Caracterização do processo fermentativo e da microbiota envolvida na produção do kefir de água

Abstract

The water kefir is a fermented product with probiotic characteristics capable of improving the condition of intestinal flora and accelerate the decomposition of organic matter used in the preparation of substrates important for an ecologically-based agriculture. The water kefir results from a sucrose fermentation with subsequent grain formation. Given the simplicity of production, the water kefir can be prepared directly in the property giving the farmer independence regarding the acquisition of similar products on the market. The production of kefir on the farm is capable to improve other uses, such as probiotic activities. This study aimed to determine the conditions of preparation of kefir water to obtain a product with viable cells that can be multiplied directly by the farmer. The work was performed in the laboratory of Microbial Ecology at Embrapa Agrobiology, Seropédica, RJ, Brazil. A solution of brown sugar ArmaZen ® (5%, 10% and 20% mv-1) in sterile distilled water (350 mL) was inoculated with washed kefir grains (35 g). Culture incubation was proceeded at 28 ° C for 7 days. Samples were collected at 1, 3 and 7 days of incubation. The following parameters were evaluated: mass production of grain, pH of the liquid phase, total protein content in solid and liquid phases, and microorganisms counting and composition in the liquid phase using MRS and DYGS culture media. Three repetitions were performed for each treatment. The largest grain mass was obtained with the 20% concentration of sugar after seven days of growth. The pH decreased over the incubation period and the highest decrease observed during the first 24 at 5% of sugar. The largest amounts of protein in the liquid phase were observed early in the incubation period, while the protein of the grains increased gradually over the period reaching a maximum at 3 or 7 days depending upon the concentration of sugar available. These results suggest that the multiplication of microorganisms occurs in the liquid phase while they gradually migrate to the grain. A total of 25 representative isolates of different morfocultural types was obtained: 11 were isolated from MRS medium and 14 from the DYGS medium. Sequencing of the 16S rDNA showed the presence of seven bacterial genera (Acetobacter, Burkholderia, Methylobacterium, Mucilaginibacter, Pseudomonas, Staphylococcus and Stenotrophomonas, one of actinobacteria (Microbacterium) and one yeast (Saccharomyces). Recovery of preparations isolated from kefir wiht 5% brown sugar presented primarily bacterial genera, including the actinobacteria, which were common to all kefir preparations independent of the sugar concentration. Yeasts appeared only at 10 and 20% sugar concentrations. The microbial succession established was characterized by the bacterial genera being more common at the beginning of the incubation period, while actinobacteria and yeast concentrations increased over this period.