Institut sur la nutrition et les aliments fonctionnels (INAF), Département des Sciences des Aliments et de Nutrition, Université Laval, G1V 0A6 QC, Canada.
Int J Food Microbiol. 2013 Aug 16;166(1):117-24. doi: 10.1016/j.ijfoodmicro.2013.06.022. Epub 2013 Jun 26.
Cheddar cheese is a complex ecosystem where both the bacterial population and the cheese making process contribute to flavor and texture development. The aim of this study was to use molecular methods to evaluate the impact of milk heat treatment and ripening temperature on starter lactococci and non-starter lactic acid bacteria (NSLAB) throughout ripening of Cheddar cheese. Eight Cheddar cheese batches were manufactured (four with thermized and four with pasteurized milk) and ripened at 4, 7 and 12°C to analyze the bacterial composition and rRNA transcriptional activity reflecting the ability of lactococci and lactobacilli to synthesize proteins. Abundance and rRNA transcription of lactococci and lactobacilli were quantified after DNA and RNA extraction by using quantitative PCR (qPCR) and reverse transcription-quantitative PCR (RT-qPCR) targeting the 16S rRNA gene, respectively. Results showed that lactococci remained dominant throughout ripening, although 16S rRNA genome and cDNA copies/g of cheese decreased by four and two log copy numbers, respectively. Abundance and rRNA transcription of Lactobacillus paracasei, Lactobacillus buchneri/parabuchneri, Lactobacillus rhamnosus, Lactobacillus brevis, and Lactobacillus coryniformis as well as total lactobacilli were also estimated using specific 16S rRNA primers. L. paracasei and L. buchneri/parabuchneri concomitantly grew in cheese made from thermized milk at 7 and 12°C, although L. paracasei displayed the most rRNA transcription among Lactobacillus species. This work showed that rRNA transcriptional activity of lactococci decreased throughout ripening and supports the usefulness of RNA analysis to assess which bacterial species have the ability to synthesize proteins during ripening, and could thereby contribute to cheese quality.
切达干酪是一个复杂的生态系统，其中细菌种群和奶酪制作过程都有助于风味和质地的发展。本研究旨在使用分子方法评估牛奶热处理和成熟温度对切达干酪成熟过程中 starter lactococci 和非 starter 乳酸菌（NSLAB）的影响。制造了 8 批切达干酪（4 批用热杀菌牛奶和 4 批用巴氏杀菌牛奶），并在 4、7 和 12°C 下成熟，以分析细菌组成和反映 lactococci 和 lactobacilli 合成蛋白质能力的 rRNA 转录活性。通过 DNA 和 RNA 提取后，使用针对 16S rRNA 基因的定量 PCR（qPCR）和反转录定量 PCR（RT-qPCR）分别定量提取乳球菌和乳杆菌的丰度和 rRNA 转录。结果表明，尽管 16S rRNA 基因组和奶酪中每克的 cDNA 拷贝数分别减少了 4 个和 2 个对数拷贝数，但乳球菌在整个成熟过程中仍然占主导地位。还使用特定的 16S rRNA 引物估计了 Lactobacillus paracasei、Lactobacillus buchneri/parabuchneri、Lactobacillus rhamnosus、Lactobacillus brevis 和 Lactobacillus coryniformis 以及总乳杆菌的丰度和 rRNA 转录。L. paracasei 和 L. buchneri/parabuchneri 同时在 7 和 12°C 下用热杀菌牛奶制成的奶酪中生长，尽管 Lactobacillus 属中 L. paracasei 的 rRNA 转录最多。这项工作表明，乳球菌的 rRNA 转录活性在成熟过程中逐渐降低，支持使用 RNA 分析来评估在成熟过程中哪些细菌具有合成蛋白质的能力，从而有助于奶酪质量。
