The biological integrity of natural poly-species symbiotic bacterial communities for the production of kefir: Basic aspects of the preservation

Abstract

An integral step in kefir production technology is the use of kefir grains, but in some cases it is necessary to maintain their population at the plant. A convenient method is freezing, but with direct freezing, kefir grains lose activity and some microorganisms die off. The use of substances with cryoprotective properties can help preserve kefir grains under direct freezing conditions. The study has examined three environments that have the potential to protect the symbiosis of kefir grains under subcryoscopic conditions: skim sterile milk, gelatin and a sterile solution of 30 % sucrose, and one environment that is stressful – sterile distilled water. At previous stages of research, it was proven that sharp defrosting aggravates the stress phenomena of the bacterial community, in particular, promotes the death of surface lactococci which leads to dysbacteriosis of the symbiosis. The work used for the first time a periodic scheme for defrosting kefir grains in a protective environment; the methods of visual and organoleptic assessment have been applied, the studies of microbiological and physico-chemical parameters of milk after fermentation of kefir starter with kefir grains have been conducted. Milk changes have been carried out using the technology of cultivating kefir grains with daily passages. It is accepted that if based on a set of indicators kefir grains from the experimental groups within 7 days correlate with the indicators detected for the control group, which was not subjected to freezing, then it is accepted that the kefir grains have completely restored viability. If this does not happen, a conclusion is drawn that the symbiosis has not been restored. As a result of the research, the prospects for using the studied substances as protective media have been proven and the need to construct specialized cryoprotective media for direct freezing of kefir grains in order to create your own kefir culture banks has been substantiated. The approach will reduce the use of bacterial substitutes for kefir like direct fermentation starters.