Effects of different drying methods on the drying characteristics, microstructure, physicochemical quality, and seed coat anthocyanins of black peanut

Peanuts are an important cash crop, freshly harvested peanuts have a high moisture content and must be dried before further processing and storage. This study employed natural drying (ND), heat pump drying (HPD), infrared drying (ID), and microwave drying (MD) to dry black peanuts, evaluating their drying characteristics, specific energy consumption, hardness, appearance, microstructure, nutritional quality (protein, fat, and amino acids), oil quality (acid value, peroxide value, and fatty acids), and anthocyanins in the seed coat. The results indicated that the drying times for ND, HPD, ID, and MD were 50 hours, 15 hours, 18.5 hours, and 2.33 hours, respectively. Among the mechanical drying methods, MD exhibited the lowest specific energy consumption, demonstrating superior energy efficiency. Compared to the ND group, the three mechanically dried peanut samples exhibited a more compact and flat structure, with significantly increased hardness, crude protein, and total amino acid content, as well as significantly reduced acid and peroxide values. Notably, MD effectively preserved anthocyanins from the fresh peanut hulls, resulting in the smallest total color difference (ΔE = 3.04), which was closest to that of the fresh sample. Furthermore, MD resulted in a higher content of monounsaturated fatty acids but a lower crude fat content, with slight swelling of the seed coat. Overall, MD offers significant advantages in shortening the drying cycle while maintaining the nutritional and sensory qualities of black peanuts and exhibits low specific energy consumption, providing a theoretical basis for their industrial processing.