Food Research and Development Centre (FRDC), Agriculture and Agri-Food Canada, St. Hyacinthe, Quebec, Canada.
J Dairy Sci. 2012 Jan;95(1):1-8. doi: 10.3168/jds.2010-4142.
Caseinomacropeptide (CMP) is a 7-kDa phosphoglycopolypeptide released from κ-casein during milk digestion and in the cheesemaking process. The objective of the study was to analyze the effect of pepsin-treated CMP from cow and goat milk on the resistance of Escherichia coli and Lactobacillus rhamnosus during acid stress. Bacterial cells in the exponential growth phase were suspended in acidified phosphate buffered saline with or without pepsin-treated CMP. Viability was determined during a 90-min incubation period. Pepsin-treated CMP exhibited bactericidal activity at pH 3.5 when added in a dose-dependent manner to E. coli, decreasing survival by more than 90% within 15 min at 0.25 mg/mL. At pH >4.5, the bactericidal activity disappeared, indicating that pepsin-treated CMP was efficient at low pH only. The effectiveness of pepsin-treated CMP at pH 3.5 was not affected by the presence of glycoconjugates linked to CMP or by the bovine or caprine origin of milk. In contrast, L. rhamnosus, a probiotic, was more resistant to acid stress when pepsin-treated bovine or caprine CMP was added to the media. Viability reached 50% after 60 min of incubation at pH 3 compared with 5% survival in the media without added pepsin-treated CMP. Neither glycosylation extent nor sequence variations between CMP from bovine milk and caprine milk affected the protective activity of hydrolyzed CMP toward L. rhamnosus. This suggests that encrypted bioactive peptides released by the pepsin treatment of CMP had an antibacterial effect on E. coli in acidic media, but improved the resistance of L. rhamnosus to acid stress. The peptide fragment accountable for bactericidal activity is the N-terminal region κ-casein f(106-124).
酪蛋白巨肽（CMP）是κ-酪蛋白在牛奶消化和干酪制作过程中释放出的一种 7kDa 磷酸糖多肽。本研究的目的是分析来自牛乳和羊乳的胃蛋白酶处理 CMP 对大肠杆菌和鼠李糖乳杆菌在酸性应激下的抗性的影响。将处于指数生长期的细菌细胞悬浮在酸化的磷酸盐缓冲液中，或添加胃蛋白酶处理的 CMP。在 90min 的孵育期间确定存活率。当以剂量依赖的方式将胃蛋白酶处理的 CMP 添加到大肠杆菌中时，在 pH3.5 下表现出杀菌活性，在 0.25mg/mL 时，在 15min 内使存活率降低超过 90%。在 pH>4.5 时，杀菌活性消失，表明胃蛋白酶处理的 CMP 仅在低 pH 下有效。在 pH3.5 下，胃蛋白酶处理的 CMP 的有效性不受与 CMP 相连的糖缀合物的存在或乳源（牛或羊）的影响。相反，当向培养基中添加胃蛋白酶处理的牛或羊 CMP 时，益生菌鼠李糖乳杆菌对酸应激的抗性更强。与不添加胃蛋白酶处理的 CMP 的培养基中 5%的存活率相比，在 pH3 下孵育 60min 后，存活率达到 50%。牛乳和羊乳 CMP 的糖基化程度或序列变异均不影响水解 CMP 对鼠李糖乳杆菌的保护活性。这表明，CMP 的胃蛋白酶处理释放的加密生物活性肽在酸性介质中对大肠杆菌具有抗菌作用，但提高了鼠李糖乳杆菌对酸应激的抗性。负责杀菌活性的肽片段是κ-酪蛋白 f(106-124)的 N 端区域。
