Natural deep eutectic solvents: A sustainable approach for extracting protein and chitin from Tenebrio molitor beetles

Natural deep eutectic solvents (NADES) permit extract protein from different biomasses without using harsh chemicals. In this work, varied NADES were studied to maximize the protein extraction from Tenebrio molitor beetles, assessing the effect of time, temperature and water addition. Higher protein yield was obtained using NADES formed with choline chloride and oxalic acid (34.1 %) and betaine and urea (Bet:Ur, 32.8 %). Higher quantity of solid enriched in chitin (56.5 % DW) was obtained using a mixture of choline chloride and glycine (1:2 M ratio). Following the optimization of NADES-based treatment, maximum protein hydrolysis (81.5 %) was obtained using Bet:Ur at 1:2 molar ratio, 30 % of water, at 90 °C, for 3 h. The protein obtained after the optimized conditions was characterized, showing high in vitro digestibility (93.8 %), 6.04 % and 5.60 % of water and oil holding capacity, respectively. Scaling-up the treatment up to 50 g of beetles' meal resulted in 91.5 % of protein hydrolysis. Also, the reuse of NADES did not compromise the protein hydrolysis, achieving 61 % on the first cycle, followed by 58 % and 48 % at the second and third cycle, respectively. This work evidence that using a NADES of betaine and urea and optimal conditions resulted in a high-quality protein, minimizing the disposal of insect by-products.