Application of conductimetry for evaluation of lactic starter cultures in soymilk

Abstract

Soymilk (SM), a potential culture medium for applying conductimetric techniques to evaluate the behavior of probiotic lactobacilli and bifidobacteria was examined. Media LAPTg, LM, and SM was standardized for the growth of Lactobacillus fermentum and Bifidobacterium longum. A dilution of 1/100 for L. fermentum and 1/1 for B. longum were considered optimal to obtain a detection time (DT) between 5 and 10 min. The relationship between the initial number of cells and the DT was linear throughout the incubation period considered (40 h). The effect of temperature (30, 37, and 42°C) on the metabolic activity of the cells was also determined after 40 h of fermentation. The higher metabolic changes were observed at 42 °C with conductance values from 600 to 800 μS and DT of 5-7 min. Results obtained were confirmed by viable counts.