Polyphasic Analysis of Pectinolytic and Stress-Resistant Yeast Strains Isolated From Ivorian Cocoa Fermentation

Abstract

Microbial preparation containing pectinolytic strains as starter culture should help to standardize cocoa fermentation and reduce the lost due to the variability of cocoa bean. In this study, carbon metabolism, fermentative capacity and effect of environmental conditions on pectinase synthesis were analyzed in four yeast strains previously characterized as highly pectinolytic and stress resistant. The strains showed a restricted carbon metabolism profile with capacity to ferment only glucose and fructose and grown maximally at 5% of these carbon sources. Furthermore, yeasts strains were able to keep round 80% of their relative growth at up to 15% of sugar concentrations and proved to be osmotolerant at 25% glucose. Theses strains expressed their highest fermentative capacity at 35 °C producing up to 10.78 cm 3 of CO 2 and lost more than 50% of this capacity at 40 °C. The isolates studied produced polygacturonase as sole pectinase, optimal production of this enzyme is reached at pH (5-6), at incubation temperature of 30 ºC for strains YS 128, YS 202 and 35 ºC for strains YS 165 and YS 201. However, stress conditions such as 0.5 % acetic acid, 2% lactic acid, 6% citric acid and 6% ethanol repress strongly polygalacturonase production in the strains analyzed. Yeast strains studied present some physiological properties potentially useful for cocoa fermentation but the use of these strains as starter should take into account, the stress conditions susceptible to hinder pectinase production.