State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi, Jiangsu 214122, China.
State Key Laboratory of Dairy Biotechnology, Shanghai Engineering Research Center of Dairy Biotechnology, Dairy Research Institute, Bright Dairy and Food Co., Ltd., Shanghai 200436, China.
J Dairy Sci. 2020 Jan;103(1):166-171. doi: 10.3168/jds.2019-17009. Epub 2019 Nov 6.
The ability to use lactose is critical for the application of Streptococcus thermophilus in fermented dairy products. Most studies have evaluated the use of lactose of S. thermophilus by measuring lactose utilization, but its correlation with β-galactosidase and urease has rarely been investigated. In this study, 10 strains of S. thermophilus isolated from fermented yak milk exhibited a diversity of β-galactosidase and urease activities, growth, and acid production in de Man, Rogosa, and Sharpe-lactose. Among the strains, 15G5 possessed the highest β-galactosidase activity and showed the highest cell growth, lactic acid production, and titratable acidity during fermentation. In contrast, 7G10, with the weakest β-galactosidase activity, produced the lowest lactic acid content and change in titratable acidity. Further investigation indicated that β-galactosidase activity of S. thermophilus showed significant positive correlations with the growth of cell densities, the production of lactic acid, and titratable acidity, and urease activity of S. thermophilus showed a significant correlation with the use of lactose and the production of lactic acid and acetaldehyde. These findings suggest that the differences of β-galactosidase and urease activities are essential for the performance in the lactose metabolism, growth, and acid production of S. thermophilus, providing new insights into strain selection and application.
能够利用乳糖对于嗜热链球菌在发酵乳制品中的应用至关重要。大多数研究通过测量乳糖利用率来评估嗜热链球菌对乳糖的利用情况，但很少有研究调查其与β-半乳糖苷酶和脲酶的相关性。在本研究中，从发酵牦牛奶中分离出的 10 株嗜热链球菌表现出β-半乳糖苷酶和脲酶活性、在德芒氏、罗高氏和夏普乳糖中的生长和产酸的多样性。在这些菌株中，15G5 具有最高的β-半乳糖苷酶活性，在发酵过程中表现出最高的细胞生长、乳酸产量和可滴定酸度。相比之下，β-半乳糖苷酶活性最弱的 7G10 产生的乳酸含量最低，可滴定酸度变化最小。进一步的研究表明，嗜热链球菌的β-半乳糖苷酶活性与细胞密度的生长、乳酸的产生和可滴定酸度呈显著正相关，而嗜热链球菌的脲酶活性与乳糖的利用以及乳酸和乙醛的产生呈显著相关。这些发现表明，β-半乳糖苷酶和脲酶活性的差异对于嗜热链球菌的乳糖代谢、生长和产酸性能至关重要，为菌株选择和应用提供了新的见解。
