ORGANIC AND INORGANIC ACIDS IN YEAST TREATMENT DURING ETHANOLIC FERMENTATION: EFFECT ON YEAST VIABILITY AND VITALITY

• Grant number: 25/06547-9
• Support Opportunities: Scholarships abroad - Research Internship - Scientific Initiation
• Start date: June 28, 2025
• End date: September 25, 2025
• Field of knowledge: Biological Sciences - Microbiology - Applied Microbiology
• Principal Investigator: Sandra Regina Ceccato Antonini
• Grantee: Gustavo Augusto Amancio
• Supervisor: Mariana Combina
• Host Institution: Centro de Ciências Agrárias (CCA). Universidade Federal de São Carlos (UFSCAR). Araras , SP, Brazil
• Institution abroad: Instituto Nacional De Tecnología Agropecuaria, Estación Experimental Agropecuaria Mendoza, Argentina
• Associated to the scholarship: 24/13259-7 - EFFICIENCY OF ORGANIC ACIDS IN REDUCING BACTERIAL CONTAMINATION DURING THE ETHANOLIC FERMENTATION PROCESS, BP.IC

Abstract

During the fermentation process for fuel ethanol production, bacterial contamination - especially by lactic acid bacteria- compromises the efficiency of the process. The use of sulfuric acid, while effective in reducing bacterial counts, has environmental impacts and high costs. Hydrochloric acid has been proposed as an alternative, though its effects on yeast are not well understood. Weak organic acids possess considerable antimicrobial activity depending on the acid type and pH and are widely used in the food industry as preservatives, but their potential in ethanol production has not yet been evaluated. Results obtained by the BEPE applicant in a prior scientific initiation project showed the effectiveness of acetic, lactic, citric, and succinic acids in reducing counts of Limosilactobacillus fermentum (a species reported to significantly impact fermentation yield) under non-proliferative conditions (pure culture) and in "pé-de-cuba" conditions (with high yeast biomass concentration) at pH 2.5. No effect was observed on the count of industrial yeast Saccharomyces cerevisiae PE-2. Other studies conducted by the advisor's research group have shown that although yeast cell numbers are not affected by sulfuric acid treatment during cell recycling in the fermentation process, significant changes occur in budding percentage and specific growth rate (both increasing), and viability percentage (decreasing), indicating that the yeast compensates for acid-induced cell death with enhanced growth strategies to maintain viable cell numbers. Monitoring yeast cell viability and vitality over time during treatment and fermentation could contribute to understanding how acid treatment affects fermentation performance, as such growth strategies may partially impair efficiency. This project aims to use flow cytometry to monitor the viability and vitality of two industrial strains, PE-2 and CAT-1, under acid treatment and fermentation using sulfuric, hydrochloric, citric, acetic, lactic, and succinic acids under optimized treatment conditions. The goal is to confirm or refute hypotheses using microscopy and growth assessment techniques regarding the effect of acid treatment on yeast cells. The effects of inorganic acids will be compared to those of organic acids-the novelty introduced by this project in replacing inorganic acids. (AU)