or extended blanch conditions) generally renders black beans pale and opaque with a gray or chocolate brown “muddy” appearance. The leaching of pigment during soaking, blanching, and thermal processing is a major quality problem associated with all colored beans, particularly black beans. The primary anthocyanin pigments in black beans include: (1) delpinidin‐O‐gluscoside, (2) petunidin‐O‐glucoside, and (3) malvidin‐O‐glucoside. These phenolic glucosides are highly soluble in water, and excessive leaching may occur, resulting in beans with a flat brownish appearance (Bushey et al. 2000, Bushey and Hosfield 2007). The deposition of pigment in black beans is relatively late in the plant growth cycle and appears to be under genetic and environmental influence (Fletcher et al. 2003). Failure to achieve full maturity of seed may result in reduced or nonuniform pigmentation.
It is recognized that black beans possessing a shiny seed coat will imbibe less water and at a slower rate, resulting in less total pigment loss than beans with dull‐appearing seed coats. This characteristic is likely associated with polar‐phased (lipids/waxes) components deposited within the cuticle of the testa. For example, Shiny Crow, a distinctive black bean cultivar released by Colorado State University in 1999, possesses a brilliant glossy seed coat sheen and is particularly valued in the fresh market sector due to its deep black pigmentation. Black beans with the highest rates of water uptake were shown to have the highest rates of pigment loss (Raven, Black Jack and Black Magic) and had about 90% pigment loss compared to Shiny Crow and Shiny Harblack, with about 50% pigment loss. Thus, these data suggest that the opaque (dull) seed coat has the highest water uptake (rate and total quantity) and the greatest pigment loss compared to shiny‐coated cultivars (Bushey et al. 2000, Bushey and Hosfield 2007).
Several soak‐water additives have demonstrated the ability to stabilize pigment leaching and/or oxidization. Citric acid, poly phosphates, and ethylene‐diamine‐tetra‐acetic acid (EDTA) are commonly used to improve pigment appearance. Pigment stabilization mechanisms likely include the chelation of iron and copper to control oxidative reactions that result in loss of distinctive pigmentation/color.
USDA STANDARDS FOR COMMON BEANS AND SELECTED PULSES
USDA grade specifications are useful for communicating quality characteristics and serve as guidelines for purchase, especially in international commerce (export or import with the United States). However, many purchasers and end users often establish internal criteria (standards and tolerances derived through practical experience) that meet their individual quality needs.
The USDA standards for dry beans/legumes are shown in Table 3.3. The USDA uses the following terminology for establishing grades of beans (USDA 2017a):
Sound beans: Sound beans shall be beans that are free from defects.
Defects: Defects for the classes baby lima and miscellaneous lima beans shall be damaged beans, contrasting classes, and foreign material. Defects for all other classes of beans shall be splits, damaged beans, contrasting classes, and foreign material.
Splits: Splits shall be pieces of beans that are not damaged, each of which consists of three‐fourths or less of the whole bean and shall include any sound bean the halves of which are held together loosely. Table 3.3. United States standards for selected classes of dry beans/pulses (% maximum limits).Source: adapted from USDA (2017a).Dry bean classesTotal defects (total damaged, foreign material, contrasting classes, splits)Total damaged (“badly damaged” for Navy)Total foreign material (including stones)Foreign material (stones only)Contrasting classesClasses that blendUS #1US #2US #3US #1US #2US #3US #1US #2US #3US #1US #2US #3US #1US #2US #3US #1US #2US #3Pinto3.05.07.03.05.07.00.51.01.50.20.40.60.51.02.05.010.015Navy (Pea beans) 12.03.01.5/3.02.03.00.3/0.30.40.80.1/0.10.20.40.1/0.10.51.00.1/0.14.04.02.0/2.0Black, kidney, small red, pink, great northern, small white2.04.06.02.04.06.00.51.01.50.20.40.60.51.02.05.010.015.0Cranberry, black‐eye/ cowpea, yellow‐eye 24.06.08.02.04.06.00.51.01.50.20.40.60.51.02.05.010.015.0Mung bean 32.04.06.02.04.06.00.51.01.50.20.40.60.51.02.05.010.015.01 Navy beans have two additional grades: “US Choice Handpicked” and “US Prime Handpicked,” for which data are shown under “US #3,” respectively.2 Yellow‐eye beans have an additional criterion for classes that blend: white beans similar in size and shape at 5% each for “US #1 & #2” and unspecified for “US #3.”3 Mung beans have an additional criterion: “Clean‐cut Weevil Bored” – 0.1, 0.2, and 0.5% for “US #1, #2, and #3,” respectively.
Damaged beans: Damaged beans shall be beans and pieces of beans that are damaged by frost, weather, disease, weevils or other insects, or other causes.
Badly damaged beans: Badly damaged beans shall be beans and pieces of beans that are materially damaged or discolored by frost, weather, disease, weevils or other insects, or other causes so as to materially affect the appearance and quality of the beans.
Foreign material: Foreign material shall be stones, dirt, weed seeds, cereal grains, lentils, peas, and all matter other than beans.
Stones: Stones shall be concreted earthy or mineral matter, and other substances of similar hardness that do not disintegrate readily in water.
Contrasting classes: Contrasting classes shall be beans of other classes that are of a different color, size, or shape from the beans of the class designated.
Classes that blend: Classes that blend shall be sound beans of other classes that are similar in color, size, and shape to the beans of the class designated, and shall include white beans in the class yellow‐eye that are similar in size and shape to the yellow‐eye beans.
Broken beans: Broken beans shall be sound beans with some, but less than one‐fourth, of each bean broken off or with one‐fourth or more of the seed coat removed.
Blistered beans: Blistered beans shall be sound beans with badly blistered or burst seed coats.
Wrinkled beans: Wrinkled beans shall be sound beans that have deeply wrinkled seed coats and/or are badly warped or misshapen.
Weevily beans: Weevily beans shall be beans that are infested with live weevils or other insects injurious to stored beans or that contain weevil‐bored beans.
Clean‐cut weevil‐bored beans: Clean‐cut weevil‐bored beans shall be beans from which weevils have emerged, leaving a clean‐cut open cavity free from larvae, webbing, refuse, mold, or stain.
Well screened: Well screened, as applied to the general appearance of beans, shall mean that the beans are uniform in size, and are practically free from such small, shriveled, underdeveloped beans, splits, broken beans, larger beans, and foreign material that can be removed readily by the ordinary process of milling or screening through the proper use of sieves.
The USDA grading standards for chickpeas designate Kabuli and Desi types. Kabuli chickpeas average 8.5–10.5 mm in diameter and weigh 49 g per 100 seeds with external beige and with a golden yellow interior color. “US #1” Grade seed specified to contain not greater than 18% moisture, 2.0% defects, 2.0% total damaged, 0.5% foreign material, 0.2% stones, 0.5% contrasting classes, and 5% classes that blend. Thus, careful selection of purchase specifications are warranted to assure appropriate quality due to the broad standards established for “US #1.” “US#2” and “US #3” grades possess much higher tolerances that are outside the standards for product quality currently expected of canned chickpeas. For example, total