Improvement of quality of cocoa beans (Theobroma cacao) through controlled fermentation

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The purpose for which cocoa beans are fermented is to produce beans with good flavour, aroma and taste for making such cocoa products as chocolate, beverages etc. This study was designed to (i) isolate and identify lactic acid bacteria (LABS) from fermenting cocoa which are one of the microorganisms responsible for the fermentation of the beans, (ii) to attempt to modify the fermentation factors using the LABS exclusively in singles and in combination to enhance the efficiency of fermentation so as to improve bean quality. To achieve the above objectives, field and laboratory experiments were carried out. The field experiments sought to monitor the temperature profile, microfloral population of the fermenting cocoa heaps and isolate and identify the lactic acid bacteria present in the three experimental areas. The laboratory experiments were mainly to ferment sterile cocoa using the four different bacterial isolates in singles or in combination at 2.6 x 108 cells of bacterial suspension per kilogram of sterile fresh cocoa beans. In the field, the results indicated that generally there was a significant difference between the mean temperatures of the top and middle of the, heaps, the top having the highest and the bottom having the lowest temperatures. The mean temperatures, of the heap were also seen to increase with time of fermentation. On MRS agar, it was observed that the bacteria increased within 48 hours and then decreased on turning the heap before the organisms increased slightly until the end, of fermentation. On malt extract agar, however, there was a gradual decrease in their numbers until none were observed as the end of the fermentation period. Lactic acid bacteria isolated were of the genera Lactobacillus, Streptococcus, Leuconostoc and Pediococcus. The laboratory experiments produced generally cocoa beans of good quality in terms of pH, moisture content, anthocyanin content and “cut” test results of the fermented and dried cotyledons of the beans. The results suggest that lactic acid bacteria used exclusively in fermentation of cocoa may improve the already good flavour of cocoa and probably come out with new flavours in cocoa depending on the different combinations or single bacteria isolates used. Other microorganisms like yeasts which are also some of the microflora in cocoa fermentation can act with these bacteria metabolites and may bring about changes in the quality of fermented beans. The yeast study is to be verified in a subsequent research.
A thesis submitted to the Board of Postgraduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirement for the award of the Degree of Master of Philosophy, 1996