Chitosan is a non-toxic polysaccharide derived from chitin, known for its antioxidant, antimicrobial, and film-forming properties [1]. Due to its distinctive properties, chitosan has attracted significant attention across various industrial sectors. In the food industry, chitosan shows strong potential as a preservative for various products, including fruits, vegetables, sausages, and meat [2]. Preservative properties of chitosan are attributed to its antimicrobial activity against microorganisms responsible for food spoilage and foodborne pathogens, as well as to its antioxidant activity [3], [4].

Molecular weight (Mw) is an intrinsic parameter that significantly affects several biological properties of chitosan, including antimicrobial and antioxidant activities [5], [6], [7], [8]. One challenge to optimizing chitosan efficiency in the food sector is using Mw that enhances biological activity. For example, Chien, Sheu, Huang, and Su [9] evaluated antioxidant capacity of chitosan with high (HMw), medium (MMw), and low (LMw) molecular weights in aqueous system and apple juice, observing that LMw chitosan exhibited higher antioxidant activity against superoxide anion radicals, DPPH (2,2-diphenyl-1-picrylhydrazyl) radicals, and hydrogen peroxide than MMw and HMw chitosan. Regarding antimicrobial activity, Liu, Chen, Park, Liu, Liu, Meng, and Yu [10] reported that LMw chitosan was more effective against E. coli than HMw or MMw chitosan. Similarly, Chien, Sheu, and Lin [11] evaluated a coating prepared with LMw and HMw chitosan on citrus fruit, reporting that LMw chitosan-based coating showed higher antifungal activity against Penicillium italicum and Penicillium digitatum. These findings suggest that reducing Mw through depolymerization treatments may be a viable strategy to enhance functional properties and applications of chitosan in the food industry.

Previous research has focused on depolymerizing chitosan using various treatments, including enzymatic, chemical, physical, and oxidative treatments [12], [13], [14], [15], [16], [17]. The most common depolymerization methods are chemical, oxidative, and enzymatic; however, they have disadvantages, including high production costs and negative environmental impacts [18]. In view of this, physical methods for depolymerizing chitosan, such as microwave irradiation, offer a more sustainable alternative due to simplicity and low environmental impact [19], [20]. Chitin is a biopolymer that serves as a structural component in organisms such as crustaceans, insects, and fungi [21]. The principal commercial sources of chitosan are crustaceans; however, recent research has identified insects as an alternative source [22], [23]. In this regard, T. molitor and Z. morio are particularly interesting due to their ease of artificial rearing and low production costs [24], [25]. Various investigations have shown that both insects exhibit high chitin yields, making them promising sources of chitosan [26], [27], [28].

Although insect chitosans represent a promising alternative source with notable functional properties, limited information exists regarding how Mw influences its antimicrobial, antioxidant, and physicochemical properties. Therefore, this study aimed to obtain chitosans with different Mw from T. molitor and Z. morio through microwave irradiation and to evaluate their physicochemical, rheological, thermal, and biological properties.