浓缩与冻结方式对牛乳品质的影响

通过膜分离将鲜牛乳浓缩成不同总固形物含量的乳样(11. 83%、14. 94%、17. 61%、23. 01%),采用4种冻结方式(冰箱冻结、冷库冻结、螺旋冻结、平板冻结)对乳样进行冻结处理。测定乳样的色度、p H值、酸度、粒度、乙醇稳定性和热稳定性,并结合共聚焦显微镜和十二烷基硫酸钠-聚丙烯酰胺凝胶电泳进行对比分析。结果表明,随着总固形物含量的升高,牛乳的p H值、酸度、乙醇稳定性和热稳定性降低,总色差值、平均粒径增大。经冻结处理后乳样中β-乳球蛋白含量均降低。在4种冻结方式中,平板冻结速率最快,乳样的乙醇稳定性和热稳定性均最高;冰箱冻结的乳样平均粒径和乳脂肪球粒径均最大。综上,推荐将鲜牛乳浓缩至总固形物含量为23. 01%,然后采用平板冻结的工艺,可以更好地维持冻结乳样的品质。

Effects of concentrating and freezing methods on milk quality

In order to investigate the effects of concentrating and freezing methods on milk quality,the milk was concentrated into samples of different total solids content(11.83%,14.94%,17.61%,23.01%)by membrane separation.Milk samples were frozen in four ways(general refrigerator,cold storage,spiral freezer,and plate freezer).The indices were determined by color,pH,titratable acidity,particle size,ethanol stability and heat stability,and the combination of confocal microscopy and sodium dodecyl sulfate-polyacrylamide gel electrophoresis(SDS-PAGE)were also measured.The results showed that with the increase of total solids content,the pH value,titratable acidity,ethanol stability and heat stability of milk decreased,and the total color difference value and mean particle diameter increased.β-lactoglobulin content in milk samples decreased after freezing treatment.Among the four freezing methods,the plate freezing rate was the fastest,and ethanol stability and thermal stability were the best.The mean particle size of general refrigerator frozen milk and the size of milk fat globules were the largest.In conclusion,milk samples concentrated to a total solids content of 23.01%and frozen with a plate freezer were recommended.