Chiang Mai Journal of Science

Using probiotic lactic acid bacteria as co-starter cultures plays a role in improving fermentation stability and the functional properties of feed ingredients. This study aimed to select thermotolerant lactic acid bacteria with probiotic potential for poultry, evaluate their feasibility as co-starter culture with Rhizopus microsporus BG5 for fermenting off-grade whole soybeans, and characterize the resulting fermented soybeans. Thirty-four lactic acid bacterial isolates from chicken feces capable of growth at 45°C were screened for acid and bile tolerant, cell-surface properties, antibacterial activity and co-aggregation with target bacteria, and hemolytic activity. Limosilactobacillus reuteri CK-8 and Enterococcus faecium TCF2-7 were selected based on multiple probiotic-associated traits. Co-inoculation of both strains with R. microsporus BG5 under semi-aseptic conditions produced fermented soybeans with uniform fungal growth and desirable physical characteristics, whereas fermentation with R. microsporus BG5 alone was non-uniform and showed signs of spoilage. Co-starter-fermented soybeans showed a higher proportion of crude protein (48.85 vs. 43.99 g/100 g DM) and lower crude fiber content (5.57 vs. 6.83 g/100 g DM) compared with unfermented soybeans, while showing significant increases in reducing sugars, free α-amino nitrogen, and soluble phosphate (p < 0.05). Viable lactic acid bacteria were also detected after drying. These findings provide preliminary support for the feasibility of using poultry-derived lactic acid bacteria with probiotic potential as co-starter cultures with R. microsporus BG5 to obtain more uniform soybean fermentation under the conditions investigated and modify the physicochemical characteristics of off-grade whole soybeans, providing a value-added approach for developing potential feed ingredients for poultry.