# Effects of Drying Methods and Temperatures on the Quality of Chestnut Flows
## 1 Introduction  
The cultivation of chestnuts (_Castanae sativa_ Mill.) is spread worldwide, especially in Asia and Europe. The European yield of chestnut fruits represents about 12% of the global crop [1]. Italy is the most productive country in Europe (fifth in the world), with nearly 56,000 tons of chestnuts (40% of the European production) harvested on average per year over the period between 1994-2020 [2]. A consistent fraction of Italian chestnuts, approximately 15-20%, are industrially dried and ground into flour [3]. Nowadays, the demand for chestnut and its derivatives is rapidly growing, especially because chestnut flour can be a great substitute for cereal flour and thus a valuable gluten-free alternative [4, 5, 6, 7]. It is, therefore, more and more essential to protect and enhance the quality of chestnut fruits and their transformed sub-products. Chestnuts are seasonal and present a 50% on a wet basis of water content [8]. One of the best methods of chestnut preservation is drying [9]. Indeed, the drying of agricultural products is a technique that is commonly used to prevent fungal growth [10]. The organoleptic, nutritional, and nutraceuticalI qualities of chestnuts often depend on the drying temperature, as well as different types of cooking. Roasting, for example, can increase the content of sugars by 25% [11]. Interest has also moved on restoring a traditional drying method called \"metato\", a two-level structure, either in stone or brick, where a fire in the ground floor heat chestnuts positioned on the upper floor. Although it is captivating to bring the tradition back into fashion, it is crucial to understand how well this ancient classical method intersects the modern need for product quality and healthiness. Various drying methods can indeed change the product's characteristics [12]. The quality of the chestnut dried into the \"metato\"might be harmed by the continuous change in temperature due to the manual managing of the wood fire. Traditional drying could even lead to a high formation of toxic volatile compounds, such as furfural, guaiacol and o-cresol [11; 13; 14]. The latter two make the product taste smokey, or even burned if present in large amounts, and are formed precisely during the thermal degradation of lignin [9]. Nutraceutical compounds are basic and primary indicators of quality. Chestnuts are good resources of antioxidants, calcium, and polyphenols [15]. Such compounds are now at the center of biomedical studies, apt to define their mechanisms of action at the molecular and cellular levels. Moreover, they should play an important role in the prevention of important chronic diseases [16]. Drying at a low constant temperature is considered the best method to maintain the nutraceutical compounds of foods and this method could be applied also to the chestnut production chain, although most of the producers think that this will completely change the quality of the traditional chestnut flour. Another problem that the traditional method must face, however, is the post-drying selection of the fruits sent to the milling. Once the fruits are dried, they need to be peeled, and only at that moment is it possible to check for the presence of damages, represented by a brown or chalky color of the flesh. These damages could be the result of the activities of insect larvae [17] or fungi, such as _Gnomoniopsis castaneae_, _Sclerotina pseudotuberosa_[18; 19], and _Aspergillus_ that might produce toxins [20]. When cut open, rotten chestnuts show a tan-brown discoloration of part or the entire nut kernel. Rots can range in color, from chalky-white to dark brown. Likewise, Aspergillus mycotoxic fungus may contaminate chestnuts and derived products [21; 22]. Aflatoxins are the most toxic products synthesized by _Aspergillus flavus_ and _Aspergillus parasitic_. The main known aflat are named B1, B2, G1, and G2, based on their fluorescence under ultraviolet light (B = Blue, G = Green) [23].