Effect of Final Fermentation pH and Pre-Drying Storage Temperature on Properties of Kefir Powder Produced by Kefir Grains

The demand of consumers for a healthier and functional diet necessitates amongst others, extending the shelf life of the natural probiotic kefir, reducing simultaneously packaging, transportation, and storage costs. Among the different drying methods, spray drying is widely used and industrially favorable to produce powdered products. The aim of the present work was to study the effect of the final fermentation pH and the pre-drying storage temperature (4 °C for 7 days) on the physicochemical properties, moisture content, pH, color, adsorption isotherms, and the microbiological characteristics of spray dried kefir. Kefir grains were used for the fermentation and the production of the samples. Viabilities of lactococci, lactobacilli, and yeasts were determined during a storage period of 45 days. Both final fermentation pH and low-temperature storage significantly affected the properties of the kefir powders and their respective reconstituted samples. According to the findings of the study, the desirable microbial populations of the reconstituted kefir powders are possible to accomplish by using an increased final fermentation pH at 5.2 and/or by applying low-temperature storage of the fermented milk, together with the kefir grains, at 4 °C for 7 days prior to drying. The yeast population was affected the least by the studied factors, and the use of kefir grains as starter culture favored the viability of lactococci and lactobacilli after spray drying and during storage up to 45 days.