The Effects of Moisture Content and Loading Orientation on Some Physical and Mechanical Properties of “Tafo Hybrid” and “Amelonado” Cocoa Beans

Abstract

The physical and mechanical properties of the newly released "Tafo Hybrid" and the traditional "Amelonado" cocoa varieties were studied. Quasi-static uniaxial compressive loads were applied along the lateral and longitudinal axes of the beans after conditioning to moisture contents between 5 and 21% (wb). Moisture-induced changes in the size of "Tafo Hybrid" (geometric mean diameter 13.085 mm) were statistically not significant (P > 0.05) while those of "Amelonado" (geometric mean diameter 12.884 mm) increased significantly (P 5 0.004). The energy absorbed at rupture point increased quadratically from the average of 60-83 mJ as moisture increased from 5 to 21%. In consequence, the rupture force decreased linearly from the average of 136.89-48.58 N. Significantly greater force was required to rupture the beans in the lateral orientation (mean value 131.79 N) compared with the longitudinal loading (mean value 46.58 N). "Tafo Hybrid" cocoa beans possessed higher mechanical strength than "Amelonado." The effects are discussed in relation to their compressive strength, compressive strain and the apparent modulus at rupture, which showed differential responses to moisture changes. PRACTICAL APPLICATIONSThe study is potentially useful for the design of handling and processing equipment for cocoa beans, especially the newly introduced "Tafo Hybrid" variety whose mechanical properties have not been evaluated. Knowledge of the physical and mechanical properties is particularly needed for the optimal design of grinding machines and determination of the corresponding energy expenditure under varying moisture conditions of the beans.

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