URTAL, INRA, 39800, Poligny, France.
Food Microbiol. 2017 Aug;65:149-159. doi: 10.1016/j.fm.2017.01.024. Epub 2017 Feb 16.
The respective inputs of plate counting and qPCR for the quantification of starters in cheese were evaluated using hard-cooked cheeses made with various starter combinations. Five starter strains were quantified at their different growth phases, from 0.5 h to day 214 of manufacture: one strain of Streptococcus thermophilus (ST) and two strains each of Lactobacillus delbrueckii (LD) and Lactobacillus helveticus (LH). Numbers of colony-forming units (CFU) were obtained by plate counting (PC) and qPCR (GN). The qPCR standard curves require a special attention since GN depends on the degree of culturability of the standard culture. Discrepancies were evidenced from the vat milk to the end of ripening. During cheese making, GN were lower than PC at the inoculation for all ST and LD samples and 83% of the LH samples, and during both the exponential and stationary phases for many of the ST and LD samples. During ripening which corresponds to the decline phase, GN were higher than PC for 90% of the ST, 78% of the LD and 69% of the LH samples. Hypotheses are discussed to explain those discrepancies. The data provided by GN and PC complement each other, providing a better description of starter growth in cheese.
采用不同起始组合制作的硬煮奶酪，评估了平板计数和 qPCR 对奶酪中起始物定量的各自输入。在从 0.5 小时到制造的第 214 天的不同生长阶段，对五种起始菌株进行了定量：一种嗜热链球菌（ST）菌株和两种德氏乳杆菌（LD）和瑞士乳杆菌（LH）菌株。通过平板计数（PC）和 qPCR（GN）获得菌落形成单位（CFU）的数量。qPCR 标准曲线需要特别注意，因为 GN 取决于标准培养物的可培养程度。从罐奶到成熟结束，都可以发现差异。在奶酪制作过程中，对于所有 ST 和 LD 样品以及 83%的 LH 样品，在接种时 GN 均低于 PC，对于许多 ST 和 LD 样品，在指数期和稳定期也是如此。在成熟过程中，即下降阶段，对于 90%的 ST、78%的 LD 和 69%的 LH 样品，GN 高于 PC。讨论了假设来解释这些差异。GN 和 PC 提供的数据相互补充，更好地描述了奶酪中起始物的生长。
