Isolamento e caracterização de bactérias ácidoláticas potencialmente produtoras de exopolissacarídeos provenientes de kefir

Abstract

Lactic acid bacteria (LAB) are commonly used in the food industry due to their probiotic and technological potential, and can act as starter and/or adjunct cultures. They produce organic acids, such as lactic acid, as well as other important metabolites such as bacteriocins, vitamins and exopolysaccharides (EPS). The EPS produced by BAL have diverse applications in the food industry (thickeners, stabilizers), as well as providing benefits as health promoters. Thus, the study aimed to isolate and characterize lactic acid bacteria, coming from different kefir samples, with potential for exopolysaccharide production, as well as evaluating the optimal cultivation conditions to increase exopolysaccharide production. From fermented milk and kefir grains (5), 44 isolates were selected, using selective medium (MRS agar) for LAB, through Gram and catalase staining tests. Subsequently, these isolates were evaluated for microbiological safety aspects such as the activity of the enzymes Dnase, hemolysin, gelatinase and susceptibility to antimicrobials for clinical use. Carbohydrate fermentation and EPS production tests on plates were also carried out in order to evaluate its technological potential. The isolates that proved to be microbiologically safe and presented the desired technological characteristics were molecularly identified through sequencing of the 16S rDNA gene and comparison with data deposited in Genbank. In the EPS production stage, isolate KLM6 showed a greater capacity to synthesize EPS compared to the other isolates, producing 0.410 g/L. It was identified as Leuconostoc mesenteroides and selected to evaluate the effects of inoculum concentration, temperature and pH on EPS production. EPS production was influenced only by pH, obtaining a maximum production of 0.746 g/L at pH 5, with inoculum concentration and temperature having no effect on biopolymer synthesis. Based on the analysis of the main and interaction effects, a stage of optimization of the cultivation conditions was carried out, which indicated an increase of 105.1% in the EPS yield (pH 5 and temperature of 50.5 °C) compared to the results obtained using non-ideal parameters. Therefore, kefir can be considered an important food matrix to isolate lactic acid bacteria with EPS production potential, and changing cultivation conditions such as pH and temperature have a determining effect on increasing the production of this metabolite, allowing its future application in efficiently in the food industry.