Evaluation of the antioxidant capacity and phenolic compounds in the soaking water of a Phaseolus vulgaris landrace ‘Gurgutuba Roxo’

Water soaking is a processing step widely employed in the food industry. Bean soaking water has attracted increasing attention due to its functional potential resulting from the migration of bioactive compounds during seed hydration. In colored common beans, this transfer is more pronounced because of the high concentration of phenolic compounds, particularly anthocyanins, in the seed coat. Therefore, the valorization of bean soaking water represents a promising strategy for the full utilization of raw materials and the development of functional ingredients. This study aimed to evaluate the phytochemical profile and antioxidant capacity of the soaking water obtained from the common bean (Phaseolus vulgaris L.) landrace ‘Gurgutuba Roxo’. Seeds were soaked in distilled water at a 1:2 (w/v) ratio for 8, 12, and 24 hours. After each soaking period, the soaking water was collected for the determination of total phenolic content using the Folin–Ciocalteu method, total flavonoids, total anthocyanins, and antioxidant capacity by DPPH, FRAP, and ABTS assays. Shapiro–Wilk (p < 0.05) and Levene’s (p < 0.05) tests were applied to verify data normality and homogeneity of variances. Data were subjected to one-way analysis of variance (ANOVA), followed by Tukey’s post hoc test (p < 0.05), using STATISTICA® version 13.3 (TIBCO Software Inc., Palo Alto, CA, USA). Increasing the soaking time promoted greater migration of bioactive compounds into the soaking water. Total phenolic content increased significantly (p < 0.05), reaching 0.815 mg GAE/mL after 24 hours, followed by 0.711 mg GAE/mL after 12 hours and 0.453 mg GAE/mL after 8 hours, indicating the progressive diffusion of water-soluble phenolic compounds from the seed coat and cotyledons. Similarly, total flavonoid content and antioxidant capacity (DPPH, FRAP, and ABTS) increased with soaking time, confirming a positive relationship with phenolic content. In contrast, total anthocyanin content reached its highest value after 12 hours of soaking (39.46 mg/L), followed by 8 hours (29.68 mg/L), whereas a significant decrease was observed after 24 hours (20.71 mg/L). This reduction may be attributed to the instability of anthocyanins during prolonged soaking, resulting from degradation, oxidation, or polymerization reactions commonly reported for these phenolic pigments. The soaking water of the ‘Gurgutuba Roxo’ common bean landrace exhibited high levels of phenolic compounds and antioxidant capacity, highlighting its potential as a functional food ingredient and supporting circular economy strategies through the valorization of agro-industrial by-products.Acknowledgements: This study was supported by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES, Finance Code 001), Fundação Araucária, and the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq).