Occurrence of High Acetic Acid-Producing Bacteria in Ivorian Cocoa Fermentation and Analysis of Their Response to Fermentative Stress

Abstract

Acetic acid produced during cocoa fermentation impact strongly the quality of fermented and dried cocoa beans and chocolate. The objective of this study was to analyze acid production in Acetic acid bacteria (AAB) and their response to fermentative conditions. AAB strains were isolated from cocoa fermentation and screened for acid production on both solid and liquid media. From 444 isolates, 15 strains yielded 2 to 38.1 g/L of acid in liquid medium. The best acid producers were identified by biochemical typing as Acetobactersp, Acetobacteraceti, A. peroxydans, A. pasteurianus and Gluconobacteroxydans. Most AAB strains showed strong tolerance to alcohol with round 45% of survival growth rate (SGR) under 12 % ethanol. AAB strains growing well at 2 % acetic acid (SGRround 47 %), failed to grow at 3 % of this acid. Lactic acid has the most hindering effect on AAB growth, provoking a drop of SGR from 100 % to less than 25 % at only 1 % of lactic acid. Maximum growth of acidifying AAB strains occurred at 35 °C. This study evidences the diversity of technological performances of AAB involved in Ivorian cocoa fermentation and allows targeting the most valuable strains as starters.