Use of the black soldier fly Hermetia illucens L. (Diptera: Stratiomyidae) as an alternative source of chitin and chitosan for the production of biopolymeric films in agro-food applications

Chitin and chitosan are natural polymer of great technological and economic interest, finding several applications in many different fields. Chitin is a structural component of the exoskeleton of arthropods and the fungal cell wall, while chitosan is its main deacetylated derivative. Currently, chitin is industrially extracted from fishery waste, mainly crustacean shells. The debate on the sustainability of this resource and the constant increase in market demand for chitin and chitosan have driven the search for alternative sources. In this context, insects are gaining great interest. In recent decades, large-scale insect breeding facilities for feed production and organic waste disposal have arisen all over the world. These farms generate large amounts of insect waste biomass (i.e., exuviae left over from moulting processes and dead insects) rich in chitin that could be exploited as a source for the extraction of this polymer. The aim of this work was to investigate different insect biomasses (larvae, pupal exuviae and adults) generated from the farming of the dipteran Hermetia illucens (the most widely bred species in Europe) as sources of chitin and chitosan. Chitosan was produced with the purpose of being used for the production of coatings for the preservation of fresh fruits. From the three different sources of H. illucens, chitin with characteristics and purity similar to that commercially available from crustaceans was extracted. The highest yield (23%) was obtained from pupal exuviae. From the analysis of the composition of the material obtained after each step of the chitin extraction process, it was possible to calculate the efficiency of the extraction methods applied, which were suitable for removing components extraneous to chitin from the raw insect sample. The chitosan obtained from the deacetylation of chitin had some different characteristics than commercial chitosan, particularly a very low viscosity and molecular weight. This, together with the presence of impurities found in one sample, suggests the need to modify the deacetylation process or some parameters of the chitin extraction method. Chitosan produced from larvae, pupal exuviae and adults of H. illucens was used to produce coating solutions that were applied to cherry tomatoes, strawberries, apricots and nectarines. The preservative effect of the insect-derived chitosan coating was evaluated by investigating changes occurred in the weight, pH, titratable acidity and total soluble solids content of fruits during the storage period. Preliminary promising results were obtained from this investigation: chitosan from H. illucens had similar or, in some cases, better effects than commercial chitosan; often no different effects were observed in coated fruits than in uncoated fruits, but coating with chitosan had better effects than coating with only solvent solution (a non-optimal formulation of the solvent is hypothesised); chitosan obtained by homogeneous deacetylation always had worse effects than heterogeneous chitosan; it was observed that bleaching treatment applied to chitin may negatively affect the performance of the resulting chitosan. Furthermore, the chitosan coating was particularly effective in reducing and delaying spontaneous mould growth on the fruit during storage. This work has therefore highlighted the potential of H. illucens as a source of chitin and chitosan to be used in the agri-food sector as an alternative packaging. The results obtained are encouraging, although further studies are needed to fully optimise the extraction processes of these polymers in order to obtain the best characteristics for the desired applications.