الفهرس 
acknowledgement
Effect of microwave treatment on milk characteristicsOnly 14 pages are availabe for public view
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Abstract
This work were carried out to determined effect of microwave on physico-chemical and microbiological propertiesof buffalo, cow and mixed milk also to follow the changes in physico-chemical and microbiological properties of examined milk samples during refrigerated storage at 1st, 2nd, 3rd, 5th and 7th days at 5±2°C, evaluate differences among microwaved, pasteurized, sterilized and in water bath heat treated milk samples in chemical composition and microbiological properties. The effect of microwave on fatty acids, vitamins and total phenolic content in tested samples comparable with raw, pasteurized and sterilized milk was determined, illustrate differences in organoleptic properties between yoghurt and Domiatti cheese manufactured by using heat treated milk and those manufactured using microwaved milk. For this, three samples of buffalo, cow and mixed milk (1buffalo:1cow) were collected and analyzed.
The results obtained could be summarized as follows:
1- Immediately microwaved milk properties
A- Buffalo milk
a- Physico-chemical properties
1- Non-significant differences (F-value) were found among treatments (control, 30s, 60s, 90s, 120s, 150s and180s) in moisture content which decreased during microwave treatment.
2- Fat content increased during microwave treatment with increasing of exposure period without significant differences (F-value).
3- Protein content increased with prolongation of exposure period to microwave with high significant differences (F-value, P<0.01).
4- High significant differences (F-value, P<0.01) were found among different treatments in ash contentwhich increase with increasing microwave exposure period.
5- Titratable acidity increased during microwavingwith high significant differences (F-value, P<0.01).
6- Sp. Gr. values also increased during microwaving without significant differences (F-value, P<0.01).
b- Microbiological quality
1- Total bacterial counts were decreased sharply during microwaving with high significant differences (F-value, P<0.01).
2- Also, high significant differences (F-value, P<0.01) were found among treatments in counts of LAB which decreased during microwaving.
3- Psychrotrophic bacteria counts were decreased as a result of microwave exposure without significant differences (F-value).
4- Lipolytic bacteria were decreased during different periods with high significant differences (F-value, P<0.01).
5- High significant differences (F-value, P<0.01) were observed among different microwave exposure periods in proteolytic bacteria counts which decreased.
6- Regarding to yeast counts, also decreased with high significant differences (F-value, P<0.01).
7- Mould counts decreased during different treatments without significant differences (F-value).
8- No coliform bacteria were detected in raw milk or microwaved one.
B- Cow milk
a- Physico-chemical properties
1- Moisture percent was decreased during microwaving with high significant differences (F-value, P<0.01).
2- Fat content in cow’s milk was increased gradually during microwave treatment without significant differences (F-value).
3- Protein content also increased during microwave treatment without significant differences (F-value).
4- Non-significant differences (F-value) were found in ash content which increased during microwave period.
5- High significant differences (F-value, P<0.01) were found in titratable acidity percent during microwaving with gradual increase.
6- Sp. Gr. increased during microwave exposure periods with high significant differences (F-value, P<0.01).
b- Microbiological characteristics
1- TBC in cow’s milk decreased with increasing of microwave exposure period with high significant differences (F-value, P<0.01).
2- LAB also were decreasedduring microwave treatment with high significant differences (F-value, P<0.01) among treatments.
3- Psychrotrophic bacteria countwas decreased during microwaving without significant differences (F-value).
4- High significant differences (F-value, P<0.01) were found among treatments in lipolytic bacteria count which decreased during microwaving.
5- proteolytic bacteria were not found in raw or microwaved milk.
6- Non-significant differences (F-value) were found in yeast counts which decreased during microwaving.
7- Non-significant differences (F-value) were found in mould count which decreased during microwaving also.
8- No coliform bacteria were found either in raw or microwaved milk.
C- Mixed milk
a- Physico-chemical properties
1- A gradual decreased were occurred in moisture content of mixed milk with high significant differences (F-value, P<0.01).
2- Fat content were increased significantly (F-value, P<0.05) during microwaving.
3- Protein percent increased during microwave treatment without significant differences (F-value).
4- High significant differences (F-value, P<0.01) were found among treatments in ash content which increased gradually during microwaving.
5- Non-significant differences (F-value) were observed in titratable acidity content which increased during microwave treatment.
6- Sp. Gr. values were increased with increasing microwave exposure period without significant differences (F-value).
b- Microbiological characteristics
1- TBC in mixed milk were decreased with increasing microwave exposure period with high significant differences (F-value, P<0.01).
2- High significant differences (F-value, P<0.01) were found among different treatment in counts of LAB which decreased as a result of prolongation of microwave exposure period.
3- Non-significant differences (F-value) were reported in counts of psychrotrophic bacteria which decreased gradually during microwaving.
4- Lipolytic bacteria were decreased gradually during microwave treatment with high significant differences (F-value, P<0.01).
5- Non-significant differences (F-value) were found among treatments in counts of proteolytic bacteria which decreased during treatments.
6- High significant differences (F-value, P<0.01) were found among treatments in counting of yeast which decreased during microwaving.
7- Mould counts were decreased also during microwaving with high significant differences (F-value, P<0.01).
8- No coliform bacteria were detected neither in raw nor microwaved milk.
2- Cold stored microwaved milkproperties
a- Physico-chemical composition
1- Moisture content were decreased during storage in case of 150s and 180s treatments without significant differences (F-value) among storage periods in all investigated milks except in treatment 150s of mixed milk which have significant differences (F-value, P<0.05).
2- Regarding to fat%, non-significant differences (F-value) were found among storage periods in fat content either in buffalo, cow or mixed milk for 150s and 180s treatments.
3- Protein content were increased during storage period without significant differences (F-value) in case of cow and mixed milk for 150s and 180s treatment while in case of buffalo’s milk high significant differences (F-value, P<0.01) were found in 150s and 180s treatments.
4- Ash content was increased during storage period without significant differences (F-value) among storage periods in all cases.
5- Titratable acidity was increased during storage without significant differences (F-value) in case of buffalo and mixed milk for 150s and 180s while in case of cow milk significant differences (F-value, P<0.05) were found in 150s treatments and high significant differences (F-value, P<0.01) were found for 180s treatments.
6- Non-significant differences (F-value) were found among storage period in Sp. Gr. value in all cases except of 180s treatment of cow’s milk which has significant differences (F-value, P<0.05). Sp. Gr. value was increased during storage.
b- Microbiological characteristics
1- TBC was increased during storage periods with non-significant differences (F-value) in case of buffalo’s milk for 150s and 180s treatment, while in case of cow’s milk non-significant differences (F-value) were found in 150s and high significant differences (F-value, P<0.01) were found in 180s treatment. Regarding to mixed milk, high significant differences (F-value, P<0.01) were found in 150s and 180s treatments.
2- LAB not found in any investigated milk either in immediately microwave or stored microwaved milk for 150s and 180s.
3- Psychrotrophic bacteria not found in buffalo milk for 150s and 180s treatments and mixed milk for 180s treatment, while non-significant differences (F-value) were found in case of cow’s milk for 150s and 180s treatments and mixed milk for 150s treatments.
4- Non-significant differences (F-value) were found among storage periods for 150s and 180s treatmentsin counts of lipolytic bacteria which increased during storage.
5- Proteolytic bacteria counts wereincreased during storage period in case of buffalo, cow and mixed milk for 150s and 180s without significant differences (F-value).
6- Yeasts not detected in immediately microwaved or stored microwaved milk for 150s and 180s treatments.
7- Moulds also not detected either in immediately microwaved or stored microwaved milk for 150s and 180s.
3- Microwaved milk and milk treated with water bath properties:
a- Physico-chemical properties
1- Moisturecontent was higher in milk treated in water bath than those of microwaved one with high significant differences (F-value, P<0.01).
2- Fat percent was higher in microwaved milk than those of milk treated in water bath with high significant differences (F-value, P<0.01).
3- Protein content was higher in microwaved milk than milk treated in water bath without significant differences (F-value).
4- Non-significant differences (F-value) were found between microwaved milk and milk treated in water bath in ash content which was higher in microwaved milk than those treated in water bath.
5- High significant differences (F-value, P<0.01) were found in titratable acidity which was higher in microwaved milk.
6- Sp. Gr. value was higher significantly (F-value, P<0.05) in microwaved milk than milk treated in water bath.
b- Microbiological characteristics
1- TBC was higher in milk treated in water bath than microwaved milk with high significant differences (F-value, P<0.01).
2- LAB not detected either in microwaved milk or milk treated in water bath.
3- Psychrotrophic bacteria not detected in microwaved milk or milk treated in water bath.
4- Lipolytic bacteria not found in microwaved milk while it found in milk treated in water bath at 87°C with high significant differences (F-value, P<0.01).
5- Proteolytic bacteria were found in microwaved and water bath treated milk at 87°C only with high significant differences (F-value, P<0.01).
6- Yeast was found in microwaved and water bath treated milk only at 87°C with high significant differences (F-value, P<0.01).
7- High significant differences (F-value, P<0.01) were found between microwaved milk and milk treated in water bath in mould countswhich appeared in microwaved and treated in water bath milk at 87°C only.
4- Microwaved, pasteurized and sterilized milk properties:
a- Physico-chemical properties
1- Moisture content was higher in pasteurized milk followed by microwaved and sterilized milk with high significant differences (F-value, P<0.01).
2- Fat percent was higher in sterilized milk followed with microwaved and pasteurized milk without significant differences (F-value).
3- High significant differences (F-value, P<0.01) were found in protein content which was higher in sterilized and microwaved milk than in pasteurized milk.
4- Ash percent was higher in microwaved milk followed by sterilized and pasteurized milk withhigh significant differences (F-value, P<0.01).
5- Titratable acidity content was higher in sterilized milk followed by microwaved and pasteurized milk with high significant differences (F-value, P<0.01).
6- Non-significant differences (F-value) were found in Sp. Gr. which was higher in sterilized milk than microwaved and pasteurized milk.
b- Microbiological characteristics
1- TBC was higher in pasteurized milk followed with microwaved and sterilized milk with high significant differences (F-value, P<0.01).
2- LAB not detected in microwaved or pasteurized and sterilized milk.
3- Psychrotrophic bacteria were higher in pasteurized milk than in microwaved milk while not found in sterilized one with high significant differences (F-value, P<0.01).
4- Lipolytic bacteria were found in pasteurized milk only with high significant differences (F-value, P<0.01).
5- High significant differences (F-value, P<0.01) were found among treatment in proteolytic bacteria which were found in pasteurized milk only.
6- Yeast not detected in any treatment.
7- Mould not detected in any treatment.
5- Effect of different treatments on fatty acids, vitamins and total phenols
A- Fatty acids
The highest fatty acids were oleic acid followed with palmitic acid. Fatty acids decreased with increasing of exposure to heat treatments.
B- Vitamins
Most vitamins decreased when exposed to heat treatment.
C- Total phenols
Total phenols content decreased affecting with heat treatment.
6- Organoleptic properties of yoghurt and Domiatti cheese:
A- Yoghurt
Yoghurt manufactured by heat treated milk had high scores than those using microwaved milk.
B- Domiatti cheese
Domiatti cheese manufactured using microwaved milk had higher score than those made using heat treated milk.
from the obtained results, it could be recommended that using microwave heating had better effect on microbiological properties, chemical composition and keeping quality of milk with less change in organoleptic properties of treated milk also fast and easy way comparable with other heat treatments.