Abstract
The purpose of this study was to investigate how the properties of Mexican kefir grains (MKG) are affected by the operating parameters used in the freeze-drying process. The factors investigated were the freezing time (3–9 h), freezing temperature (−20 to −80 °C), pressure (0.2–0.8 mbar), and lyophilization time (5–20 h). The maximum range of change and one-way analysis of variance showed that lyophilization time and freezing time significant affects (p < 0.05) the response variables, residual moisture content and water activity, and pressure had a significant effect on the color difference and survival rate of probiotic microorganisms. The best drying conditions were a freezing time of 3 h, a freezing temperature of −20 °C, a pressure of 0.6 mbar, and a lyophilization time of 15 h. Under these conditions, we obtained a product with residual moisture content below 6%, water activity below 0.2, and survival rates above 8.5 log cfu per gram of lactic acid bacteria and above 8.6 log for yeast.
Highlights
Kefir grains are the culture used to produce kefir: a probiotic and popular beverage in the functional food market
Survival rate of lactic acid bacteria (LAB) and yeasts before and after lyophilization are expressed as log, which was determined using the pour plate method
The residual moisture and water activity were mainly influenced by the operating lyophilization time (p < 0.05)
Summary
Kefir grains are the culture used to produce kefir: a probiotic and popular beverage in the functional food market This culture is a complex mixture of bacteria and yeasts that live in a symbiotic relationship [1,2,3]. The grains are initially very small but increase in size during the fermentation process, but they can only grow from preexisting grains [7] Their complex microbiological mixture depends on their origin, quality, and type of milk used for reproduction. As a result, obtaining a defined and uniform starter culture for the industrial kefir market is difficult [8] For this reason, dehydration of kefir may provide a solution to increase the market value of this dairy product [9]
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