Concentrations of condensed tannins and anthocyanins in common bean seed coats

Abstract

Seed coat colour in common bean (Phaseolus vulgaris L.) is determined by activity of the flavonoid biosynthetic pathway resulting in the presence or absence of specific anthocyanins, tannins and glycosidic flavanols. These secondary metabolites have anti-oxidant properties in the case of anthocyanins and glycosidic flavonols and strongly influence dietary mineral bioavailability in the case of tannins. The modification of tannin content is a goal of biofortification breeding programs, while almost all bean improvement considers seed colour in selection priorities as this affects consumer preference and food quality. In the present study, we analyzed condensed tannins, tannin monomers and anthocyanin levels in an inter-genepool population derived from the cross DOR364 × G19833 using HPLC and spectrophotometric methods. The overall average for condensed tannins expressed as percentage in seed coats was 20.04%. The ranges were between 8.0% and 27.9% for soluble tannins (ST), 1.5% and 5.4% for insoluble tannins (IT), and 10.7% and 30.9% for total tannins (TT). Anthocyanins in seed coats averaged 0.08% (0.013–0.21% range) expressed as delphinidin-3-glucoside equivalents for the population with the distribution biased towards low content. All traits had large variability between genotypes and showed transgressive segregation, indicating quantitative inheritance for tannin content and oligogenic control of anthocyanins. Condensed tannins in the genotypes were mainly composed of catechin (60.3%), gallocatechin (25%), and afzelechin (14.7%) as monomeric units