Effects of Initial Rice Bran Concentration and Inoculum's Ratio on Microbial Growth of Co-culture Fermentation

Co-culture fermentation is widely applied for its synergistic effects. The synergistic effects of lactic acid bacteria (LAB) and propionic acid bacteria (PAB) are reported to improve the ruminant feed efficiency through the supplementations of probiotics. However, although co-culture fermentation of LAB and PAB has been recently demonstrated, the effects of carbon source and inoculum’s ratio on the microbial growth in co-fermentation are still not well-explored. Thus, this study was carried out to investigate the effect of rice bran concentration, as carbon source and inoculum’s ratio on the growth of L. casei and P. jensenii in co-culture fermentation. Reducing sugar content was extracted from rice bran through autoclave at 121℃ for 15 minutes. Co-culture fermentation was carried out in 2 stages: rice bran extract concentration’s variation and inoculum’s ratio variation. Co-culture in 20% w/v of RBE concentration showed the highest yield coefficient of YX/S of 0.265 g biomass/g substrate and YP/S of 0.715 g propionic acid/g substrate. Therefore, 20% w/v RBE concentration was used for the study of inoculum’s ratio. The YX/S (0.254 g biomass/g substrate) and YP/S (0.653 g propionic acid/g substrate) of ratio 1:4 was slightly lower than ratio 1:8, but the viability of L. casei (8.934 log10 CFU/mL) and P. jensenii (9.420 log10 CFU/mL) was the highest in ratio 1:4. Although increase of PAB ratio can increase biomass produced, but ratio 1:4 can achieve higher microbes’ viability which is important in the development of probiotics products.