Effect of temperature on the drying characteristics, colour and ascorbic acid content of green and gold kiwifruits

Abstract

The drying characteristics of green and gold kiwifruit were determined using an air velocity of 0.20 m/s at ambient humidity and different temperatures (60, 80 and 100°C). The colour values (L*, a* and b*) and ascorbic acid content were also measured for the different fresh and dried kiwifruits. The drying of green and gold kiwifruit slices consists of a constant rate period (CRP) and two parts of falling rate period (FRP). The CRP drying rate, first and second FRP drying coefficients increase with drying temperature for both the green and gold kiwifruit slices. The first critical moisture content (CMC) and the dynamic equilibrium MC decrease with drying temperature for both the green and gold kiwifruit slices. The second CMC for both green and gold kiwifruit slices were not affected by drying temperature. The values for chroma of the dried green kiwifruit increased while the dried gold kiwifruit decreased with higher temperature as compared with the fresh samples. The values for hue angle of dried green and gold kiwifruits decreased at higher temperature. Lastly, the values for browning index of dried green and gold kiwifruits increased at higher temperature. There was not much change on the ascorbic acid contents of fresh and dried green and gold kiwifruits when drying at 60 and 80°C. But there was about 19% decrease in the ascorbic acid content of dried green and gold kiwifruits after drying at 100°C.