Exploring the extraction, antioxidant activities and its stabilities of peanut skins crude proanthocyanidins extract

Peanut skin is a low-value by-product in the peanut oil and peanut product industry, with only a small amount utilized as animal feed while the majority discarded as waste. However, peanut skin contains high-value proanthocyanidins. Identifying an appropriate extraction process for these proanthocyanidins could significantly enhance the utilization value of peanut skins. Therefore, the objective of this paper is to optimize the extraction conditions for proanthocyanidins, thereby increasing the added value of peanut skins. The extraction process of crude proanthocyanidins extract via ultrasound-assisted ethanol secondary extraction was optimized through single-factor experiments, Plackett-Burman design, steepest ascent experiments, and response surface methodology. The results demonstrated that under the optimal conditions—liquid-solid ratio 1 (50:1 mL/g), temperature 1 (50°C), ethanol concentration 2 (65%), and time 2 (16 min) — the yield of lyophilized crude proanthocyanidin extract reached 129.14 ± 2.45 mg/g, with a proanthocyanidins purity of 50.61 ± 2.27%. The crude proanthocyanidins extract exhibits significant free radical scavenging activity, reducing power, metal ion chelating capacity, and lipid peroxidation inhibition activity. Under conditions including temperatures below 65°C, pH values less than 7, and the presence of Na⁺, K⁺, Ca²⁺, Cu²⁺, Mg²⁺, Zn²⁺, glucose, sucrose, ascorbic acid, sodium bisulfite, as well as microwave sterilization, boiling water sterilization, pasteurization, and UV sterilization, the crude proanthocyanidins extract demonstrates favorable antioxidant stability. Therefore, the crude proanthocyanidins extract prepared in this study can be directly utilized as a natural antioxidant in food processing applications such as baked goods, meat products, and beverages. Furthermore, it can be further isolated and purified into high-purity proanthocyanidins for application in functional foods. The process optimization and antioxidant activity investigation of the crude proanthocyanidins extract provide novel insights for the comprehensive processing and utilization of peanut skins.