# Effects of Drying Process on the Volatile and Non-Volatile Flavor Compounds of _Lentinual edodes_
## 1 Introduction  
_Lentinual edodes_ (Berk.) Sing or Shitake mushroom, accounting for about 17% of global mushroom production, is the second largest cultivated edible mushroom in the world [1, 2]. The global production of cultivated mushrooms has increased more than 73% in the last 10 years (FAOSTAT, 2019). _L. edodes_ is one of the most popular edible and medicinal mushrooms in East Asia for its rich nutrients, favorable medicinal properties as well as desirable flavor [3, 4]. Shitake mushroom has been widely used as a flavor enhancer in meat and fermented products due to its unique flavor [5, 6].  
The desirable flavor of shitake mushrooms is composed of volatile and non-volatile components [3]. It has been identified with various volatile compounds from _L. edodes_. The major volatile components are eight-carbon (C8) compounds and sulfur compounds [1]. Both C8 and sulfur compounds are produced by enzymatic reactions, in which lipoxygenase and hydroperoxide lyase catalyze linoleic acid to produce C8 compounds, such as 1-octen-3-one and 1-octen-3-ol, whereas \(\gamma\)-glutamyl transpeptidase and cysteine sulfoxide lyase catalyze lentithinic acid to produce sulfur compounds, including 1,2,4-trithiolane and lentithione [7, 8]. Among these volatile compounds, 1-octen-3-ol, widely present in mushrooms, is responsible for a typical mushroom-like odor, whereas lenthionine,a cyclic 5-sulfur compound, also contributes to the aroma of _L. edodes_[9; 10]. Fresh shitake mushroom gives off a slight odor by the abundance of 1-octen-3-ol. However, the unique aroma of shitake mushroom develops due to the increase of sulfur compounds after drying [1]. The taste of mushrooms is mainly triggered by several small water-soluble substances, including organic acids, 5\({}^{\prime}\)-nucleotides and free amino acids [11]. Thus, it is vital to investigate the effects of processing methods on volatile and non-volatile compounds of shitiake mushrooms.  
Drying is a convenient and effective technique to prolong the shelf life of fresh shitake mushrooms by decreasing the moisture content [12; 13]. However, the quality of mushrooms (flavor, nutrients, texture and color) is affected by the drying method [12]. Hot-air drying (HAD), freeze-drying (FD) and natural drying (ND) are the three most typical drying methods for shitake mushrooms. [PERSON] et al. [14] studied the changes of volatile components in _L. edodes_ during the vacuum freeze-drying process. [PERSON] et al. [15] evaluated the changes in aroma profile of _L. edodes_ during different stages of HAD. [PERSON] et al. [12] investigated the effects of different drying methods (CD (convective drying), FD (freeze-drying), VMD (vacuum-microwave drying) and CPD-VMFD (vacuum-microwave finish-drying)) on volatile composition and sensory profile (inner color and sponginess) of _L. edodes_. However, the influence of the drying methods of hot-air drying (HAD), freeze drying (FD) and natural drying (ND) on both the volatile and non-volatile flavor compounds in _L. edodes_ has never been studied.  
The objectives of this work were to analyze the volatile and non-volatile flavor components' profile of _Lentiunala edodes_ by three drying methods (HAD, FD and ND). The results could provide theoretical evidence for new product developments with _Lentiunala edodes_.