Effect of lactic acid bacteria and yeasts on the structure and fermentation properties of Tibetan kefir grains

To better understand the effects of lactic acid bacteria (LAB) and yeasts on the structure and fermentation properties of Tibetan kefir grains (TKGs), we treated TKGs for 1 month with high doses of mycillin and cycloheximide to inhibit LAB and yeasts, respectively. The results showed that in each group of TKGs, Lactobacillus kefiranofaciens was the only dominant and stable bacterial species, and it exhibited two distinct morphologies in TKGs, short rods in the LAB-inhibited group, and long rods in the yeast-inhibited and control groups, which might directly result in the inability of the grains in the LAB-inhibited group to grow further. Compared with bacteria, the relative abundance of yeasts in TKGs was very low. However, even though yeast had no effect on the structure and growth characteristics of TKGs, they had a great influence on the fermentation characteristics of Tibetan kefir, such as acid production and aroma.