常见热杀菌方式对关中羊乳品质的影响

采用5种常用热杀菌方式处理关中羊乳,即低温长时巴氏杀菌(65 ℃/30 min)、高温短时巴氏杀菌(72 ℃/15 s)、超巴氏杀菌(95 ℃/5 min)、高温高压灭菌(121 ℃/20 min)和超高温瞬时灭菌(137 ℃/7 s),在测定蛋白沉淀率、酒精稳定性、pH、红度值、粘度和脂肪球变化基础上,结合内源荧光光谱和聚丙烯酰胺凝胶电泳(SDS-PAGE)分析,探究热杀菌处理对关中羊乳品质的影响。结果表明,高温高压灭菌羊乳蛋白沉淀率最高、酒精稳定性最差、pH明显下降、红度值明显增大,但5种杀菌方式对粘度没有显著影响(p>0.05);羊乳脂肪球经巴氏杀菌和超巴氏杀菌后,表观直径略微增大,而高温高压灭菌和超高温瞬时灭菌,尤其是高温高压灭菌则导致其明显变小;荧光光谱表明,高温高压灭菌羊乳蛋白结构改变最大,内源荧光强度剧烈升高;电泳显示,巴氏杀菌(65 ℃/30 min和72 ℃/15 s)对羊乳酪蛋白和乳清蛋白影响较小,超巴氏杀菌(95 ℃/5 min)乳清蛋白开始变性、聚集或部分降解,高温高压灭菌和超高温瞬时灭菌,尤其是高温高压灭菌则使乳清蛋白明显降解甚至消失,酪蛋白出现聚集和解聚。结果表明,高温高压灭菌和超高温瞬时灭菌,尤其是高温高压灭菌对关中羊乳品质影响较大,超巴氏杀菌影响次之,而巴氏杀菌则对其影响较小。

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.