Screening of Lactic Acid Bacteria Capable to Breakdown Citric Acid during Ivorian Cocoa Fermentation and Response of Bacterial Strains to Fermentative Conditions

Aims: The breakdown of citric acid contained in the pulp during cocoa fermentation is an important and key property for bacterial growth and for obtaining a well fermented cocoa. The objective of this study was to analyze citrate metabolism in lactic acid bacteria (LAB) isolated from Ivorian fermenting cocoa beans and evaluate their capacity to grow effectively under fermentation conditions.

Place and Duration of Study: Laboratory of Biotechnology, UFR Biosciences, University Félix Houphouet-Boigny (Côte d’Ivoire), between August 2014 and April 2015.

Methodology: Spontaneous heap fermentations were conducted in three cocoa producing regions during 6 days. Bacteria isolation was performed using plate culture on MRS medium and strains were screened for citrate metabolism using Kempler and McKay medium whereas gas and acetoin productions from citrate were searched. Additionally, the viability of cells under stress conditions related to cocoa fermentation was tested.

Results: The results show that a wide rate of LAB strains (75%), mainly heterofermentative possess citrate metabolism, and most of these strains produce gas from citrate but were not able to produce acetoin from citrate. Moreover, some LAB presenting citrate metabolism show a remarkable thermotolerance at 45°C with more than 50% of survival growth rate (SGR), while some exhibited a poor viability (less than 10%) at this temperature. Ethanol at 8-12% was found to have no adverse effect on bacterial growth. In contrast, lactic acid, acetic acid and citric acid exerted individually full inhibition on LAB strains that failed to grow at 0.4% of acid.

Conclusion: Taken together, the results indicate that strains studied may preferentially produce lactic acid from citrate and their high proportion should contribute to efficiently break down citric acid during cocoa fermentation. However, occurrence of a high acidity could seriously limit the growth of these valuable potential starter strains in fermentation conditions.