Optimization of the fermentation parameters for the growth of Lactobacillus in soymilk with okara flour

The soybean and its derivatives contain many compounds of biological interest. These compounds comprise a food matrix suitable for the incorporation of probiotic microorganisms. This study aimed to establish the optimal conditions of pH and temperature of soymilk containing 3% (w/v) of okara flour for the growth of Lactobacillus plantarum BG 112 and Lactobacillus acidophilus LA3 using a central composite rotational design (CCRD). The optimized conditions were used for the analysis of total phenolic compounds, isoflavone aglycones, antioxidant activity, protection against DNA oxidation, pH, acidity and growth during 72 h of fermentation. The maximal response is in the central point for Lactobacillus plantarum BG 112 and Lactobacillus acidophilus LA3, with correlation coefficients of approximately 0.85 obtained for each microorganism. The 24 and 48 h fermentation times for LPBG 112 and LA3 showed counts above 9.5 log CFU g−1 of sample with averages of 6.23 and 6.15 μmol g−1 of total isoflavone aglycones, respectively. The antioxidant activity measured by DPPH• and ABTS +• assays resulted in the average values of 0.288 and 1.14 μmol mL−1 of sample (LPBG 112) and 0.260 and 1.08 μmol mL−1 of sample (LA3). All fermented samples showed the ability to protect plasmidial DNA against oxidation.