Testa or Seed Coat

Phenolic compounds are the most widely distributed secondary metabolites present in the plant kingdom (Dicko et al. 2006). They can be divided into three major categories simple phenolics, flavonoids, and tannins. Phenolics are usually derived from benzoic or cinnamic acids (Figure 17.4). On the other hand, flavonoids and anthocyanins are built from two units a C6-C3 unit from cinnamic and a C6 fragment from malonyl-CoA. Tannins are polymers of 5-7 units or more of flavan-3-ol or catechins. Most phenolics associated with cereal grains are present in the pericarp, testa or seed coat, aleurone, and glumes or husks. 

The identification and isolation of genes involved in flavonoid biosynthesis has benefited from the fact that many of the flavonoids are colored compounds. Mutant phenotypes are therefore often easily identifiable based on variation in color. In Arabidopsis many of the genes involved in flavonoid bioysnthesis have been uncovered based on the change in seed coat (testa) color. Wild-type Arabidopsis seeds have a brown color, and mutations in flavonoid biosynthetic genes result in yellow or pale brown color because the underlying cotyledons are visible. These mutants are referred to as... 

Tamarind seed eonsists of the seed coat or testa (20-30%) and the kernel or endosperm (70-75%) (Coronel, 1991 and Shankarachaiya, 1998, both cited in (5)). Tamarind seed is a typical underatilized material (77). Commercially, tamarind seed is a by-product of the commercial utihzation of the fruit pulp and has been reported to have several uses (5, 17). Tamarind seeds can be used for extracting tamarind gum, whereas the seed coats, a by-product of manufacturing tamarind gum, were found as a source of natural antioxidants 18). The seeds are presently gaining importance as an alternative source of proteins (5). 

The groundnut or peanut is made up of the outer shell or hull, the seed coat, or testa and the kernel. The hull is separated either by hand or mechanically and the oil extracted by expelling and subsequent solvent extraction. The oil is pale yellow and has the flavour and odour of peanuts. A number of alternative oil extraction procedures have been proposed (Ayres, 1983). Crude oil can have a free fatty acid content as low as 0.3% but most commercial oil is in... 

A young plant, or embryo, before germination consists of a bud, a root, and one or two seed leaves, the cotyledons, all surrounded by a seed coat (testa). In endospermic seeds, such as wheat and castor plant, the seed coat also encloses the endosperm which surrounds the embryo and provides it... 

FIGURE 4.3 Microphotograph detailing the microstructure of the pericarp and aleurone layer of the sorghum caryopsis. E = epicarp M = mesocarp S = starch granules CC = epicarp cross cells T = epicarp tube cells SC = seed coat or testa A = aleurone cells P = peripheral endosperm (courtesy of C. McDonough and L. W. Rooney, Texas A M University). 

Seeds. The seeds are produced in pods containing two or three seeds. The kernels are almost spherical to roughly cylindrical (0.4—1.1 g each) and consist of a thin coat (testa) containing two cotyledons and the embryo. Cotyledons contain protein bodies, Hpid bodies, and starch granules. 

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