Physicochemical and antibacterial properties of chitosan extracted from swimming crab shells and wooden grasshoppers using different extraction methods

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Marine by-products and insects are among the sources of chitin used in chitosan production and increase the value of the product that may be used in the food industry. The conversion of chitin to chitosan requires proper extraction methods in order to minimise energy use and waste while also producing good-quality chitosan. This study aimed to evaluate different methods of extracting chitosan from two sources and to characterise its physicochemical and antibacterial properties. The study utilised two distinct chitosan sources, i.e. crab shells and wooden grasshoppers, as well as two distinct extraction methods, i.e. conventional and green chemistry methods. The yield, water-ash content, solubility, physicochemical properties as determined by infrared spectroscopy (FTIR), degree of deacetylation (DD), crystallinity (XRD), microstructure (SEM) and antibacterial activity were all evaluated for chitosan quality. The results indicated that the green chemistry extraction of crab shells (M2P1 treatment) produced the highest yield, solubility and crystallinity index of all treatments, with a DD of 60.9%. The functional groups and microstructure of chitosan were remarkably similar across all treatments. Antibacterial activity was determined using the microdilution method against Grampositive (Clostridium acetobutylicum) and Gram-negative (Escherichia coli) bacteria and the minimum inhibitory concentrations were identified, notably 2000 ppm for the green chemistry method. The green chemical extraction method using crab shells (M2P1) demonstrated that the extracted chitosan possessed beneficial physicochemical properties, especially on yield and solubility, and antimicrobial properties against both Gram-positive and Gram-negative bacteria. As such, based on the DD percentage and antibacterial activity, this implies that the extracted chitosan may be used as an alternative for the preservation of food in the food industry.