In this study, Lactobacillus paracasei LZ9077 was used as a test strain to investigate the application of this bacterium and commercial fermenter agents in fermented milk. The acid production ability, the number of live bacteria, sensory evaluation and other evaluation indexes were used for process optimization. The optimal fermentation conditions were obtained by single factor test and orthogonal test, and the changes of yogurt during fermentation were determined. The results showed that the optimal fermentation conditions were as follows: the inoculum amounts of L. paracasei LZ9077 and commercial fermenter were 4% (V/V) and 0.1% (m/V), respectively, and the fermentation time was 6 h. The addition of L. paracasei LZ9077 increased the number of viable bacteria and the acid-producing efficiency of the fermented milk, and the number of viable bacteria was up to 9.22 (lg (CFU/mL)) at the end of the fermentation, and the titration acidity was (99.94 ± 0.36) °T, and the viscosity and stability of yoghurt were significantly improved.

The optimization of culture temperature, initial medium pH, and carbon and nitrogen sources for improved production of extracellular polysaccharides by Lactobacillus plantarum XN1904E was carried out using one-factor-at-a-time (OFAT) and orthogonal array design methods. The results showed that the optimal culture conditions were determined as follows: initial pH 6.5, temperature 37 ℃, galactose as the best carbon source, and fish peptone as the best nitrogen source. Under these conditions, the production of extracellular polysaccharide was 235.41 mg/L. The polysaccharide at 0.2 mg/mL had antioxidant activity in terms of scavenging rate (27.54%) against 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical.