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.

Effects of culture conditions on acetic acid production by bacteria isolated from Ivoirian fermenting cocoa (<i>Theobroma cacao</i> L.) beans

“…These data clearly explains why Afoakwa et al (2013) found that acidity level, due probably to acetic acid, was highest at 40 °C 35 °C b 3 days of fermentation. In addition, in previous studies, Soumahoro et al (2015) reported a good growth capacity of these strains at pH values ranged 3 to 7. Consequently, variation of the pH values during a cocoa fermentation essay could not affect acetic acid production capacity of tested strains.…”

“…Our results also showed that no acetic acid production was observed at temperature above 45 °C. Yet, in previous studies, Soumahoro et al (2015) demonstrated that all tested strains are able to growth at 45 °C and strains 49 D, 139 D and 56 AB at 50 °C. On the other hand, Saeki et al (1997) demonstrated the increase in stability with increase of temperature (above 50 °C) of enzymes notably alcohol dehydrogenase and aldehyde dehydrogenase implicated in conversion of ethanol into acetic acid (Tayama et al, 1989).…”

“…Bacterial strains : Five (5) AAB strains including Gluconobacter oxydans strain (49 D), A. pasteurianus (123 D), A. peroxydans (56 AB), A. aceti (139 D) and A. pasterianus (121 D) isolates recovered previously from Côte d'Ivoire cocoa fermentation were tested in this study. These strains were selected because of their high capacity to produce acetic acid in solid and liquid media (Soumahoro et al, 2015). Analysis of acid production under various culture conditions Effects of temperature and pH on acetic acid production: Effects of temperature and pH were evaluated in Hestrin-Schramm (HS) agar medium supplemented with green bromocresol and 4 % ethanol as described by Andelib and Nuram (2009).…”

“…In this context, selected strains should be able to grow and produce metabolite essential for cocoa high quality under heap fermentation stress conditions mainly high temperature, variation of acids and ethanol concentrations. Previous studies have already evaluated the capacity of AAB strains to grow under fermentations conditions (Soumahoro et al, 2015).The aim of this work was to analyse the capacity of these isolates to produce acetic acid under different fermentations stress conditions.…”

Diversity of Yeasts Involved in Cocoa Fermentation of Six Major Cocoa-Producing Regions in Ivory Coast

“…Ho V. , Zhao, Srzednicki, & Fleet, 2013). Among these microorganisms, yeasts are essentials because considered as initiators of this process (Soumahoro, et al, 2015. Ho, Zhao, & Fleet, 2014.…”