Studies on the pectolytic enzyme activity of some pure yeast strains and their utilisation in control fermentation of cocoa

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Fermentation of fresh cocoa beans (Amazon hybrid) was conducted using Kluvveromyces fragilis, Candida norvengensis, Torulopsis candida and Saccharomyces chevalieri under sterile conditions to enhance sweating yield. As control experiment, cocoa beans were fermented under natural conditions. Saccharomyces chevalieri had the highest sweating potential (P < 0.05) and was capable of producing average increases in yield of 171% and 126% over periods of 12 and 48 hours respectively. Much of the sweating process occurred within the first 12 hours of fermentation. All the yeast strains studied had polymethylgalacturonase activity but lacked pectin esterase activity. The type of polymethylgalacturonase present in S.chevalieri and K. fragilis appeared to be of the exo and endo- types respectively. The yeast strains had optimal pH ranging from 3.5 - 4.5 with that of S. chevalieri falling within cocoa pulp pH and thus could be used naturally without the need for pH adjustment during fermentation. Optimal temperatures of the strains activities ranged from 40 - 55°C. These temperatures fall within the temperatures normally attained during natural cocoa fermentation. With respect to sweating rate and pectin degradation, combinations of strains did not offer any advantage over individual yeast strains (P < 0.05). To obtain high pectin containing sweating drainage of sweating must be done within the first 6 hours after yeast seeding of cocoa bean mass. On the contrary low pectin sweating would be obtained around 24th hour of fermentation. Cocoa beans seeded with yeasts and fermented under sterile and controlled temperature condition gave good quality beans as judged by quality indices.
A thesis submitted to the Board of Postgraduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirements for the award of the Degree of Master of Philosophy in Biochemistry, 1995