Northeast Dairy Foods Research Center, Department of Food Science, Cornell University, Ithaca, NY 14853, USA.
J Dairy Sci. 2010 Dec;93(12):5588-600. doi: 10.3168/jds.2010-3169.
The production of serum protein (SP) and micellar casein from skim milk can be accomplished using microfiltration (MF). Potential commercial applications exist for both SP and micellar casein. Our research objective was to determine the total SP removal and SP removal for each stage, and the composition of retentates and permeates, for a 3×, continuous bleed-and-feed, 3-stage, uniform transmembrane pressure (UTP) system with 0.1-μm ceramic membranes, when processing pasteurized skim milk at 50°C with 2 stages of water diafiltration. For each of 4 replicates, about 1,100 kg of skim milk was pasteurized (72°C, 16s) and processed at 3× through the UTP MF system. Retentate from stage 1 was cooled to <4°C and stored until the next processing day, when it was diluted with reverse osmosis water back to a 1× concentration and again processed through the MF system (stage 2) to a 3× concentration. The retentate from stage 2 was stored at <4°C, and, on the next processing day, was diluted with reverse osmosis water back to a 1× concentration, before running through the MF system at 3× for a total of 3 stages. The retentate and permeate from each stage were analyzed for total nitrogen, noncasein nitrogen, and nonprotein nitrogen using Kjeldahl methods; sodium dodecyl sulfate-PAGE analysis was also performed on the retentates from each stage. Theoretically, a 3-stage, 3× MF process could remove 97% of the SP from skim milk, with a cumulative SP removal of 68 and 90% after the first and second stages, respectively. The cumulative SP removal using a 3-stage, 3× MF process with a UTP system with 0.01-μm ceramic membranes in this experiment was 64.8 ± 0.8, 87.8 ± 1.6, and 98.3 ± 2.3% for the first, second, and third stages, respectively, when calculated using the mass of SP removed in the permeate of each stage. Various methods of calculation of SP removal were evaluated. Given the analytical limitations in the various methods for measuring SP removal, calculation of SP removal based on the mass of SP in the skim milk (determined by Kjeldahl) and the mass SP present in all of the permeate produced by the process (determined by Kjeldahl) provided the best estimate of SP removal for an MF process.
使用微滤（MF）可以从脱脂乳中生产血清蛋白（SP）和胶束酪蛋白。SP 和胶束酪蛋白都有潜在的商业应用。我们的研究目的是确定在 50°C 下使用 2 级水渗滤处理巴氏杀菌脱脂乳时，3×连续渗滤-进料、3 级、均匀跨膜压力（UTP）系统中陶瓷膜 0.1-μm 时，每个阶段的总 SP 去除率和 SP 去除率，以及截留物和渗透物的组成。对于 4 个重复中的每一个，约 1100kg 的脱脂乳被巴氏杀菌（72°C，16s），并通过 UTP MF 系统以 3×的速度进行处理。第 1 阶段的截留物冷却至<4°C 并储存，直到下一个处理日，用反渗透水稀释至 1×浓度，然后再次通过 MF 系统（第 2 阶段）处理至 3×浓度。第 2 阶段的截留物储存在<4°C，并在下一个处理日，用反渗透水稀释至 1×浓度，然后在 3×的条件下通过 MF 系统处理，共 3 个阶段。对每个阶段的截留物和渗透物进行凯氏定氮法分析总氮、非酪蛋白氮和非蛋白氮；对每个阶段的截留物还进行了十二烷基硫酸钠-PAGE 分析。理论上，3 级 3×MF 工艺可从脱脂乳中去除 97%的 SP，第 1 阶段和第 2 阶段的累积 SP 去除率分别为 68%和 90%。在本实验中，使用 0.01-μm 陶瓷膜的 UTP 系统进行 3 级 3×MF 工艺，当使用每个阶段渗透物中去除的 SP 质量计算时，第 1、第 2 和第 3 阶段的累积 SP 去除率分别为 64.8±0.8、87.8±1.6 和 98.3±2.3%。评价了各种 SP 去除率的计算方法。考虑到各种测量 SP 去除率的方法的分析局限性，基于凯氏法测定的脱脂乳中 SP 质量（由凯氏法测定）和过程中产生的所有渗透物中 SP 质量（由凯氏法测定）计算 SP 去除率，为 MF 工艺提供了 SP 去除率的最佳估计。
