The role of micro-organisms and endogenous pectolytic enzymes in the fementation of cocoa
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Date
1983-05-08
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Abstract
The cause of sweating of cocoa and the involvement of micro-organisms in the process were investigated. The roles of microbial and non-microbial pectolytic enzymes in the fermentation of cocoa pulp were studied by means of aseptic micro-fermentation methods. Fermentations were carried out on a laboratory scale under sterile and non-sterile (natural) conditions and the sweating rates and yields monitored over the first 12 hr of fermentation. The beans were subsequently assessed for quality after 6 days of fermentation, and drying.
Sweating obtained under sterile conditions was attributed to endogenous enzymes. Increased yield and rate of sweating observed under natural conditions, however, suggested that microorganisms played a significant role in the process. In a 12-hr collection under natural conditions, there were increases in yield of the order of 130% over sweating yield under sterile conditions.
Enzymological studies under both sterile and natural conditions revealed the presence of two types of pectolytic enrynes in pulp. Pectin Esterase, (P.E.) and Polygalacturonase (P.G.) activities were detected in pulp. Inhibition of P. B. produced a 31.7% reduction in yield of sweatings, suggesting a partial involvement of the enzyme in the process. Changes in viscosity of sweatings, as well as histological Studies of the enzyme’s action on pulp indicated that P.G. is the cause for sweating. Further indications of this were obtained when the addition of different concentrations of “Commercial P.G.” to fermenting cocoa beans produced large increases in sweating rate and yield. Increases in drainage of over 200% adversely affected the quality of the bean, whilst below 150%, they were acceptable.
Of several microorganisms isolated from fermenting cocoa beans, A. niger and a Penicillium sp. were found to be strongly peotolytic. When applied to cocoa beans, they produced increases in yield of about 190% and 170% respectively. Two other fungi obtained from the American type Culture Collection produced significant increases in sweating rate and yield when applied to cocoa beans. A. oryzae produced about 60%, G. candidium approximately, 35% increases in yield.
Thus, depending on the choice of organism, pectolytic fungi can be employed as starter cultures in the fermentation of cocoa, to give optimum yields of sweatings within the first 12 hours of fermentation.
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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 Science in Biochemistry, 1983