A New Approach to the Use of Kefir Grain: Potential Application as a Postbiotic in the Production of Nonfat Yogurt

The use of dried kefir grains containing kefiran with high water retention capacity in yogurt production is anticipated to improve the rheological attributes and nutritional value of yogurt and also provide a functional dimension. In addition, such an application could contribute to the utilization of surplus kefir grains leftover from traditional kefir production instead of disposing of them as waste. The aim of the current study was to investigate selected microbiological, physicochemical, and sensory characteristics of set-type yogurt produced from reconstituted milk fortified with dried kefir grains. Four different yogurt samples were produced from milk fortified with 0% (control), 0.1%, 0.2%, and 0.3% (w/w) dried kefir grains before heat treatment. The counts of Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus, titratable acidity, pH, gel hardness, viscosity, water holding capacity, color (L*, a*, b*), fat, protein, and total solids content of the yogurt samples were determined after 1, 15, and 30 days of storage at 4°C. Kefir grain powder had no significant effect on the activity of S. thermophilus (8.50-9.84 log cfu/g) and L. delbrueckii subsp. bulgaricus (8.48-9.39 log cfu/g), pH (4.17-4.43), titratable acidity (1.31%-1.41%), viscosity (1995-2302 mPa·s), water holding capacity (94.91%-96.42%), or sensory qualities of the experimental yogurts but significantly reduced the hardness values (340.5-456.6 g). The addition of kefir grain powder significantly decreased the a* values of the yogurt samples, resulting in a greener color. Unexpectedly, the viability of yogurt bacteria was not altered by the addition of kefir grain powder. However, the yogurts produced with the addition of kefir grain powder were assigned slightly higher scores by the panelists. Our results support the hypothesis that kefir grain powder may be used as a potential postbiotic ingredient in producing yogurt that is more appealing to health-conscious consumers.