Comparison of biochemical changes during alcoholic fermentation of cocoa juice conducted by spontaneous and induced processes for the production of ethanol

Abstract

Ivory Coast (Côte d´Ivoire) is the biggest cocoa producing country in the world with an average 1405 000 metric tons of cocoa beans. It also produces several quantities of cocoa mucilage juice during cocoa harvesting. In spite of its high sugar and over minerals content, cocoa juice is currently abandoned in farms. This study aims to compare the nature of products resulted from a spontaneous fermentation conducted by uncontrolled or indigenous yeasts to those from a controlled fermentation made by using commercial bakery yeast such as Saccharomyces cereviciae at a rate of 30g/hL during 3 to 5 days of cocoa mucilaginous juice. To conduct this study, fermentations were held at different temperatures 28, 30, 35 and 41°C. Chemical analyses related to the pH by pH-meter, total sugar content using standard method and to the measurement of the yield of ethanol using a gas chromatography (CPG), microbial count were carried out. Analyses showed that yeast, mould, aerobic mesophilic and lactic acid bacteria were isolated in almost all samples. Cocoa shield was shown to contain the highest number of yeast and mould at 1.6x104 CFUcm-2, aerobic mesophilic flora at 1.5x105 CFUcm-2 and lactic acid bacteria at 2.1x104 CFUcm-2. Whatever the type of fermentation, yields of ethanol was highest at 30°C. Fermentation conducted with controlled yeast gave a better yield of ethanol with 8.4 % than spontaneous fermentation that yielded only 4.3 %. There were significant differences (p<0.05) between both alcohol productivity and yield at spontaneous and controlled fermentation. Total sugar content decreased drastically during the fermentation process but a residual content was observed at the end due to the incomplete fermentation. Residual sugar content was highest with values ranging from 35 to 80 g/L at 35°C and 41°C in the controlled fermentation. Production of ethanol was associated with increase in pH value ranging from 4.5 to 4.9.

Key words: Yeasts, Cocoa juice, Fermentation, Ethanol