Exploring an eco-friendlier strategy for chitosan production and valuable compounds recovery from mushroom by-products with modified subcritical water

Chitosan is the deacetylated derivative of chitin, the second most abundant polysaccharide in nature. It is a promising eco-friendly polymer with immense potential owing to its unique properties and high versatility, offering notable contributions to various industries. Conventionally, chitosan is recovered from several biomasses, primarily from marine sources, using chemical or biological methods. Subcritical water (SCW) extraction is a promising sustainable and innovative technology that can address the main drawbacks of conventional methods. This study explores the use of SCW to extract chitosan from mushroom (Pleurotus ostreatus) by-products, considering different temperatures (120 ◦C, 150 ◦C and 180 ◦C) and malic acid concentrations (0 %, 5 % and 10 %). The highest chitosan yield (6.26 % ± 0.09 %) was achieved with SCW at 120 ◦C and 10 % (w/v) of malic acid, which is 4.8 times higher than that of conventional methods. SCW modified the polymer’s structure, which may have influenced its functionality. A partial deacetylation of chitin, as indicated by a 20 % decrease in acetylation degree, and a decrease in the crystallinity index were highlighted. In addition, the remarkable simultaneous recovery of valuable compounds in liquid residues was achieved, attributed to the hydrolysis mechanisms facilitated by SCW.