Centro de Investigación y Desarrollo en Criotecnología de Alimentos (CIDCA, CONICET-UNLP), Calle 47 y 116, CP 1900, La Plata, Argentina.
J Dairy Res. 2012 Aug;79(3):262-71. doi: 10.1017/S0022029912000179. Epub 2012 Apr 17.
We report here a comparative analysis of the growth, acidification capacity, and chemical and microbiologic composition between kefir grains after 20 subcultures in whey at 20, 30, and 37°C and the original kefir grains coming from milk along with a determination of the microbiological composition of the fermented whey as compared with that of traditional fermented milk. When fermentation was carried out repeatedly at 30 or 37°C, kefir grains changed their kefir-like appearance, exhibited reduced growth rates, had a lower diversity of yeasts and water content, and a higher protein-to-polysaccharide ratio compared with the original kefir grains. In contrast, at 20°C kefir grains could remain in whey for prolonged periods without altering their acidification capacity, growth rate, macroscopic appearance or chemical and microbiologic composition-with the only difference being a reduction in certain yeast populations after 20 subcultures in whey. At this incubation temperature, the presence of Lactobacillus kefiranofaciens, Lb. kefir, Lb. parakefir, Lactococcus lactis, Kluyveromyces marxianus, Saccharomyces unisporus, and Sac. cerevisiae was detected in kefir grains and in fermented whey by denaturing-gradient-gel electrophoresis (DGGE). In whey fermented at 20°C the number of lactic-acid bacteria (LAB) was significantly lower (P<0·05) and the number of yeast significantly higher (P<0·05) than in fermented milk. Since the DGGE profiles were similar for both products, at this temperature the microbiologic composition of fermented whey is similar to that of fermented milk. We therefore suggest a temperature of 20°C to preserve kefir grains as whey-fermentation starters.
我们在此报告了一项比较分析，即在 20°C、30°C 和 37°C 下的乳清中对经过 20 次传代的克菲尔粒与原始的来自牛奶的克菲尔粒的生长、酸化能力以及化学成分和微生物组成进行了比较，并将发酵乳清的微生物组成与传统发酵乳进行了比较。当在 30°C 或 37°C 下反复进行发酵时，克菲尔粒改变了其克菲尔样外观，表现出较低的生长速度，较低的酵母多样性和含水量，以及较高的蛋白质-多糖比，与原始的克菲尔粒相比。相比之下，在 20°C 下，克菲尔粒可以在乳清中长时间保持而不会改变其酸化能力、生长速度、宏观外观或化学成分和微生物组成-唯一的区别是在乳清中经过 20 次传代后某些酵母种群减少。在这个培养温度下，通过变性梯度凝胶电泳（DGGE）在克菲尔粒和发酵乳清中检测到了发酵乳清中存在的植物乳杆菌、乳双歧杆菌、副干酪乳杆菌、乳酸乳球菌、马克斯克鲁维酵母、酿酒酵母和酿酒酵母。在 20°C 下发酵的乳清中的乳酸菌（LAB）数量显著降低（P<0·05），而酵母数量显著升高（P<0·05），与发酵乳相比。由于两种产品的 DGGE 图谱相似，在这个温度下，发酵乳清的微生物组成与发酵乳相似。因此，我们建议使用 20°C 来保存克菲尔粒作为乳清发酵的起始物。
