发酵乳产品的菌种组成与活菌数的含量是产品质量的关键。该文通过选择性培养基、基质辅助激光解吸电离飞行时间质谱(matrix-assisted laser desorption/ionization time of flight mass spectrometry,MALDI-TOF-MS)快速鉴定技术及多相鉴定技术探究3种发酵乳中乳酸菌的活菌数及种类。研究结果表明,3种发酵乳产品中,GB 4789.35对乳酸菌总数的计数结果均高于选择性培养基,M17培养基对嗜热链球菌的计数结果均高MC培养基。MALDI-TOF MS快速鉴定表明M17、MRS(含50 μg/mL的万古霉素)、双歧杆菌培养基可以选择性的分离发酵乳中的嗜热链球菌(Streptococcus thermophilus)、干酪乳酪杆菌(Lacticaseibacillus casei)和双歧杆菌(Bifidobacterium spp.),酸化MRS培养基对德氏乳杆菌(Lactobacillus delbrueckii)的选择性较差,不能在含有双歧杆菌的发酵乳中选择性分离德氏乳杆菌。进一步通过多相鉴定确定3种发酵乳产品中乳酸菌在种或亚种水平的微生物组成,鉴定结果均与发酵乳的菌株标识一致。该研究对发酵乳中乳酸菌的多种选择性计数方法进行了比较,对复合菌发酵乳产品的质量控制和行业监管具有重要参考意义。
The microbial composition and the number of viable bacteria are essential for the quality of fermented milk. This study detected the number of viable count and species composition of different lactic acid bacteria in fermented milk using selective media, MALDI-TOF MS rapid identification system and polyphasic taxonomy methods. The results showed that for the three fermented milk products, the total number of lactic acid bacteria enumerated by the GB 4789.35 method was higher than that of the selective medium, and the total number of Streptococcus thermophilus enumerated by the M17 medium was higher than that of the MC medium. MALDI-TOF MS rapid identification results showed that M17, MRS (containing 50 μg/mL vancomycin) and bifidobacterium medium could selectively isolated Streptococcus thermophilus, Lactobacillus casei and Bifidobacterium spp. But acidified MRS medium had poor selectivity to Lactobacillus delbrueckii, it could not selectively isolate L. delbrueckii from fermented milk containing Bifidobacterium spp. Through polyphasic taxonomy identification, the microbial composition of lactic acid bacteria in the three fermented milk products at the species or subspecies level was further determined, and the identification results were consistent with the product claims of fermented milk. This study compared different selective enumeration methods of lactic acid bacteria in fermented milk and provided a scientific basis for the quality control and regulation of fermented milk products with complex bacteria.
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