Defatted Tenebrio molitor meal time-dependently altered sensory quality and nutritional value of turbot Scophthalmus maximus during growing-out phase

Abstract

The yellow mealworm Tenebrio molitor (TM) is promising feed ingredient for aquafeed. However, consumers might reject insect-fed fish unless they know their quality. Nevertheless, reports on how TM influences fish quality were rare and yielded conflicting results; furthermore, there are no evaluations on quality of turbot Scophthalmus maximus fed TM. Therefore, turbot with an initial body weight of 150 g were fed six experimental feeds containing increasing levels of defatted TM to replace fishmeal for 85 days. The substitution levels were 0% (control), 15% (TM15), 22 30% (TM30), 45% (TM45), 60% (TM60), and 75% (TM75). The result showed TM replacing up to 45% of fishmeal did not negatively impact growth performance or fillet yield. Dietary TM optimized the health value of muscle fatty acids regarding thrombogenicity index, atherogenicity index, and hypocholesterolemic to hypercholesterolemic fatty acids ratio but linearly decreased the muscle contents of hydroxyproline, collagen, and n-3 PUFA. However, turbot fed TM15 maintained the contents of these nutrients compared with those fed the control diet. The naked eye cannot perceive skin color changes induced by TM; but the odor, flavor, and texture of cooked fillets changed by TM at both sampling times could be distinguished by sensory evaluation. Furthermore, texture analyzer reported that the hardness of raw fillets significantly decreased by the end of the experiment but not on the 56th day. Correlation analysis revealed that the fillet was softened due to the muscle water content increase and muscle ultrastructure (lengths of H band, bright band, dark band, sarcomere) alternation. In conclusion, there were time-dependent effects of TM on turbot growth performance and fillet texture. Substitution of fishmeal with TM at 15% or less level did not influence the nutritional quality, but TM at any dose softened the fillet, which could be attributed to its influence on moisture content and myofibrillar structure.