Skip to main content
ARS Home » Midwest Area » East Lansing, Michigan » Sugarbeet and Bean Research » Research » Publications at this Location » Publication #125781
Title: THE EPICUTICULAR WAX LAYER AND WATER UPTAKE IN BLACK BEANS

Author
item Bushey, Shawna
item OWENS, SHIRELY - MICHIGAN STATE UNIVERSITY
item Hosfield, George

Submitted to: Bean Improvement Cooperative Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 3/1/2001
Publication Date: N/A
Citation: N/A

Interpretive Summary: Black beans that leach (lose color) during cooking and canning are unappetizing and often rejected by consumers. Seed coat shininess is also important in black beans. Beans with a shiny seed coat retain more color after cooking or canning, however, they imbibe less water and are less palatable than beans with opaque (dull) seed coats. Color in black beans is sdue to water soluble compounds called anthocyanins localized in special cells of the seed coat. Experiments were conducted with three black bean cultivars to study how much water each would take up during a two hour soaking period and ascertain whether seed factors may be associated with water uptake and color leaching. After soaking seeds from two cultivars with opaque (dull) and one with a shiny seed coat, they were examined using an electron microscope (SEM). Seeds with shiny seed coats imbibed water at a slower rate than seeds with opaque seed coats. SEM revealed that shiny yseeds had a smooth, thick wax layer that covered the surface of the seed coat and apparently inhibited water movement. Opaque beans had a wax layer that was very uneven and varied greatly in thickness across the seed coat surface. There also were cracks in the wax layer of opaque seeds that apparently favored rapid water penetration into the seed. The results of the present study provide plant breeders with the first new information to use in their quest to breed new black bean cultivars with the water uptake properties necessary to give a high quality cooked product, but which leach noticeably less than the commercial cultivars currently grown. Black bean cultivars that retain their color after canning will eliminate a major obstacle in the canning plant, and, thus, lower operating costs which, in turn, can be passed on to consumers.

Technical Abstract: Seed color of black beans (Phaseolus vulgaris L.) is determined by water soluble anthocyanins localized in the palisade cells of the seed coat. When beans are cooked the anthocyanins often leach into the broth and discolor it. Seed coat luster is also an important food quality factor in black bean. Black beans with shiny seed coats imbibe water at a slower rate, cook kmore slowly, and retain more of their color than beans with opaque (dull) seed coats. Experiments with three black bean cultivars were conducted to study imbibition and seed factors that may be associated with water uptake and color leaching. Seed of 'Shiny Crow'(shiny seed coat) imbibed the least (3% of its dry weight) while seed of 'Raven'(opaque seed coat) imbibed the most (100% of its dry weight) water of the three cultivars during soaking. 'Black Magic'(opaque seed coat) was intermediate to 'Shiny Crow' and 'Raven' in the amount of water imbibed. Seed coat surfaces investigated dwith a scanning electron microscope (SEM) revealed that the epicuticular wax layer of 'Shiny Crow' was contiguous over the seed coat and varied only slightly in thickness. On the other hand, wax deposition of 'Raven' and 'Black Magic' was unevenly distributed and varied in thickness by more than 1 micron over the seed coat. Cracks were associated with areas of the seed coat in which wax distribution was thinly layered. No cracks in the wax layer were observed for 'Shiny Crow'. Based on our results, beans with opaque seed coats leached more than the shiny ones because wax layer cracks facilitated rapid imbibition of water which, in turn, migrated quickly into palisade cells, thus, facilitating anthocyanin solubilization and subsequent leaching.