The main objective of the study was to determine the kinetics of the polyphenol oxidation reaction in cocoa beans during air drying at various air temperatures and humidities. The temperatures used were between 40 and 60°C and the relative humidities were between 50 and 80%. The higher the temperature and relative humidity of the drying air, the lower the amount of polyphenol residue in the cocoa beans, because of enzymatic oxidation of polyphenols. At higher drying temperatures, non-enzymatic oxidation of polyphenols could also occur. Computer simulation results gave rate constants for the polyphenol oxidation reaction (k 1 ) and the condensation reaction (k 2 ), at various air conditions, in the range of 0.055-0.200 and 0.136-0.155 h )1 respectively. The activation energies obtained for the polyphenol oxidation reaction were in the range of 27 800-30 312 J K )1 mol )1 . The reaction kinetics of the enzymatic browning reaction fitted a pseudo first-order reaction.

Optical chemical sensors have promoted escalating interest in the determination of various pollutants in the environment, which are creating toxicity and may cause serious health problems. This review paper focuses particularly on the recent progress and developments in this field; the working principles and basic classes of optical chemical sensors have been briefly described.

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