## 1 Introduction  
Food and agro-industrial production are processes annually generating large amounts of exploitable by-products. Within the European Union, the sectors of agriculture, fishery, and forestry were recorded as producing 21 million tons of wastes for the year 2016 alone [1]. Over subsequent decades, the projected increase of the world's population is expected to amplify the produced amount of wastes as a consequence of the relative increase of nutritional needs, highlighting the need of finding a solution regarding their proper disposal [2]. It is evident that the inadequate future management of these materials can provoke serious environmental issues, with adverse effects on human and animal health. The European Commission's Circular Economy Action Plan promotes waste depletion and has legislated several strategies to encourage resource efficiency towards a more sustainable world [3]. In this respect, it must be noted that the practice of disposing the wastes in open fields and the burning of waste are not considered as options due to their negative environmental impact, whereas their incorporation in animal feeding programs presents serious limitations connected with low digestibility and various antinutritional factors [4]. According to Directive 2008/98/EC of the European Parliament, all materials characterized as agro-industrial wastes must have the potential to be utilizable directly in other applications while avoiding any other processes. Accordingly, all endeavors concerning their exploitation must obey the environmental standards and laws avoiding any negative impact on the environment and human health. The vast majority of wastes generatedfrom agro-industrial activities are characterized by a variability in their composition [5]. In general, they contain high amounts of cellulose, hemicellulose, and lignin, justifying their categorization as lignocellulosic materials. On the other hand, they also contain proteins, lipids, minerals, sugars, and polyphenols [4; 6], highlighting them as valuable raw materials that are suitable for use as substrates easily assimilable by various microorganisms. These wastes, because of their rich nutritional content, are suitable for colonization by several microorganisms, including filamentous fungi, through the performance of the solid state fermentation (SSF) process [7]. The latter constitutes the most suitable biotechnology process for the conversion of these materials into high-added-value products [8]. In this respect, intensively cultivated worldwide edible mushrooms such as _Pleurotus ostreatus_ constitute a potent source of specific hydrolytic and oxidative enzymes that are capable of acting as lignocellulosic degradation agents. This ligninolytic enzyme system is applicable for the valorization of various agro-industrial wastes through the production of high-added-value products by an environmentally acceptable method [4]. Mushrooms are also appreciated for their flavor, texture, and rich nutritional composition. They consist of a plethora of bioactive compounds such as \(\beta\)-glucans, which have a beneficial impact on human and animal health. \(\beta\)-glucans are the predominant material of plant cell walls in cereals, yeast, fungi, and mushrooms, which are composed of D-glucose units linked by \(\beta\)-D-glycosoidic bonds. Mushrooms' \(\beta\)-glucans are linked with b-(1,3) and (1,6) linkages. This branching pattern is responsible for their antitumor and immune-stimulating properties [9; 10]. Hemp (_Cannabis sativa_ L.) is included among the herbaceous annual plants that belong to the Cannabinaceae family [11]. Industrial hemp constitutes a cheap source of natural fiber and cannabinoids. It is differentiated from marijuana by the tetrahydrocannabinol (THC) content, which is limited to 0.2% for Europe and 0.3% for Canada. The hemp plant originated from India and Persia, but its cultivation has spread throughout countries of temperate and tropical climates.