مقايسه تغييرات شاخص پروتئوليز در شير خام و پاستوريزه تحت تاثير درجه حرارت و زمان نگهداري

A Comparison of Proteolysis Changes in Raw as Pasteurized Milk as Influenced by Temperature and Storage Time

The effects of pasteurization, storage time and temperature on proteolysis of milk were evaluated. Two replicates of each of raw and pasteurized milk were assigned to three temperatures (5, 16 and 25 ʹc) and 3 storage periods (I, 2 and 3 day) in a 2x3x3 full factorial design. For all the samples, pH and indices of proteolysis were determined. The effectof all the three main factors (pasteurization, storage time and temperature) as well as their two and threeway interactions were significant on pH and proteolysis indices. As storage time and temperature increased pH of either one of raw or pasteurized milk, decreased. Proteolysis indices also increased in both cases, but the change of these two factors for pasteurized milk were lower thanthose for raw milk. Degradation of each one of nukj proteins was demonstrated through SDS-PAGE (10-20%). Correlations were observed to be negative between levels of% casein and % proteolysis products. With increase in temperature %casein decreased while proteolysis products being increased. But a-lactalbumin and p- lactoglubolin did not vary with change in temperature and during the storage time.