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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48 h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、ldh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ldh的表达不利于乙醛含量的积累。
OBJECTIVE: To analyze the acetaldehyde-producing characteristics of Streptococcus thermophilus and Lactobacillus bulgaricus during the ripening of fermented milk and to study the relationship between the synthesis of acetaldehyde and the expression of its key regulatory genes. Methods: Streptococcus thermophilus and Lactobacillus bulgaricus were selected from the traditional fermented dairy products. The test strains were subjected to single-bacteria fermentation in reconstituted whole milk. After the fermentation (pH 4.5 ~ 4.6) were refrigerated at 4 ℃, and the content of acetaldehyde in fermented milk was measured within 48 h. The expression of pdc, pdh, ald, and ldh, the key regulatory genes of acetaldehyde, was detected by reverse transcription polymerase chain reaction (RT PCR). Results: The production of acetaminophen among 6 Streptococcus thermophilus strains ranged from 2.59 to 14.53μg / g. The production of acetaminophen from 6 strains of L. bulgaricus was between 9.17-39.45μg / g. pdc, ald and pdh increased, but negatively correlated with the expression of ldh. CONCLUSION: Different strains of Streptococcus thermophilus and Lactobacillus bulgaricus produce different yields of acetaldehyde during the ripening period of fermented milk. The acetaldehyde production of the same strain differs significantly at different ripening times, with strain-specific and temporal variability. Regulatory genes pdc, pdh and ald have the role of promoting acetaldehyde synthesis, gene ldh expression is not conducive to the accumulation of acetaldehyde content.