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STUDY OF PHYSIOLOGICAL AND ENVIRONMENTAL ASPECTS INVOLVED IN ALCOHOLIC FERMENTATION IMPROVEMENTS

Objective

THE MAIN PURPOSE OF THE PROJECT IS TO OBTAIN HIGH FINAL CONCENTRATIONS OF ETHANOL IN ALCOHOLIC FERMENTATION IN ORDER TO REDUCE DISTILLATION COSTS OR, OTHERWISE, TO DEVISE ALTERNATIVE EXTRACTION METHODS.

THE PRODUCTIVITY OF ALCOHOLIC FERMENTATIONS CONDUCTED BY SCCHAROMYCES BAYANUS OR KLUYVEROMYCES FRAGILIS IMPROVES EITHER BY THE ADDITION OF COMPLEX NUTRITIVE SUPPLEMENTS (SOY FLOUR, PEPTONE) OR BY THE USE OF A NATURAL RICH FERMENTATION MEDIUM SUCH AS JERUSALEM ARTICHOKE JUICE (DIRECTLY FERMENTABLE BY K. FRAGILIS), WHEN COMPARED WITH SIMPLE MEDIA. DIFFERENCES IN THE FERMENTATION PROFILES ARE ASSOCIATED WITH THE HIGHER TOLERANCE PRESENTED BY YEAST CELLS TOWARDS HIGH CONCENTRATIONS OF ETHANOL WHEN COMPLEX NUTRIENTS (ACTING AS SURVIVAL FACTORS) ARE PRESENT. ETHANOL INDUCED SPECIFIC DEATH IS THUS DECREASED, AND ITS ADDITION TO A FERMENTATION MEDIUM AFTER FERMENTATION STOPPAGE LEAD TO ITS RAPID RESUMPTION. THE COMPONENTS PRESENT IN COMPLEX MEDIA WHICH MAY BE RESPONSIBLE FOR THESE EFFECTS ARE BEING IDENTIFIED. AMINOACIDS AND METAL IONS (CA2+, ZN2+, CU2+) HAVE ALREADY BEEN FOUND TO HAVE A POSITIVE EFFECT AS SURVIVAL FACTORS, QUALITATIVELY IDENTICAL TO THE COMPLEX MEDIA.
OCTANOIC AND DECANOIC ACIDS ARE TOXIC BY-PRODUCTS OF ALCOHOLIC FERMENTATION. THEIR PRESENCE, EVEN IN LOW CONCENTRATIONS (2-15 PPM) LED TO THE INCREASE OF THE SPECIFIC THERMAL DEATH RATE AND TO THE DECREASE OF THE SPECIFIC GROWTH RATE OF S. BAYANUS. THE MECHANISMS UNDERLYING THESE EFFECTS ARE BEING STUDIED AND RESULTS OBTAINED SUGGEST THAT THE TARGETS FOR THE ACTION OF THOSE TOXICS, AS WELL AS ETHANOL, ARE LOCATED ON YEAST MEMBRANES.
ETHANOL FERMENTATION WITH K. CARRAGEENAN IMMOBILIZED CELLS OF S. BAYANUS LEAD TO FINAL CONCENTRATIONS OF 120 G/L AS COMPARED WITH 75 G/L WHEN FREE SUSPENDED CELLS WERE USED. IN THIS EXPERIMENT, STARTING GLUCOSE CONCENTRATION WAS 300 G/L. EXECUTIVE FERMENTATION SYSTEMS USING IMMOBILIZED YEAST CELLS ARE BEING DEVELOPPED.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

INSTITUTO SUPERIOR TECNICO
Address
1,Avenida Rovisco Pais 1
1049-001 Lisboa
Portugal