Effect of Pre-treatment and Drying Method on Colour Degradation Kinetics of Dried Salak Fruit During Storage

Effect of heat treatment on colour stability of dried salak fruit during storage was investigated by using hot air (40-90 degrees C), heat pump (isothermal and intermittent modes, 26-37 degrees C) and freeze-drying. Influence of pre-treatment on the colour property was studied as well by blanching the sample at three levels of temperature (50-70 degrees C). Total colour change (Delta E*) was used to assess the colour degradation kinetics and quantify the degree of browning during processing and storage. It was found that the dried pre-treated sample under heat pump isothermal drying recorded the highest Delta E* value during storage followed by non-pre-treated samples under heat pump intermittent drying, freeze-drying, hot air-drying and heat pump isothermal drying. Weibull model is found to better fit the experimental data as compared with zero-order and first-order kinetics models. Analysis on the kinetics constants reveals that the heat treatment could affect the microstructure, water sorption properties and concentration of reacting species of the dried product. This in turn contributes to the colour changes of the dried product during storage.