Microbiological changes of kefir traditionally produced from different milks according to storage time

Abstract

Kefir is a fermented dairy product known for its positive effects on health. It has been reported to have positive effects on gastrointestinal diseases, hypertension, metabolic disorders, and the immune system due to its lactic acid bacteria, yeasts, and various bioactive compounds. The study aimed to investigate the microbiological properties of kefirs produced from different milk types and pasteurization processes. Different types of milk were used in kefir production, such as UHT cow, pasteurized cow, open cow, and pasteurized goat. For each milk, kefir was produced with a 24-hour incubation period followed by microbial analysis on days 1, 7, 14, and 21. The microbial flora was assessed based on total bacterial counts, as well as specific enumeration of Lactobacillus sp., Lactococcus sp., coliform bacteria, molds, and yeasts. The pH levels of the kefir samples were also measured. The analysis showed that pH values decreased with increasing storage time in all kefir types. Especially the Lactobacillus sp. count of kefirs produced from goat’s milk was lower than other milk types and decreased until day 21. It was also observed that the number of coliform bacteria decreased faster in kefir produced with UHT milk, while it was not detected in other kefirs after the 14th day. The study revealed that the microbial structure of kefirs varied significantly according to milk type, pasteurization method, and storage time. Open cow’s milk kefirs produced by traditional methods were found to be richer in probiotic bacteria but at risk of contamination.

Keywords

• Diet
• kefir
• kefir grain
• traditional food

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