Di Marzo Larissa, Wojciechowski Karen L, Barbano David M
Northeast Dairy Food Research Center, Department of Food Science, Cornell University, Ithaca, NY 14853.
Northeast Dairy Food Research Center, Department of Food Science, Cornell University, Ithaca, NY 14853.
J Dairy Sci. 2016 Sep;99(9):7679-7689. doi: 10.3168/jds.2016-10848. Epub 2016 Jun 22.
Our objectives were to develop a method to produce milk somatic cell count (SCC) reference materials for calibration of electronic somatic cell count (ESCC) using gravity separation and to determine the effect of refrigerated storage (4°C) and freeze-thaw stability of the skim and whole milk SCC reference materials. Whole raw milk was high-temperature short-time pasteurized and split into 2 portions. One portion was gravity separated at 4°C for 22 h and the second portion was centrifugally separated to produce skim milk that was also gravity separated with somatic cells rising to the surface. After 22 h, stock solutions (low SCC skim milk, high SCC skim milk, high SCC whole milk) were prepared and preserved (bronopol). Two experiments were conducted, one to compare the shelf-life of skim and whole milk SCC standards at 4°C and one to determine the effect of freezing and thawing on SCC standards. Both experiments were replicated 3 times. Gravity separation was an effective approach to isolate and concentrate somatic cells from bovine milk and redistribute them in a skim or whole milk matrix to create a set of reference materials with a wider and more uniformly distributed range of SCC than current calibration sets. The liquid SCC reference materials stored using the common industry practice at 4°C were stable (i.e., fit for purpose, no large decrease in SCC) for a 2-wk period, whereas frozen and thawed reference materials may have a much longer useful life. A gradual decrease occurred in residual difference in ESCC (SCC × 1,000/mL) versus original assigned reference SCC over duration of refrigerated storage for both skim and whole milk SCC samples, indicating that milk ESCC of the preserved milks was gradually decreasing during 28 d of storage at 4°C by about 15,000 SCC/mL. No difference in the ESCC for skim milk was detected between refrigerated and frozen storage, whereas for whole milk the ESCC for frozen was lower than refrigerated samples. Future work is needed to determine the time and temperature of longer term frozen storage over which the SCC results are stable.
我们的目标是开发一种方法，利用重力分离来生产用于校准电子体细胞计数（ESCC）的牛奶体细胞计数（SCC）参考物质，并确定冷藏储存（4°C）以及脱脂和全脂牛奶SCC参考物质的冻融稳定性的影响。全脂原料奶经过高温短时巴氏杀菌后分成两份。一份在4°C下重力分离22小时，另一份进行离心分离以生产脱脂奶，该脱脂奶也通过重力分离使体细胞升至表面。22小时后，制备储备溶液（低SCC脱脂奶、高SCC脱脂奶、高SCC全脂奶）并保存（溴硝醇）。进行了两项实验，一项比较脱脂和全脂牛奶SCC标准品在4°C下的保质期，另一项确定冻融对SCC标准品的影响。两项实验均重复3次。重力分离是从牛乳中分离和浓缩体细胞并将它们重新分布在脱脂或全脂牛奶基质中的有效方法，从而创建一组SCC范围比当前校准组更宽且分布更均匀的参考物质。按照行业常规做法在4°C下储存的液体SCC参考物质在2周内是稳定的（即符合用途，SCC没有大幅下降），而冻融后的参考物质可能具有更长的使用寿命。在脱脂和全脂牛奶SCC样品的冷藏储存期间，ESCC（SCC×1,000/mL）与原始指定参考SCC的残余差异逐渐减小，这表明在4°C储存28天期间，保存牛奶的牛奶ESCC逐渐下降约15,000 SCC/mL。在冷藏和冷冻储存之间未检测到脱脂奶ESCC的差异，但对于全脂奶，冷冻后的ESCC低于冷藏样品。需要进一步开展工作来确定SCC结果稳定的长期冷冻储存时间和温度。
