Submitted to: HortScience
Publication Type: Abstract Only
Publication Acceptance Date: April 27, 1999
Publication Date: N/A
Technical Abstract: Seed coat color in dry bean (Phaseolus vulgaris L.) is determined by the presence or absence of tannins, flavonols, and anthocyanins. Black beans contain three main anthocyanins in seed coats; delphinidin 3-O-glucoside, petunidin 3-O-glucoside, and malvidin 3-O-glucoside. Leaching of anthocyanins occurs in many black bean genotypes during thermal processing (i.e., blanching and cooking). Black beans that leach during processing ar unacceptable to the industry. Since the marketability of black beans can be adversely affected by thermal processing, an experiment was conducted to ascertain whether pigment leaching was due to qualitative or quantitative changes in anthocyanins. Four black bean genotypes which showed differential leaching of color were investigated. 'Harblack' retains most of its black color after processing while 'Raven' loses most of its color. 'Black Magic' and 'Black Jack' are intermediate between 'Harblack' and 'Raven' in processed color. Bean samples (119 +/- 1.5 g) of the four genotypes were thermally processed in 100 x 75 mm tin cans in a pilot laboratory. Seed coats were removed from the cooked beans,freeze dried, and placed in solutions of formic acid:water:methanol 10:65:25 to extract anthocyanins. The extracts were analyzed by HPLC. Although all genotypes retained some color, there were no detectable anthocyanins in seed coats of the cooked beans. In a second experiment, raw beans of each genotype were boiled in distilled water for 15 minutes. All four genotypes lost color during boiling, but 'Harblack' retained most of its color and had a five fold higher concentration of the three anthocyanins than did the other genotypes. 'Harblack' may retain color better than other black beans because of physical characteristics of the seed coat.