Insect Residues

Chitin is the second-most common polysaccharide found in nature, being present in animals, plants and fungi. Nevertheless, its use and applicability are still underexplored in many industries. Chitin is formed by two N-acetyl-D-glucosamine with covalent-1,4 bonds, which may originate parallel chains (α-chitin), antiparallel chains (β-chitin) or more stable but yet to be further studied chains (γ-chitin). The chitin is usually converted into chitosan by substituting acetyl groups with an amino group, obtaining an aminated polysaccharide with better properties than chitin, such as higher solubility, capacity to form materials, biodegradability and richness in bioactivity properties. There are varied sources of chitin and chitosan, but the principal source is the exoskeletons of crustaceans and the fungi’s cell walls. Insects’ cuticles can be a potential source; the chitin content varies according to the life stage, with a higher amount being found more often in the adult stage of development. Nonetheless, the insect industry focuses mainly on the larvae given their high protein and low chitin content, while the adult insects are only maintained during rearing to lay the eggs and produce the larvae. Once their life cycle expires, the adults are often discarded, since their high chitin content reduces the nutritional value of protein. Therefore, the use of this biomass to obtain chitin and chitosan allows implementing a cost-effective approach in the insect industry based on circular economy guidelines while simultaneously exploring and/or improving the chemical, biological and physical extraction methods of chitin and chitosan of insect origin. There are different insects produced around the world with uses in several industries. Indeed, the exoskeletons of adults of black soldier fly ( Hermetia illucens ) and yellow mealworm adults ( Tenebrio molitor ) may contain between 20% and 30% of chitin, respectively, indicating the high value of this biomass as a source of chitin, promoting the circular economy cycle on the production of this polysaccharide. In the European Union, a considerable industry of edible insects is already being established for food and feeding purposes, highlighting the production of black soldier fly and yellow mealworm. Specifically, the industry of black soldier fly represents around 80% of all insect production in the European Union. There are several types of extraction and purification processes of chitin, including biological, chemical and physical techniques. Although the biological procedures are more desirable given their low environmental cost, they still present some drawbacks, such as lower yields and lower purity of the final chitin in comparison to the chemical and physical procedures. In this sense, chemical techniques are the most widely implemented, consisting mainly of two steps: demineralization and deproteinization. The demineralization usually involves strong acids and low alkalis to extract all minerals, while the deproteinization consists in using a strong acid and alkali. Therefore, despite the higher efficiency of chemical methods, they come with a high environmental cost. Today, there are several non-conventional and green extraction methods to obtain different fractions, including chitin, from edible insects, such as ultrasound‐assisted extraction, ionic liquids, deep eutectic solvents, enzyme-based extraction and supercritical extraction methods. The use of these extraction methods may upgrade the green stamp of chitin production. Chitin and chitosan have several uses on different industries, highlighting their use in biomedicine and for food and feeding purposes, such as colour stabilizers, and emulsifying and thickening agents. In biomedicine, chitin and its derivates can be used as potential materials because they are biocompatibility, biodegradability and non-toxic. Also, the antimicrobial and biocompatibility capacity of chitosan widens its use to treat injuries. In conclusion, edible insects can be a potential source of chitin and chitosan, but more research needs to be carried out to explore novel and eco-saving procedures to extract these polysaccharides in a cost-effective manner. Although the uses of chitin and derivates are well known, they should be studied for further applications, as well as for ways to improve existing ones and implement them in different industries.