Avaliação da qualidade microbiológica e físico-química de kefir e da atividade biológica da bebida, de Lactobacillus spp. isolados de diferentes grãos e exopolissacarídeos

Abstract

Kefir grains are characterized by an exopolysaccharide matrix in which is inserted a complex community of bacteria and yeast. The activity of these microorganisms characterizes kefir grains and drinks they ferment, presenting, in that manner, several applications for the food industry. Thus, the objective of this study was to evaluate the microbiological quality and physicochemical properties of kefir; the biological activity of the beverage and of Lactobacillus spp. isolated from different grains and exopolysaccharides. In milk and water kefir, bacteria and yeasts are distributed on the surface and inside its grain. Milk kefir samples have LAB count greater than 107 CFU/mL during 28 days of storage and showed chemical composition in accordance with national and international legislations. In general, water kefir samples have LAB counts above 107 CFU/mL. However, this may decrease during 28 days’ storage. Beverages show antagonistic activity in vitro against Escherichia coli (ATCC 25922), Enterococcus faecalis (ATCC 19433), Listeria monocytogenes (ATCC15313), Shigella flexneri (ATCC 12022), Staphylococcus aureus (ATCC 29213) and Salmonella enterica sorovar Typhimurium (ATCC14028) in MRS agar. The production of EPS was observed in different growth conditions of Lactobacillus spp. and was directly extracted from milk or water kefir grains. These EPS have a diverse chemical composition and primary structural organization. Lactobacillus spp. isolated from kefir grains are capable of antagonizing the invasion but not the adhesion of S. Enteritidis in vitro, indicating potential probiotic properties. EPS produced by lactobacilli isolated from kefir grains and extracted from water and milk kefir grains are able to exert an antagonistic effect in vitro against Salmonella adhesion to Caco2 cells/TC-7. The metatranscriptômica analysis showed that the most active bacterial species in Curitiba milk kefir (KLCU) were L. mesenteroides (61,93%), L kefiranofaciens (3,86%), Yarrowia lipolytica (9,43%) and Saccharomyces cerevisiae (3,41%); Salvador (KLSA) L. mesenteroides (4,65%), L. kefiranofaciens (20,78%), Yarrowia lipolytica (10.21%) and Saccharomyces cerevisiae (1,70%); the water kefir Curitiba (KACU) Oenococcus kitaharae (12,76%), Gluconobacter oxydans (7,77%) and Saccharomyces cerevisiae (66,45%); Salvador (KASA), Oenococcus kitaharae (14,69%), Gluconobacter oxydans (4,42%) and Saccharomyces cerevisiae (72,9%). Transcribed genes of glycosyltransferase enzyme involved in the synthesis of glucose homopolysaccharide were found in KACU and KASA samples. While transcribed genes of β- galactosidase enzymes, phosphoglucomutase, UDP-glucose pyrophosphorylase, galactose-4-epimerase and UDP-galactose-4-epimerase involved in the synthesis hetepolissacarideo glucose and galactose, were found in KLCU and KLSA samples.