Development and validation of ultrasound assisted extraction (UAE) and HPLC-DAD method for determination of polyphenols in dry beans (Phaseolus vulgaris)

Abstract

An analytical method for extraction and quantitative determination of the main phenolic compounds (hydroxycinnamic acids and derivatives, anthocyanins and flavonols) in dry beans (Phaseolus vulgaris) is described. The best extraction conditions were: 100% sonication amplitude, 10.3 min extraction, 46% ethanol, 1.5 g dry bean flour and 30 mL of solvent. The developed method was validated in terms of accuracy and precision. Good linearity was obtained, with correlation coefficients exceeding 0.999 and the quantification limits ranged from 0.25 μg/g (p-coumaric acid) to 1.38 μg/g (kaempferol). The accuracy ranged between 88 and 92% and the reproducibility of the method was always < 5.8% (RSD). The method was applied to a set of 17 accessions with different phenotypes. Results showed a greater presence, in all cases, of ferulic acid derivatives, compared to the sinapic acid and p-coumaric acid derivatives. Except for the white variety Xana, flavonoids were detected in all samples. Higher levels of anthocyanins were detected in Black Turtle Soup, a black bean, characterized by a higher content of delphinidin 3-O-glucoside, petunidin 3-O-glucoside and malvidin 3-O-glucoside. The flavonols showed a remarkable diversity, the 3-glucoside derivatives being the most abundant in all samples.