Effects of Different Drying Methods on Quality of Tuber indicum

In this research,hot air drying and vacuum freeze drying were used to dry fresh Tuber indicum slices,and the effects of different drying methods on qualities and microstructure of Tuber indicum were investigated. Then sensory quality(color,texture),rehydration characteristics,nutritional ingredients(reducing sugar,total protein,vitamin C,total flavonoids)and microstructure were used as evaluation indexes to study the impact of drying methods on the quality of Tuber indicum. After that,the mobility ratio and distribution of moisture during the drying were studied by low field MRI. The results showed that L^* was higher and a^* was lower in the vacuum freeze drying products,the color of which could be well preserved. The browning degree of the hot air drying products was higher. Vacuum freeze drying products had lower hardness and high fragility. Hot air drying products had high hardness and low fragility. Besides,the rehydration ratio and speed of vacuum freeze drying products were significantly higher than those of hot air drying products. After 10 min of drying,the rehydration ratio of vacuum freeze drying was 3.00,which was significantly higher than that of hot air drying(2.26)(P<0.05).The rehydration speed of freeze drying was 0.30 min^-1 and significantly higher than that of hot air drying(0.22 min^-1)(P<0.05). No significant change was found in the total protein content of the Tuber indicum after drying,the retaining quantity of vitamin C,reducing sugar and total flavonoids of drying products were significantly lower than fresh Tuber indicum. The retaining quantity of vitamin C,reducing sugar and total flavonoids in vacuum freeze drying products was significantly higher than that in hot air drying products(P<0.05).The low field MRI was found that T₂₃ signal intensity attenuation rate of vacuum freeze drying products was higher than those of hot air drying products,vacuum freeze drying had higher efficiency. SEM observation of the microstructure showed that the cell tissue of hot air drying products was contracted and collapsed,and the structure was very dense,while the vacuum freeze drying products showed porous structure. The aggregate analysis shows that vacuum freeze drying is more suitable for drying and processing of Tuber indicum products. This research provides a theoretical basis for improving the processing quality of Tuber indicum drying products.