Development of a Functional Mixed-Starter Culture for Kefir Fermentation

Kefir 배양용 기능성 복합 Starter 개발

Kefir, which originates in the Caucasian mountains, is a cultured milk beverage produced by a combination of acidic and alcoholic fermentation. Kefir products are commonly used as food vehicles to deliver health-promoting materials including kefran and lactic acid bacteria to consumers. The aim of this study was to develop a freeze-dried starter culture without yeast and assess the suitability of kefir-like dairy products for the growth of lactic acid bacteria and the acidification of milk. Pasteurized whole milk (SNF 8.5%) stored at $25^{\circ}C$ was aseptically inoculated with starter cultures (0.002% w/v); it was kept at $25^{\circ}C$ until the pH attained a value of 4.6. Ten grams of the kefir-like product sample was diluted with 90 mL of 0.15% peptone water diluent in a milk dilution bottle, followed by uniform mixing for 1 min. Viable cells of Lactobacillus species were enumerated on modified-MRS agar (pH 5.2), with incubation at $37^{\circ}C$ for 48 h. Viable cells of Lactococcus species were enumerated on M17-lactose agar, with incubation at $32^{\circ}C$ for 48 h. The pH attained a value of 4.6 after fermentation for 9 h 30 min (Starter 1), 9 h 45 min (Starter 2), and 12 h (Starter 3). The viable cell count of Lactobacillus sp. and Lactococcus sp. was initially $10^5{\sim}10^6CFU/g$; it increased significantly to $10^9CFU/g$ after 12 h of incubation. During the storage of the kefir-like products at $4^{\circ}C$ for 1 4 days, the total viable cell numbers were unchanged, but the pH decreased slightly. The consistency of the kefir products increased gradually during the storage. The organoleptic properties of the kefir products fermented using the new starter culture are more desirable than those of commercial kefir. These results suggest that the newly developed starter culture without yeast could be suitable for kefir fermentation.