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Microbial pectinolytic strains are targeted as potential starter to control cocoa fermentation. This study analyses the ability of yeasts pectinolytic strains to grow under stress conditions. After an initial growth, a decline trend was observed in yeast growth cycle during the cocoa fermentation. The 36 yeasts pectinolytic strains screened from 205 isolates showed tolerance to both alcoholic stress (10-12% alcohol) and thermic stress (up to 40°C) corresponding to surviving population round 75%. However, temperature-alcohol cross stress provokes full inhibition of strains that failed to grow at only 35°C under 8-10% alcohol. As acid stress, citric acid at 4% has the same effect as alcohol. In contrast, acetic acid and lactic acid respectively at 0.5% and 2% exerted individually, a higher pressure on yeast growth inhibiting up to 60% the fungal population. However, the viability of yeasts strains to a given concentration of lactic (1%) or acetic (0.25%) acid proved to be relatively stable with YS201 at increasing temperature up to 40°C. Cross stress involving temperature and alcohol or single acid stress may be the limiting factor for yeasts pectinolytic growth as starter in controlled cocoa fermentation.

<p>Microbial preparation containing pectinolytic strains as starter culture should help to standardize cocoa fermentation and reduce the lost due to the variability of cocoa bean. In this study, carbon metabolism, fermentative capacity and effect of environmental conditions on pectinase synthesis were analyzed in four yeast strains previously characterized as highly pectinolytic and stress resistant. The strains showed a restricted carbon metabolism profile with capacity to ferment only glucose and fructose and grown maximally at 5% of these carbon sources. Furthermore, yeasts strains were able to keep round 80% of their relative growth at up to 15% of sugar concentrations and proved to be osmotolerant at 25% glucose. Theses strains expressed their highest fermentative capacity at 35 °C producing up to 10.78 cm³of CO₂ and lost more than 50% of this capacity at 40 °C. The isolates studied produced polygacturonase as sole pectinase, optimal production of this enzyme is reached at pH (5-6), at incubation temperature of 30 ºC for strains YS 128, YS 202 and 35 ºC for strains YS 165 and YS 201. However, stress conditions such as 0.5 % acetic acid, 2% lactic acid, 6% citric acid and 6% ethanol repress strongly polygalacturonase production in the strains analyzed. Yeast strains studied present some physiological properties potentially useful for cocoa fermentation but the use of these strains as starter should take into account, the stress conditions susceptible to hinder pectinase production. <strong></strong></p>

Cocoa beans (Theobroma cacao L.) are the raw material for chocolate production. Fermentation of cocoa pulp is crucial for developing chocolate flavor precursors. This fermentation is led by a succession of complex microbial communities where yeasts play key roles during the first stages of the process. In this study, we identified and analyzed the growth dynamics of yeasts involved in cocoa bean fermentation of six major cocoaproducing regions in Ivory Coast. A total of 743 yeasts were isolated, and were identified by sequencing of D1/D2 regions of 26S rDNA gene. These isolates included 11 species with a predominance of Pichia kudriavzevii (44,81 %), Pichia kluyveri (20,99 %) and Saccharomyces cerevisiae (18,97 %) respectively. In addition, the length polymorphism of the genetic marker ITS1-5.8S-ITS2 and PCR-RFLP analysis revealed an intraspecific diversity within the three-main species involved in cocoa fermentation of six major local regions in Ivory Coast. This intraspecific diversity could be exploited for selecting appropriate starter cultures.

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 Original Research Article