Extratos vegetais fermentados por Kefir: desenvolvimento, caracterização e potencial antimicrobiano

Abstract

Fermented foods have several beneficial properties ranging from the presence of live microorganisms to antimicrobial substances, and can be used as food products and added to other foodstuffs to act as natural preservatives. However, one of the most used and consumed matrices in the fermentation process is milk, which for many people who have food restrictions, whether due to pathologies (food intolerances and allergies) or by choice, becomes a problem. Thus, the search for alternative sources drives research that meets these demands. Vegetable drinks are among the foods under study that contribute to the development of new products with the aforementioned characteristics. On the other hand, kefir is a symbiosis of micro-organisms from artisanal cultivation, with several positive effects associated with its consumption. In this context, the objective of this work was to characterize vegetable extracts fermented by kefir and their potential antimicrobial activity. The vegetable extracts of white rice, brown rice, cashew nuts, Brazil nuts, and coconut were prepared and characterized as to the proximate composition (protein, lipid, ash, and carbohydrate moisture), physicochemical (pH, total soluble solids, moisture, and color) and microbiological parameters (Salmonella sp., thermotolerant coliforms, mesophilic aerobics and molds, and yeasts). The extracts were fermented with kefir and subjected to determination of proximate composition, viable cell count, antimicrobial activity (Escherichia coli and Staphylococcus aureus), as well as pH, total soluble solids, moisture, and color. The compositions of pasteurized vegetable extracts showed different energy values, corresponding to their raw materials. The physicochemical parameters varied and did not have a good correlation through linear regression analysis, probably due to the lack of homogeneity of the products. All pasteurized extracts were suitable for consumption in accordance with current legislation. Vegetable extracts fermented by kefir, on the other hand, showed different caloric values ​​compared to non-fermented ones due to the presence of microorganisms and their adaptation to the environment. Through the results of microbiological and physicochemical analyzes it was possible to verify different behaviors in relation to the fermentation process, revealing the influence of raw materials on microbial development The pH reached values ranging from 6.44 ± 0.08 (Brazil nut extract) to 5.28 ± 0.09 (coconut extract) after 24 hours of fermentation, revealing that the fermentation time in vegetable extracts is different from that of milk. For soluble solids and moisture, the values and behavior of these parameters were similar to those of pasteurized extracts, and it is not possible to infer on the role of kefir in the medium. Regarding color, the most expressive change was in the L* coordinate, whose values ranged from 44.63 ± 1.98 to 66.98 ± 3.44, to 71.05 ± 4.00 to 82.05 ± 2.43 in 24 hours, with increased luminosity after fermentation. The high count of microorganisms used as a microbiological requirement for kefir showed that it is capable of adapting to different substrates, expanding its use possibilities. In this count, after 24 hours of fermentation, lactic acid bacteria reached 5.25 x 10 8 CFU/mL in brown rice extract, for yeasts, the highest value obtained in brown rice and Brazil nut extracts was 2, 53 x10 8 CFU/mL, while for mesophilic aerobics, the largest amount found was in Brazil nut extract with 4.44 x 10 8 CFU/ml. Regarding the antimicrobial activity, only vegetable extracts fermented from brown rice and Brazil nuts showed action against the tested microorganisms, confirming its possibility not only as a product but also as a natural preservative for various types of food.