Study of the Drying Rate and Colour Kinetics during Stepwise Air-Drying of Apricot Halves

The drying rate and colour kinetics of apricot halves were studied during stepwise air-drying compared to continuous drying. The tested stepwise temperature profiles exhibited two successive falling rate periods, which differed from the drying rate period of the constant drying temperature profile. Three chromatic indices, namely browning index, chroma and hue were analysed. The analysis showed that treatment with ascorbic acid was more effective during the step up temperature profile, whilst its antioxidant activity was lost during the step down temperature profile due to the initially used high drying temperatures. The chromatic indices were described by a modified kinetic model, the parameters of which were estimated by the Levenberg-Marquardt optimization algorithm and in all cases was derived R-2 (adj) >= 0.88 and MRD < 4.88%.