Geer S R, Barbano D 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. 2014;97(4):2027-38. doi: 10.3168/jds.2013-7629. Epub 2014 Feb 15.
Our objective was to determine the role that immunoglobulins and somatic cells (SC) play in the gravity separation of milk. The experiment comprised 9 treatments: (1) low-temperature pasteurized (LTP; 72°C for 17.31s) whole milk; (2) LTP (72°C for 17.31s) whole milk with added bacteria and spores; (3) recombined LTP (72°C for 17.31s) whole milk with added bacteria and spores; (4) high-temperature pasteurized (HTP; 76°C for 7min) whole milk with added bacteria and spores; (5) HTP (76°C for 7min) whole milk with added bacteria and spores and added colostrum; (6) HTP (76°C for 7min) centrifugally separated, gravity-separated (CS GS) skim milk with HTP (76°C for 7min) low-SC cream with added bacteria and spores; (7) HTP (76°C for 7min) CS GS skim milk with HTP (76°C for 7min) high-SC cream with added bacteria and spores; (8) HTP (76°C for 7min) CS GS skim milk with HTP (76°C for 7min) low-SC cream with added bacteria and spores and added colostrum; and (9) HTP (76°C for 7min) CS GS skim milk with HTP (76°C for 7min) high-SC cream with added bacteria and spores and added colostrum. The milks in the 9 treatments were gravity separated at 4°C for 23h in glass columns. Five fractions were collected by weight from each of the column treatments, starting from the bottom of the glass column: 0 to 5%, 5 to 90%, 90 to 96%, 96 to 98%, and 98 to 100%. The SC, fat, bacteria, and spores were measured in each of the fractions. The experiment was replicated 3 times in different weeks using a different batch of milk and different colostrum. Portions of the same batch of the frozen bacteria and spore solutions were used for all 3 replicates. The presence of both SC and immunoglobulins were necessary for normal gravity separation (i.e., rising to the top) of fat, bacteria, and spores in whole milk. The presence of immunoglobulins alone without SC was not sufficient to cause bacteria, fat, and spores to rise to the top. The interaction between SC and immunoglobulins was necessary to cause aggregates of fat, SC, bacteria, and spores to rise during gravity separation. The SC may provide the buoyancy required for the aggregates to rise to the top due to gas within the SC. More research is needed to understand the mechanism of the gravity-separation process.
我们的目标是确定免疫球蛋白和体细胞（SC）在牛奶重力分离过程中所起的作用。实验包括9种处理方式：（1）低温巴氏杀菌（LTP；72°C处理17.31秒）全脂牛奶；（2）添加了细菌和孢子的低温巴氏杀菌（72°C处理17.31秒）全脂牛奶；（3）添加了细菌和孢子的重组低温巴氏杀菌（72°C处理17.31秒）全脂牛奶；（4）添加了细菌和孢子的高温巴氏杀菌（HTP；76°C处理7分钟）全脂牛奶；（5）添加了细菌和孢子以及初乳的高温巴氏杀菌（76°C处理7分钟）全脂牛奶；（6）高温巴氏杀菌（76°C处理7分钟）离心分离、重力分离（CS GS）脱脂牛奶与高温巴氏杀菌（76°C处理7分钟）低体细胞含量稀奶油，并添加细菌和孢子；（7）高温巴氏杀菌（76°C处理7分钟）CS GS脱脂牛奶与高温巴氏杀菌（76°C处理7分钟）高体细胞含量稀奶油，并添加细菌和孢子；（8）高温巴氏杀菌（76°C处理7分钟）CS GS脱脂牛奶与高温巴氏杀菌（76°C处理7分钟）低体细胞含量稀奶油，添加细菌和孢子以及初乳；（9）高温巴氏杀菌（76°C处理7分钟）CS GS脱脂牛奶与高温巴氏杀菌（76°C处理7分钟）高体细胞含量稀奶油，添加细菌和孢子以及初乳。9种处理方式的牛奶在4°C下于玻璃柱中进行23小时的重力分离。从玻璃柱底部开始，按重量收集每种柱处理方式的五个部分：0至5%、5至90%、90至96%、96至98%以及98至100%。对每个部分中的体细胞、脂肪、细菌和孢子进行测量。该实验在不同周使用不同批次的牛奶和不同的初乳重复进行了3次。同一批次的冷冻细菌和孢子溶液的部分用于所有3次重复实验。全脂牛奶中脂肪、细菌和孢子正常重力分离（即上升到顶部）需要体细胞和免疫球蛋白同时存在。仅存在免疫球蛋白而没有体细胞不足以使细菌、脂肪和孢子上升到顶部。体细胞与免疫球蛋白之间的相互作用对于在重力分离过程中使脂肪、体细胞、细菌和孢子的聚集体上升是必要的。由于体细胞内的气体，体细胞可能为聚集体上升到顶部提供所需的浮力。需要更多研究来了解重力分离过程的机制。
