Effect of Common Thermal Sterilization Methods on the Quality of Guanzhong Goat Milk

Guanzhong goat milk was treated by five common thermal sterilization:low temperature long-time pasteurization(65 ℃/30 min),high temperature short-time pasteurization(72 ℃/15 s),ultra-pasteurization(95 ℃/5 min),high temperature high pressure sterilization(121 ℃/20 min)and ultra-high temperature instantaneous sterilization(137 ℃/7 s)in this research,and protein precipitation rate,alcohol stability,pH,color value,viscosity and fat ball,as well as endogenous fluorescence spectrum and SDS-PAGE were measured to explore the influence of thermal sterilization on quality of goat milk. The results showed that goat milk treated by high temperature high pressure sterilization displayed the highest protein precipitation rate,the lowest alcohol stability,significant pH reduction and red value increase,while viscosity showed no significant difference among five thermal sterilization methods. Moreover,fat ball diameter increased slightly for pasteurization and ultra-pasteurization versus obvious decrease for high temperature high pressure sterilization and ultra-high temperature instantaneous sterilization especially high temperature high pressure sterilization. In addition,high temperature high pressure sterilization resulted in dramatically increase of endogenous fluorescence intensity,which indicated obvious change of milk protein structure. SDS-PAGE showed 65 ℃/30 min and 72 ℃/15 s pasteurization had limited effect on casein and whey protein;95 ℃/5 min ultra-pasteurization caused whey protein to denature,aggregate and slightly degrade;137 ℃/7 s especially 121 ℃/20 min,brought obvious dissociation or even disappearance for whey protein,and polymerization as well as depolymerization for casein. Therefore,ultra-high temperature especially high-pressure sterilization had more obvious impact on the quality of Guanzhong Goat milk,followed by ultra-pasteurization,while pasteurization had small impact.