弱后酸化瑞士乳杆菌的筛选及发酵特性研究

Isolation and characterization of a Lactobacillus helveticus strain with reduced post-acidification

【目的】在大健康背景下,发酵乳凭借其优良的营养和保健功能备受青睐。后酸化是发酵乳在贮存、运输和销售等过程中活性乳酸菌继续代谢产酸导致的,严重影响产品的感官品质,降低菌株的存活率。本文通过筛选弱后酸化的瑞士乳杆菌,改善发酵乳的后酸化问题。【方法】本研究以瑞士乳杆菌L551为出发菌株,硫酸新霉素为筛选压力,筛选弱后酸化的瑞士乳杆菌。以鲜牛奶为基料,比较弱后酸化菌株与原始菌株发酵特性之间的差异。【结果】筛选得到了弱后酸化瑞士乳杆菌L551-1,其发酵过程产酸变慢,42°C发酵7–8 h产酸速度为9°T/h,较原始菌株(19°T/h)降低53%;42°C发酵24h酸度为155°T,较原始菌株(259°T)降低40%;发酵乳4°C存储21d的酸度为122°T,较原始菌株(158°T)降低23%。采用气相色谱-质谱联用仪(gas chromatography-massspectrometry,GC-MS)比较两株菌发酵乳的挥发性风味物质组成和含量,未见显著差异。【结论】通过硫酸新霉素筛选获得的弱后酸化瑞士乳杆菌L551-1可显著改善后酸化问题,这对直投式发酵剂的开发与应用具有重要意义。

[Objective] Fermented dairy are favored for their excellent nutrition and health functions concomitantly. Post-acidification is caused by the continuous metabolism of active lactic acid bacteria during the process of storage, transportation and sales, which seriously affects its sensory quality and the number of viable strains. This study screened the low-post-acidification Lactobacillus helveticus to resolve the post-acidification of its fermented dairy. [Methods] In this study, Lactobacillus helveticus L551 was used as the original strain. Using neomycin sulfate as the selection pressure select the weakly acidified Lactobacillus helveticus. Comparing the difference of fermentation characteristics between the weakly acidified strain and the original strain. [Results] The acid production rate of weakly acidified Lactobacillus helveticus L551-1 was slowed down. The acid production rate of 7–8 h at 42 °C was 9 °T/h, which was 53% lower than the original strain(19 °T/h);the acidity of fermentation at 42 °C for 24 h was 155 °T, which was 40% lower than that of the original strain(259 °T);the post-acidification of fermented milk was 122 °T stored at 4 °C for 21 days, which was 23% lower than the original strain(158 °T). Using gas chromatography-mass spectrometry(GC-MS) compared the composition and type of volatile flavor compounds in fermented milk of the two strains, and there was no significant difference. [Conclusion] Through neomycin sulfate, the weakly post-acidified Lactobacillus helveticus L551-1 was obtained, which can significantly improve the post-acidification problem of fermented milk, and have a great significance to the development and application of direct starter.