Effect of Different Pre-drying Methods on the Quality Attributes of Instant Controlled Pressure Drop Puffing Dried Shiitake (Lentinus edodes) Crisps

In order to explore the effect of pre-drying methods on the quality attributes of instant controlled pressure drop puffing (DIC) dried whole shiitake (Lentinus edodes) crisps and develop ready-to-eat L. edodes snack food, this study investigated the influence of three different pre-drying methods, viz., hot air drying (HAD), heat pump drying (HPD) and vacuum freeze drying (FD) on the quality attributes of L. edodes crisp. The results showed that the total drying time of L. edodes crisps depended on the pre-drying method, following the order of HAD-DIC<HPD-DIC<FD-DIC. Opposite tendency was observed in the average drying rate. The total color difference of L. edodes followed the order of FD-DIC<HPD-DIC<HAD-DIC. The puffing degree of L. edodes crisps followed the order of HPD-DIC>HAD-DIC>FD-DIC. The rehydration ratio of L. edodes crisps followed the order of FD-DIC>HPD-DIC>HAD-DIC. HAD-DIC resulted in the highest hardness and lowest brittleness. FD-DIC resulted in the lower hardness and crispness. HPD-DIC resulted in the highest crispness and optimal hardness. The total sugar content of L. edodes crisps followed the order of FD-DIC>HPD-DIC>HAD-DIC. Low field nuclear magnetic resonance (LF-NMR) revealed that compared with HAD and FD, the proportion of tightly bound water and immobilized water in L. edodes after HPD was higher, and the proportion of tightly bound water was lower, which was conductive to water flash evaporation during DIC processing thus providing sufficient driving force for the puffing of Lentinus edodes. In conclusion, HPD was the best pre-drying method for L. edodes crisps.