Effects of different processing techniques on oxidation during mealworm protein fractionation and simulated gastrointestinal digestion

Abstract

Effects of different processing techniques on oxidation during mealworm protein fractionation and simulated gastrointestinal digestion Alternative protein sources are increasingly in demand to replace, at least in part, meat in the human diet. Commonly, these alternative protein sources are of vegetable origin, but could also include protein from insect, such as mealworm (Tenebrio molitor). Several processing steps are required to extract and purify mealworm protein from its original matrix. Little is known how the oxidative quality of mealworm is affected by the killing and drying method, protein extraction, and subsequent gastrointestinal digestion. In this study, mealworms were subjected to two different killing methods: blast-freezing (-38°C, 4h) or blanching (100°C, 40s), and two different drying methods: oven drying (65°C, 3d) or freeze-drying (-20°C, 4d), and then ground into four different full-fat flours. These flours were then defatted with ethyl acetate (1:3) to produce four defatted flours and finally subjected to isoelectric point precipitation to produce four different protein concentrates. This way, a total of twelve samples were obtained and subjected to in vitro digestion, simulating the conditions from the mouth to the small intestine. HPLC-FLD was used to measure the levels of lipid oxidation products (hexanal, propanal, and 4-hydroxy-2-nonenal) and the glycoxidation product pentosidine. In addition, total Maillard reaction products (MRPs) were extracted using methanol and determined spectrophotometrically. The different processing and extraction steps had a clear effect on the levels of oxidation products found in the mealworm extracts and after their in vitro digestion. Freeze-drying promoted lipid oxidation in full-fat flours and increased further during in vitro digestion. In oven-dried samples, the amount of lipid oxidation products was almost absent. All defatted flours, independent of prior treatment, showed relatively very low amounts of lipid oxidation products, which were probably lost during defatting and did not increase after digestion. In the protein concentrates, the blanched samples showed an increase in lipid oxidation products, however the blast-frozen samples did not. Compared to the other treatments, relatively high levels of pentosidine and MRPs were formed in all the blast-frozen oven-dried samples, these were also present in the protein concentrate prepared by blast-freezing and freeze-drying. In vitro digestion did not increase the pentosidine concentration, but increased the amount of MRPs. Of interest, all samples with high glycoxidation concomitantly contained relatively low levels of lipid oxidation products. In summary, varying processing techniques influenced the oxidative quality of mealworm protein extracts. Also, the study revealed a potential link between elevated glyc(o)xidation and reduced lipid oxidation during both processing and digestion