Combination of natural antimicrobials for contamination control in ethanol production
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Presence of bacterial contaminants at levels > 107 colony forming units per milliliter (CFU/mL) during ethanol production processes reduces the alcoholic fermentation yield by 30%. Antibiotics are currently used to control contamination, but their residues may be detected in yeast extract, restricting this by-product trade to several countries. Thus, the objective of this study was to assess antimicrobial activity of the natural compounds hops extract, 4-hydroxybenzoic acid, nisin Z, and lysozyme against Lactobacillus fermentum, Leuconostoc mesenteroides, and Saccharomyces cerevisiae, aiming development of a formula. Minimum Inhibitory Concentration of each antimicrobial was determined for bacteria and subsequently, nisin (30 mg/L) and hops extract (5 mg/L) were tested together, showing inhibitory effects combining doses of each antimicrobial that were equivalent to an eightfold reduction of their original Minimum Inhibitory Concentrations (3.75 and 0.625 mg/L, respectively), resulting in a FICIndex of 0.25. Thereon, a formula containing both compounds was developed and tested in fermentation assays, promoting reductions on bacterial population and no severe interferences in yeast viability or population even at extreme doses. Therefore, these compounds have great potential to successfully substitute conventional antibiotics in the ethanol industry.
KeywordsAntimicrobial formula Hops extract Lactic-acid bacteria Nisin Sugarcane mills
The authors would like to acknowledge Pontifícia Universidade Católica do Paraná for the financial support through scholarships provided for the students involved in this research.
This study was funded by Sugar Cane Ltd. (Brazil). Additionally, this work was performed at Pontificia Universidade Católica do Paraná (Brazil), which also granted scholarship to the students involved in the research. Luciano, Maia and Rigotti hold a patent at INPI - Instituto Nacional da Propriedade Industrial (Brazil) on the developed formulation described in the present work. Register Number: BR1020160260205, deposited in 11/2016. Also, we point that Silva Junior is vinculated to Sugar Cane Inc., funding source of this research.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no potential conflict of interest.
This article does not contain any studies with human participants or animals performed by any of the authors.
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