EFFECT OF SSB (SUPERHEATED STEAM BLANCHING) TIME AND DRYING TEMPERATURE ON HOT AIR IMPINGEMENT DRYING KINETICS AND QUALITY ATTRIBUTES OF YAM SLICES

The effects of SSB (superheated steam blanching) time (0, 3, 6, 9 and 12 min) and drying temperature (50, 60, 70 and 80C) on drying kinetics and quality of yam slices under air impingement drying were investigated in this paper. Results indicated that the positive effect of SSB on drying rate might be overshowed by the negative effect of starch gelatinization and appropriate SSB could accelerate drying rate, whereas the effect of excessive SSB is reversed. The moisture effective diffusivity ranged from 1.1540 X 10-9to 2.8431 X 10-9 m2/s, calculated using Fick's second law of diffusion. The activation energy determined from the slope of the Arrhenius plot, ln(Deff) versus 1/(T + 273.15), was 20.925 kJ/mol. Moderate increase in SSB time or decrease in drying temperature can improve the whiteness index of dried yam slices, whereas increase in SSB time and drying temperature can decrease the rehydration ratio of dried yam slices. PRACTICAL APPLICATIONS Yam is a nutritional, economical and healthy plant, which has been widely used in traditional Chinese medicine. Fresh yams having relatively high-moisture contents are very sensitive to microbial spoilage. Drying is one of the most common methods used for yam preservation. In China, the natural sun-drying method is commonly used for drying yam. However, it requires a long drying time and the final product may be contaminated by dust and insects, especially toxic substances. Blanching is an essential step before the processing of vegetables and fruits, as it can accelerate the drying rate and prevent quality deterioration. Air impingement drying is an efficient drying technology, which has been successfully used in paper and textile industries. Understanding the effect of superheated steam blanching time and drying temperature on hot air impingement drying kinetics and quality of yam slices is helpful for improving the drying process efficiency and quality of dried yam slices.