ABSTRACT
Aims: This work intends to screen and to identify thermotolerant acetic acid bacteria with acetic acid production capacity at high temperature in cocoa beans fermentation from six cocoa producing regions of Côte d’Ivoire. Study Design: Thermotolerant acetic acid bacteria were isolated from cocoa fermentation. These thermotolerant strains were biochemically characterized and tested for the production of acetic acid in culture medium. Place and Duration of Study: This study was performed in Biotechnology Laboratory, University Félix Houphouët-Boigny (Côte d’Ivoire) from January to November 2017. Methodology: Several strains of acetic acid bacteria were isolated from the traditional cocoa beans heap fermentation process occurred in six major cocoa producing regions of Côte d’Ivoire. These isolates were screened to select thermotolerant strains that were able to produce a good amount of acetic acid. Biochemical identification of thermotolerant acetic acid bacteria was carried out on the basis of biochemical characteristics analysis as acid production from ethanol, oxidation of acetate and lactate, ketogenesis from glycerol or mannitol, formation of water-soluble brown pigment, growth on different carbon sources and acid production from sugars and sugar alcohols. Results: A total of 821 acetic acid bacteria strains were isolated from the cocoa beans heap fermentation of these six regions. Among them, 26 (31.15%) showed growth capacity at 45°C and six (6) grown at 50°C. These 26 strains displayed also acid production capacity at 35°C and at 45°C with acid amount ranged from 1.2 to 24.63 and 0.80 to 1.70 respectively. Biochemical analyses of these thermotolerant strains revealed that the isolates belong to three genera notably Acetobacter, Gluconacetobacter or Gluconobacter. Moreover, all strains were able to grow in medium containing 10% ethanol and to produce acid from various carbohydrates sources. In addition, strain T6HS14 displayed acetoin production capacity while 8 strains were able to produce brown pigment on Yeast extract-Ethanol-Peptone-Glucose medium. Conclusion: This study highlighted the presence of thermotolerant acetic acid bacteria strains involved in Ivorian cocoa fermentation. Furthermore, some isolates displayed a diversity of technological properties which could be used for the improvement of cocoa fermentation process. These predictors, however, need further work to validate reliability.
ABSTRACT
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.