Food & Nutrition

Arab Journal of Food & Nutrition
List C: English Abstracts of Ph.D. Student Theses in Jordan in
Food Science and Technology until December,2010.
1. Influence of Some Heating and Processing Methods on Chemical Changes of
Lipids in Selected Locally Produced Dairy Products (2003)
Saqer M. Herzallah\ University of Jordan
Supervisor: Dr. Mohammad A. Humeid
Co-Supervisor: Dr. Khalid Al-Ismail
Milk lipids are the most diverse milk components as they contain more than 400
fatty acids and sterols, mostly cholesterol. Some of the fatty acids are found to have
anticarcinogenic properties such as conjugated linoleic acid (CLA), and butyric acid.
Milk lipids are usually the most susceptible milk component to oxidation and chemical
changes during heat treatment and storage. This will lower their nutritive value and
may adversely affect the consumer’s health.
The objectives of this study were to investigate the effect of heating treatments
(pasteurization and boiling), microwaving, processing steps and storage of milk and
some locally produced dairy products on chemical changes of milk lipids. Peroxide
value (POV) p- anisidine value (p-AV), thiobarbituric acid (TBA), free fatty acid, and
totox value were evaluated. Furthermore, the cholesterol contents, 7-ketocholesterol,
trans-isomers formation, CLA content and fatty acid profiles were measured using GC,
HPLC and FTIR.
The results revealed that heating treatments of milk do significantly increase the
levels of the oxidation parameters such as POV compared to those of fresh raw milk.
The highest POV value (mEq O 2 / kg fat) was for milk pasteurized at 95± 1.0°C for 15
min (0.435), followed by milk heated at 63 ± 1.0°C for 30 min (0.381), whereas, the
lowest value was for milk pasteurized at 85 ± 1.0°C for 16 sec (0.234).
Cholesterol oxides, mostly 7-ketocholesterol were not detected (ND) in all raw
milk samples. On the contrary, heating milk led to formation of these oxides in
different quantities. UHT milk prepared from milk powder heated at 140 ± 1.0°C for 4
sec was found to have the highest value of 7-ketocholesterol (80.97μgg-1), followed
by microwave heated milk for 5 min (31.29μgg-1), whereas the lowest value was in
milk pasteurized at 85 ± 1.0°C for 16 sec (3.125μgg-1).
The conventional heating methods of milk did not cause any significant increase
in the trans-isomers content, with the exception of milk heated at 63 ± 1.0°C for 30
min and milk microwaved for 5 min, which were significantly increased by ca. 19%
and 31%, respectively.
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