COMPARISON OF FERMENTATION PERFORMANCE AND METABOLITES OF WATER KEFIR GRAINS

Background. Water kefir is a kind of beverage from a brown sugar solution fermented by water kefir grains. It has probiotic functions and unique flavour, and is widely popular in the international market. However, there are few comparative studies on water kefir grains sourced domestically and internationally. Therefore, the purpose of this study was to compare the fermentation performance and metabolites of 6 different water kefir grains from different sources in brown sugar water, in order to provide a theoretical basis for subsequent functional studies and to identify advantages for the development of water kefir. Methods. The fermentation characteristics of 6 kinds of water kefir grains (HY, GS, LS, SJ, JW, M339) were studied by measuring the wet weight of water kefir grains and the pH value, acidity, polysaccharide yield and anti-bacterial activity of the fermentation solution. Then the metabolites were analysed by GC-MS. Finally, an orthog-onal partial least squares discriminant score (OPLS-DA) was used to identify the differences among the groups. Results. Among the 6 kinds of water kefir grains, JW had the fastest proliferation, SJ produced more acid and its fermentation broth had the best inhibition effect on E. coli, and the yield of exopolysaccharides of LS was the highest. A total of 131 metabolites were detected in 6 kinds of water kefir, including 22 kinds of carbohydrates, 35 kinds of esters, 29 kinds of acids, 10 kinds of alcohols, 8 kinds of nucleosides, 6 kinds of amino acids, 4 kinds of ethers and aldehydes, and 17 kinds of other organic compounds. OPLS-DA showed significant variation among different water kefir groups. Conclusion. Determination of several important indicators of water kefir grain fermentation and GC-MS analysis of metabolites can clearly identify the differences of water kefir grains from different sources, which is conducive to its targeted development and utilisation.