Food Microbiology Research Laboratories R&D Division, Meiji Co., Ltd., 1-29-1 Nanakuni, Hachioji, Tokyo 192-0919, Japan.
Food Development Laboratories, R&D Division, Meiji Co., Ltd., 1-29-1 Nanakuni, Hachioji, Tokyo 192-0919, Japan.
J Dairy Sci. 2021 Feb;104(2):1454-1464. doi: 10.3168/jds.2020-19244. Epub 2020 Dec 11.
Yogurt is a well-known nutritious and probiotic food and is traditionally fermented from milk using the symbiotic starter culture of Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus. However, yogurt consumption may cause health problems in lactose-intolerant individuals, and the demand for lactose-free yogurt has been increasing. The standard method to prepare lactose-free yogurt is to hydrolyze milk by lactase; however, this process has been reported to influence the fermentation properties of starter strains. This study aimed to investigate the fermentation properties of an industrial starter culture of L. bulgaricus 2038 and S. thermophilus 1131 in lactose-hydrolyzed milk and to examine the metabolic changes induced by glucose utilization. We found that the cell number of L. bulgaricus 2038, exopolysaccharide concentration, and viscosity in the coculture of L. bulgaricus 2038 and S. thermophilus 1131 was significantly increased in lactose-hydrolyzed milk compared with that in unhydrolyzed milk. Although the cell number of S. thermophilus 1131 showed no difference, production of formic acid and reduction of dissolved oxygen were enhanced in lactose-hydrolyzed milk. Further, in lactose-hydrolyzed milk, S. thermophilus 1131 was found to have increased the expression of NADH oxidase, which is responsible for oxygen reduction. These results indicated that glucose utilization promoted S. thermophilus 1131 to rapidly reduce the dissolved oxygen amount and produce a high concentration of formic acid, presumably resulting in the increased cell number of L. bulgaricus 2038 in the coculture. Our study provides basic information on the metabolic changes in starter strains in lactose-hydrolyzed milk, and demonstrates that lactose-free yogurt with increased cell number of L. bulgaricus can be prepared without delay in fermentation and decrease in the cell number of S. thermophilus.
酸奶是一种众所周知的营养和益生菌食品，传统上是使用嗜热链球菌和德氏乳杆菌保加利亚亚种的共生发酵剂从牛奶中发酵而来。然而，酸奶的消费可能会导致乳糖不耐受个体的健康问题，并且对无乳糖酸奶的需求一直在增加。制备无乳糖酸奶的标准方法是使用乳糖酶水解牛奶；然而，据报道，该过程会影响发酵剂菌株的发酵特性。本研究旨在研究工业保加利亚乳杆菌 2038 和嗜热链球菌 1131 的发酵特性在乳糖水解乳中，并研究葡萄糖利用引起的代谢变化。我们发现，与未水解乳相比，乳糖水解乳中保加利亚乳杆菌 2038 的细胞数、胞外多糖浓度和 2038 和 1131 嗜热链球菌共培养物的粘度显著增加。尽管 1131 嗜热链球菌的细胞数没有差异，但在乳糖水解乳中产生的甲酸和溶解氧的减少得到增强。此外，在乳糖水解乳中，发现 1131 嗜热链球菌增加了负责还原氧的 NADH 氧化酶的表达。这些结果表明，葡萄糖利用促进了 1131 嗜热链球菌快速降低溶解氧含量并产生高浓度的甲酸，可能导致共培养物中保加利亚乳杆菌 2038 的细胞数增加。本研究提供了关于乳糖水解乳中发酵剂菌株代谢变化的基本信息，并表明可以在不延迟发酵和减少嗜热链球菌细胞数的情况下制备具有增加的保加利亚乳杆菌 2038 细胞数的无乳糖酸奶。
