Effects of Different Pretreatment on the Quality Characteristics and Microstructure of Hot Air Dried Yam Slices

In order to comprehensive evaluate the effects of different drying pretreatment on the quality and microstructure of yam slices. Fresh sliced yam was pretreated by three different methods: High voltage electrostatic field, ultra-high pressure and freezing. Low field nuclear magnetic resonance and characteristic drying curve were used to determine yam's water status, distribution and content, and analyze changes in microstructure, color, rehydration and other characteristics. Results showed that the freezing pretreatment had the most severe damage on yam slices and the minimum drying time, reduced moisture ratio to 0.1 in 160 min. The high voltage electrostatic field pretreatment was better than other methods in preserving the microstructure of yam. The content of original pectin and cellulose in yam were significantly (P<0.05) higher, which were 11.91% and 14.65%, respectively. The shrinkage was slighter than that of other methods and the rehydration (3.53) was higher. Ultra-high pressure pretreatment could better retain the flavor substances of yam and significantly (P<0.05) improved the whiteness color of dried yam, which was 35.10% higher than before. In summary, different pretreatment methods had significant effects on the quality characteristics and microstructure of hot air dried yam slices. Therefore, the actual demand and the production cost need to be considered in selecting the best pretreatment method to yam slices before drying.