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This thesis covers chemical studies on the effect of maturity on selected chemical constituent of cocoa bean and its wastes, the utilization of cocoa endocarp, the utilization of cocoa pod pulp sweating and the effect of maturation process (during curing) on the volatile carbonyls of cocoa beans. The work done in this thesis is characterized by the application of a large number of chemical analytical techniques.
The introduction describes the cocoa industry in Sri Lanka. The scope of the thesis is also described briefly in the introduction. In the literature review, the following are described briefly, the main chemical constituents of cocoa, the curing of cocoa, physical and chemical changes during fermentation and drying, more details on the cocoa industry in Sri Lanka, major products of cocoa industry and utilization of cocoa wastes.
The first part of the experimental work of this thesis describes the effect of maturity on selected chemical constituents of cocoa. The fat content of the bean increased remarkably during the final stages of maturation. The cocoa ben was found to contain sis fatty acids (nyristic acid, palmtic acid, stearic acid, oleic acid, linoleic acid and linolenic acid) at all stages of maturity. Palmitic, stearic acid and oleic were the major fatty acids. The pectin content of the husk declined during maturity. The rate of decline was much higher in the endocarp than in the rest of the husk. The fully matured husk contained 8.3 Percent pectin while the endocarp contained 12.2 percent pectin. Study of the sugars of the pod pulp during development of cocoa fruit showed that mainly sucrose was present in the early stages. As maturation progressed sucrose content declined and glucose increased. Fructose was also detected during some stages of maturity. Alcohol content (produced form the sweatings after fermentation) increased with maturity especially in the last two weeks of development. The fully mature state resulted in formation of nearly 10% alcohol. In unripe pods, methanol was also present in significant quantities.
The utilization of cocoa endocarp were studied extensively. The direct incorporation of cocoa endocarp in jam were investigated. The jams set well, but were highly coloured by a browning reaction giving a very poor appearance. To inhibit the browning reaction two mechanisms were employed: (i) heat inactivation by blanching and (ii) use of sodium metabisulphite. The jam prepared using treated endocarp pectin gave a suitable firm setting. No flavor changes were noted, but the jam had a slightly thicker texture in comparison to the standard product. The standard pectin jam and cocoa pectin jam were very similar in appearance, taste, colour and flavor. Some chemical parameters of cocoa endocarp and husk were studied.
The general methods of isolating pectin were examined. In the alcoholic precipitation method solvent losses are inevitable and at a laboratory level 12.4% of the alcohol used was lost. In the CaC12 method, the pectin extracted was of much lighter colour than the A1C13 precipitated pectin. However, examination of the jelly arising from these two pectin’s show that A13+ precipitated pectin set more rapidly and was lighter in colour; its viscosity was also much greater than the CaC12 extracted pectin. The effect of blanching on pectin extraction was also investigated. It showed that during the blanching process about one percent of the pectin was lost the quality of pectin isolated was far superior.
The utilization of cocoa pulp sweating was studied o two different lines, directed towards (a) sugar derived products and (b) alcohol or alcoholic beverage (by allowing the sugar to ferment naturally). In order to prevent the sugar from being fermented three methods of inhibition were tried out: (i) vaiaria copallifera bark, (ii) Ca(OH)2 and (iii) Na2S2O5. Results show that the sweatings were not a good starting material for preparation of sugar based products. The free amino acid content of the fresh and fermented pulp was found to be 96% and 1.1% mg respectively. Although 16 amino acids were detected in the fresh pulp, only 11 amino acids were found in the fermented pulp. The non-volatile organic acid present in the fresh and fermented pulp were also analysed. Results showed that depending on the treatment, the quantity of acid as well as the acidic constituents present varied. The studies on the effect of metals on cocoa bean and pulp showed that of the metals studied, aluminum posed the least problems. Field studies showed that sweating was nearly complete by 30h and fermentation sugar to alcohol began simultaneously with sweating. By the end of 18h the sweatings contained the maximum amount of alcohol (11.7%). It is concluded that the best use of the sweatings is the conversion of the free sugar to alcohol.
The effect of the maturation process on volatile carbonyls of cocoa bean was investigated. The maturation process during curing increased total carbonyl content significantly. The major effects were the marked increase in butyraldehyde (combined, n and also) content and the appearance of acetaldehyde and another carbonyl (probably nonanaldehyde). The C5 aldehyde concentration declined noticeably.
