Comparative Evaluation of a Modified Acetic Method for Extraction of Antioxidant Compounds from Black Beans ( Phaseolus vulgaris)

Abstract

Extraction of phenolic compounds from bean seed coats by acetic acid was evaluated and compared to conventional extraction with 80% methanol. Total phenols, flavonoids and free radical scavenging capacity were determined by col- orimetric methods. Furthermore, qualitative flavonoid characterization was performed via HPLC diode array. The acetic acid extract contained 73.4 ± 7 mg/g of sample expressed as gallic acid equivalents (GAE), and 41.3 ± 4 mg/g as cate- chin equivalents (CE). The acetic acid extract (at 1 mg/mL) showed over 89% efficiency to scavenge the 1,1 diphenyl- 2-picrylhydrazil (DPPH) radical (EC50 = 6.13 mg extract/mg standard). Gallic acid, delphinidin-3-glycoside, petunidin- glycoside, petunidin, malvidin-3-glycoside, myricetin-glycoside, quercitin-glycoside, saponin (?-g), and 3-hydroxy-5, 7-megastigmadien-9-one were identified in both extracts. Additionally, kaempferol-3-glycoside was found in the acetic acid extract. Sequential acetic acid extractions indicated that the antiradical activity was about 90% in DPPH radical scavenging within the first 8 h of extraction, when compared to a 24 h extraction. In general, acetic acid offered a faster and