Characterization of polar and non-polar lipids of Hermetia illucens and Tenebrio molitor meals as animal feed ingredients

Abstract

Although increasingly used in animal feeding, the black soldier fly (Hermetia illucens - HI) and mealworm (Tenebrio molitor - TM) larvae and pupae require the characterization and modulation of their fat profile for use in the feed industry. In this study, we provide a comprehensive fatty acid profile of the total lipid triglycerides and phospholipids, and sterol composition. For a more detailed characterization of the nutritional properties, we defined the profile of esterified fatty acids (FAs) in the sn-2 position of the triglycerides, which represents the most adsorbed fraction by animals during digestion. Twenty-four batches (12 batches per species divided into 6 batches of larvae and 6 batches of pupae) of 70 subjects were used for the analysis. For each of the developmental stages, individuals in the intermediate stage were considered (2 months and 8 days for TM larvae and pupae respectively; 9 days and 7 days for HI larvae and pupae respectively). Some fatty acids (decanoic, lauric, or myristic acid) were more abundant in HI than in TM. These FAs were produced de novo, indicating that HI produce them from carbohydrates as a source of acetyl-CoA. Hermetia illucens showed a higher level of conjugated linoleic acid (CLA) isomers, a class of fatty acids with positive health effects. In contrast, TM showed a similar fatty acid profile to the plant lipid source (such as soy and sunflower) due to the high level of linoleic acid. Analysis of the triglyceride fraction showed a different affinity for the three glyceride positions. In particular, lauric acid, polyunsaturated fatty acids n-3 and CLA isomers esterified preferentially in sn-2, and therefore were the most adsorbed by the animal during digestion. As for the phospholipids, HI showed a higher level, above all in terms of the phosphatidylethanolamine fraction. Interestingly there was no sphingomyelin in the pupae of both species. The high level of phospholipids is a useful feature for the emulsion of fats in animal feed diets. Lastly, we observed a considerable amount of phytosterol in the sterol profile of both species, which makes these insects a valid alternative to other food sources of plant origin for animal nutrition. We believe that our findings provide new nutritional information for the use of TM and HI in the animal diet.