الفهرس 
REVIEW OF LITERATURE
Heat treatmentsOnly 14 pages are availabe for public view
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Abstract
Milk is usually subjected to several technological processing for production a wide range of dairy product. Perhaps one of the most important of these technological processes is heat treatments which are commonly applied to ensure the microbial safety and to extend shelf life of dairy products. Also, heat treatment of milk is widely used to alter its functional properties. Common heat treatments employed in the commercial processing of milk and milk products, preheat treatments, pasteurization and UHT technology. This variation in heat treatments applied in dairy industry consequently, effects on milk characteristics especially milk proteins.
The present work was planned to study the effect of some technological processing such as heat treatments and cooling storage on chemical, Physical and microstructure properties of skim buffalo’s milk.
Part I:
EFFECT OF HEAT TREATMENTS ON BUFFALO S’ MILK
The obtained results could be summarized as:
1- Heat treatment caused significant increase in acidity which reached to 0.197 % for heat treated samples at 137 ° C/ 3 sec. for all samples the pH decreased with increasing intensity of heat treatment.
2- Increasing the heat treatments caused decrease ethanol stability to a minimum for milk sample treated at high temperatures (110º C/ 10 min and 137º C/ 3 sec).
3- Heat treatments of milk samples resulted in a slight increase of surface tension
4- Applied heat treatments had no obvious effect on NPN content of both heated and unheated milk. Whereas, significant changes due to heat treatment were the increase in CN with a corresponding decrease in WPN. Also, increasing heat treatment caused decrease in non-casein nitrogen.5- A marked increase in protein carbonyl contents (as indicator to cause oxidation of protein) of heated samples at 110º C/ 10 min and 137º C/ 3 sec.
6- Cooling storage of raw and heat treated skim buffalo milk up to 28 days at 7ºC caused significant increases in protein carbonyl contents and had the significantly higher increase at storage at 25°C.
7- The protein breakdown (%) increased with storage period up to 28 days at 7ºC and 25°C indicating that proteolysis increased, whereas protein breakdown decreased at the heat treatment increased.
8- A marked decrease both of essential amino acid index and biological value of milk heat treated at 110º C/ 10 min and 137º C/ 3 sec. Consequently, heat treatment at 110ºC/10 min and 137ºC/ 3sec caused decrease both of protein efficiency ratio (PER) and chemical limiting score of lysine due to Millard reaction.
9- Electrophoretic patterns of milk samples showed different protein bands with different heat treatment and whey proteins were fully disappeared forming high molecular weight complexes in samples treated at 110 °C/10 min and 137 °C/3 Sec.
10- Heat treatment at 72ºC for 15 s, caused a slight denaturation of β-lg about 14% and the ratio reached to 95% at 90ºC/10 min.
11- HMF contents determined in this work are dramatic increase in milk samples treated at 110ºC/10 min and 137ºC/3 sec to level of 2214.59 and 1683.74, respectively.
12- Lactulose is a substance of high-heated milks. It resulted from thermal treatments at 110 ºC for 10 min and 137 ºC/ 3 sec and its concentration was very high, 1490 mg/L and 840 mg/L respectively.
13- Heat treatment at 137 ºC/ 3 sec caused formation of Dimethyl Dimethyl sulfide that causes the off flavor.
14- Rennet coagulation time was significant increased with increasing the heat treatment while the synresis value decreased. 15- Significant increase in penetration values for milk samples treated at 137 ºC/ 3 sec
16- Slightly increased in dynamic viscosity after the heat treatment at 72ºC/15 sec. While, heat treatment at 110ºC/10 min and 137ºC/3 sec caused dramatic increase in the dynamic viscosity values, which reached 3.20 and 3.36 CP, respectively.
17- Higher heat treatments at 110ºC/10 min and 137ºC/3 sec have changed the flow behavior of milk to the fully non-Newtonian type, since n values were reduced to the level of 0.734 and 0.716, respectively.
18- The lightness (L-values), were decreased in milk heat treated at 137ºC/ 3 sec. while yellowness (b-values) was decreased during storage up to 3 months.
19- Heat treatment buffalo milk caused some changes in distribution and structural changes in the casein micelles which reflected in micrographs taken by TEM.
Part II:
EFFECT OF HEAT TREATMENT ON FUNCTIONAL PROPERTIES OF MILK PROTEIN
1- Heat treatment at 72ºC/ 15 sec and 90ºC/10 min improved foam volume stability % at pH 5. On contrary, casein prepared from milk heated at 110ºC/10 min and 137ºC/3 sec showed lowest values for foam capacity and stability.
2- The higher values of the emulsion activity index at alkaline pH, Also heat treatment of milk at 72ºC/ 15 sec and 90ºC/10 min led to improve the emulsion properties.
3- The emulsion activity index was pH dependent. The minimum value was obtained at pH 5.0.
4- Water and oil binding capacities of buffalo’s rennet milk protein preparations were increased at 72ºC/ 15 sec and 90ºC/10 min. on contrary, rennet milk protein prepared from milk heated at 110ºC/ 10 min showed decreased in water and oil binding capacities.
5- A marked change in buffer capacity curves between milk proteins were prepared from unheated milk and milk heated at110ºC/10 min and 137ºC/3.
Part III:
EVALUATION OF INDUSTRY PROCESSING OF EGYPTIAN MARKET MILK
1- All random samples no obvious effect on NPN content of both heated and unheated milk. Whereas, significant increase in CN with a corresponding decrease in WPN of UHT milk samples Also, remarkable decrease in non-casein nitrogen in UHT samples.
2- Remarkable increase in protein carbonyl contents of UHT samples.
3- Increase formation of both of HMF and lactulose in UHT samples comparing with unheated milk and pasteurized milk .
4- A marked variation in b- value in UHT samples. Also, decreased in L-value (lightness) in UHT milk samples.