Research on the Drying Process and Nutritional and Functional Activities of Walnut Meal Powder with High Added Value

Abstract

The optimal drying process for walnut meal was determined, and the antioxidant and lipid-lowering functions of walnut meal powder extracts were evaluated to achieve high-value utilization of walnut meal. Walnut meal after desalination was dried using low-temperature hot air drying, microwave drying, and vacuum freeze drying, followed by sieving through a 60-mesh sieve. The vacuum freeze drying process was identified as the optimal drying method based on the determination of polyphenol, flavonoid, polysaccharide, and protein contents, with polyphenol content at 22.88 mg/g, flavonoid content at 0.71 mg/g, polysaccharide content at 16.37 mg/g, and protein content at 91.7 mg/g. Using this as the raw material, the antibacterial circles of the water and alcohol extracts of walnut meal powder against Escherichia coli OP50 were determined. The effects of water and alcohol extracts of walnut meal powder at concentrations of 1.25 mg/mL, 2.5 mg/mL, and 5 mg/mL on the malondialdehyde (MDA) content, superoxide dismutase (SOD) activity, glutathione peroxidase (GSH-PX) activity, catalase (CAT) activity, triglyceride (TG) content, oil red O staining, and optical density of Caenorhabditis elegans (C. elegans) were evaluated to assess their antioxidant capacity and lipid-lowering effects. The results showed that within the concentration range of 1.25 mg/mL to 5 mg/mL, both the water and alcohol extracts of walnut meal powder could increase the activities of SOD, CAT, and GSH-PX in C. elegans, reduce the content of the oxidative product MDA (P<0.05), and decrease the TG content in C. elegans, thereby reducing fat deposition. Moreover, the antioxidant capacity and lipid-lowering effects increased with increasing dosage, with the alcohol extract of walnut meal powder exhibiting higher activity than the water extract.