PREPARATION AND CHARACTERIZATION OF SOY MILK FERMENTED BY MICROORGANISMS ISOLATED FROM KEFIR

CELESTRE R.; CARASI P.; SERRADELL, MARÍA DE LOS ANGELES; BOLLA, P. A.

Rosario

Congreso; IX CONGRESO ARGENTINO DE MICROBIOLOGÍA GENERAL SAMIGE; 2013

The presence of soy milk is increasing in the occidental diet. Its high nutritional level could be attributed to the amount of proteins and oils. Fermentation with probiotic microorganisms could constitute an alternative manner to improve the nutritional quality of soy milk. Probiotics are defined as “living microorganisms, which when administered in adequate amounts confer health benefits on the host”. Kefir is a fermented product obtained through fermentation of milk with mixed microbial population confined to “kefir grains”. Different health-promoting properties have been associated with its consumption, and several strains isolated from kefir have been characterized as probiotics. The aim of this work was to obtain and characterize a product based on fermentation of soy milk with a mixture of selected microorganisms isolated from kefir. Two bacteria (Lactobacillus kefir CIDCA 8348, Lactococcus lactis subsp. lactis CIDCA 8221) and one yeast (Kluyveromyces marxianus CIDCA 8154) were selected, and they were inoculated in sterile commercial soy milk (Nutrilon, Nutricia, BAGO) at a concentration of 1x108 lactobacilli/ml, 1x107 lactococci/ml and 1x106 yeasts/ml. Microbial growth was studied by counting of viable microorganisms in different media (MRS agar for lactobacilli, 1.1.1 agar for lactococci and YGC for yeasts) and pH was monitored. After 48 hs of incubation at 30°C, the fermented soy milk achieved a pH 4,2 and concentrations of viable microorganisms increased approximately 1 log for both bacteria and yeasts. On the other hand, the production of organic acids was evaluated by HLPC. The presence of lactic acid, acetic acid, propionic acid and butyric acid was detected in the supernatant of fermented soy milk after 48 hs of incubation. Besides, the preservation of the microbial mixture in soy milk (without fermentation) was evaluated by different strategies: freeze-drying followed by storage at 4°C and freezing at -80°C, with or without the addition of a cryoprotectant (0.3M sucrose). Our first results showed that both L. kefir CIDCA 8348 and L. lactis CIDCA 8221 did not loss viability after freeze-drying, regardless the presence of cryoprotectant. However, the viability of K. marxianus CIDCA 8154 decreased approximately 2 logs after lyophilization without cryoprotectant, meanwhile the presence of 0,3M sucrose significantly improved its survival (P