Natural polymers like chitin, starch, cellulose, hemicellulose, and alginate are widely used in our daily lives to perform various essential functions (Silva et al., 2021; Muthukumaran et al., 2022). Polysaccharides and their derivatives, especially chitin and starch, attract considerable attention due to their extraordinary chemical properties. Starch and chitin are byproducts classified as modified polymers, derived biopolymers, and polysaccharide-containing materials (Crini, 2005). Chitin has the chemical formula (C8H13O5N)n. The structure of chitin is most similar to that of cellulose, while its function is most similar to that of keratin. There are minor structural differences between cellulose and chitin, but they are chemically identical. Chitin has an acetamide group at the C₂ position instead of a hydroxyl group within the glucose unit (Hamed et al., 2016).

Chitin is a naturally occurring polysaccharide found abundantly in nature. Microfibrils of chitin are structural components found in the extracellular matrix of various invertebrates, including sponge skeletal fibers, mollusk shells, nematodes eggshell and pharynx, crustacean shells, arthropod exoskeletons, and fungi cell walls, forming natural biocomposites (Roberts, 1992; Ehrlich et al., 2007; Chen and Peng, 2019; Liu et al., 2019; Yu et al., 2024). Chitin in fungi is primarily sourced from the mycelium of species like Mucor rouxii, Aspergillus niger, and Lentinus edodes (Huq et al., 2022). Chitin makes up the exoskeleton, the wings, the antennae, and the trachea (Mei et al., 2024).

Chitosan and chitin are polysaccharides composed of N-acetyl-D-glucosamine and D-glucosamine units. Chitosan is derived from chitin through several methods, primarily involving chemical and enzymatic processes. Chemical methods are the predominant approach that involves the deproteination, demineralization, decolorization, and deacetylation of chitin (Gandhi et al., 2014; Ibitoye et al., 2018). Deacetylation is a process that eliminates acetyl groups from chitin’s molecular chain, yielding chitosan. The degree of deacetylation (DD) determines the extent of chitin conversion to chitosan (Kumar et al., 2020). DD varies based on factors such as NaOH concentration, reaction temperature, and duration. Chitosan’s DD can span from 56% to 99%, influenced by production techniques and species. Chitosan represents a partially deacetylated form of chitin, where a portion of N-acetyl-D-glucosamine transforms into D-glucosamine (Kumari and Kishor, 2020). Enzymatic methods utilize chitinases and chitosanases to transform chitin into chitosan. This method is increasingly attracting attention due to its ability to produce chitosan with a well-defined structure and a lower environmental impact compared to chemical methods (Kaczmarek et al., 2019; Pratiwi et al., 2023). In microbial methods, certain fungi, such as Pleurotus spp., can extract chitosan through fermentation processes. This approach is regarded as eco-friendly and can yield chitosan with notable antimicrobial properties (Johney et al., 2016). The efficiency, cost, and environmental impact of these methods differ significantly, with enzymatic and microbial approaches offering more sustainable alternatives to conventional chemical extraction. Chitin and chitosan are not present in mammals but can be degraded in the body by several proteases such as lysozyme, papain, and pepsin (Pangburn et al., 1982). Chitin and its derivatives, chitosan, are utilized in various fields such as water treatment, cosmetics, healthcare, and agrochemicals. Their biodegradable nature and non-toxic properties make them valuable for sustainable practices. They are employed in producing organic fertilizers that have been shown to enhance crop productivity. Chitin promotes plant growth by fostering beneficial microbial activity in the soil, enhancing nutrient availability and absorption by plants. This results in higher crop yields and improved plant health (Sharp, 2013; Malerba and Cerana, 2020a). Chitin and its derivatives enhance plants’ ability to withstand both biotic and abiotic stresses by activating their defense mechanisms. This protection helps safeguard crops against pathogens and environmental challenges, ultimately leading to increased productivity (Malerba and Cerana, 2020b; Shahrajabian et al., 2021). Chitin functions as a bioadsorbent, facilitating the remediation of contaminated soils by extracting heavy metals and enhancing soil characteristics. This process not only boosts soil fertility but also promotes sustainable agricultural practices (Malerba and Cerana, 2020b; Anedo et al., 2024). A recent study has shown that fertilizers enriched with chitin are effective in controlling nematode populations, which pose a threat to crops. This approach decreases the reliance on chemical nematicides, providing an environmentally friendly alternative (Kisaakye et al., 2024). Additionally, chitin is utilized in various industrial processes, including creating edible films and as a thickening and stabilizing agent in foods and food emulsions. Insoluble fibers, such as chitin, are indigestible in the human gastrointestinal tract. They are essential for increasing stool bulk and softness, which helps promote regular bowel movements and reduce intestinal transit time. Moreover, chitin serves as a dietary fiber that enhances gut microbiota, playing a crucial role in gut health. This enrichment can lead to improved gut function and may help prevent conditions such as constipation and hemorrhoids (Rodriguez et al., 2020; Kipkoech, 2023). However, insects offer an efficient method for chitin production, requiring significantly less land, water, and feed, which reduces their environmental impact. Their shorter life cycles and rapid growth allow for frequent harvesting, enhancing production efficiency. Additionally, insect farming is generally more cost-effective due to these lower resource demands and quicker growth rates, further decreasing overall production costs. Insect farming often uses organic waste as feed, promoting waste reduction and resource recycling in line with circular economy principles (Zainol Abidin et al., 2020a; Triunfo et al., 2022; Rehman et al., 2023; Saenz-Mendoza et al., 2023). These environmental and economic benefits make insect-based chitin a promising alternative to traditional sources. This review aims to qualitatively and quantitatively compare the primary sources of chitin production, focusing on their chemical properties, production methods, environmental impacts, and applications across various fields, including agriculture, healthcare, and industrial processes. It seeks to highlight the advantages and limitations of traditional and alternative sources, such as insect farming and evaluates sustainable and eco-friendly methods of chitin extraction.

Chitin is widely found in animal and plant kingdoms and is a crucial constituent of the exoskeletons of insects, crustaceans, and other arthropods. Its primary function is to provide a protective barrier for the inner soft tissues. Chitin acts as a watertight barrier, preventing delicate tissues from drying out. This helps to ensure the survival of these organisms by providing hydration protection to their inner tissues (Roberts, 1992; Moussian, 2019). The cuticles of insects, crustaceans, and spiders are mostly composed of sclerotized chitin, which can have diverse appearances. Chitin is also found in the iridophores of the eyes, the epidermis of cephalopods and arthropods, as well as the cuticles of some vertebrates (Zhang et al., 2021). It is also present in the cell walls of fungi and some algae. The exoskeleton of oysters and spiders, particularly Theraphosidae also contains chitin (Machałowski et al., 2020). Insects usually have 30%–45% protein, 25%–40% lipids, and 10%–15% chitin in their exoskeletons. In contrast, crustacean shells consist of 20%–40% protein, 20%–50% calcium carbonate, and 15%–40% chitin. Nevertheless, certain insects may contain more than 40% chitin in their exoskeletons (Spranghers et al., 2017; Mohan et al., 2020; Basawa et al., 2023).

Chitin is a major component of the insect’s external body, providing the necessary support and protection against various external factors, such as physical damage, predators, and environmental stresses. Therefore, chitin plays a significant role in insects’ survival, growth, and interaction with their surroundings. Insects heavily rely on chitin to form their cuticles and peritrophic membranes. However, the importance of chitin in insects can be summarized as follows: (Figure 1).

• Chitin provides structural support to insects’ exoskeletons, protecting internal organs and safeguarding them from physical damage, providing and maintaining rigidity and shape to their bodies.

Overall, the unique properties of chitin make it an essential component in various biological contexts, and its metabolism is tightly regulated during growth and morphogenesis (Merzendorfer and Zimoch, 2003; Yu et al., 2024).

The physicochemical characteristics of chitin found in insects and other organisms can vary slightly, which affects properties like mechanical strength and stiffness (Figure 3 and Table 3). Some traits that may exhibit differences include crystallinity, molecular weight, acetylation level, fiber structure, and cross-linking with other molecules (Wang et al., 2013; Zargar et al., 2015; Moussian, 2019; Khajavian et al., 2022). Chitin is a linear polymer of N-acetylglucosamine units linked by β-1,4 glycosidic bonds. It forms a robust and flexible matrix in insects and other organisms, offering structural support and protection. Chitin imparts mechanical strength and toughness to insect and crustacean exoskeletons, with properties influenced by crystallinity, molecular weight, and acetylation degree. Despite a similar basic structure, variations in chitin’s physicochemical properties contribute to diverse functions and adaptations in these organisms (Merzendorfer and Zimoch, 2003; Erko et al., 2013; Moussian, 2013; Liu et al., 2019; Machałowski et al., 2020; Mohan et al., 2020; Zhang et al., 2021). However, the physicochemical, morphological, and structural characteristics of chitin and chitosan are influenced by the characteristics of the species, such as life stage, metamorphosis type, and genus (Mohan et al., 2020; Mohan et al., 2022). The main characteristics of chitin are (Figure 2).

Besides chitin and proteins, the arthropod cuticles and crustacean shells also contain various minerals that make them strong and rigid. These minerals include calcium carbonate, calcium phosphate, and magnesium carbonate. (Erko et al., 2013; Moussian, 2013). The minerals found in arthropod cuticles and crustacean shells are crucial for their mechanical properties and structure. They add strength and rigidity to the cuticle, which acts as a protective shield for the animal’s body against any damage. Some animals have heavily mineralized cuticles, which makes them appear as if they have a hard, shell-like exterior. This is commonly observed in crustaceans like crabs and lobsters (Plotnick, 1990; Erko et al., 2013). The main sources of chitin differ in their demineralization requirements during the extraction process. The demineralization step is crucial for crustacean shells due to their high mineral content, while it is less critical for insect cuticles and not required for fungal chitin. The use of dilute HCl is the most common method for demineralization across all sources, but the specific conditions, such as acid concentration, temperature, and duration, may vary depending on the source (Younes and Rinaudo, 2015; Ibram et al., 2019; Abidin et al., 2020; Pellis et al., 2022).

Here’s a comparison of the common chitin sources based on the demineralization step (Zhao et al., 2010; Ibram et al., 2019; Vicente et al., 2021; Pellis et al., 2022; Novikov et al., 2023): Crustacean shells: Chitin from crustacean shells requires a demineralization step to remove the high mineral content, primarily calcium carbonate. Insect cuticles: Insects have fewer minerals than the shells of crustaceans (Khayrova et al., 2021). However, chitin from insect exoskeletons also requires a demineralization step, but the mineral content is generally lower than in crustacean shells. As a result, chitin and chitosan extracted from insects may have different physicochemical attributes than those extracted from crabs and shrimp (Saenz-Mendoza et al., 2023). Fungal chitin: Chitin derived from fungal cell walls does not require a demineralization step, as fungi generally have a lower mineral content than crustacean shells. Unlike other invertebrates (such as sponges, mollusks, or crustaceans), the cuticle of spiders lacks minerals such as CaCO3, which allows for the elimination of the demineralization step during chitin separation (Machałowski et al., 2020). The origin of chitin affects not only its crystallinity and purity but also its polymer chain arrangement and thus its properties (Rinaudo, 2006; Kumari and Kishor, 2020). The dosage of the main mineral elements present in the exoskeleton of different chitin sources shows that the content varies with the species and thus the processing conditions (Tolaimate et al., 2003). Two separate studies have shown differences in the structure of chitin obtained from different species of insects. In the first study (Waśko et al., 2016), chitin isolated from adults of Hermetia illucens was found to have a relatively smooth surface and was composed of parallel distributed fibers. In comparison, the larval chitin had a more complex structure, with a convex shape composed of repeated honeycomb-like units. In the second study (Erdogan and Kaya, 2016a), chitin obtained from adults and nymphs of Dociostaurus maroccanus was found to be composed of long nanofibers with large nanopores. High similarity was found in the properties of chitin and chitosan from nymphs and adults of the species. In experiments conducted on the potato beetles, Leptinotarsa decemlineata, it was found that chitin extracted from the adults and larvae of the species had a similar structure to nanofibers but differed in the number of pores. A study investigated chitin structure in four grasshopper species using various analytical techniques. Differences in chitin quantity and surface structure were observed between male and female grasshoppers. Despite gender variations, elemental analysis, thermal properties, and crystalline index values for chitin were similar. Enzymatic digestion showed no significant differences in digestion rates between chitins from both sexes and commercial chitin (Kaya et al., 2015e).

The deproteinization process for chitin extraction involves the removal of protein content from the raw material. The deproteinization method should be used to extract chitin from different sources. Deproteinization of chitin involves the use of alkaline solutions, primarily NaOH, to eliminate the protein content present in the raw material (Zainol Abidin et al., 2020b).

There are three different crystalline allomorphs of chitin found in nature which include α-chitin, β-chitin, and γ-chitin (Erdogan and Kaya, 2016a; Kaya et al., 2017a; Hou et al., 2021). α-chitin is the predominant chitin in insects and other arthropods (Figure 4). It has a highly ordered crystalline structure, with chitin molecules arranged in parallel chains. α-chitin is recognized for its high tensile strength and rigidity (Hou et al., 2021). It is the most consistent polymorphic form of chitin in nature and is present in crustaceans such as shrimps, lobsters, and crabs, as well as in the chitinous cuticles of insects. It can also be found in fungal cell walls (Ifuku et al., 2009; Hassainia et al., 2018). In a study, the structure of α-chitin has been determined through X-ray diffraction, revealing an orthorhombic unit cell with specific dimensions and a space group of P212121. The chains form hydrogen-bonded sheets and have a statistical mixture of side-chain orientations. The structure contains two types of amide groups with different hydrogen bonding, explaining the lack of swelling in water due to extensive intermolecular hydrogen bonding (Minke and Blackwell, 1978).

β-chitin is a less common form of chitin found in certain species, such as some crustaceans and mollusks. It has a different crystal structure compared to α-chitin, with the chains of chitin molecules arranged in an antiparallel fashion. This form of chitin is less rigid than α-chitin. It is characterized by loosely packed parallel chains with weak intermolecular interactions, making it more soluble and droplet-like than the α form. Additionally, the β form of chitin has been derived from squids (Pillai et al., 2009; Hamed et al., 2016; Hossin et al., 2021; Hou et al., 2021). γ-chitin is a type of chitin that is found in certain types of algae and fungi. It has a unique crystal structure that distinguishes it from the more well-known α-chitin and β-chitin. This is a less common form of chitin that has a disordered structure with random orientations of N-acetylglucosamine units. However, further research is required to fully comprehend its characteristics and prevalence in insects and other arthropods (Hou et al., 2021). A schematic shape of three forms is depicted in Figure 4. There is a mix of α and β forms in γ-chitin. The presence of γ-chitin is lower than that of α and β forms, and it has been examined in only a few studies. It is noteworthy that α chitin can convert to the β form, but the reverse is not true (Velásquez and Pirela, 2016; Hou et al., 2021).

Both α and β chitins keep a powerful network dominated by intrachain hydrogen bonds between the groups of C═O⋯NH and C═O⋯OH within an interval of 0.47 nm. In α form conformation, supernumerary inter-chain hydrogen bonds connect the hydroxymethyl groups while this type of interaction is not observed in the β conformation (Roy et al., 2017). These three types differ mainly in the degree of hydration, the size of the unit cell, and the number of chitin chains in each cell (Merzendorfer and Zimoch, 2003; Yu et al., 2024). On the other hand, the properties of pure chitin depend on their molecular weight, degree of acetylation, purity, and dispersion index. For example, in a study, the chitin of crab shells and mealworms was determined by X-ray diffraction and FTIR analysis. In this research, α form of chitin was observed in four crystalline reflections, shown at 9.4°, 19.3°, 20.8°, and 23.3° in the chitin of crab shell, and at 9.44°, 19.3°, 20.7°, and 23.3° in the chitin of mealworm by crystalline structure. α-form showed doublet at amide I band in crab shell and mealworm chitin (Kaur and Dhillon, 2015). In another study, chitin was extracted from various marine crustacean shells using chemical methods, showing a chitin content of 17.50%–23.75% on a dry weight basis. The chitin had low molecular weight and was similar to commercial chitin based on various analyses. The extracted chitin exhibited α-form characteristics, with a crystalline index value ranging from 80.3% to 80.8%. Analysis showed nanofiber and nanopore structures (Mohan et al., 2021). Chitin polymorphs α, β, and γ were isolated and analyzed for their crystalline structures and characteristics using various spectroscopic and analytical techniques. Molecular weights, spectral features, X-ray diffraction patterns, and thermal properties were determined for each chitin type. Differences in crystalline reflections, thermal decomposition temperatures, and activation energies were observed, highlighting the distinct properties of α-chitin, β-chitin, and γ-chitin. The study also demonstrated the temperature sensitivity differences among the chitin polymorphs based on their activation energies (Jang et al., 2004). Chitin can have different crystalline organizations and interact with chitin-binding proteins to create higher-order structures. This combination defines the mechanical properties of tissues and organisms (Moussian, 2019). Analysis through techniques like ATR-FTIR, NMR spectroscopy, and WAXS confirmed Bombyx mori as a promising source of α-chitin (Jędrzejczak et al., 2024). Overall, chitin, an abundant biopolymer, exhibits diverse structural conformations through natural processes like biopolymerization and self-assembly, leading to unique physical effects and mechanical properties (Hou et al., 2021).

Chitin is an amino polysaccharide found in yeast cells, arthropod cuticles, fungal cell walls, and crustacean shells (Rehman et al., 2023; Sanjanwala et al., 2024). When comparing these sources of chitin, several factors come into play: Purity, as the purity of chitin extracted from different sources can vary. Some sources may require more extensive purification processes to remove impurities such as proteins and minerals; Yield: The quantity of chitin extracted from a specific source varies depending on the species, size, and processing methods employed. Some sources may contain higher amounts of chitin compared to others. The quality of chitin can also vary depending on factors such as the degree of deacetylation (which affects its solubility and other properties) and the presence of contaminants; Cost and availability: The cost and availability of chitin from various sources can vary depending on factors such as geographical location, seasonal variability, and demand.

The choice of chitin source depends on factors such as intended applications, availability, cost considerations, and sustainability concerns. Researchers and industries are exploring various sources and methods for chitin extraction to meet the increasing demand for this versatile biopolymer. If we are ranking sources based solely on the amount of chitin that can be obtained, it generally follows this order (Merzendorfer and Zimoch, 2003; Ma et al., 2020; Khayrova et al., 2021; Iber et al., 2022; Lv et al., 2023; Thakur et al., 2023): Crustacean shells: Crustaceans have relatively large exoskeletons compared to insects and fungi. Therefore, they typically yield the highest amount of chitin per individual organism; Insect exoskeletons: Although insects have smaller bodies than crustaceans, they often exist in larger populations and have a higher overall biomass. Therefore, insect exoskeletons can still yield a significant amount of chitin, especially if sourced from species that are abundant or cultivated in large numbers; Fungal cell walls: Fungi generally have smaller biomass than insects and crustaceans. Additionally, not all fungi produce chitin in significant quantities. Therefore, while fungal cell walls can be a source of chitin, the overall yield may be lower compared to insect and crustacean sources. So, based solely on the amount of chitin that can be obtained from each source, the ranking would be crustacean shells˃ insect exoskeletons˃ fungal cell walls.

One way to compare the chitin content of various organisms is through chemical analysis of the chitin found in their exoskeletons or cell walls. This involves isolating the chitin from the tissues and quantifying it using techniques like Fourier Transform Infrared Spectroscopy (FTIR) or High-Performance Liquid Chromatography (HPLC) (Qin et al., 2019; Ghosh and Dhepe, 2021; Tsurkan et al., 2021). Another approach is to assess the thickness or density of chitinous structures in different organisms, as these traits can indicate the amount of chitin present. For instance, insects with thicker exoskeletons may have higher chitin content than those with thinner exoskeletons. Furthermore, genetic studies can help compare chitin content across organisms by examining the genes related to chitin synthesis and degradation. This allows researchers to understand how chitin production and turnover are regulated in various species. Combining chemical, morphological, and genetic analyses can comprehensively compare chitin content in different organisms, providing insights into the role of chitin in their biology (Kabalak et al., 2020; Khayrova et al., 2021; Lv et al., 2023). The chitin content in the shells of commercial organisms like shrimps, crabs, and crayfish is approximately 20%. In contrast, certain insect species have a chitin content of around 15%. Additionally, the chitin content in some aquatic insect species ranges from 10% to 20% (Table 5) (Susana Cortizo et al., 2008; Sagheer et al., 2009; Wang et al., 2013).

Chitin content, purity, and structural properties differ among species, developmental stages, sexes, and body parts. Additionally, abiotic factors like processing methods and environmental and cultivation conditions influence the quality and quantity of chitin (Weiss, 2012; Chan et al., 2018; Hahn et al., 2020). Table 5 presents chitin yields across various insect species and other organisms. The data, organized by species, order, class, and yield, facilitates comparisons of chitin levels. This information is valuable for applications that utilize chitin due to its versatility in pharmaceuticals, biotechnology, agriculture, and materials science. Certain insects, such as B. eri (45%) and H. illucens puparium (59.9%), exhibit notably high chitin yields. These species may be prioritized for chitin extraction due to their superior yields, making them more efficient sources.

The amount of chitin in different species is presented in Table 5. Certain insects have less chitin than shrimp exoskeletons, but this is not universally true. For instance, B. eri, Coridius nepalensis, and P. cicadae have notably higher chitin levels at 45.0%, 44.0%, and 36.6% respectively (Figure 7). These amounts surpass the chitin content of shrimp, a significant source of commercial chitin and chitosan. It should be noted that in a fermentation process, the chitin yield of H. illucens puparium and adults was substantially higher (Xiong et al., 2023). Edible insects boast rich biodiversity and significant chitin content, positioning them as an underutilized asset (Ndiritu et al., 2023). Of the studied insects, the chitin content was highest in B. eri, followed by two hemipteran species (C. nepalensis, P. cicadae), and H. illucens. However, the black soldier fly, H. illucens, is an edible insect that can be easily raised under various conditions and is considered a potent source of chitin, even at the commercial level (Eggink and Dalsgaard, 2023; Pedrazzani et al., 2024). In this line, a study explored the potential of the black soldier fly (BSF) as a chitin source compared to shrimp shells. Different extraction methods were tested, and BSF chitin was found more challenging to extract and purify due to strong protein binding. The purity of BSF chitin ranged from 47.6% to 79.9%, lower than shrimp chitin at 88.3% (Pedrazzani et al., 2024). In another study, chitin was extracted from different developmental stages of the BSF, with varying chitin content. The physicochemical evaluation revealed that BSF chitin was α-chitin, similar to shrimp chitin (Soetemans et al., 2020). Research explores using black soldier fly puparium and adults with a continuous fermentation method employing specific bacteria for chitin extraction. Results show successful extraction of α-chitin with varying rates and yields based on the developmental stage of the flies. The study suggests that simultaneous continuous fermentation could offer a novel biological approach for chitin extraction from black soldier flies (Xiong et al., 2023). Comparing this research’s results with others indicates the significant effect of the extraction method on chitin yield. However, the increasing demand for sustainable alternatives to crustaceans as a source of chitin and chitosan highlights bioconverter insects like H. illucens as potential sources. A study (Triunfo et al., 2022) emphasized the suitability of pupal exuviae for high chitin yields. Analysis shows that insect-derived polymers are similar to commercial ones, making them suitable for industrial and biomedical applications. The chitin from H. illucens is noted for its fibrillary nature, conducive to producing fibrous materials, while chitosan exhibits properties that could support antimicrobial applications (Triunfo et al., 2022). Researchers have found that the larvae of B. eri are a promising source of chitin (Huet et al., 2020). A study compared the chitin extracted from B. eri larvae to shrimp chitin. While both exhibited similar characteristics in terms of crystallographic structures and thermal stability, they differed in crystallinity and morphological structures. Furthermore, insect chitins treated with room-temperature ionic liquid showed higher digestibility when subjected to enzymatic degradation, making them a more promising source for N-acetyl-D-glucosamine production (Huet et al., 2020). Another study focused on extracting chitin from the edible insect, C. nepalensis and compared it with commercial shrimp chitin. Results showed a chitin yield of 44.0% from C. nepalensis with a degree of acetylation of 57. 7%. The extracted chitin displays a mixture of chitin and chitosan, differing in crystalline structure and surface morphology from shrimp chitin. This research highlights the potential of C. nepalensis as a novel biomaterial source (Sharbidre et al., 2021). Research on the impact of various food wastes on H. illucens larvae revealed no significant differences in chitin and chitosan composition based on feeding substrates. The study underscores the importance of understanding how feeding substrates relate to valuable by-products, such as chitosan, in industrial insect production (Soetemans et al., 2020; Eggink and Dalsgaard, 2023; Xiong et al., 2023; Adamaki-Sotiraki et al., 2024; Pedrazzani et al., 2024). However, when choosing the best sources of chitin for extraction, several factors such as the amount of chitin, the purity, and the availability of its sources need to be considered. Although some insects can provide the highest amount of chitin, crustacean shells (such as those of crabs, shrimp, and krill) have been the traditional commercial sources due to their moderate but consistent yield of chitin. These shells are usually readily available from seafood processing industries. However, insects offer a potentially more sustainable option with a consistent supply, making them a promising source of high yield and purity of chitin. That being said, crustacean shells remain a good option due to their established processing techniques and easily available supply.

Insect chitin degrades more easily than shrimp chitin when treated with 6 N HCl and the enzyme chitinase. N-deacetylation of insect chitin is also simpler than that of crustaceous chitin. In a study, the enzymatic reaction of beetle and shrimp chitins was conducted heterogeneously in an acetate buffer solution. The hydrolysis rates of beetle and shrimp chitins by chitinase vary, with beetle chitin being hydrolyzed faster than shrimp chitin, suggesting that cockroach chitin has a higher affinity for chitinase than shrimp chitin (Zhang et al., 2000). The catechol compounds in insect cuticles inhibit chitin crystallinity, making the amorphous structure of insect chitin more easily destructible. N-deacetylation of insect chitin is simpler compared to crustaceous chitin, with approximately 94.0% of N-acetyl groups removed in a single treatment using 40% NaOH for 4 h at 110°C. Silkworm chitin, when treated with 2 N HCl under similar conditions, had 55% of its N-acetyl groups removed. Beetle chitin exhibited greater chitinase affinity than shrimp chitin (Zhang et al., 2000). The deacetylation process results in a copolymer of N-acetyl-glucosamines and glucosamines. When the resulting copolymer contains more than 50% N-acetyl-glucosamine units, it is typically referred to as chitin. For chitin polymers, the percentage of N-acetyl-glucosamine units is termed the degree of acetylation (DA) and can vary from 50% to 100% (Sivashankari and Prabaharan, 2017). A higher degree of acetylation reduces the solubility of chitin. Shrimp shells usually contain chitin with a degree of acetylation exceeding 50% (Sivashankari and Prabaharan, 2017; Yanat et al., 2023). This high acetylation level contributes to its lower solubility. Insects, however, offer chitin with superior characteristics. Studies indicate that chitin sourced from insects has a more favorable balance of deacetylation and acetylation than aquatic crustaceans (Kumar et al., 2020). While crustacean shells, such as those from shrimp, have long been the traditional and reliable source of chitin due to established processing methods and consistent yields, insects—particularly species like H. illucens, B. eri, and C. nepalensis—are emerging as promising alternative sources. Insects offer several advantages, including higher chitin content in certain species, greater biodegradability, and potentially more efficient extraction methods, making them a sustainable and underutilized resource for chitin production. Furthermore, the distinct characteristics of insect chitin, such as its more favorable balance of deacetylation, suggest it may provide unique benefits in industrial and biomedical applications. However, factors such as purity, yield, and the availability of these insect sources must be considered when selecting the optimal chitin provider, as crustaceans still maintain an advantage in specific commercial contexts. Nevertheless, the growing demand for eco-friendly and sustainable alternatives positions insects as a viable future chitin and chitosan production source.

Chitin, the second most abundant polysaccharide on Earth, is a crucial resource with diverse applications in agriculture, medicine, and industry. Its sources, crustaceans, insects, fungi, and mollusks, each have distinct advantages and limitations. Crustaceans provide high chitin yield and superior crystallinity but present environmental and economic challenges due to their mineral content and seasonal availability. In contrast, insects serve as a sustainable alternative, offering high-purity chitin with lower environmental impact and minimal resource requirements, while also contributing to organic waste recycling. Fungal chitin, despite its lower purity and yield, holds promise for biomedical applications due to its consistent availability and cruelty-free sourcing. Mollusks provide unique mechanical and biocompatible properties, though in limited quantities. The physicochemical properties such as crystallinity, molecular weight, and degree of deacetylation vary among these sources, affecting their functionality for various applications. These insights emphasize the need for eco-friendly, cost-effective extraction methods tailored to each source to enhance chitin’s utility. Additionally, the potential of insect-based chitin aligns with circular economy principles, advocating for its wider adoption. Future research should aim to refine extraction processes, improve chitin yield and purity, and investigate novel applications to fully utilize this biopolymer in a resource-constrained environment.