Effect of Cooking Combined with Different Drying Methods on the Quality Characteristics and Microstructure of Chinese Chestnut Powder

Raw and cooked chestnut powders were prepared from fresh and cooked Chinese chestnuts, respectively, by four drying methods: hot air drying (HAD), vacuum freeze drying (VFD), radio frequency-vacuum drying (RFVD) and air-impingement jet drying (AJID). The aim of this study was to investigate the effects of cooking treatment and different drying methods on the quality characteristics and microstructure of chestnut powder. The results showed that the raw and cooked chestnut powders prepared by HAD had higher fat contents, but possessed poorer color and quality and uneven particle size distribution. The raw and cooked chestnut powders dried by VFD had the lowest moisture content (3.01% and 4.29%, respectively) and better storability, and their starch and free phenol contents were the highest. Moreover, they had the highest brightness and whiter color, while the raw powder particles showed an irregular large-scale lamellar structure. The raw and cooked powders prepared by RFVD and AJID had higher reducing sugar contents, and the content of free phenol was significantly higher in them than in the counterparts prepared by HAD. Furthermore, their microstructure was maintained well, but their color was poor. After cooking, the water-holding capacity and bulk density of chestnut powders prepared by different drying methods were increased, while the free phenol content and brightness (L*) were decreased, and the powder particles became swollen with a surface rougher, which was folded and wrinkled. In summary, cooking treatment and different drying methods had significant effects on the quality characteristics and microstructure of chestnut powder. Therefore, the production cost and the requirements for industrial need to be considered in selecting the best method to prepare chestnut powder.