Department of Agricultural, Food, and Nutrition Sciences, University of Alberta, Edmonton, AB, Canada.
The Metabolomics Innovation Centre (TMIC), University of Alberta, Edmonton, AB, Canada; Department of Chemistry, University of Alberta, Edmonton, AB, Canada.
Food Res Int. 2023 Nov;173(Pt 2):113467. doi: 10.1016/j.foodres.2023.113467. Epub 2023 Sep 12.
Kefir is fermented traditionally with kefir grains, but commercial kefir production often relies on fermentation with planktonic cultures. Kefir has been associated with many health benefits, however, the utilization of kefir grains to facilitate large industrial production of kefir is challenging and makes to difficult to ensure consistent product quality and consistency. Notably, the microbial composition of kefir fermentations has been shown to impact kefir associated health benefits. This study aimed to compare volatile compounds, organic acids, and sugar composition of kefir produced through a traditional grain fermentation and through a reconstituted kefir consortium fermentation. Additionally, the impact of two key microbial communities on metabolite production in kefir was assessed using two modified versions of the consortium, with either yeasts or lactobacilli removed. We hypothesized that the complete kefir consortium would closely resemble traditional kefir, while the consortia without yeasts or lactobacilli would differ significantly from both traditional kefir and the complete consortium fermentation. Kefir fermentations were examined after 12 and 18 h using two-dimensional gas chromatography-time-of-flight mass spectrometry (GC × GC-TOFMS) to identify volatile compounds and high performance liquid chromatography (HPLC) to identify organic acid and sugar composition. The traditional kefir differed significantly from the kefir consortium fermentation with the traditional kefir having 15-20 log(fold change) higher levels of esters and the consortium fermented kefir having between 1 and 3 log(fold change) higher organic acids including lactate and acetate. The use of a version of kefir consortium that lacked lactobacilli resulted in between 2 and 20 log(fold change) lower levels of organic acids, ethanol, and butanoic acid ethyl ester, while the absence of yeast from the consortium resulted in minimal change. In summary, the kefir consortium fermentation is significantly different from traditional grain fermented kefir with respect to the profile of metabolites present, and seems to be driven by lactobacilli, as evidenced by the significant decrease in multiple metabolites when the lactobacilli were removed from the fermentation and minimal differences observed upon the removal of yeast.
克菲尔传统上是用克菲尔粒发酵的，但商业克菲尔生产通常依赖于浮游培养物的发酵。克菲尔与许多健康益处有关，然而，利用克菲尔粒促进克菲尔的大规模工业生产具有挑战性，并且难以确保产品质量和一致性。值得注意的是，克菲尔发酵的微生物组成已被证明会影响克菲尔相关的健康益处。本研究旨在比较通过传统谷物发酵和通过重组克菲尔联合体发酵生产的克菲尔中的挥发性化合物、有机酸和糖组成。此外，使用两种改良的联合体评估了两个关键微生物群落对克菲尔代谢产物产生的影响，其中去除了酵母或乳杆菌。我们假设完整的克菲尔联合体将非常类似于传统的克菲尔，而没有酵母或乳杆菌的联合体将与传统的克菲尔和完整的联合体发酵有很大的不同。使用二维气相色谱-飞行时间质谱（GC×GC-TOFMS）在 12 和 18 小时后检查克菲尔发酵，以鉴定挥发性化合物，并使用高效液相色谱（HPLC）鉴定有机酸和糖组成。传统的克菲尔与克菲尔联合体发酵有显著差异，传统的克菲尔中酯的水平高出 15-20 倍，而联合体发酵的克菲尔中乳酸和乙酸等有机酸的水平高出 1-3 倍。使用缺乏乳杆菌的克菲尔联合体的一个版本导致有机酸、乙醇和丁酸乙酯的水平降低了 2-20 倍，而从联合体中去除酵母则导致变化最小。总之，克菲尔联合体发酵在存在的代谢物谱方面与传统的谷物发酵克菲尔有显著差异，并且似乎由乳杆菌驱动，这从去除发酵中的乳杆菌时多种代谢物显著减少以及去除酵母时观察到的最小差异得到证明。
