The potential of three indigenous bacterial strains (Lactobacillus delbrueckii N2, Lactobacillus cellobiosus TM1, and Lactobacillus plantarum G88) for the production of biosurfactants using sugar cane molasses or glycerol as substrates was investigated through emulsifying, surface tension, and antimicrobial activities. The different biosurfactants produced with molasses as substrate exhibited high surface tension reduction from 72 mN/m to values ranged from 47.50 ± 1.78 to 41.90 ± 0.79 mN/m and high emulsification index ranging from 49.89 ± 5.28 to 81.00 ± 1.14%. Whatever the Lactobacillus strain or the substrate used, the biosurfactants produced showed antimicrobial activities against Candida albicans LV1, some pathogenic and/or spoilage Gram-positive and Gram-negative bacteria. The yields of biosurfactants with molasses (2.43 ± 0.09 to 3.03 ± 0.09 g/L) or glycerol (2.32 ± 0.19 to 2.82 ± 0.05 g/L) were significantly (p < 0.05) high compared to those obtained with MRS broth as substrate (0.30 ± 0.02 to 0.51 ± 0.09 g/L). Preliminary characterization of crude biosurfactants reveals that they are mainly glycoproteins and glycolipids with molasses and glycerol as substrate, respectively. Therefore, sugar cane molasses or glycerol can effectively be used by Lactobacillus strains as low-cost substrates to increase their biosurfactants production.

Background: Biosurfactants are natural surface-active compounds produced by a variety of microorganisms. The high cost of culture media limits the large-scale production and use of biosurfactants. It is therefore necessary to develop an efficient and cost-effective bioprocess to improve the yield of biosurfactants from microorganisms. In this study, the response surface method was used to optimize the production of biosurfactants by a Lactobacillus strain and the antimicrobial activity of the biosurfactants was assessed. Results: The biosurfactant-producing strain was identified as Lactobacillus paracasei subsp. tolerans N2 after 16S rRNA gene analysis. Among the different variables studied using a Plackett-Burman statistical design, temperature and peptone and sugar cane molasses concentrations were found to be the main factors that had significant (p < 0.05) influence on biosurfactant production. The results of this study showed that molasses concentration at 59.5 g/L, peptone at 6.20 g/L and temperature of 33 °C were optimal conditions for biosurfactant production, with a maximum yield of 2.70 g/L. The biosurfactant exhibited surface tension reduction of 37.85 mN/m and antimicrobial activity expressed as inhibition diameter of 63 mm. Partial characterizations by elemental, biochemical and Fourier transmission infrared spectroscopy analysis of the biosurfactant produced revealed that it was glycolipoprotein in nature. The biosurfactant exhibited bactericidal activity against Pseudomonas aeruginosa PSB2, Pseudomonas putida PSJ1, Salmonella sp. SL2, Escherichia coli MTCC 118, Bacillus sp. BC1 and Staphylococcus aureus STP1 at concentrations ranging from 6.4 to 50 mg/mL. Conclusion: The yield of biosurfactant was four-fold higher after optimization of media components and culture conditions using response surface methodology. The results of this study suggested that sugar cane molasses can be used as a low-cost substrate to enhance the yield of biosurfactants with antimicrobial activity.

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Owing to its composition, meat is recognized as one of the best media for microbial growth leading to meat spoilage and food-borne illness. The ability of microorganisms to adhere to surfaces where meat is deposited during selling is a nonnegligible cause of meat contamination. This work was performed to assess the microbial profile of fresh beef sold in the markets of Ngaoundéré town and evaluate the antiadhesive activity of a biosurfactant derived from Lactobacillus paracasei subsp. tolerans N2 against selected pathogenic strains isolated in fresh beef. All fresh beef samples analysed were contaminated with both pathogenic and spoilage microorganisms at levels higher than the microbiological criteria set by the European Commission. A total of 151 strains belonging to 12 species (Pseudomonas putida, Pseudomonas aeruginosa, Pseudomonas sp., Escherichia coli 1, Escherichia coli, Salmonella enteritidis, Salmonella sp., Staphylococcus epidermidis, Staphylococcus xylosus, Staphylococcus aureus, Candida albicans, and Candida sp.) were isolated and identified. A specific relationship between the microbial diversity of fresh beef and the sampling sites was observed. Biosurfactant displayed antiadhesive activity against all the tested strains and the complete inhibition (100%) of Bacillus sp. BC1, S. aureus STP1, and S. xylosus STP2 was noticed at biosurfactant concentration of 10 mg/mL. This study indicates the microbial diversity of fresh beef sold in Ngaoundéré markets and suggests the potential use of biosurfactant as an antiadhesive agent in the meat industry.

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