Residues 

AR Antibiotic Residue 

EMA European Medicines Agency 

EU European Union 

FAO Food and Agriculture Organization United Nation 

FP Freezing Point 

HPLC High-Performance Liquid Chromatography 

Kg Kilogram 

LC Liquid Chromatography 

LC-MS/MS Liquid chromatography-tandem mass spectrometry  

Max Maximum 

Min Minimum 

MoA Minister of Agriculture 

MRL Maximum Residue Limit 

PCBS Palestinian Central Bureau of Statistics (PCBS) 

pH Hydrogen ion concentrations 

SCAMAC Standing Committee on Analytical Methods for Additives and 

Contaminants 

SNF Solid not Fat 

TS Total Solids 

UHT Ultra-Heat Treatment 

US United State 

VAPRO Vapor Pressure Osmometer 

WHO World Health Organization 

 

 



vii 

TABLE OF CONTENT 

 
Dedication ................................................................................................. iii 

Acknowledgment ...................................................................................... iv 

Declaration ................................................................................................. v 

List of abbreviation ................................................................................... vi 

Table of Content ....................................................................................... vii 

List of tables .............................................................................................. ix 

List of figures ............................................................................................. x 

Abstract ..................................................................................................... xi 

Chapter One ............................................................................................. 1 

1.1. Introduction.................................................................................... 2 
1.2. Objectives ...................................................................................... 4 
1.3. Research Problem .......................................................................... 4 

Chapter Two ............................................................................................. 6 

2. Literature Review ........................................................................... 7 
2.1.      Physiochemical Properties of Milk ........................................... 7 
2.2. Milk Production in Palestine ....................................................... 8 
2.2.1        Fat ........................................................................................ 9 
2.2.2 Protein ...................................................................................... 11 
2.2.3 Solids not fat (SNF) .................................................................. 12 
2.2.4 Lactose ...................................................................................... 12 
2.2.5        Hydrogen ion Concentration (pH) ...................................... 13 
2.2.6 Freezing point ........................................................................... 14 
2.2.7 Milk Salts (Ash) ........................................................................ 15 
2.2.8 Milk Osmolality ........................................................................ 15 
2.3. Effect of heat treatment on milk composition ............................ 16 
2.4.      Antibiotics .............................................................................. 16 
2.4.1 Antibiotic Residues in milk ....................................................... 18 
2.4.2       Antibiotic resistance ............................................................. 21 
2.4.3      Antibiotic resistance mechanism .......................................... 23 
2.4.4      Adverse effect of Antibiotic.................................................. 25 
2.4.5       Maximum Residue Limits .................................................... 25 
2.4.6      Detection of antibiotic residues in milk ................................ 26 
2.4.6.1    Classification by detection principle .................................... 27 
2.4.6.2     Classification by their degree of quantification ................... 28 

Chapter Three ........................................................................................ 31 

3 Materials and Methods ................................................................. 32 
3.1. Samples ....................................................................................... 32 



viii 

3.2. Sampling ..................................................................................... 32 
3.3. Detection of antibiotic residues ................................................... 32 
3.4. Osmolality test ............................................................................ 33 
3.5. Milk Composition Test ................................................................ 33 
3.6. pH Test ........................................................................................ 34 
3.7. Data Analysis .............................................................................. 34 

Chapter Four .......................................................................................... 35 

4 Results and discussion.................................................................. 36 
4.1. Antibiotic residue ........................................................................ 36 
4.1.1 Raw Milk Samples. ................................................................... 37 
4.1.2. Heat Treated Milk Samples ...................................................... 39 
4.2. Osmolality ................................................................................... 41 
4.3 Freezing Point .............................................................................. 46 
4.4 pH  ……………………………………………………………………………………………..47 
4.5   Milk components ........................................................................ 49 
4.5.1 Fat content ................................................................................. 49 
4.5.2 Solid not Fat (SNF) content ....................................................... 51 
4.5.3 Protein ....................................................................................... 52 
4.5.4 Lactose ...................................................................................... 53 
4.5.5 Solids (Ash) ............................................................................... 53 

Chapter Five ........................................................................................... 56 

5.1. Conclusion ................................................................................... 57 
5.2. Recommendations ........................................................................ 57 

 
 

 

 

 

 

 

 

 

 

  



ix 

LIST OF TABLES 
 

Table (1): Proximate composition of whole bovine milk from different 

countries. .................................................................................................... 7 

Table (2): In 2015, the imported and exported amounts of milk in 

thousands of dollar. .................................................................................... 9 

Table (3): The average quantity of monthly consumed milk in liters by 

Palestinian household, 2006-2011. ............................................................. 9 

Table (4): Antibiotics classification according to chemical structure. ....... 17 

Table (5): Maximum residue limits (MRL) for beta-lactams. ................... 26 

Table (6): Maximum residue limits (MRLs) for tetracycline. ................... 26 

Table (7): Advantages and disadvantages of some screening methods ..... 28 

Table (8): Presence of antibiotic residues in function of heat treatment .... 36 

Table (9): Percentage of contaminated raw milk samples in function of 

sampling time. .......................................................................................... 38 

Table (10): Percentage of contaminated raw milk samples in function of 

seasons. .................................................................................................... 38 

Table (11): Percentage of contaminated pasteurized milk samples in 

function of months. .................................................................................. 39 

Table (12): Percentage of contaminated pasteurized milk samples in 

function of seasons ................................................................................... 40 

Table (13): Percentage of contaminated pasteurized milk samples 

according to manufacturers. ..................................................................... 41 

Table (14): Milk samples osmolality according to treated method. ........... 44 

Table (15): Osmolality t-test of milk samples. .......................................... 44 

Table (16): Milk samples osmolality average according to seasons. ......... 46 

Table (17): Physiochemical properties of pasteurized milk samples 

according to seasons. ................................................................................ 54 

Table (18): Physiochemical properties of UHT milk samples according to 

seasons. .................................................................................................... 55 



x 

 List of figures 

Figure (1): Milk composition ..................................................................... 8 

Figure (2): Structure of lactose molecule .................................................. 13 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 



xi 

Assessment of Milk Quality and Antibiotic Residues Detection in Milk 

Samples from Palestinian Market 

By 

Dalal Hamdan 

Supervisor 

Prof. Ansam Sawalha 

Dr. Amjad IzzEldein Hussein 

Abstract 

This study was conducted to evaluate the quality of milk in the 

Palestinian market during a period of 8 months, from June 2017 to January 

2018. A total of 118 milk samples, of which 79 pasteurized, 14 raw and 25 

(UHT) were collected randomly from the market, using the production date 

as the collection criteria. The samples were screened for antimicrobial 

residues using Delvotest SP-NT, and their osmolality was measured using 

Vapor Pressure Osmometer (VAPRO). In addition, the pasteurized and 

UHT milk samples were evaluated for physicochemical properties (fat, 

solids not fat; SNF; protein, lactose, ash, freezing point and pH), using 

(Ultrasonic Milk Analyzer) and pH meter. The results of the antibiotic 

screening test SP-NT showed that (36%) raw milk samples contained 

antibiotic residues above MRL. Meanwhile, the pasteurized milk samples 

(27%) were contaminated with antibiotic residues above MRL. None of 25 

UHT milk samples were contaminated with antibiotic residue.  

  The average content of fat and solids in pasteurized milk samples 

was higher during winter (3.38%, 0.65%, respectively). The Freezing point 

and pH average were higher during summer (-0.5048°C, 6.78, 

respectively). Moreover, the average content of SNF, Protein and lactose 



xii 

were higher in autumn (8.04%, 2.96%, and 4.41%, respectively). The 

average content of (fat, SNF, ash, protein, lactose) and FP of pasteurized 

milk samples revealed non-significant differences (P>0.05) between 

seasons. Meanwhile, the average pH showed significant differences 

(P<0.05) between seasons. 

The results showed that the average content of fat and protein in 

UHT milk samples were higher in spring (3.28%, 3.18%, respectively), the 

average content of solids and freezing point were higher in summer 

(0.65%, -0.5087°C, respectively). Moreover, the average of SNF and pH 

were higher in autumn (8.01%, 6.74, respectively). The Physiochemical 

properties average (fat, solids not fat; SNF; protein, lactose, ash, freezing 

point and pH) of UHT milk samples revealed non-significant differences 

(P>0.05) between seasons. 

  The osmolality average of raw milk samples, pasteurized and UHT 

was (309±37.86, 273±24.08, 271.76±7.46 mOsmol/kg, respectively). 

Moreover, the osmolality average of milk samples revealed significant 

differences (P<0.05) between raw and heat-treated milk samples. 

  The present study concluded that physiochemical properties and the 

osmolality of milk were affected by seasonal variation. Also, the study 

showed that the percentage of contaminant raw milk samples by antibiotic 

residue above MRLs is higher compared to that heat-treated milk samples. 



1 
 

 

 

 

 

 

 

 

CHAPTER ONE  

Introduction 

 

 

 

 

 

 

 

 

 

 

 



2 

Chapter One 

1.1. INTRODUCTION 

 

Milk contains an optimal balance of proteins, fats, carbohydrates, 

vitamins (A, B2, B12 and D), calcium, phosphorus, potassium and other 

minerals providing a range of benefits for growth, immunity, and 

development for the calves and also to humans (Padol et al., 2015; 

Mahmoudi et al., 2014). Cow’s milk is one of the most consumed foods by 

all populations from newborn to the elderly. Thus milk and milk products 

intended for human consumption must be safe, without microbiological, 

physical or chemical contaminants like toxic metals, mycotoxins, 

radionuclides, pesticide and veterinary drug residues. Milk must not be 

adultered by water addition (Trombete et al, 2014; Zanella et al., 2010). 

Cow’s milk contains approximately 87% water. All components vary 

within the same species, and also from one dairy to the other, depending on 

cows' race, age, the period of lactation, diet and other environmental factors 

( Büttel et al., 2008; Guetouache et al., 2014). The osmolality of milk is a 

significant value owing to its being highly preserved even when collected 

from a larger population of animals. Therefore, osmolality can be used in 

milk quality control (Büttel et al., 2008). 

Antibiotics are widely used in food animal production. They are used 

for treating the bacterial infections at large dosage, and as feed additive at a 

low dosage for a long period in order to prevent diseases, promote growth 

and increase feed efficiency (Abbasi et al., 2011; Aalipour et al., 2013; 



3 

Darwish et al., 2013). The extensive use of these antimicrobials, 

insufficient withdrawal period and lack of good veterinary practice cause 

the presence of residues in milk. Illegal or off-label use of drugs and 

incorrect dosage levels or dosing schedule enlarge the problem. (Al-Zuhair, 

2012; Kebede et al., 2014; Padol et al., 2015). 

Antibiotic residues in milk are a potential hazard for public health. 

They may cause allergic reactions (B-Lactams), development of bacterial 

resistance which can transfer to human through the food chain and 

environment, making treatment of human infections difficult (Darwish et 

al., 2013), carcinogenicity (Sulphamethazine, Oxytetracycline, 

Furazolidone), mutagenicity, immunopathological effects, autoimmunity, 

nephropathy (Gentamicin), hepatotoxicity, reproductive disorders, bone 

marrow toxicity (Chloramphenicol), (Nampoothiri et al., 2014; Darwish et 

al., 2013; Padol et al., 2015; Nisha, 2008; Abdelmoaty, 2015). Antibiotic 

residues interfere with the balance of intestinal micro-flora and cause delay 

or failure in dairy fermentation like cheese and yogurt causing economic 

losses (Aalipour et al., 2013; Kaya et al., 2010; Movassagh, 2011). 

About 50-80% of antibiotics are excreted through urine and feces. 

Using manure as fertilizer can contaminate soil, surface, and groundwater 

which results in contamination of food and drinking water (Rasouli et al., 

2015; Gothwal et al., 2014). 



4 

The degree of milk contamination with antibiotic residues varies from 

country to another, depending on the level of education, legislation, and 

food inspection (Kaya, 2010). 

To ensure human food safety, worldwide regulatory authorities such as 

world health organization (WHO) (1999) and the food and agriculture 

organization (FAO) (2008) have set standards for acceptable daily intake 

(ADI) and maximum residue levels (MRLs) for several veterinary drugs in 

food. (Mesragi et al., 2011; Oluwafemi et al., 2018). 

1.2. OBJECTIVES 

 The objective of the present study is to assess the quality of raw, 

pasteurized and Ultra Heat Treated (UHT) milk sold in the Palestinian 

market through: 

1- Screening milk samples for antibiotic residues. 

2- Determining the osmolality of milk samples. 

3- Determining the milk’s physiochemical properties (fat, protein, SNF, 

solids, lactose, FP and pH). 

4- Determining the effect of the season’s variation on the quality of 

milk. 

1.3. RESEARCH PROBLEM 

Understanding the quality and safety of milk and milk products sold in 

the local Palestinian market is very crucial. No studies have been done and 



5 

there is a need to screen marketed milk from different sources. This study 

will cover the presence of antibiotic residues, the presence of added water 

and other physiochemical properties of milk in relation to season so as to 

assess the quality and safety of milk. 

Milk producers and farmers will be assessed indirectly for 

understanding the importance of hygiene practices during cows breeding, 

milking, and processing of milk. In addition, it will help regulatory 

authorities and milk industry in the formulation of control strategies on the 

use of antibiotics as a veterinary drug, and also understand the 

environmental variations and its effect on physicochemical properties of 

milk. 



6 

 

 

 

 

 

 

 

CHAPTER TWO 

Literature Review 



7 

Chapter Two 

2. LITERATURE REVIEW 

2.1. PHYSIOCHEMICAL PROPERTIES OF MILK 

Milk is the normal mammary secretion of milking animals obtained 

from one or more animals  without either addition to it or extraction from 

it, intended for consumption as liquid milk or for further processing (FAO 

Codex, 1999). Milk contains all of the nutrients necessary for survival and 

the initial growth of mammalian neonates. The nutrients in milk include 

sources of energy (lipids and carbohydrates), proteins to provide amino 

acids, vitamins and minerals for electrolytes, and water (Husvéth, 

2011). The major cow milk producers worldwide are The European Union 

(148.1 million kg3), The United States of America (85.9 million kg3), India 

(45.1 million kg3), and Russia (32.3 million kg3). Table 1 and figure 1 

show the proximate composition of whole bovine milk from different 

countries (Schönfeldt et al., 2010).  

Table (1): Proximate composition of whole bovine milk from different 

countries. 
Whole bovine 

milk/100g 

South 

Africa 

USA UK Denmark Australia New 

Zealand 

Water 88.0 88.3 87.8 87.8 87.5 

Energy by KJ 260 252 275 269 278 

Protein 3.25 3.22 3.20 3.40 3.30 

Lactose 4.80 5.26 4.80 4.64 4.70 

Fat 3.43 3.25 3.90 3.50 4.00 



8 

 

Figure (1): Milk composition 

2.2. MILK PRODUCTION IN PALESTINE 

Livestock in Palestine is not only an economic or income generation 

activity but also a distinctive trait, cultural and tradition of the Palestinian 

people. There were 33,980 cows raised in the Palestinian territory, 

including 25,612 cows in the West Bank and 8,368 in the Gaza Strip. Of 

which, 32% were local cows (Baladi and mixed breeds) and 68% other 

strains (Holstein, Friesian, and hybrid cows) (PCBS, 2013). 87.6% of cows 

are raised through intensive breeding, 12.2% through semi-intensive 

breeding, and 0.2% by an unknown type of breeding (PCBS, 2010). Local 

demand for milk and dairy products was estimated at 204 million litter a 

year. 89% of local market needs are produced locally and the remaining 

gap is covered by imports, approximately 17,416 million litter of liquid 

milk equivalent are imported a year. Table 2 shows the imported and 

exported amounts of milk in thousands of dollars (PCBS, 2017). 



9 

Table (2): In 2015, the imported and exported amounts of milk in 

thousands of dollars. 
Country Imported Exported 

Jordan 0 186 

Egypt 53 0 

France 2 0 

Israel 5,772 315 

The consumption amount of fresh and pasteurized milk was 

estimated in 2015 at 33,031,993 liters. Industrial production includes 10 

processing plants that process 155,000 tons of raw cow’s milk per year 

(MoA, 2014).  

The average quantity of Palestinian household monthly consumption 

of milk (Table 3) was 4.4 liters, 4.7 liters of yogurt and 1.5 kg of different 

types of cheese (PCBS, 2010; PCBS, 2017). 

Table (3): The average quantity of monthly consumed milk in liters by 

Palestinian household, 2006-2011.  

Year West-Bank Gaza Average 

2006 5.475 2.489 4.478 

2007 5.005 1.833 3.982 

2009 4.852 1.270 3.730 

2010 4.894 1.979 3.977 

2011 4.807 0.884 3.527 

2.2.1 FAT 

Most of the lipids in milk are in the form of triglycerides, and these 

are the primary source of dietary energy in milk. Triglycerides are 

composed of three fatty acids and glycerol (Husvéth, 2011). Milk fat has 



11 

the most complex fatty acid composition of the edible fats. Over 400 

individual fatty acids have been identified in milk fat (Mansson, 2008). 

However, approximately 15 to 20 fatty acids make up 90% of the milk fat. 

Milk fat globules have an average diameter of less than 0.1μm to 

approximately 18 μm and consist of a triglyceride core surrounded by a 

natural biological membrane (Ghalib, 2014). 

Milk fat can be degraded by enzyme action, exposure to light, and 

oxidation. Enzymes that degrade fat are called lipases, and the process is 

called lipolysis. Usually, the action of lipase causes undesirable rancid 

flavors in milk. Pasteurization inactivates lipases and increases the shelf 

life of milk. Milk fat is fully melted at (40°C). Typical high-temperature 

short time (HTST) pasteurization conditions do not affect the functional 

and nutritional properties of milk fat. Higher heat treatments may stimulate 

oxidation reactions and cause fat deterioration and off-flavors such as Ultra 

High Temperature (UHT). Milk fat acts as a solvent for the fat-soluble 

vitamins A, D, E and K and also supplies essential fatty acids (linoleic, 

linolenic and arachidonic) (Cortes, 2011). Milk fats are the most variable 

compounds, being under the influence of species, breed, lactation stage, 

feeding, season, and health condition (Grădinaru, et al., 2015; Linn, 1988). 

A study conducted by Galib to investigate raw cow milk composition 

showed that the average fat content was found as 5.03±0.04% during the 

winter season, and 4.30 ±0.6% during summer season (Ghalib, 2014), In 

Kenya, Kabui found that the average of fat content was 3.8% (Kabui, 

2012). In Iran, Nateghi et al reported that fat content was 3.8% in summer 



11 

and 3.41% in winter (Nateghi et al., 2014). Abd Elrahman reported that the 

average fat content was 4.14% in a study conducted in Sudan. 

2.2.2 PROTEIN 

Proteins are chains of amino acid molecules connected by peptide 

bonds. There are 20 different amino acids in proteins. The content and 

sequence of amino acids in a protein affect its properties. Some proteins 

contain substances other than amino acids, e.g. lipoproteins. The dominant 

class of protein in milk called casein.  Bovine milk contains about 3.5% 

protein, casein constitutes about 80% and it is easily separated from milk, 

either by acid precipitation or by adding rennin. Whey proteins constitute 

about 20% and exist as individual units dissolved in the water phase of 

milk. The major whey proteins are beta-lactoglobulin and alpha-

lactalbumin. (Cortes, 2011; Linn, 1988). Mirzadeh found that milk protein 

was 3.3±0.22% in a study conducted in Iran (Mirzadeh et al., 2010). In 

another study conducted in Sudan by Elsheikh, milk protein was found as 

3.58±0.33% (Elsheikh et al., 2015). In the world, Friesian and Holstein 

cow milk averagely contains 3.3% protein (Mirzadeh et al., 2010). Abd 

Elrahman studied the physicochemical properties of bovine milk and 

showed that milk protein average was 3.47±0.012 (Abd Elrahman, et al., 

2009). Kabui found that the average of milk protein was as 3.1% (Kabui, 

2012). Natighi found that milk protein amounts in summer and winter were 

3.71% and 3.01%, respectively (Nateghi et al., 2014). These variations are 



12 

results of different animal feeding in summer and winter, age and health, 

and the environment (Abd Elrahman, et al., 2009; Nateghi et al., 2014). 

2.2.3 SOLIDS NOT FAT (SNF) 

Solid not fat contains the protein, the minerals, and the milk-sugar 

which collectively make milk such valuable and palatable food. Liquid 

milk for human consumption must contain at least 8.5 percent, solids-not-

fat (Snook, 1960). Kabui, 2012 found the average of SNF in milk was 

8.2%. In another study, Thomas found that the solid not fat percentage in 

milk was 8.3% (Thomas et al., 2015). Galib found that the average content 

of solids not fat of milk samples was 11.52±2.3% during the winter season. 

Similarly, the mean value of SNF was 11.21±0.6 % in summer (Galib, 

2014). 

2.2.4 LACTOSE 

Lactose (Figure 1) is the major carbohydrate fraction in milk. It is 

made up of two sugars, glucose, and galactose. The average lactose content 

of milk varies between 4.7% and 4.9%. Mastitis reduces lactose secretion. 

Lactose is dissolved in the serum (whey) phase of fluid milk. The lactose 

content of milk in summer and winter being reported by Nategi as 4.61% 

and 4.58% respectively (Nateghi et al., 2014). Ghalib showed that the 

average lactose content in milk samples was 4.62 ±0.2 in winter and 

4.72±0.2 in summer.  



13 

 

Figure (2): Structure of lactose molecule 

2.2.5 HYDROGEN ION CONCENTRATION (PH)  

The pH or the hydrogen ion concentration of milk gives a measure of 

the acidity of milk. In normal cow milk, the pH ranges from 6.6 to 6.8. The 

pH value can be lower than 6.6. The pH of milk is mainly attributed to the 

phosphates, citrates and carbon dioxide present in milk. The pH value can 

be greater than 6.8 mainly due to mastitis (Kabui, 2012). The pH of milk is 

more dependent on temperature than that of buffers, such as phosphate; 

since milk is a complex buffer system and variation in temperature causes 

many changes. Differences in pH and buffering between individual lots of 

fresh milk reflect compositional variation (Gakkhar et al., 2015) 

Milk pH can be determined directly or indirectly. Direct 

measurement is through the use of indicator dyes, titratable acidity or use 

of pH meters. Indirect measurement is done through the clot on boiling and 



14 

alcohol tests (Kabui, 2012). Kabui found an average milk pH of 6.63 in a 

study conducted in Kenya. In a study conducted by Abd Elrahman et al the 

mean of milk pH was 7.02 (Abd Elrahman et al., 2009).       

2.2.6 FREEZING POINT 

The freezing point of milk is the minimum temperature at which the 

milk flow becomes null, and the milk viscosity becomes maximum. It is a 

transition point of liquid-solid phases (Bouisf et al., 2018).  

The freezing point of cow's milk has long been recognized as one of 

its most constant values (Watrous et al., 1975) and it is an indirect measure 

of the osmotic pressure. Depression of the milk freezing point was often 

related to an increase in protein and solids content. The freezing point of 

milk is slightly lower than that of water, because of the presence of 

dissolved solids. The maximum limits of the freezing point of both raw and 

heat-treated drinking milk were ≤ –0.520°C according to EU regulations 

(Buttel et al., 2008). A total of 295 samples of heat-treated drinking milk 

was examined by Navratelova over a period of one year, 145 of them were 

pasteurized milk and 150 UHT. The average freezing point was found as -

0.516°C, -0.514°C, respectively. (Navratelova et al., 2006). Bouisf et al 

showed that the mean of milk FP was -0,521°C. (Bouisf et al., 2018). Abd 

Elrahman et al found that the average of raw and pasteurized milk FP was 

respectively -0.520°C, -0.447°C (Abd Elrahman et al., 2009). 



15 

2.2.7 MILK SALTS (ASH) 

Milk salts are mainly chlorides, phosphates, and citrates of sodium, 

calcium and magnesium. Although salts comprise less than 1 % of the 

milk, they influence its rate of coagulation and other functional properties. 

Calcium, magnesium, phosphorous and citrate are distributed between the 

soluble and colloidal phases.  

Their equilibria are altered by heating, cooling and by a change in 

PH, milk also contains trace elements that come to the milk from feeds or 

milking equipment such as copper, iron, nickel and zinc (Cortes, 2011). 

The average ash content varied from 0.74% for Holsteins to 0.83% percent 

for Jerseys. The highest calcium and phosphorus contents in milk were 

reported for Jerseys (Linn, 1988). Elbagermi et al., 2014 reported that the 

average content of ash in cow milk was 0.63% in a study conducted in 

Libya (Elbagermi et al., 2014).  

2.2.8 MILK OSMOLALITY 

Osmolality is the number of solute molecules that are dissolved in 1 

kg of solvent (Buttel et al., 2008). Osmolality is the concentration of solute 

particles in a solution (James, 2018). The osmolality of milk is a significant 

value owing to its being highly preserved even when collected from a 

larger population of cows. Osmolality has been used for quality control of 

milk because the water content is a preserved parameter changed by 

external factors. When milk processing takes place water may be mixed 



16 

into the milk. This can occur intentionally by adding water or accidentally 

through water presence in milking machine pipes. The osmolality value is 

277 mOsmol/kg corresponds to -0.515°C as recommended by the German 

Food Regulations for Milk (Buttel et al., 2008). Milk has an osmolality of 

280–290 mosmol/kg (James, 2018). In Germany, the osmolality of 12 heat-

treated milk samples was tested by Buttel et al., and the average was found 

as 271 mOsmol/Kg. 

2.3. EFFECT OF HEAT TREATMENT ON MILK COMPOSITION 

Pasteurization does not reduce the fat content of milk. Pasteurization 

has little effect on the nutritional value of milk. There is some loss of 

vitamin C and B group vitamins, but this is insignificant (FOA, 2013). The 

process kills many fermentative organisms as well as pathogens. 

Pasteurized and ultra-high treatment milk keeping protein and lactose 

content similar to raw milk. (Pestana, 2015).  

2.4. ANTIBIOTICS 

Antibiotics are organic chemical compounds that kill (Bactericidal) 

or inhibit the growth (Bacteriostatic) of microorganisms but cause little or 

no damage to the host (Albayoumi, 2015; Metzeler, 2018). Antibiotics are 

medicines used to prevent and treat bacterial infections (WHO, 2018). 

They are naturally produced by microorganisms such as fungi (e.g. 

penicillin) and bacteria (e.g. tetracycline) or can be semi-synthetically 

produced (e.g. amoxicillin) or totally synthetically produced (e.g. 



17 

sulfonamides) (Albayoumi, 2015). Antibiotic compounds are differentiated 

as antibacterial, antifungals and antivirals to reflect the group of 

microorganisms they affect (Etebu, 2016). Table 4 shows the chemical 

structure of certain antibiotics among β-lactams, Quinolones, 

Nitroimidazoles, Quinoxalines, Aminoglycosides, Macrolides, Phenicols, 

Phosphoglycolipids, Lincosamides, Nitrofuran, Ionophores, Sulfonamides, 

Tetracyclines and Polypeptides (Kebede et al, 2014).  

Table (4): Antibiotics classification according to chemical structure. 

Antibiotics have been used in the dairy industry for more than five 

decades. The main uses of antibiotics in the dairy industry include: 



18 

1. Therapeutic: For disease treatment. The infected animals receive a 

course of antibiotics in high doses for a short period of time.  

2. Prophylactic: For disease prevention in sub-therapeutic doses of 

antibiotics for a group of healthy animals via feed or drinking water. 

3. Disease control: for a group of animals when some of them are sick. 

4. Growth Promoters: To increase growth-rate and productivity (Sahu 

et al., 2014; Hahn et al., 2016; Barton, 2000). 

In North America and Europe, it is estimated that about 50% of all 

antimicrobial production is used in food-producing animals and poultry 

(WHO, 2001). Van Boeckel et al., 2015 estimated that global consumption 

of antibiotics in agriculture will increase by 67 percent from 2010 to 2030, 

and the consumption of antibiotics amongst the BRICS will increase by 

99 percent in that same time period (O’Neill, 2015).  

2.4.1 ANTIBIOTIC RESIDUES IN MILK 

Antibiotic residues are small amounts of drugs or their active 

metabolites, which remain in milk after treating the cows (Aytenfsu et al., 

2016). Antibiotic residues in milk are unacceptable for two reasons. Firstly, 

there is a potential human health hazard and secondly, antibiotic residues 

can interfere with the manufacturing process inhibiting yogurt and cheese 

starter cultures (Edmondson, 2002). The occurrence of antibiotic residues 

in milk is strongly associated with certain variables such as milk production 



19 

rate at the time of treatment, the type and amount of antibiotic used, the 

type of vehicle used in antibiotic formulations, and the disease state of the 

animal (Rasoli et al., 2014). Intermammary infusion of antibiotic for 

treating mastitis is the most common reason for antibiotic residues in milk 

(92%) followed by injections (6%), and other causes (2%) (Ghowdhary et 

al., 2015).  

A withdrawal period is established to safeguard humans from 

exposure to antibiotic residues. The withdrawal time is the time required 

for the residue of toxicological concern to reach safe concentration as 

defined by tolerance. It is the interval from the time an animal is removed 

from medication until the permitted time of milking (Nisha, 2008). 

According to the results of the technical report prepared for milk 

hygiene, by World Health Organization and Joint Expert Committee on 

Food Additives (JECFA), the rate of contamination of milk and dairy 

products with antibiotic residues in developed countries such as USA, 

Australia, UK, and Scotch land was 7-10% until 1969, after that year, the 

rate of contamination of the same products decreased to 0.5% in the USA, 

2.1% in Australia, 1.5% in the UK and 3.4% in Scotland due to the 

precautions are taken after the given date. The same report indicates that in 

underdeveloped and developing countries the contamination for milk and 

dairy products might be higher (Kaya, 2010). 



21 

In the USA, a study conducted by the Food and Drug Administration 

(FDA) found that from 1912 samples, 15 (0.79%) was positive for 

antibiotic residue (FDA, 2015). 

In Croatia, from a total of 1259 samples tested for antibiotic residues 

over three years period, 36 was positive (Bilandzic et al., 2011). In Brazil, 

a study conducted by Brado et al., to investigate the presence of 

tetracycline’s in pasteurized milk showed that 3 (3%) of 100 samples were 

positive (Prado et al., 2015). In another study by Fonseca et al., who 

reported from 100 UHT milk samples, 4 (4%) was positive (Fonseca et al., 

2009). Oleviera et al., showed that none of 50 samples of raw milk and 20 

pasteurized milk contain antibiotic residue (Oleviera et al., 2012). 

Reasons for bulk milk contamination by antibiotic residues: 

(Edmondson, 2002; Galib, 2014).  

 Milk from treated cow are accidentally routed into the milking tank  

 An antibiotic-treated dry cow unintentionally milked.  

 The same milking unit was used to milk an antibiotic-treated cow 

before milking untreated cows. The milking unit was not cleaned and 

sanitized between uses.  

 Lactating cows were purchased and the new owner was unaware of 

recent antibiotics prior to sale.  

 Equipment used to milk treated cows handled carelessly, for 

example, vacuum from the milk pipeline was used to operate dump 

milk buckets.  



21 

 All antibiotic-treated dry cows were milk last, but the milk line was 

not diverted from the bulk tank.  

 Medicated feed was accidentally mixed into lactating cow feed.  

 Cows drank from medicated footbath.  

 One-quarter of a cow was treated for mastitis and withheld from the 

bulk tank. However, milk from the other three quarters was not 

withheld and was permitted to enter the pipeline. 

 Use of dry cow therapy to treat lactating cows. 

There are many natural medicines that are topical and cause little risk 

for contamination of milk or meat. A few of these “natural treatments” 

have the potential to be effective in treating mastitis by intermammary 

infusion. Natural antimicrobials such as caprylic acid, eugenol, trans-

cinnamaldehyde, carvacrol, and thymol have been found to be inhibitory, in 

vitro, towards an array of pathogenic microorganisms and may be potential 

candidates for effective on antibiotic treatments for mastitis (O’Donnell, 

2011). 

2.4.2 ANTIBIOTIC RESISTANCE 

Antimicrobial resistance is the ability of a microorganism (like 

bacteria viruses and some parasites) to stop an antimicrobial (such as 

antibiotics, antivirals, and antimalarial) from working against it. As a 

result, standard treatment becomes ineffective, infections persist and may 



22 

spread to others (WHO, 2018).  Antibiotic resistance occurs naturally, but 

overuse and misuse of antibiotics whether in humans or in animals 

accelerate the process. O’Neill reported that of 139 academic studies 

affiliated to universities that address the issue of antibiotic in agriculture, 

only 7 (5%) argued that there was no link between antibiotic consumption 

in animals and resistance in humans, while 100 (72%) found evidence of a 

link (O’Neill, 2015). Antibiotic-resistant bacteria have become a major 

global public health (Hahn et al., 2016; WHO, 2018), food security and 

development concern today (WHO, 2018).  

Antimicrobial-resistant infections in food-producing animals may 

have major financial implications for both farmers and consumers (WHO, 

2013). Resistant bacteria could transfer to human potential through direct 

contact with an animal, from consumption of undercooked or unpasteurized 

animal products, or via the spread of resistant bacteria into environmental 

reservoirs, which may then transmit resistance genes to human bacteria, or 

come into contact with humans directly (O’Neill, 2015). For example, a 

clone of Salmonella typhimurium DT104 that has become prevalent in 

many countries including the UK, Germany and the USA, is resistant to 

commonly used antibiotics including ampicillin, tetracycline, streptomycin, 

chloramphenicol and Sulphonamides. Multi-drug resistance has been noted 

in other Salmonella spp (WHO, 2001). The introduction of fluoroquinolone 

use in poultry has been associated with a dramatic rise in the prevalence of 

fluoroquinolone-resistant Campylobacter jejuni isolated in live poultry, 

poultry meat and infected humans (WHO, 2001). 



23 

Elmanama and Abdelatif, (2012) conducted a study to investigate the 

antimicrobial resistance for enteric pathogens isolated from acute 

gastroenteritis patients in the Gaza strip. The study showed that diarrhea 

was more frequent among peoples living in houses rearing poultry and 

pigeons. They isolated Salmonella, Campylobacter coli/jejuni, Aeromonas 

hydrophilia, Shigella boydii and Yersinia enterocolytica. All isolates were 

resistant for more than one antimicrobials especially Campylobacter 

coli/jejuni.  

Liu et al., (2015) examined areas in China where colistin is routinely 

given to pigs and they found colistin-resistant E. coli in more than 20% of 

animals and in 15% of raw meat samples, these bacteria all had colistin 

resistance that could easily be transferred between different bacteria, they 

also found that about 1% of hospital patients sampled were infected by E. 

coli or Klebsiella bacteria that had the same piece of DNA, making them 

resistant to colistin too (O’Neill, 2015).  

In many studies conducted from 2002 to 2013, among private and 

government hospitals in India, a high level of resistance against common 

antibiotics was found in several bacteria known to cause common and 

severe infections (Sahu et al., 2014). 

2.4.3  ANTIBIOTIC RESISTANCE MECHANISM 

Bacteria have genetic plasticity that allows them to respond to 

environmental threats, including the presence of antibiotic molecules. 



24 

Bacteria use two major genetic strategies to adapt to the antibiotic “attack”, 

first, mutations in gene(s) often associated with the mechanism of action of 

the compound, and second, acquisition of foreign DNA coding for 

resistance determinants through horizontal gene transfer. 

     Antibiotic resistance mechanisms can be classified according to the 

biochemical route involved in resistance, as follows:  

1- Modifications of the antimicrobial molecule.  

2- Prevention to reach the antibiotic target (by decreasing penetration or 

actively extruding the antimicrobial compound) 

3-  Changes and/or bypass of target sites. 

4- Resistance due to global cell adaptive processes (Munita et 

 al., 2016). 

To prevent and control the spread of antibiotic resistance, the WHO 

recommended the agriculture sector: 

 Only give antibiotics to animals under veterinary supervision. 

 Not use antibiotics for growth promotion or to prevent diseases in 

healthy animals. 

 Vaccinate animals to reduce the need for antibiotics and use 

alternatives to antibiotics when available. 



25 

 Promote and apply good practices at all steps of production and 

processing of foods from animal and plant sources. 

 Improve biosecurity on farms and prevent infections through 

improved hygiene and animal welfare (WHO, 2018). 

2.4.4 ADVERSE EFFECT OF ANTIBIOTIC 

Antibiotics have the following adverse effects:  

1. Allergic or toxic reactions to residues.  

2. Chronic toxic effects occurring with sub dosage of antimicrobials for 

prophylactic or as growth promotion.  

3. Development of antimicrobial-resistant bacteria in treated animals. 

These bacteria might then cause difficult-to-treat human infections. 

 4. Disturbance of normal human microflora in the intestine, which acts 

as a barrier to foreign pathogenic bacteria. Antibiotics might 

selectively kill some important species and reduce their total number 

(Etebu et al., 2016; Albayoumi, 2015; Jumaa et al., 2015). 

2.4.5 MAXIMUM RESIDUE LIMITS 

The maximum residue limits (MRL) is the maximum allowed 

concentration of residue in a food product obtained from an animal that has 

received a veterinary medicine or that has been exposed to a biocidal 

product for use in animal husbandry (EMA, 2018). MRLs for Beta-lactams 



26 

(Table 5) and Tetracycline (Table 6) have been set by the European Union 

for food producing animals and carry out control programs and monitoring 

for drug residues in food to protect public health and avoid economic loss 

(Kebede et al., 2014). 

Table (5): Maximum residue limits (MRL) for beta-lactams. 

Antibiotics MRL(ppb) 

Penicillin G 4 

Ampicillin 4 

Amoxycillin  4 

Cloxacillin  30 

Dicloxacillin  30 

Oxacillin  30 

Table (6): Maximum residue limits (MRLs) for tetracycline. 

Antibiotics MRL(ppb) 

Tetracycline  100 

Chlorotetracycline  100 

Oxytetracycline  100 

Doxycycline  100 

2.4.6 DETECTION OF ANTIBIOTIC RESIDUES IN MILK 

Different kinds of analytical methods were developed to determine 

antibiotic residues in milk such as microbiological, chromatographic, 

immunochemical, receptor and enzyme-based tests (Trombete et al., 2014; 

Padol et al., 2015; Kebede et al., 2014).  

Each screening method has its own advantages and disadvantages as 

shown in table 7. The Community Reference Laboratory Residues (CRL) 

classifies screening methods by different means as follows: 



27 

2.4.6.1 CLASSIFICATION BY DETECTION PRINCIPLE 

 Biological methods detect cellular responses to analytes (e.g. 

oestrogenic effect, inhibition of bacterial growth, cellular effect, 

hormonal effect). These methods are not selective and can cover 

several chemical classes of active analytes (e.g. hormones, 

antimicrobials). They do not allow the identification of individual 

analyte. 

 Biochemical methods detect molecular interactions (e.g. antigens, 

proteins) between analytes and antibodies or receptor proteins 

(ELISA, RIA). Chemical labelling of either the analyte or 

antibody/receptor allows the interaction to be monitored and 

measured. These methods are either selective for a family of analytes 

having related molecular structures or are sometimes analyte 

specific. 

 Physicochemical methods distinguish the chemical structure and 

molecular characteristics of analysts by separation of molecules (e.g. 

TLC, GC, HPLC) and the detection of signals related to molecular 

characteristics (e.g. UV- DAD, MS, tandem MS). They are able to 

distinguish between similar molecular structures and allow the 

simultaneous analysis of several analysts (CLRs, 2010). 

 

 



28 

Table (7): Advantages and disadvantages of some screening methods 

Test Advantages Disadvantages 

 

 

 

 

 

 

Elisa 

 Easy to use 

 Availability for a good number of 

specific compounds. 

 Availability for families of 

compounds (e.g. sulfanomides, 

estilbenes). 

 Large number of samples (42) per 

kit for a single analyte. 

 Reduced time to obtain the results 

(2-2.5 h for most kits). 

 High sensitivity and specificity. 

 Possibility to use within the food 

processing facility 

 Increased cost 

 Limited storage (few months) 

under refrigeration. 

 The need for waste disposal. 

 Interferences giving some false 

positives. 

 Only one kit per residue 

searched. 

 

 

 

 

Biochip 

array 

biosensors 

 Easy to use. 

 Results available in short time. 

 Multiples residues analyzed in one 

shot (as many as in an array). 

 Full automation: higher 

productivity. 

 High through-put technique: up to 

120 samples per hour and array. 

 High operative costs, chips and 

equipment cost. 

 Analysis restricted to available 

chips 

 

 

 

HPLC 

 Reduced time (few hours) to obtain 

results. 

 Sensitive 

 Automation leading to higher 

productivity. 

 Specificity depending on a detector 

 Expertise required. 

 Needs sample preparation 

(Extraction, filtration, addition 

of internal standards, etc.). 

 Expensive 

 

 

 

Microbial 

methods 

 Can be used for large surveillance 

programmers. 

 Basic laboratory equipment. 

 Broad spectrum. 

 Easy to use. 

 Economical. 

 Difficult to standardize 

preparation procedures. 

 Some test could not insure 

MRLs compliance.  

  Sample preparation required 

to remove false positives due 

to protein bacterial inhibitors.  

 Low sensitivity 

2.4.6.2 CLASSIFICATION BY THEIR DEGREE OF QUANTIFICATION 

1. Qualitative methods give a yes or no response, with no indication of 

the concentration of the putative analyte. Examples include: 



29 

 bacterial growth inhibition tests which give a result of either no zone 

or zone of inhibition. 

 Inhibition tests which give a color change; 

 Immunochemical ligand binding tests, where a response is 

considered as above or below a Cut-Off Level. 

 Chromatographic tests (HPLC, LC-MS/MS), where a peak is 

considered as present or absent.  

2. Semi-quantitative methods give an approximate indication of the 

concentration of the putative analyte. Examples include:  

 Microbial growth inhibition tests where an attempt is made to relate 

the size of the inhibitory zone to the putative analyte concentration;  

 Biochemical tests which include a calibration curve (e.g. ELISA, but 

only if the test is specific for a single analyte). 

 Chromatographic tests, calibrated over a short-range which may not 

include the sample response.  

 Physicochemical test (e.g. HPLC, LC-MS/MS) where the measured 

method precision characteristics do not meet the requirements for 

quantitative tests.  

3. Quantitative methods meet the same requirements for accuracy, 

dynamic range, and precision as confirmatory tests. And thus, when 



31 

the quantification is required, these methods shall be validated as 

confirmatory methods, as detailed in the Commission Decision 

2002/657/EC (CRLs, 2010). 

 



31 

 

 

 

 

 

 

CHAPTER THREE 

Materials and Methods 

 

 

 

 

 

 

 

 

 



32 

Chapter three 

3 MATERIALS AND METHODS 

3.1. SAMPLES 

A total of 118 milk samples, of which 79 pasteurized, 14 raw and 25 

Ultra Heat Treatment (UHT) were purchased from the market from June 

2017 to January 2018 using the production date as the collection criteria. 

3.2. SAMPLING 

The milk samples were collected by random sampling method for a 

period of 8 months, using the production date as the collection criteria. The 

volume of the samples was 100 ml, placed in sterile cups, each labeled with 

a specific code, sampling date, and production date. Samples were 

transferred in the ice bag and stored in a freezer at -20 °C until analysis. 

The heat-treated milk samples were of 6 local different brands and three 

foreign brands available in the Palestinian market. 

3.3. DETECTION OF ANTIBIOTIC RESIDUES  

The Delvotest SP NT kit supplied by DSM Food Specialties B.V., 

(The Netherlands) containing 96 wells microtiter plate was used to detect 

the antibiotic residue in milk samples. Detection is based on the microbial 

activity, Bacillus Stearothemophillus var. calidolactis, in the presence of 

pH indicator. If there is no AR in milk, the bacteria grow and increases the 

acidity of the medium, changing its color to yellow, and no color change 

means the milk sample contaminated with AR residues.  



33 

The test was conducted as directed by the manufacturer. Milk 

samples were melted in a water bath at 23 °C and gently shaken. The 

aluminum foil was removed from the plate, each test well was given a 

number representing the sample, then filled with a volume of 0.1ml of milk 

sample using a disposable one-way pipette, one pipette for each sample. 

The wells were carefully sealed with an adhesive foil and incubated in a 

preheated water bath at 64 ± 2 °C, for three hours until the negative sample 

color changed to yellow, and the results recorded. 

3.4. OSMOLALITY TEST 

    The osmolality of the milk samples was determined by using Vapor 

Pressure Osmometer (VAPRO 5520). 

A 10 microliter specimen is aspirated into a micropipette tip. The 

specimen is then inoculated into a solute-free paper disc in the sample 

holder, whereupon the sample holder is pushed into the instrument and the 

sample chamber is locked. The result appears in 75 seconds on the device 

screen and then recorded. 

  3.5. MILK COMPOSITION TEST 

The chemical analysis of milk samples was determined by using 

milk analyzer Lactoscan (Ultrasonic Milk Analyzer) according to the 

manufacturer`s instructions to determine fat, protein, lactose, SNF, solids, 

freezing point, and pH of the milk samples. 



34 

A volume of 25 ml of milk was poured in the sample holder of the 

analyzer after being shaken gently. The sample holder was put in the recess 

of the analyzer. The analyzer sucked in the milk, made the measurements 

and returned the milk in the milk holder and the display shows the results, 

then the results were recorded.  

  3.6. PH TEST 

The pH of the milk samples was determined by a pH meter device 

(JENWAY 3310). 

  3.7. DATA ANALYSIS 

 The data obtained from laboratory analysis of milk samples for 

physicochemical properties and osmolality were analyzed by descriptive 

and analysis of variance (ANOVA) using IBM SPSS Statistics for 

Windows, version 20. The data obtained from the antibiotic screening test 

of milk samples were analyzed using Microsoft Excel (2013).  

 



35 

 

 

 

 

 

 

 

CHAPTER FOUR 

Results and Discussion 

 



36 

Chapter four 

4 RESULTS AND DISCUSSION 

4.1. ANTIBIOTIC RESIDUE 

Delvotest SPNT test was used in this study to screen milk samples 

for antibiotic residues. It is a qualitative test that provides an indication of 

the presence of the antibiotics by inhibiting microbial growth. However, 

the high sensitivity ensures that even trace amounts of contaminating 

antibiotic residues are detected (Amoxicillin 2.5ppb Cephapirin 5.8 ppb 

Ampicillin 3.0ppb Penicillin G 1.5 ppb) (Tech news, 2016). It was reported 

that the two tests of Delvo and Copan can detect milk contamination to 

Penicillin, Cloxacillin Sodium, Sulfamethazine, Cephalexin and 

Gentamicin based on the standards set by the European Union. These two 

tests are simple and low-error (Foruozan et al., 2014; Moghadam et al., 

2016; Mahmoudi et al., 2013).    

Table (8) shows that 5 (36%) raw milk samples of 14, and 21 of 79 

pasteurized milk samples representing (27%) were contaminated with 

antibiotic residues. None of 25 UHT milk samples were contaminated. 

Table (8): Presence of antibiotic residues in the function of heat 

treatment 

Treatment method NO. Sample Positive (%) 

Raw 14 5 (36 %) 

Pasteurized 79 21(27 %) 

UHT 25 0(0 %) 

TOTAL 118 27(23 %) 



37 

The high occurrence of antibiotic residues in milk samples is related 

to the uncontrolled medicines market, weak monitoring system (smuggling 

and fraud, medicines abuse), weakness of regulatory for the standards and 

grades of livestock products, the lack of quality assurance programs (MoA, 

2014), insufficient withdrawal period and the costs of analyses (Al-

Zuhair,2012). In a study conducted by AL Zuhair in West Bank for the 

detection of B-lactams in 18 milk samples, and Tetracycline’s residues in 

16 milk samples of which 4 (22.2%) were above the MRLs for B-Lactams 

and 3 (18.7%) were above MRLs for Tetracyclines (Al-Zuhair,2012(. 

Alipour et al., showed that 19.4% of 187 (154 pasteurized and 33 UHT) 

milk samples contain residues above the EU-MRLs in Iran (Alipour et al., 

2013). A study conducted in Azerbaijan by Forouzan et al., 848 samples of 

pasteurized milk analyzed for antibiotic residues, results showed that 

30.14% were contaminated and 3.19% of these samples suspected 

(Forouzan et al., 2014). Moghadam et al., reported that 62 (24.8%) of 251 

pasteurized milk samples contaminated by antibiotic residues in a study 

conducted in Iran (Moghadam et al., 2016). In Algeria, a study carried out 

by Layada et al., reported that out of 154 raw milk samples analyzed 39 

were positive forming 25.3% of the total samples (Layada et al., 2016). 

4.1.1 RAW MILK SAMPLES. 

Table (9) shows, the highest percentage of contaminated raw milk 

samples of antibiotic residues was in October (100% 2 of 2), meanwhile 

august and September, had no positive samples.  



38 

Table (9): Percentage of contaminated raw milk samples in the 

function of sampling time. 

Table (10) shows, autumn had the highest number of contaminated 

samples 4 (67%) of 6, and the lowest in summer 1(13%) of 8 raw milk 

samples. It was determined that the probability of detecting antibiotic in 

milk during spring and autumn is higher than that in other seasons (Kaya et 

al., 2010). Moreover, it was noted that in autumn and winter, mastitis 

occurs more frequently due to climatic changes, and as a result, antibiotic 

therapy is carried out more often (Grandinaru et al., 2011; Rasoli et al., 

2014). 

Table (10): Percentage of contaminated raw milk samples in the 

function of seasons. 
Season NO. of Samples Positive, % 

Summer 8 1 (13%) 

Autumn 6 4 (67%) 

 

 

 

Raw Samples 

Month No. of Samples Positives (%) 

July 3 1 (33%) 

Aug 3 0 (0%) 

Sep 2 0 (0%) 

Oct 2 2 (100%) 

Nov 4 2 (55%) 

Total 14 5 (36%) 



39 

4.1.2. HEAT TREATED MILK SAMPLES 

Table (11) shows, the highest percentage of contaminated samples 

with antibiotic residues was on November, 4 (50%) of 8, meanwhile, the 

lowest number was on June 1(9%) of 11.  

Table (11): Percentage of contaminated pasteurized milk samples in 

the function of months. 
Pasteurized 

Month No.of Samples Positive (%) 

Jun 12 1 (8%) 

July 10 2 (20%) 

Aug 11 2 (18%) 

Sept 10 3 (30%) 

Oct 12 4 (33%) 

Nov 8 4 (50%) 

Dec 9 3 (33%) 

Jan 7 2 (29%) 

TOTAL 79 21 (27%) 

In the function of season table (12) shows, the highest percentage of 

positive pasteurized milk samples was in autumn, (37%), followed by 

winter (31%), and the lowest was in summer (15%). This is in accordance 

with the results of Alipour who showed that the contamination rate during 

(April-June) was 18.5%, and 11.6% was observed during (March‑May) 

(Alipour et al., 2013). In addition 

Moghadam et al., 2016 found that the percentage of positive 

pasteurized milk samples in the different seasons of the year, was (26.4%), 

(25.4%), (24.1%) and (17.1%) in winter, autumn, spring, and summer, 

respectively in a study conducted in Iran over five years. In another study, 



41 

evaluation of raw and pasteurized milk samples, Mahmoudi et al., showed 

that (20.83%) of milk samples taken in spring contaminated with antibiotic 

residues. Meanwhile, in summer, (37.5%) of samples were positive for 

antibiotic residue (Mahmoudi et al., 2014).  In another study, Mahmoudi et 

al., found that the winter milk samples (32.50%) had the most 

contamination with antibiotic residues compared to summer milk samples 

(25.00%) (Mahmoudi et al., 2013) 

Table (12): Percentage of contaminated pasteurized milk samples in 

function of seasons 
Pasteurized 

Season No. of Samples Positive (%) 

Summer 33 5 (15%) 

Autumn 30 11 (37%) 

Winter 16 5 (31%) 

The high rates of contamination in pasteurized milk could be 

asserted that antibiotic residues in milk would not be inactivated by normal 

pasteurization procedures (71°C for 15 sec) (Moats, 1987; Alipour et al., 

2013; Zorraquino, 2010). Moreover, in dairy factories, usually good quality 

raw milk without antibiotics and preservatives are used to produce 

fermented dairy products such as yogurt and cheese. In preparation of 

sterile milk (UHT), high-quality raw milk is also used. As a result, low 

quality and contaminated milk are directed toward pasteurized milk 

production lines, which is highly consumed (Mahmoudi et al., 2013).  



41 

The highest percentage of contaminated milk samples was from 

manufacturer (C) as shown in table (13), and this could be asserted that 

antibiotics may be used as a preservative in order to increase shelf life or to 

inhibit microbial growth in order to cover poor sanitation (Galib, 2014; 

Schlemper et al, 2017). The high frequency of positive samples reveals the 

need to establish regular residue testing programs in Palestine. 

Table (13): Percentage of contaminated pasteurized milk samples 

according to manufacturers. 

Producer Sample No. Positive (%) 

A 28 2 (7%) 

B 15 3 (20%) 

C 17 15 (88%) 

D 4 0 (0%) 

E 4 1 (25%) 

F 8 0 (0%) 

G 3 1 (33%) 

Total 79 22 (28%) 

4.2. OSMOLALITY 

The osmolality of milk is a significant value owing to its being 

highly preserved. Milk containing additional water has a significantly 

decreased osmolality, corresponding to an increased freezing point. 

Osmolality has been used for quality control of milk for quite a while. 

(Buttel et al., 2008).  

 



42 

Milk samples that contain additional 

water have a significantly decreased osmolality, corresponding to an 

increased freezing point 

Milk samples that contain additional 

water have a significantly decreased osmolality, corresponding to an 

increased freezing point 

Milk samples that contain additional 

water have a significantly decreased osmolality, corresponding to an 

increased freezing point 

Milk samples that contain additional 

water have a significantly decreased osmolality, corresponding to an 

increased freezing point 

Milk samples that contain additional 

water have a significantly decreased osmolality, corresponding to an 

increased freezing point 

Milk samples that contain additional 

water have a significantly decreased osmolality, corresponding to an 

increased freezing point 

Milk samples that contain additional 



43 

water have a significantly decreased osmolality, corresponding to an 

increased freezing p 

Milk samples that contain additional 

water have a significantly decreased osmolality, corresponding to an 

increased freezing p 

Milk samples that contain additional 

water have a significantly decreased osmolality, corresponding to an 

increased freezing p 

Milk samples that contain additional 

water have a significantly decreased osmolality, corresponding to an 

increased freezing p 

Table (14) shows the osmolality average of raw milk samples as 

309±37.86 mOsmol/kg, the highest value was 430 mOsmol/kg, and the 

lowest was 281 mOsmol/kg. Moore reported that the osmolality of whole 

cows’ milk is less than 300 mOsm per kg (Moore et al., 2016) which is not 

agreed with the current study results.  

While the osmolality mean of UHT milk samples was 271.76±7.46 

mOsmol/kg, the highest value was 288 mOsmol/kg, and the lowest was 248 

mOsmol/kg, and the osmolality average of pasteurized milk samples was 

273±24.08 mOsmol/kg, the highest value was 331 mOsmol/kg, and the 

lowest was 227 mOsmol/kg.  



44 

Table (14): Milk samples osmolality according to the treated method. 

N Minimum

14 281

79 227

25 248 7.46UHT

430

331

288

309

273.68

271.76

Treated method Maximum Mean Std. Deviation

Raw 

Pasteurized

37.87

34.09

 

Table (15) shows milk samples osmolality revealed significant 

differences (P<0.01) between raw milk samples and heat-treated milk 

samples (pasteurized and UHT) and non-significant differences (P>0.05) 

between pasteurized and UHT milk samples. The cleaning water of the 

pipeline may be polluting milk with cleaning acid or neutralizing agents 

(residual salts), this cause a depression of the freezing point corresponds to 

an increase in osmolality. Milk dilution occurs intentionally by adding 

water or accidentally by water residues in pipelines when milk processing 

takes place, which causes depression of milk osmolality corresponds to an 

increase in freezing point (Buttel et al., 2008). 

Table (15): Osmolality t-test of milk samples. 

Heat-treated Method Heat-treated Method P-Value 

Raw Pasteurized 0.00064 

Raw UHT 0.000062 

Pasteurized UHT 0.26 

In Germany, the osmolality of 12 heat-treated milk samples was 

tested by Buttel et al., and the average was found as 271 mOsmol/Kg, the 

Min value was 263 mOsmol/kg and the Max was 282 mOsmol/kg. After 

mixing with 10% water by volume, the average decreased to 242 



45 

mOsmol/kg, and after mixing with 50% water, the resulting mean 

osmolality was 129 mOsmol/kg (Buttel et al., 2008).  

According to seasons, table (14) showed that the osmolality average 

of raw milk samples in summer and winter was 310 and 309 mOsmol/kg 

respectively. While the osmolality average of pasteurized milk samples in 

summer was 280 mOsmol/kg which is higher than that in autumn and 

winter, with 274, 275 mOsmol/kg respectively. Also, the osmolality 

average of UHT milk samples in summer and spring was the same (273 

mOsmol/kg), in winter it was 272 mOsmol/kg and in autumn it was 266 

mOsmol/kg, which is the smallest value.  

The osmolality of raw milk samples average showed non-significant 

differences (P>0.05) between seasons and with a confidence interval (289-

329) mOsmol/kg. Similarly, the osmolality average of Pasteurized and 

UHT milk samples showed non-significant differences between seasons 

and with confidence intervals (274.1-280.2), (268.8-274.9) mOsmol/kg, 

respectively. Table (16) shows the summary for different types of milk 

samples osmolality according to seasons. 

 



46 

Table (16): Milk samples osmolality average according to seasons. 

 

4.3 FREEZING POINT 

The reported results showed that the freezing point of milk is a 

useful index for detecting added water (Shipe, 1959; Hanus et al., 2011). 

Depression of the milk freezing point was often related to an increase in 

protein and solids content as well as to a decrease in the lactose (Bouisf et 

al., 2018). Also, freezing point affected by the concentration of lactose and 

pH (Zagorska et al., 2013; Shipe, 1959).  

  In the present study, Table (17) shows freezing point average of 

pasteurized milk samples was ( -0.5048±0.0186°C), higher during summer 

(-0.5048±0.097°C), and lower during winter (-0.5120±0.018°C). These 

results are lower than those reported by Abd Elrahman et al., (-0.447°C) for 

pasteurized milk samples (Abd Elrahman et al., 2009). Similarly, the 

freezing point average of UHT milk samples during summer was the lowest 

value (-0.5087±0.01°C), and the highest was in autumn (-0.4974±0.02°C). 

The freezing point of pasteurized and UHT milk samples revealed non-

Item Measurements Summer Autumn Winter Spring Total P Value CI 
Mean±Std 309.88 308 309±37.87 0.95 289-329 

Min 281 290 

Max 430 326 

Pasteurized Mean±Std 280.8±15.7 274.54±13.47 275.6±10 277±13 0.19 274.1-280.2 

Min 262 227 252 

Max 331 303 299 

UHT Mean±Std 273.17±2.17 266.2±11.41 272±6.47 273.75±7.25 271.76±7.46 0.32 268.8-274.9 

Min 270 248 263 265 248 

Max 276 275 280 288 288 

Raw 



47 

significant differences between seasons (P>0.05) and the confidence 

interval was (-0.4945-0.5223°C), (-0.4994-0.5102°C), respectively. The 

maximum limits of the freezing point of both raw and heat-treated drinking 

milk were ≤ –0.520°C according to EU regulations (Buttel, 2009), which is 

not agreed with the current results.  

The highest values of the freezing point are found in summer, and in 

the early autumn, the reason probably lies in higher milk yields and the 

decrease in milk component and fat-free dry matter contents. Variability 

may be induced by exposure of dairy cows to heat stress, stage of lactation 

and, most importantly, dairy cows’ nutrition (Zagorska et al., 2013; Shipe, 

1959; Navrátilová et al., 2006). 

A total of 295 samples of heat-treated drinking milk was examined 

by Navratelova over a period of one year, 145 of them were pasteurized 

milk and 150 were UHT milk. The average freezing point was found as -

0.514°C, -0.516°C respectively. (Navratelova et al., 2006). Bouisf et al., 

showed that the mean of milk FP was -0,521. (Bouisf et al., 2018). 

Mirzadah et al., reported that the FP average of raw milk samples was -

0.56°C (Mirzadah et al., 2010). Moreover, Hanus et al quantified 72,607 

bulk raw cow milk samples. The highest FP was in spring (−0.52097 ± 

0.004877 °C), the lowest in autumn (−0.52516 ± 0.005725 °C) (Hanus et 

al., 2011). 

4.4 PH 

 The acidity of milk is due to the amount of casein, phosphate, citrate 

and carbon dioxide. But then at the end of the bacterial activity the lactic 



48 

acid was formed and the milk acidity increased (Ozrenk et al., 2008). In 

normal cow milk, the pH ranges from 6.6 to 6.8 (Kabui, 2012). 

In the present study, the pH average of pasteurized milk samples was 

found as 6.78±0.29, the max was 7.69 and the min was 6.24 during 

summer. In autumn the average was 6.65±0.47, the max was 7.22 and the 

min was 5.37, while in winter the average was 6.7±0.24, the max was 7.11 

and the min was 6.31. pH revealed significant differences between seasons 

(P<0.05) and the confidence interval was (6.59-6.75), see table (17). The 

average pH of UHT milk samples was the lowest during summer 

6.53±0.13, and the highest in autumn (6.74±0.40). These results revealed 

non-significant differences between seasons (P>0.05) and the confidence 

interval was (6.54-6.77), see table (18). Milk is usually slightly acidic, with 

a pH value between 6.5 and 6.7, but if the pH value of cow milk is 

measured to be above 6.8, it may point out the mastitis disease or a 

neutralized substance added in milk. If pH value is smaller than 6.5, it 

means colostrum may be present or bacterial growth or spoilage may be 

occurred in milk (Pelvan, 2011). 

  Kabui found that the average milk pH of 6.63 in a study conducted in 

Kenya. In another study conducted by Abd Elrahman et al., the mean milk 

PH was 7.02 (Abd Elrahman et al., 2009). Chen et al., found that milk pH 

was significantly higher in spring than in summer and autumn. (6.73) 

(Chen et al., 2014). Ozrenk et al., reported that the average milk pH in 

winter and summer was 6.50±0.205, 6.50±0.472, respectively (Ozrenk et 

al., 2008). 



49 

4.5   MILK COMPONENTS  

Cow's milk is an essential part of most daily diets and is a complex 

mixture of specific bioactive molecules such as proteins, lipids, 

saccharides, and biologically active substances including immunoglobulins, 

enzymes, oligosaccharides, hormones, and cytokines. Cow milk 

composition differs not only between species but also within species, 

through genetics, farming practices or environment (temperature, humidity, 

wind) (El-Hamdani et al., 2017). Cow milk production and composition 

can be directly influenced by the season as it affects feed availability. The 

different season of the year is often related to different food regimes for 

cows (Nateghi et al., 2014; Kabil et al., 2015; El-Hamdani et al., 2017). 

Heat stress affected both quantity and synthesis of milk components 

(protein, fat, lactose) (Thomas et al., 2015; Bernabucci et al., 2014). Heat 

stressed animals may have lower levels of blood protein and energy due to 

the in-efficiencies of rumination and metabolism during this heat challenge. 

Both blood protein and energy levels can influence milk and milk fat 

yields. In addition to eating less and drinking more, feeding patterns change 

during heat stress (Bernabucci et al., 2014). 

  4.5.1 FAT CONTENT 

Table (18) shows, the average of the fat content of pasteurized milk 

samples was found in summer to be 3.13±0.35%, max was 3.63 and the 

min was 2.52. In autumn the average was 3.25±0.52%, max was 3.9 and 



51 

the min was 1.97. During winter the mean was 3.48±0.54, the max was 

4.44 and the min was 2.52. Fat variability depends on several factors such 

as weather conditions, stage of lactation, and feeding (El- Hamdani et al., 

2017).  

In the present study, the fat content average in pasteurized milk 

samples was higher in winter (3.48±0.54), followed by autumn 

(3.25±0.52%), the lowest was in summer (3.13±0.35%).  These results 

revealed non-significant differences between seasons (P>0.05), and the 

confidence interval was (3.14-3.36). Similarly, Kabil et al found fat content 

in winter (3.6 ±0.055) higher than in summer (3.1 ± 0.058 ) (Kabil et al., 

2015).  Nateghi et al.,  found that the amount of fat in summer (3.39% ) 

was higher than that in winter(3.41 ) which is not agreed with the current 

results (Nateghi et al., 2014). Additionally, minimum fat (4.3) content was 

observed in summer, and a maximum (5.4) in winter, in a study conducted 

by Yasmeen et al., (Yasmeen et al., 2012). 

Hill reported that fat minimum in August, maximum in October in a 

study carried out over ten years (1991-2001) in the USA (Hill, 2011). Chin 

et al reported that the autumn period had significantly higher fat content 

than in other periods which is broadly in line with the UK national statistics 

(Chin et al., 2014). 

The average content of fat in UHT milk samples was higher in spring 

(3.28±0.23) and the lowest was in summer (2.58±0.66). The current results 

revealed non-significant differences between seasons (P>0.05), and the 



51 

confidence interval was (2.83-3.28). Also, Povel showed that the mean fat 

content was higher in spring morning 3.91±0.23, and the lower in summer 

morning 3.51±0.31, (Povel et al., 2011).  In Sudan, a study conducted by 

Galib to investigate raw cow milk composition showed that the average of 

fat content was found as 5.03±0.04% during the winter season, and 4.30 

±0.6% during the summer season (Ghalib, 2014). 

  4.5.2 SOLID NOT FAT (SNF) CONTENT 

Table (17) shows the highest average content of solid not fat of 

pasteurized milk samples was in autumn (8.04±0.47%), and the lowest was 

in winter (7.91±0.44%). The highest average content of solid not fat of 

UHT milk samples was in autumn (8.01±0.47%) and the lowest was in 

winter (7.85±0.51). Solid not fat average of pasteurized and UHT milk 

samples showed non-significant differences between seasons (P>0.05), and 

the confidence interval was (7.9-8.1), (7.78-8.14), respectively. Kunda et 

al., reported that the average SNF content of pasteurized milk was 8.6% 

(Kunda et al., 2015). Our results were lower than those revealed by 

Thomas et al which showed that the average SNF in winter was 8.5% and 

in summer 8.4% (Thomas et al., 2015). Moreover, the results obtained by 

Abd Elrahman et al., showed the average SNF content of raw milk was 

8.58±0.035, and pasteurized 7.93±0.007 which is almost agreed with the 

current study (Abd Elrahman et al., 2009).  

 



52 

4.5.3 PROTEIN 

  Table (17) shows the highest average protein content of pasteurized 

milk samples was in autumn (2.96±0.17), followed by summer 2.94±0.2, 

and the lowest was in winter 2.92±0.17. Meanwhile, the protein content 

average of UHT milk was higher in spring (3.18±0.53), and the lowest 

during the winter (2.87±0.19) table(18). Protein content average of 

pasteurized and UHT milk samples revealed no significant differences 

between seasons (P>0.05), and the confidence interval was (2.91-2.99), 

(2.87-3.11), respectively. Similarly, El- Hamdani et al., found the average 

protein was 3.6 and there were no differences between seasons (El- 

Hamdani et al., 2017). Kabil et al., found that there is a variation between 

seasons and the highest average value was in winter 3.5 ± 0.046, and the 

lowest was in spring (3.0. ±0.045) (Kabil et al., 2015) which is not agreed 

with the current study.  In another study Nateghi et al., showed that the 

amount of protein contained in summer milk was higher than in winter 

milk as its amounts in summer and winter milk were 3.71% and 3.01%, 

respectively (Nateghi et al., 2014). Additionally, the highest protein content 

(3.22) was in winter, and the lowest (2.3) in the summer season (Yasmeen 

et al., 2012). The milk protein content is affected by seasonal changes and 

locality and its variability is known to be higher than that of fat content (El- 

Hamdani et al., 2017).   

 Similarly, Povel et al., showed that the highest protein content was in 

spring morning 3.41±0.05, and the lowest was in summer morning 



53 

3.16±0.11 (Povel et al., 2011), and also Chin et al., reported the higher 

protein content was observed in spring compared to the summer and 

autumn periods (Chin et al., 2014 

4.5.4 LACTOSE 

Table (17) shows the maximum average content of lactose in 

pasteurized milk samples was during autumn (4.41± 0.26), and the 

minimum was during summer (4.33±0.49). Similarly, the highest average 

content of lactose in UHT milk samples was during autumn, and the lowest 

was during winter and spring, see table (18). The average content of 

pasteurized and UHT milk samples revealed non-significant differences 

between seasons (P>0.05), and the confidence interval was (4.36-4.42), 

(4.27-4.48) respectively. Yasmeen et al., found that the minimum average 

lactose was in summer (4.93), and the maximum in winter (6.26) (Yasmeen 

et al., 2012). The lactose content of milk in summer and winter was 

reported by Nategi et al., as 4.61% and 4.58% respectively (Nateghi et al., 

2014). Ghalib showed that the average lactose content in milk samples was 

4.62 ±0.2 in winter and 4.72±0.2 in summer (Galib, 2014).  

4.5.5 SOLIDS (ASH) 

The average content of solids in pasteurized milk samples during 

summer, autumn and winter did not change and was found as 0.65±0.04. 

The average content of solids in UHT milk samples was the highest 

during summer and autumn (0.65±0.04), and the lowest during winter and 



54 

spring (0.64±0.04). These results revealed non-significant differences 

between seasons (P>0.05). The confidence interval for pasteurized and 

UHT milk samples was (0.64-0.66), (0.63-0.66), respectively. 

Abd Elrahman et al., found that the average solid content in raw and 

pasteurized milk samples was 0.778±0.003, 0.718±0.001, respectively 

(Abd Elrahman et al., 2009). 

Table (17): Physiochemical properties of pasteurized milk samples 

according to seasons. 

NO. of Samples 31 30 18

Measurements Summer Autumn Winter Total P-value CI

Mean±Std 3.12±0.35 3.25±0.52 3.48±0.54 3.25±0.48 0.32 3.14-3.36

Min 2.52 1.97 2.52

Max 3.64 3.9 4.45

Mean±Std 8.03±0.49 8.04±0.47 7.92±0.44 8±0.47 0.65 7.9-8.1

Min 7.15 7.07 7.07

Max 9.91 9.19 8.89

Mean±Std 0.65±0.04 0.65±0.04 0.65±0.04 0.65±0.04 0.82 0.64-0.66

Min 0.58 0.58 0.57

Max 0.81 0.75 0.72

Mean±Std 4.33±0.27 4.41±0.26 4.35±0.24 4.36±0.26 0.053 4.31-4.42

Min 3.9 3.89 3.9

Max 5.45 5.05 4.89

Mean±Std 2.94±0.2 2.96±0.17 2.92±0.17 2.95±0.19 0.4 2.91-2.99

Min 2.62 2.59 2.59

Max 3.63 3.36 3.25

Mean±Std 0.5048±0.0976 0.51±0.0249 0.512±0.0186 0.5084±0.0631 0.12 0.4945-0.5223

Min 0.42 0.47

Max 0.62 0.56 0.56

Mean±Std 6.78±0.29 6.56±0.47 6.70±0.24 6.67±0.37 0.046 6.59-6.75

Min 6.24 5.37 6.31

Max 7.67 7.22 7.11

Fat %

SNF %

Ash %

Lactose %

Protien %

FP (-)

pH

Item

 

 

 



55 

Table (18): Physiochemical properties of UHT milk samples according 

to seasons. 
No. of Samples 7 7 6 6

Measurements Summer Autumn Winter Spring Total P-Value CI

Mean±Std 2.58±0.67 3.2±0.33 3.03±0.7 3.28±0.23 3.06±0.53 0.19 2.84-3.28

Min 1.78 2.67 1.78 2.83

Max 3.37 3.59 3.66 3.47

Mean±Std 7.98±0.57 8.01±0.46 7.85±0.51 7.99±0.26 7.96±0.45 0.92 7.78-8.14

Min 7.07 7.48 6.03 7.72

Max 8.89 8.82 8.36 8.4

Mean±Std 0.65±0.04 0.65±0.04 0.64±0.04 0.64±0.02 0.65±0.04 0.97 0.63-0.66

Min 0.58 0.6 0.56 0.62

Max 0.72 0.72 0.68 0.67

Mean±Std 4.38±0.31 4.41±0.24 4.35±0.34 4.35±0.2 4.38±0.26 0.96 4.27-4.48

Min 3.89 4.1 3.81 4.23

Max 4.89 4.85 4.84 4.51

Mean±Std 2.93±0.20 2.97±0.16 2.87±0.19 3.18±0.53 2.99±0.31 0.32 2.87-3.11

Min 2.59 2.73 2.53 2.86

Max 3.25 3.22 3.05 4.23

Mean±Std 0.5087±0.0059 0.4974±0.02 0.5057±0.0059 0.5080±0.0159 0.5048±0.014 0.61 0.4994-0.5102

Min 0.52 0.52 0.51 0.54

Max 0.5 0.46 0.5 0.49

Mean±Std 6.53±0.13 6.74±0.4 6.68±0.26 6.65±0.35 6.65±0.30 0.61 6.54-6.77

Min 6.36 6.08 6.41 6.32

Max 6.74 7.1 7017 7.15

Fat %

SNF %

Ash %

Item

Lactose %

Protien %

FP (-)

pH

 



56 

 

 

 

 

 

 

 

 

CHAPTER FIVE 

CONCLUSION AND RECOMMENDATION 



57 

5.1. CONCLUSION 

From the present study, the following conclusion could be drawn: 

 Physicochemical properties such as fat, solids not fat, acidity, 

lactose, and protein content showed that the milk samples were of 

good quality . 

 Physiochemical properties of milk (fat, protein, lactose, SNF, and 

total solids, PH, FP) are affected by seasonal variation. 

 As a result of the antibiotic screening test, the study revealed that 

5(36%) of 14 raw milk samples contained antibiotic residues, and 

21(27) of 79 pasteurized milk samples were contaminated by 

antibiotic residues. None of the 25 UHT milk samples was 

contaminated by antibiotic residues. 

 The osmolality of milk affected by seasonal variation 

5.2. RECOMMENDATIONS 

The following measures must be put into consideration in order to 

prevent or reduce the incidence of antibiotic residues in milk: 

1- The farmers should not have access to veterinary antibiotics, whose 

distribution should be regulated. 

2- The uses of antibiotics for the treatment of mastitis or any other 

infection should be under veterinary inspection. 



58 

3- An established network of scientists and regulators to implement a 

residue control program.  

4- Drug screening tests on-farm should be used.  

5- More studies on drug residues in food animal and establishment of 

suitable regulations and inspection systems are needed to reduce the 

risks of antibiotic and other drug residues for public health  

6- Adequate withdrawal period should be observed in all milking cows 

following the therapeutic use of antibiotics. 



59 

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