Chitosan–Glucan Biopolymer Design: Extraction from Champignons with Improved Antioxidant and Antimicrobial Features

In this study, biopolymer chitosan–glucan from fruiting bodies of Agaricus bisporus (Cs-Agrif) was extracted and characterized as a sustainable alternative to commercial low molecular weight (LMW) chitosan obtained from crab shells (Cs-1). Cs-Agrif was prepared through an alkaline treatment process that included deproteination and deacetylation in the same step. The obtained sample was evaluated for its molecular weight, rheological behavior, degree of deacetylation (DD), crystallinity, and β-glucan and phenolic contents. Furthermore, the antioxidant properties of the prepared chitosan were determined under in vitro conditions using four spectrophotometric methods. Finally, its antimicrobial activity was tested against two pathogenic bacteria, one yeast, and mycotoxigenic fungi. Cs-Agrif had low molecular weight, of 45.70 ± 5.20 kDa, with pseudoplastic flow behavior. The degree of deacetylation was 92.7%. FT-IR and XRD analyses confirmed a chitosan-like structure and lower crystallinity in Cs-Agrif compared to pure commercial chitosan. The mushroom-derived chitosan contained β-glucans and phenols, indicating a chitosan–glucan complex. Antimicrobial assays showed low Cs-Agrif microbicidal concentrations (≤2.5 mg mL−1) for Escherichia coli, Enterococcus faecalis, and Candida albicans. The growth of Aspergillus flavus was significantly reduced after five days of incubation. The laboratory-prepared Cs-Agrif exhibited strong antioxidant activity at 5 mg mL−1, comparing to standards. Mushroom-derived chitosan–glucan biopolymer displays excellent physicochemical, antimicrobial, and antioxidant properties, confirming its potential use in biomedicine, food, and the pharmaceutical and cosmetic industries, among many others.