Analysis of some functional properties of acetic acid bacteria involved in Ivorian cocoa fermentation

Abstract

Objective: To investigate some functional properties of acetic acid bacteria (AAB), involved in Côte d’Ivoire cocoa fermentation.
Methods and results: Six day heap fermentation on banana leaves was conducted at farm level and AAB growth was monitored during this process at 24 h interval by numeration on plate agar. Functional properties such as acid production, thermotolerance, resistance to alcoholic stress carbon metabolism and over oxidation of acetic acid were conducted on either plate agar or liquid medium. During fermentation, AAB reached maximum load at 72 h, corresponding to a high temperature 44 °C of fermenting mass and a pH round 4.45. All the 86 strains isolated proved to be thermotolerant with ability to grow up to 45 °C and 63 % of them showed particularly high tolerance to alcohol up to 15 %. The temperature between 30 and 40 °C and alcohol at high concentration (15 %) did not notably affect acid production. However, beyond 40 °C, the acidification ability of the most acidifying strains was strongly affected. A high proportion of strains 80 %, were able to further oxidize acetic acid into water and carbon dioxide and subsequently belong to Acetobacter genus. The strains displayed a poor carbon metabolism profile with the capacity to utilize only glucose as carbon source.
Conclusion and application of findings: This study shows that Ivoirian AAB fermenting mass possesses some technological traits potentially useful for their utilization as valuable starters in cocoa fermentation.

Key words: Acetic acid bacteria, alcohol-tolerance, cacao, fermentation, thermotolerance.