嗜热链球菌产酸特性及其发酵乳中有机酸组分分析

Acid-Producing Ability of Streptococcus thermophilus and Organic Acid Composition in Fermented Milk

选取实验室分离自自然发酵乳制品中的5株嗜热链球菌菌株为研究对象,进行单菌株发酵酸乳,在发酵期间和酸乳4℃贮藏504 h阶段,分别测定菌株发酵时间、滴定酸度、p H值、活菌数以及采用反相高效液相色谱法测定有机酸含量变化,研究嗜热链球菌发酵产酸特性及其酸乳贮藏期间后酸化及其有机酸组分的变化特性。结果表明：在42℃发酵期间,5株菌在发酵2 h后p H值迅速下降,达到发酵终点时间在5~9 h,发酵时间最短的是菌株IMAU10632和IMAU20772。在4℃贮藏504 h期间,5株菌的p H值下降幅度在0.5左右,最终p H值稳定在4.2左右,产酸速度均较缓慢,均表现出嗜热链球菌后酸化能力弱的特点,且酸度值均在90 oT以下。初步筛选出一株菌株IMAU10632,凝乳时间短、产酸速率快、后酸化能力较弱,在4℃贮藏期间活菌数维持在108 CFU/m L以上。

In the present study, 5 strains of Streptococcus thermophilus which were isolated from traditional fermented dairy products were selected to perform fermentation experiments. During the fermentation process and 504 h of storage at 4 ℃, some indexes such as fermentation time, titratable acidity（TA）, p H value and viable cell counts were determined, and the composition of organic acids was tested by reverse phase high performance liquid chromatography（RP-HPLC）. Fermentation and acid-producing properties of Streptococcus thermophilus were evaluated; meanwhile changes in organic acid composition and post-acidification characteristics during storage were determined. After 2 h of fermentation at 42 ℃, the p H of fermented milk by each of the five strains declined rapidly. The fermentation reached its end-point at 5–9 h, and the shortest fermentation time was required for strains IMAU10632 and IMAU20772. Over the 504 h storage period, the p H of milks fermented by Streptococcus thermophilus was reduced by about 0.5 and finally reached a stable level of about 4.2, and acids were produced at lower rates in all fermented milks until the acidity values reached levels below 90 oT, suggesting the weak post-acidification ability of the 5 strains. Furthermore, IMAU10632 was selected from these strains, which could shorten milk coagulation time, increase acid-producing rate, enhance post-acidification ability and reach a viable cell count exceeding 108 CFU/m L which remained unchanged over the entire storage period.