The effect of ultrasound on the quality of peeled and unpeeled walnut kernel beverage

In this study, the functional features, physicochemical properties, quality attributes, flavor characteristics, and storage stability of peeled and unpeeled walnut beverages were studied after being treated with ultrasound (25 kHz at 100 W for 10 minutes). The results showed that gallic acid, ellagic acid, sugars, particle size, viscosity, L*value, a*value, whiteness index, and E* (color difference) all increased after storage (4°C, 180 days), while total phenolic content, DPPH, FRAP, b*value, C* values reduced significantly. The total phenolic content of unpeeled walnut beverages was notably higher (3 folds) than peeled walnut beverages. The highest FRAP values were determined in unpeeled ultrasonicated (UPUS) samples. The peeled ultrasonicated (PUS) samples exhibited the lowest D4,3 value (96 μm), whereas peeled control (PC) samples showed the highest D4,3 value (198.67 μm). The PC samples had the highest concentration of linoleic acid (60.71 - 64.65%), whereas UPUS had the lowest. Ellagic and gallic acid was the most abundant phenolic compounds in all the walnut beverage samples. Sucrose, followed by fructose and glucose sugars, increased with storage, and sucrose was shown to be the most prevalent basic sugar component of walnut beverages. Among the analyzed samples, UPC had the greatest magnesium (Mg) level at 95.92 mg/L, while PUS had the lowest at 70.80 mg/L. The PC samples were more appreciated, and the most liked.