Total lactic acid bacteria, ethanol content, antioxidant activity, and organoleptic quality of kefir as affected by fermentation duration

Abstract

Kefir is a traditional fermented milk beverage produced through the symbiotic metabolic activity of lactic acid bacteria (LAB) and yeasts harboured in kefir grains. The duration of fermentation is a principal process variable governing the microbiological, chemical, and sensory characteristics of the final product. This study aimed to evaluate the effects of fermentation duration on total LAB counts, ethanol content, antioxidant activity, and organoleptic quality (alcohol aroma and milk aroma) of kefir produced from commercial full-fat liquid milk. A completely randomised design (CRD) with five fermentation durations 0, 8, 16, 24, and 32 h and three replicates per treatment was employed. Milk was sterilised, inoculated with 3% (v/v) kefir grain starter culture, and incubated at 37°C. One-way analysis of variance (ANOVA) revealed that fermentation duration had a highly significant effect (P < 0.01) on all measured parameters. Total LAB counts increased from Log 4.20 to Log 9.10 CFU mL−1, ethanol content from 0.08% to 1.60%, and antioxidant activity (% DPPH inhibition) from 38.90% to 59.62% as fermentation duration extended from 0 to 32 h. Concurrently, alcohol aroma intensity increased progressively, whereas milk aroma decreased. Duncan’s multiple range test (DMRT) indicated that a fermentation duration of 24 h yielded kefir meeting the microbiological and chemical requirements of Codex STAN 243 while maintaining a sensory profile acceptable to trained panelists, and was therefore identified as the most suitable fermentation duration under the conditions of this study.