Improving the quality of dried Theobroma cacao beans using a solar assisted desiccant-based dryer : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, Palmerston North, New Zealand

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Massey University
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"Theobroma cacao" beans are an economically significant commodity for the Fiji Islands. The cocoa beans are harvested in the wild and then fermented and sun-dried under tropical weather conditions. The high relative humidity (RH) as well as the unpredictable weather conditions extend the sun-drying time and causes quality issues in the final dried product. Maintaining product quality is important as export quality cocoa beans are sold at premium prices to chocolate manufacturers internationally. The problems in sun-dying can be solved by reducing the RH of drying air stream. This is possible with desiccant wheel technology (DWT). The solid desiccant material in DWT desorbs moisture from air and reduces humidity. The desiccant material can be regeneration between 60 and 100 °C for the next cycle. This temperature conditions can be achieved by using a solar dryer. This study tested the drying conditions below 20% RH on small batches (6 kg) of fermented Fijian cocoa beans at 45 °C and 55 °C. Impact of these conditions on the drying kinetics and bioactive quality was tested. Experimental data was used to validate a mechanistic drying model. The model was developed using partial differential equations (PDEs) with an implicit scheme for a targeted drying time of 72 hours. Finite difference method (FDM) was used to solve PDEs. The model output was comparable to experimental data from drying runs in Fiji. Reducing the RH at 45 °C showed a better retention of key bioactive compounds, such as polyphenols, caffeine, and theobromine when compared to other treatments. These findings are presented in detail in this thesis and suggests that DWT can provide consistent drying conditions in a tropical environment. The drying model is a useful tool for predicting the drying conditions for cocoa beans based on multiple input variables. The model can be used to advise cocoa farmers on the estimated processing time for cocoa beans to meet the demands of the export market.
Cacao beans, Drying, Fiji, Solar dryers, Design and construction, Drying agents