Chemical and Microbiological Properties of Kefir Produced by Kefir Grains in Raw and Pasteurized Cow’s Milk

Abstract

The traditional production of kefir uses raw milk as a fermentation substrate which is not acceptable due to food safety issues. However, kefir grains were reported to have antimicrobial properties. Hence, this study determined if kefir grains inhibited certain spoilage and pathogenic microorganisms by comparing the chemical and microbiological properties of the initial substrates: raw milk (RM) and pasteurized milk (PM) to the final products: raw milk kefir (RMK) and pasteurized milk kefir (PMK). Both final products had a significant decrease in fat, moisture, and pH, and a significant increase in protein, total solids, and titratable acidity than RM and PM, respectively. Total solids, titratable acidity, pH, total alcohol, and ethanol were significantly higher in PMK than RMK. RMK had a significantly lower coliform count than RM while both RMK and PMK had significantly higher lactic acid bacteria, yeast and mold count than RM and PM, respectively. Kefir grains’ microbial inhibiting activity was examined if plates were positive or negative against spoilage and pathogenic microorganisms. Escherichia coli-positive plates in Levine’s eosin methylene blue agar decreased in RMK. Salmonella spp.-positive plates in bismuth sulphite agar (BSA), Hektoen enteric agar, and xylose lysine deoxycholate agar decreased in RMK and PMK except for RMK in BSA. Staphylococcus aureus-positive plates in Baird-Parker agar decreased in RMK. RMK and PMK attained the kefir’s standard values for the chemical composition, lactic acid bacteria, yeast and mold count. Nonetheless, the mere presence of spoilage and pathogenic microorganisms in the final products made it unsafe for consumption.