WATER UPTAKE AND ITS RELATIONSHIP TO PIGMENT LEACHING IN BLACK BEANS (PHASEOLUS VULGARIS, L.)

Authors: Bushey, Shawna; Hosfield, George; BENINGER, C - FORMER ARS SCIENTIST

Submitted to: Bean Improvement Cooperative Annual Report
Publication Type: Proceedings
Publication Acceptance Date: 3/1/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: The Asp gene determines whether the seed coat of seeds of common bean (Phaseolus vulgaris L.) is shiny or opaque (dull). When a bean carries the dominant Asp allele it has a shiny seed coat whereas the recessive asp/asp alleles condition an opaque seed coat. There are numerous anecdotal reports that beans with shiny seed coats imbibe less water during soaking than beans with opaque seed coats. Several experiments were conducted to ascertain whether black beans containing the Asp allele imbibed less water than their asp/asp counterparts. Over a time course of 180 minutes, black beans with opaque (asp/asp) seed coats imbibed more water and at a faster rate than beans with shiny seed coats (Asp/_). Beans with opaque seed coats also leached more pigment into the soaking and cooking broth than beans with shiny seed coats. The leaching of pigments during the canning of black beans and impaired water uptake during soaking and cooking are bean marketing and processing industry problems that lower the value of beans and reduce profits at every step of the marketing chain. The current experiments on water imbibition and the leaching of pigments during cooking provided strong evidence that cultivars with opaque seed coats imbibe more water and at a faster rate and are more prone to pigment leaching than cultivars with shiny seed coats. This information is useful to geneticists and breeders to make further advances to understand the water imbibition/seed coat leaching phenomenon. An expected outcome of the research is the engineering of genes that influence water imbibition and change bean anatomy through altering the function of the Asp, asp alleles. In the long run, the grower, processing industry and consumer will benefit through higher quality black beans, which are sold at a premium.

Technical Abstract: Anthocyanins give black seeded beans (Phaseolus vulgaris L.) their color. Leaching of anthocyanins occurs in many black seeded cultivars during thermal processing. Black bean color loss after canning is unacceptable to processors. Raven, Shiny Crow, Shiny Harblack, Black Magic, and Black Jack were the cultivars used to study the relationship between anthocyanin content, the amount of leaching during thermal processing, and the ability of seeds to imbibe water. Shiny Harblack and Shiny Crow carry the dominant Asp allele and have shiny seed coats; Raven, Black Magic, and Black Jack carry the recessive asp/asp alleles and have opaque seed coats. For the water imbibition study, bulked seed from harvested plants was divided into three lots. Ten representative seeds from each lot were weighed, placed into beakers and soaked in 20 ml of distilled water at 27 deg C. Every 30 min the 10 seeds from each cultivar were blotted dry and reweighed. The change in the weight of the beans was taken as the amount of water imbibed Except for Shiny Crow, the amount of leaching of each cultivar was determined by quantifying the amount of anthocyanins remaining in the seed coat. Seeds of Raven hydrated at the most rapid rate, had the highest percentage of water uptake and had the greatest amount of leaching of the cultivars. Shiny Harblack and Shiny Crow imbibed essentially no water after 180 minutes, and Shiny Harblack leached the least of the cultivars tested. Considerable anthocyanin leaching occurred in seed coats of Black Magic and Black Jack with percent leaching values of 89.6 and 89.8. The data suggest that cultivars with opaque seed coats imbibe more water, at a faster rate, and are more prone to pigment leaching than those cultivars with the shiny seed coat.