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 colorimetric 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 catechin 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, petunidinglycoside, petunidin, malvidin-3-glycoside, myricetin-glycoside, quercitin-glycoside, saponin (β-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 more efficient approach for the extraction of phenolic
Highlights
Common beans (Phaseolus vulgaris) and other leguminous are one of the milestones in most Latin-American and African diets [1]
The use of acetic acid for extraction of antioxidants of phenolic nature is justified by its polarity, which is higher in comparative terms than that of other organic solvents [15]
This phenomenon plays a key role in the proposed extraction method, since formation of hydrogen bonds with oxygen-containing functional groups present in flavonoids enhances molecular interaction
Summary
Common beans (Phaseolus vulgaris) and other leguminous are one of the milestones in most Latin-American and African diets [1]. Flavonoids are known antioxidants that help protect the organism against cellular damage, reactive oxygen species (ROS), and other negative physiological effects [3,4]; their consumption—same as for other phytochemicals like anthocyanins, flavones, and flavanols has proven beneficial in the prevention of diseases like ischemic heart disease, stroke, and cancer [5,6,7] Taking these nutritional sources into consideration, it is not surprising that many modern diets look towards an increase in the consumption of antioxidant compounds. The rationale behind the use of these methods is the fact that a polar solvent should interact with the highly polar functional groups bonded to the backbone of antioxidants In this sense and for the particular case of black beans, an extraction method using 2:8 water in methanol (v/v) has been typically used to isolate polyphenolic compounds [11], along with HPLC-MS as the analytical method of choice to characterize the polyphenolic composition obtained. Comparative Evaluation of a Modified Acetic Method for Extraction of Antioxidant Compounds from Black Beans (Phaseolus vulgaris)
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