Characterisation of fatty acid profiles of Tenebrio molitor larvae reared on diets enriched with edible oils

Abstract

Several species of insects have been indicated as suitable and alternative sources of nutrients for humans and animals. A crucial aspect is that their nutritional composition and development time can be influenced by the substrate used for rearing. The main objective of this study is to evaluate how the fatty acid composition of Tenebrio molitor (Coleoptera: Tenebrionidae) larvae changes with different rearing substrates. For this purpose, a standard diet (51.8% wheat bran + 40.7% soybean meal) was alternatively supplemented with addition of 7.5% (w/w) sunflower, linseed or fish oil. Dry matter, percentage of proteins and lipids, ash and fibre of larvae and substrates, as well as insect development time were determined, highlighting slower growth for insects raised on oil-enriched diets, compared to the control. Gas-chromatography was used to evaluate the fatty acid profile of larvae and substrates. A total of 15 fatty acids was identified and quantified. Palmitic, oleic and linoleic acids were always the most abundant fatty acids detected in larvae, suggesting the presence of physiological regulation mechanisms in T. molitor. The larval content of palmitoleic, oleic, alpha-linolenic and eicosapentaenoic acids was correlated with their content in the rearing diets, indicating strict dependence on diet mainly for PUFA n-3. The n-6/n-3 ratio was influenced by the substrate as well, showing a similar trend between insects and diets but with less variability in larvae. Principal component analysis conducted on the fatty acids profile of larvae displayed several clusters based on the different growing media. This study highlights the importance of the diet in determining the final fatty acid profile of mealworm larvae, although fatty acid enrichment could be dampened by physiological processes of the insects.