Growth capacity of yeasts potential starter strains under cocoa fermentation stress conditions in Ivory Coast

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.