Fig. 4

SEM image of uninoculated SBM and FSBM during two-stage fermentation. a Uninoculated SBM; b the SBM was inoculated with B. velezensis 157 and fermented at 37 °C for 24 h; c the first-stage fermentation was inoculated with B. velezensis 157, incubated at 37 °C for 24 h, then were inoculated with L. plantarum BLCC2-0015 and fermented under anaerobic conditions at 37 °C for another 24 h; d the first-stage fermentation was inoculated with B. velezensis 157, incubated at 37 °C for 24 h, then were inoculated with L. plantarum BLCC2-0015 and fermented under anaerobic conditions at 37 °C for another 48 h. All the images were at 1000 (a), 1500 (b), 3000 (c) and 5000 (d) fold magnification