Antimicrobial and antioxidant properties of crude chitosan extracted from cultivated Agaricus bisporus

Abstract

Chitosan is a natural biopolymer that could be used in clay modification to adsorb mycotoxins, secondary metabolites of filamentous fungi commonly found in cereal grains and animal feed. Only a small number of mushrooms have chitosan, which is mostly produced from chitin through the deacetylation process. In this work, chitosan was extracted from the fruiting bodies of commercially grown Agaricus bisporus with 9 M NaOH for 1.5 h in an autoclave followed by the treatment with 5% acetic acid (150 °C, 6 h), precipitated under alkaline conditions and neutralized. The antioxidant properties of prepared chitosan were determined under in vitro conditions by using spectrophotometric tests, while antibacterial activity was tested using broth microdilution assay (C= 0.078-5 mg/ml conc). The mycotoxigenic strain of Aspergillus flavus was grown on a solid medium enriched with 20 mg/ml of chitosan. The percentage of inhibition of the mycelium growth compared with the control was calculated. Additionally, the composite of bentonite with chitosan isolated from the mushroom was prepared and modified with surfactant hexadecyltrimethylammonium bromide. Adsorption of mycotoxin zearalenone using composite at pH 3 by HPLC was determined. The scavenging ability of free DPPH• radicals of the laboratory-prepared chitosan at a concentration of 5 mg/mL was 99.35%, while the ability to neutralize ABTS+• radical cations was in the range of 31-94%, depending on the concentration. The ferrous ions chelating ability of this sample was 98.50% at 5 mg/ mL. Low bactericidal concentrations were detected, 2.5 mg/ml for Escherichia coli (ATCC 25922) and 0.625 mg/ml for Enterococcus faecalis (ATCC 29219). A. flavus was inhibited for approximately 36% after three days of growth on the agar with chitosan, compared with control. Clay-chitosan- surfactant composite adsorbed 91.75% of zearalenone, compared to the clay-chitosan composite (7.25%), which means that surfactant molecules have a main role in toxin adsorption. The antioxidative and antimicrobial activity of crude chitosan from mushrooms makes it a potential material for food packaging, while a clay-chitosan-surfactant composite could be used for decontamination of animal feed contaminated with mycotoxins