嗜热链球菌对瑞士乳杆菌发酵乳后酸化的影响

Influence of Streptococcus thermophilus on the Postacidification of Fermented Milk Containing Lactobacillus helveticus

瑞士乳杆菌是潜在的功能发酵乳发酵剂,为改善瑞士乳杆菌的发酵特性,使用嗜热链球菌配合瑞士乳杆菌用于发酵乳制备。结果表明:嗜热链球菌与瑞士乳杆菌混合发酵将凝乳时间缩短了3.5 h,黏度提高了1.8倍,改善了乳清析出和质构;嗜热链球菌的使用有效减弱了发酵乳的后酸化,贮藏20 d发酵乳的pH值仍大于4.2。为研究这一现象的原因,测定发酵乳中的活菌数、乳糖消耗量、谷氨酸脱羧酶和β-半乳糖苷酶活性,结果表明,混合发酵乳贮藏期间具有较低的谷氨酸脱羧酶和β-半乳糖苷酶活性,乳糖利用量较低,这是后酸化减弱的主要原因。与嗜热链球菌混合发酵是提高瑞士乳杆菌发酵特性的有效手段。

To improve the fermentation performance of Lactobacillus helveticus, Streptococcus thermophilus as a potential starter culture for functional fermented milk was utilized together with L. helveticus to produce fermented milk. As results, the mixed culture fermentation shortened the curding time by 3.5 h, increased yogurt viscosity by 1.8 times and improved whey syneresis and texture properties as compared to L. helveticus alone. Interestingly, S. thermophilus weakened the postacidification of fermented milk containing L. helveticus, maintaining a pH value greater than 4.2 for 20 d of storage. To account for this finding, the number of living bacterial cells, lactose consumption and the activity of glutamate decarboxylase and β-galactosidase were measured. It was found that the activity of glutamate decarboxylase and β-galactosidase of the fermented milk containing the two strains was lower, resulting in a lower lactose consumption and consequently weakening yogurt postacidification. This study concluded that co-fermentation with S. thermophilus was an effective means to improve the fermentation performance of Lactobacillus helveticus.