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Insects as alternative sources of value-added by-products: A study of different extraction approaches and characterization of chitin and chitosan from two edible insect species (T. molitor and A. domesticus) and by-products

Publication . Navarro, Pedro Jorge Silva; Cunha, Luís Miguel Soares Ribeiro Leite da; Domingues, Fernanda da Conceição; Anjos, Ofélia Maria Serralha dos

Chitin and chitosan are two well-known biopolymers, that have a wide range of physiochemical and biological properties which makes them extremely versatile, and capable of being applied in sectors like the agricultural, biomedical, pharmaceutical, food, amongst others. Crustaceans and their by-products are the main source of chitin extraction and chitosan production, and the chitosan market is in constant expansion, and it is estimated that by 2027 the market will reach 4.7 billion USD. However, chitin is also synthesized in several other living organisms such as insects, fungi, and algae. In particular insects are of special interest due to the growing popularity of entomophagy. This popularity is manifested on both the industry (increase in insect rearing companies and food products incorporating insects) and in academia, with a vast selection of studies focusing on insect fractionation (proteins, lipids, and chitin). As such, chitin extraction and chitosan production from insects presents an opportunity to increase the economic value of edible insects. The current study aimed to examine two different edible insect species as alternative sources for the extraction of these polymers, namely yellow mealworm larvae (T. molitor), adult house cricket (A. domesticus) as well as by-products (legs and wings) generated by house cricket rearing. The extraction was achieved through an optimized chemical treatment based on sequential acid and alkaline hydrolysis. In an attempt for a greener extraction, an alternative method based on natural deep eutectic solvents was also employed. After the extraction the samples were physiochemical and biologically characterized. The chemical treatment resulted in total chitin yields of 8.15%, 7.77% and 13.85% (Dry Weight basis), for T. molitor larvae, A. domesticus (adult) and A. domesticus by-products, respectively. Concerning the extraction with the natural deep eutectic solvents, the resultant chitin yields were very high in comparison to the chemical treatment which indicates high impurity of the samples and for that reason, further analysis of these samples were abandoned. The FTIR results of the different extracted chitin samples showed patterns of a-chitin while the chitosan results indicated the effectiveness of the deacetylation. Additionally, the FTIR results from the insect samples were similar to those from the commercial shrimp samples and were also confirmed throughout FT-RAMAN analysis. The highest degree of deacetylation was found in the chitosan from adult A. domesticus (63.7%), followed by T. molitor chitosan (62.3%) and lastly L&W chitosan (62.0%). The x-ray diffraction analysis also confirmed the obtained results from the spectroscopy and in addition demonstrated that chitosan had a more amorphous structure than chitin, due to the patterns and crystallinity index (CrI) values obtained. The molecular weight of the different chitosan samples was 302.58 kDa, 332.58 kDa and 245.77 kDa for T. molitor larvae, A. domesticus (adult) and A. domesticus by-products, respectively. SEM images revealed different surface morphologies for all the samples, although the majority showed microporous and fibrous structures. The thermogravimetric analysis results for the chitin samples demonstrated higher thermal stability for the commercial chitin, however, in the case of chitosan the more thermal stable sample was the chitosan extracted from T. molitor larvae. From the biological activity evaluation, it was possible to conclude that all chitosan samples showed capacity to inhibit oxidative peroxidation in the ß-carotene bleaching test. However, no scavenging activity in the DPPH test was observed. All samples displayed low antimicrobial activity against different Gram-positive and Gram-negative bacteria and the highest antibacterial activity was observed against Klebsiella pneumoniae. Nonantifungal activity was found during the assays.

2022-11-29Master thesis

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