Abstract
The objectives of this study were to optimize the conditions for cell growth and exopolysaccharides (EPS) production by using pure and mixed microbial cultures of Streptococcus thermophilus and Lactobacillus bulgaricus , and to evaluate the antioxidant and antibacterial activities of EPS in vitro . The mixed cultures of two strains showed a higher cell growth whereas the higher EPS production was detected in pure culture with S. thermophilus . The optimal medium were determined as follows (g/l): sucrose 50, yeast extract 10, KH 2 PO 4 3 , MgSO 4 .7H 2 O 0.05 and pH initial 6.5 at 30°C. Under the optimized conditions, the values of dry cell weight (DCW) and EPS were 5.2± 0.8 g/l and 56.8 ± 0.62 mg/ml, respectively. The EPS demonstrated a positive antioxidant potential on DDPH radical scavenging. The agar diffusion assay showed that purified EPS exhibited antibacterial activities against tested pathogens such as Escherichia coli ATCC 250922 and Staphyloccocus aureus ATCC 250923 at (62-1000) μg/mL. In conclusion, EPS have an antioxidant activity and could have applications in the food industry.
Highlights
Lactic acid bacteria (LAB) have received attention for their exopolysaccharides (EPS) producing ability
Antioxidant and Antibacterial Activities of Exopolysaccharides from Lactic Acid Bacteria 31 parameters have a high impact upon the viability and economics of the bioprocess, their optimization holds great importance for process development
A classical yogurt starter culture produces a smooth viscous gel, with a desirable fermented product aroma and flavor polysaccharides derived from S. thermophilus and L. bulgaricus show large variation in composition, charge, spatial arrangement, rigidity and ability to interact with proteins
Summary
Lactic acid bacteria (LAB) have received attention for their exopolysaccharides (EPS) producing ability. Antioxidant and Antibacterial Activities of Exopolysaccharides from Lactic Acid Bacteria 31 parameters have a high impact upon the viability and economics of the bioprocess, their optimization holds great importance for process development. Microbial polysaccharide production is greatly influenced by fermentation conditions such as pH, temperature, oxygen concentration and agitation as well as by the composition of the culture medium (Bryan, Linhardt, & Daniels, 1986). A classical yogurt starter culture produces a smooth viscous gel, with a desirable fermented product aroma and flavor polysaccharides derived from S. thermophilus and L. bulgaricus show large variation in composition, charge, spatial arrangement, rigidity and ability to interact with proteins. Among the LAB, a crude EPS of S. thermophilus was obtained, optimized and examined for its antioxidant and antibacterial activities to find a functionally active EPS
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