Effect of Camelina and Linseed Cake Supplementation on the Antioxidant and Amino Acid Contents, Oxidative Stability, Water Activity and Sensory Attributes of Tenebrio molitor Larvae

Camelina and linseed cakes were included in the diet of Tenebrio molitor (TM) larvae at two levels (5% and 10%) to evaluate their effects on antioxidant and amino acid contents, oxidative stability, water activity (a(w)), and sensory attributes. Six experimental diets were tested: a standard diet used by the insect farm (STD), a commercial control diet (CON), and CON with two inclusion levels of camelina (CAM 5, CAM 10) or linseed (LIN 5, LIN 10) cakes. Each treatment consisted of 12 replicates of five-week-old larvae reared until commercial size (9 weeks). Camelina and linseed cake inclusion affected the a(w) of dried larvae, with the highest values in CAM 5 and the lowest in LIN 10 (0.69 vs. 0.45, respectively; p = 0.016). The highest linseed inclusion level increased susceptibility to lipid oxidation during storage (11.3 vs. an average 2.93 meq O-2/kg fat, respectively; p < 0.0001), despite elevated antioxidant concentrations (alpha, delta, gamma -tocopherols and beta-carotene). Larvae fed with CAM 5 and LIN 5 diets had a higher content of most essential amino acids compared to the other treatments (p < 0.0001). Conversely, increasing the inclusion level to 10% determined a reduction in total amino acid content and in key essential amino acids, particularly lysine (p < 0.0001). Non-essential amino acids displayed a similar trend, except glycine, whose highest value was observed in the LIN 10 group (933 vs. 652 mg/100 g, on average). Sensory evaluation showed that LIN 10 larvae achieved the highest scores for visual and overall acceptability, although some results need further investigation. Overall, camelina and linseed cakes appear to be promising, sustainable agro-industrial by-products to be exploited in TM farming, especially at moderate inclusion levels, as the nutritional quality and market appeal of TM biomass were ensured.