发酵乳后熟期间嗜热链球菌和保加利亚乳杆菌产乙醛特性

Acetaldehyde-Producing Properties of Streptococcus thermophilus and Lactobacillus bulgaricus in Fermented Milk during Post-Ripening

目的：分析嗜热链球菌和保加利亚乳杆菌在发酵乳后熟期间产乙醛特性，并研究乙醛合成与其关键调控基因表达量之间的关系。方法：以传统发酵乳制品中筛选出的具有优良发酵特性的嗜热链球菌和保加利亚乳杆菌为研究对象，将各试验菌株在复原全脂乳中进行单菌发酵，发酵结束后（pH4．5～4．6）于4℃冷藏后熟，测定48h内发酵乳中的乙醛含量；采用反转录定量PCR技术检测乙醛合成关键调控基因pdc、pdh、ald、1dh的表达特征。结果：6株嗜热链球菌产乙醛量介于2．59～14．53μg／g之间，6株保加利亚乳杆菌产乙醛量介于9．17～39．45μg/g儋之间；乙醛合成量随着基因pdc、ald及pdh表达量的升高而增加，而与基因ldh的表达量呈负相关。结论：发酵乳后熟期间嗜热链球菌和保加利亚乳杆菌不同菌种、不同菌株乙醛产量差异显著，相同菌株在不同后熟时间产乙醛量差异明显，存在菌株特异性和时序变异性；调控基因pdc、pdh及ald具有促进乙醛合成的作用，基因1dh的表达不利于乙醛含量的积累。

The aim of this study was to analyze the acetaldehyde-producing characteristics of Streptococcus thermophilus and Lactobacillus bulgaricus in fermented milk during post-ripening and to investigate the relationship between the expression of key regulatory genes and acetaldehyde synthesis. Methods： Fermented milk was obtained from single strain fermentation of reconstituted whole milk by potent strains of S. thermophilus and L. bulgaricus isolated from traditional fermented milk products. After the end of fermentation （pH 4.5 4.6）, the fermented milk was ripened by storage at 4 ~C for 48 h. During the storage period, the change in acetaldehyde content was determined, and the expression characteristics of the key regulatory genes pdc, pdh, ald, and ldh involved in acetaldehyde synthesis were examined by reverse transcription- qPCR. Results： The amounts of acetaldehyde produced by 6 S. thermophilus strains were 2.59-14.53 μg/g and 9.17-39.45 μg/g by 6 Lactobacillus bulgaricus strains. The synthesis of acetaldehyde was positively correlated with the expression levels ofpdc, aM and pdh but negatively correlated with the expression level of ldh. Conclusion： Different bacterial species and different strains have significantly different capacities to produce acetaldehyde during post-ripening, and one strain produces significantly different amounts of acetaldehyde at different post-ripening times, suggesting strain and temporal specificity of acetaldehyde production. The regulatory genes pdc, aM, and pdh promote the synthesis of acetaldehyde, while the gene Idh has a negative effect on acetaldehyde production.