# Current Status and Economic Prospects of Alternative Protein Sources for the Food Industry
## 2 Alternative Protein Sources
### Fungi  
Mushrooms have received renewed interest due to their nutritional properties and high protein content but especially for their sensory profile which is acceptable for their use in meat analogues ([PERSON] et al., 2022) [82]. Their relatively simple production protocol using low value materials such as sawdust and branches ([PERSON], 2022) [83] justifies why fungi-based proteins are a steep-growing trend in the food sector. Indeed, their estimated consumption exceeds 12.7 million tons ([PERSON] et al., 2022) [84]. The cost of industrial mushroom production can be as low as USD 0.026 per fresh kg, or even lower USD 0.014 cents per fresh kg, with optimized heating and cooling systems ([PERSON] et al., 2020) [85]. The growth period, depending on the species, can be as short as 42 days to produce 25,000 kg of fresh white button mushrooms (_A. bisporus_). The biological efficiency of converting growth substrate to mushroom biomass can be as high as 250%, which is an impressive efficiency compared to other crops where 80-90% of biomass is left unused after harvest ([PERSON] et al., 2000) [86].  
Their high protein content (average 27.5% on a dry basis) and complete amino acid profile by FAO standards ([PERSON], 2013) [87] differentiate them from most non-animal proteins. For instance, individual chemical scores of nine essential amino acids of three commonly consumed mushrooms (_Agaricus bisporus, Pleurotus ostreatus_ and _Lentinus eodes_) satisfy the FAO standards (FAO/WHO/UNU, 2007) [54]. Additionally, evidence shows that mushroom protein has antioxidant activity ([PERSON] et al., 2021; [PERSON] et al., 2022) [88; 89] and therapeutical properties ([PERSON] et al., 2013; [PERSON] & [PERSON], 2005; [PERSON] et al., 2016) [90; 91; 92].  
Despite these advantages, the incorporation of mushroom biomass or protein into food matrices, and their processing into protein concentrates and food ingredients are recent. Mushroom processing is generally divided into three main categories: (1) post-harvest processing for fresh market, (2) processing into convenient earned, sauces or pickled foods, and (3) extraction of high-value ingredients for functional and pharmaceutical applications ([PERSON] et al., 2021) [93]. While post-harvest processing focuses on drying and irradiation techniques to extend the shelf-life of fresh mushrooms ([PERSON] et al., 2021) [94], the use of mushroom-derived ingredients is more developed for high-end pharmaceutical applications.  
As AP source, the use of mushrooms in meat analogues such as nuggets or patties is limited, but sensory acceptance has been positive when mushrooms were used as partial replacement ([PERSON] et al., 2022) [82]. Alkaline extraction followed by isoelectric precipitation has been the only method tested so far for the extraction of mushroom protein aiming at the production of fungi-based protein concentrates. One interesting study analyzed proteins of 50 different mushrooms under the Osborne classification, based on protein solubility ([PERSON], 2001) [95]. Common culinary mushrooms such as white button mushrooms (_A. bisporus_), shitake mushrooms (_L. codes_), and oyster mushrooms (_P. ostreatus_) contain only 20-30% globulin (salt-soluble) fraction. This contrasts with plant proteins that largely contain storage globulin proteins ([PERSON] et al., 2016) [51], that favor protein production through isoelectric precipitation. On the contrary, protein fractions such as albumin (water soluble) are left unrecovered in the liquid phase during protein production ([PERSON] et al., 2022) [96].