Cereals grain structure

Phytate (myo-inositol hexaphosphate Fig. 15.3, structure 33) is found in many food species and can be considered as a phytochemical. Its role in the plant is primarily as a phosphate store in seeds, but it is found in other tissues as well, for example, tubers (Harland et al., 2004). Phytate and its hydrolysis products are anti-nutrients that chelate metal ions and thus reduce their bioavailability (Persson et al., 1998 House, 1999). This is particularly a problem with cereal grains, but pre-processing can improve mineral absorption from these foods (Agte and Joshi, 1997). There is some concern that high phytate foods could also contain higher levels of toxic heavy metals caused by natural accumulation. Plants also contain phytate-degrading enzymes that can also influence metal ion bioavailability (Viveros et al., 2000). 

These organelles occur in the endosperm of cereal grains and their structures are tissue specific. They are about 2-5 im in diameter and often contain globoid and occasionally crystalloid inclusions. Prolamin accumulates in small or large spherical bodies. Crystalline protein bodies are the sites of accumulation of nonprolamin storage proteins. 

The most common source of aflatoxins is moldy food, particularly nuts, some cereal grains, and oil seeds. The most notorious of the aflatoxins is aflatoxin B1( for which the structural formula is shown in Figure 19.1. Produced by Aspergillus niger, it is a potent liver toxin and liver carcinogen in some species. It is metabolized in the liver to an epoxide (see Section 7.3). The product is electrophilic with a strong tendency to bond covalently to protein, DNA, and RNA. Other common aflatoxins produced by molds are those designated by the letters B2, G1( G2, and M,. 

It is not always clear whether cell-wall polysaccharides have a structural or reserve function because some, for example, the /3-glucans of cereal grains, may have dual roles. However, it is likely that the /3-glucans and other hemicelluloses in cell walls of tissues other than those in... 

Saccharides are present in food raw materials in quantities ranging from about 1% in meats and fish, to about 4.5% in milk, 18% in potatoes, and 15-20% in sugar beets, to about 70% in cereal grains. Polysaccharides participate in the formation of structures in plants. They are also stored in plants as starch and in muscles as glycogen. Other saccharides are dissolved in tissue fluids or perform different biological functions in free nucleotides, as components of nucleic acids, or bound to proteins and lipids. 

It is worth noting that in many cases some of the resorcinolic lipids present in biological material still remain structurally uncharacterised. For instance, chromatographic analysis of acetone extracts from cereal grains shows the presence of at least 4 other components that probably belong to the group of resorcinolic lipids. Two of them have been identified as 5-(2-oxoalkyl) resorcinol and 5-(2-oxoalkenyl) resorcinols [178] and the another as a 5-(2-hydroxyalkyl) resorcinol [181]. 

In contrast to the cell walls of parenchymatous tissues of dicotyledons, those of cereal grains (wheat, barley, etc.) contain very little, or no, pectic substances. The primary walls of most cereal grains have cellulose microfibrils, which are closely associated with glucomannan, and these fibrillar structures are embedded in an amorphous matrix of hemicelluloses, which consists mainly of arabinoxylans and/or P-D-glucans, some of which are cross-linked by phenolic esters and/or proteins (Selvendran,... 

In recent years, treating SBM with exogenous enzymes prior to feeding has received attention. These enzymes could potentially break down some of the carbohydrate fraction, thereby making the carbohydrates more available to the animal. A difficulty exists with SB structural polysaccharides in that the SB polysaccharides are more complex than those found in cereal grains (Annison Choct, 1993). This makes it potentially difficult to target cell wail components as a whole. Huisman et al. (1999)... 

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