Citation: Lam, I.L.J.; Mohd Affandy, M.A.; ‘Aqilah, N.M.N.; Vonnie, J.M.; Felicia, W.X.L.; Rovina, K. Physicochemical Characterization and Antimicrobial Analysis of Vegetal Chitosan Extracted from Distinct Forest Fungi Species. Polymers 2023, 15, 2328. https:// doi.org/10.3390/polym15102328 Academic Editor: Vladimir A. Belyy Received: 10 February 2023 Revised: 21 March 2023 Accepted: 22 March 2023 Published: 16 May 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). polymers Article Physicochemical Characterization and Antimicrobial Analysis of Vegetal Chitosan Extracted from Distinct Forest Fungi Species Iversen Luk Jun Lam, Mariah Aqilah Mohd Affandy, Nasir Md Nur ‘Aqilah, Joseph Merillyn Vonnie , Wen Xia Ling Felicia and Kobun Rovina * Faculty of Food Science and Nutrition, Universiti Malaysia Sabah, Kota Kinabalu 88400, Sabah, Malaysia * Correspondence: rovinaruby@ums.edu.my; Tel.: +60-88320000 (ext. 8713); Fax: +60-88-320993 Abstract: The main goal of this investigation is to conduct a thorough analysis of the physical, chemi- cal, and morphological characteristics of chitosan derived from various forest fungi. Additionally, the study aims to determine the effectiveness of this vegetal chitosan as an antimicrobial agent. In this study, Auricularia auricula-judae, Hericium erinaceus, Pleurotus ostreatus, Tremella fuciformis, and Lentinula edodes were examined. The fungi samples were subjected to a series of rigorous chemical extraction procedures, including demineralization, deproteinization, discoloration, and deacetylation. Subsequently, the chitosan samples were subjected to a comprehensive physicochemical character- ization analysis, encompassing Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), degree of deacetylation determination, ash content determination, moisture content determination, and solubility determination. To evaluate the antimicrobial efficacy of the vegetal chitosan samples, two different sampling parameters were employed, namely human hand and banana, to assess their effectiveness in inhibiting microbial growth. Notably, the percentage of chitin and chitosan varied significantly among the distinct fungal species examined. Moreover, EDX spectroscopy confirmed the extraction of chitosan from H. erinaceus, L. edodes, P. ostreatus, and T. fuciformis. The FTIR spectra of all samples revealed a similar absorbance pattern, albeit with varying peak intensities. Furthermore, the XRD patterns for each sample were nearly identical, with the exception of the A. auricula-judae sample, which exhibited sharp peaks at ~37 ◦ and ~51 ◦ , while the crystallinity index of this same sample was approximately 17% lower than the others. The moisture content results indicated that the L. edodes sample was the least stable, while the P. ostreatus sample was the most stable, in terms of degradation rate. Similarly, the solubility of the samples showed substantial variation among each species, with the H. erinaceus sample displaying the highest solubility among the rest. Lastly, the antimicrobial activity of the chitosan solutions exhibited different efficacies in inhibiting microbial growth of skin microflora and microbes found on the peel of Musa acuminata × balbisiana. Keywords: chitosan; biodegradable polymer; vegetal; fungi; antimicrobial analysis 1. Introduction Biopolymers are an attractive class of compounds that possess an array of repeat- ing monomers that are linked through chemical bonding, determined by their distinct chemical structures. These biopolymers are generally categorized into three groups based on their source and synthesis method, namely, natural, microbial, and synthetic biopoly- mers [1]. Naturally occurring biopolymers, such as proteins, lipids, and polysaccharides, can be extracted from a variety of sources. Meanwhile, the microbiologically synthesized biopolymer, pullulan, is a unique example of a biopolymer that is exclusively synthesized by microorganisms. In contrast, synthetic biopolymers, including polylactic acid (PLA), poly(ε-caprolactone) (PCL), and poly(butylene succinate) (PBS), are commonly employed in modern-day applications [2]. Polymers 2023, 15, 2328. https://doi.org/10.3390/polym15102328 https://www.mdpi.com/journal/polymers