Extraction Optimization, Characterization, and Antioxidant Capacity of Phenolics from Cowpeas (Vigna Unguiculata)

Ethanol-water extraction of phenolics from cowpeas was modeled and optimized by response surface methodology (RSM). The ethanol concentration and extraction temperature were shown to have a significant effect on phenolic extraction and antioxidant capacity. Modeling predicted that extraction of phenolics from cowpea flour for 42.8 minutes at 58.6°C with 58.4% ethanol would maximize the radical scavenging capacity of solutes. Extraction of phenolics under these optimized conditions yield yielded 11.05 ± 0.10 mg chlorogenic acid equivalents (CAE)/g cowpea flour. These extracts contained 10.41 % ± 0.11% phenolics by weight and had an antioxidant capacity of 0.45 ± 0.02, closely approximating the predicted phenolic content of 10.11% ± 0.44% and antioxidant capacity of 0.42 ± 0.04. Extracted material was characterized by HPLC, and the predominant phenolic compounds detected were epicatechin and ferulic acid. Cowpea’s low cost, ease of storage, and high antioxidant capacity reflect their potential for use as a naturally-derived antioxidant additive in foods.