Biogenic red wine silver nanoparticles as an antimicrobial in non-sterile industrial fermentations

Abstract

Bacterial contamination within the biofuels industry is a major challenge, with Lactic Acid Bacteria (LAB), wild yeasts, and fungi among the main contaminants found during yeast fermentations, reducing ethanol yields and thereby decreasing production efficiency. The predominant antimicrobial control strategy is the use of antibiotics which significantly contributes to the development of antimicrobial resistance. Recently, green synthesized silver nanoparticles (AgNPs) have demonstrated strong antibacterial activities; suggesting that they could have applications in controlling biological contamination in the biofuels industry. Therefore, this study aimed to evaluate the effect of AgNPs that were green-synthesized using red wine (RW) extract as an antibacterial control strategy in non-sterile fermentations. RESULTS: RW-AgNPs were synthesized under optimized green synthesis conditions. The antibacterial activity of RW-AgNPs to Lactiplantibacillus plantarum and potential toxicity to Saccharomyces cerevisiae were evaluated using microbiological assays, growth curve analysis, and anaerobic non-sterile fermentations. The RW-AgNPs exhibited broad-spectrum, concentration dependent antibacterial activity against S. cerevisiae, L. plantarum ATCC 8014, and E. coli, with a greater susceptibility observed in L. plantarum (MIC 6.25 μg/mL; MBC 25 μg/mL). Growth curve and fermentation analyses of high-gravity fermentations showed minimal inhibitory effects of RW-AgNPs on S. cerevisiae, but significant inhibition of L. plantarum, resulting in reduced lactic acid production and significantly improved ethanol yields and overall fermentation efficiency in treated samples compared to untreated controls. Scanning electron microscopy further confirmed reduced bacterial cell presence following treatment with the RW-AgNPs. CONCLUSION: We demonstrate the potential application of RW-AgNPs as an alternative antibacterial strategy for controlling bacterial contamination in industrial biofuel fermentations.