Free and Conjugated Phenolics in Soaking Water from Chilean Common Bean Cultivars: Characterization and Antioxidant Potential

The phenolic composition and antioxidant capacity of soaking water from two Chilean common bean (Phaseolus vulgaris L.) cultivars, Magnum and Peumo, were analyzed. The soluble phenolics were extracted and partitioned into free, esterified, and etherified fractions. Phenolic acids and flavonoids were identified and quantified, and the antioxidant capacity was evaluated using 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), ferric reducing antioxidant power (FRAP), 2,2-diphenyl-1-picrylhydrazyl (DPPH), and oxygen radical absorbance capacity (ORAC) assays. Among the phenolic compounds identified across the three fractions, rutin was the only compound detected in all of them. The free fraction showed the greatest phenolic diversity, dominated by catechin, chlorogenic acid, and trans-ferulic acid. Soaking water from Magnum beans exhibited significantly higher total phenolic content and greater antioxidant capacity than that from Peumo. These results suggest that bean soaking water, typically discarded as waste, is a source of phenolic compounds with high antioxidant potential and could be valorized as a functional food ingredient.