Effect of Lactic Acid Bacteria on Urease in Viable Type Fermented Soybean Compound Protein Beverages
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Abstract:
In this study, the effects of four lactic acid bacteria on urease in viable type fermented soybean compound protein beverages were investigated. The Lactobacillus reuteri CICC6118, Lactobacillus casei GBHM-21, Lactobacillus bulgaricus CLB134-1 and Streptococcus thermophilus ST-L134-7-P were inoculated to the soybean milk culture medium without urease with different ratios. After cultivation for 8 h at 37 ℃, beverages were stored for 3 weeks at 4 ℃ and 25 ℃, respectively, and then the amount of viable bacteria and the activity of urease (qualitative and quantitative) were detected in these fermented soybean compound protein beverages during fermentation and storage. The results showed that the beverages fermented by either single or mixed lactic acid bacteria could generate the urease, which presented weakly positive, and the highest activity of urease didn’t exceed 0.020 U/g. The activity of urease in samples fermented by single bacterial was positively correlated with the amount of viable bacteria, but the urease activity showed no significant difference (p>0.05). The initial activity of urease in samples fermented by mixed bacteria had significant difference, while the activity of urease gradually transformed from a significant difference (p<0.05) to no significant difference (p>0.05) as the extension of fermentation time. The activity of urease could decline or disappear accompanying with the decrease of viable bacteria amount during the storage at 4 ℃ and 25 ℃.
