不同保存条件对牛奶成分测定的影响

防腐剂、保存温度、保存时间均可影响牛奶成分测定的准确性,本试验旨在研究不同保存条件对牛奶成分测定的影响。试验样品为5头荷斯坦牛的牛奶,试验设计对照(CON)、0.60g/L的重铬酸钾(potassium dichromate,PD)、1.00g/L的苯甲酸钠(sodium benzoate,SB)和1.00g/L的山梨酸钾(potassium sorbate,PS)四个处理组,每个处理设置-20℃、4℃、25℃和40℃四种保存温度,测定不同防腐剂和温度条件下,5头牛的奶样在18d保存期内乳脂率、乳蛋白率、乳糖率、非脂固形物含量和尿素氮浓度的变化规律,以期得出最佳保存条件。结果表明:添加PD和SB不影响牛奶成分的测定结果,PS会导致乳蛋白率和非脂固形物检测结果显著升高(P<0.05);PD可在10d内保持牛奶成分的稳定,其防腐效果优于SB和PS;4℃下奶样的保存效果优于-20℃,25℃和40℃下奶样不能较长时间保存。

Effects of Different Preservation Conditions on Determination of Milk Composition

The objective of the present experiment is to analyze the effects of different preservatives,preservation temperature and preservation time on determination of milk composition.Five Holstein cows with the same genetic background was sellected,there were four treatments,no preservatives,0.60 g/L potassium dichromate,1.00 g/L sodium benzoate,1.00 g/L potassium sorbate,each treatment setting four preservation temperature,-20℃,4℃,25℃and 40℃.In order to obtain the optimum preservation conditions,the changes of milk fat percentage,milk protein percentage,lactose percentage,non-fat solids(NFS)percentage and urea nitrogen concentration of 5 dairy cows were determined under different treatments during 18 days of preservation.The results shows that milk composition isn’t affected by potassium dichromate and sodium benzoate.However,the added potassium sorbate increased milk protein and NFS content significantly.Potassium dichromate can maintain the stability of milk composition within 10 days,and the antiseptic effect was better than sodium benzoate and potassium sorbate.The preservation effect of milk samples under 4℃was better than which under-20℃,and milk samples under 25℃and 40℃could not be preserved for a long time.