Cereals, phenolic acids

Arabinoxylans with a substitution of the P-(l—>4)-D-xylopyranose backbone at position 2 or 3 with ArbF can be esterified partly with phenolic acids. This type is frequently found in the starchy endosperm and the outer layers of cereal grains. 

High performance LC is commonly employed for separation and quantifying phenolic compounds in cereal grains (126), especially due to the existence of considerable evidence linking the presence of phenolic acids in grain to disease resistance and resistance to mold damage. 

Phenolic acids, and especially ferulic acid, which is abundantly present in cereals, is found esterified to the polysaccharides present in primary and secondary cell walls of plants. Ferulic acid is the major phenolic acid occurring in the cell walls of monocotyledons and appears as cis and the more abundant trans isomers (reviewed in [Klepacka and Forna, 2006]). Ferulic acid is found in wheat, maize, rye, barley [Sun et al., 2001], oats, spinach, sugar beet, and water chesnuts [Clifford, 1999], generally esterified, and rarely as free form, such as in barley [Yu et al., 2001]. It is esterified in primary cell walls to arabinoxylans (Fig. 2.4) in the aleurone layer and pericarp [Clifford, 1999], as in spinach [Fry, 1982] or in wheat bran [Smith and Hartley, 1983], Ferulic acid can also be found esterified to other hydroxycinnamic acids such as in Mongolian medicinal plants where it is found as feruloylpodospermic acid, which is... 

Ferulic acid has often been reported as a model compound for the investigation of bioavailability of phenolic acids, as free or esterified forms (Table 2.3), since it is abundantly present in food. Absorption via the gastrointestinal tract has also been found for dimers of ferulic acid, or diferulic acids, released from cereal brans [Andreasen et al., 2001b]. 

Rao, R. S. P. and Muralikrishna, G. (2004a). Non-starch polysaccharide-phenolic acid complexes from native and germinated cereals and millet. Food Chem. 82, 527-531. 

Andreasen, M.F. Christensen, L.P. Meyer, A.S. Hansen, A. 2000. Content of phenolic acids and ferulic acid dehydrodimers in 17 rye (Secale cereal L.) varieties. J. Agric. Food Chem. 48 2837-2842. 

Maga J.A. and Lorenz K. (1973) Taste threshold values for phenolic acids which can influence flavor properties of certain flours, grains and oilseeds. Cereal Sci. Today 18 (10), 326-8. 

Hatcher, D.W. and Kruger, J.E., Simple phenolic acids in flours prepared from Canadian wheat Relationship to ash content, color, and polyphenol oxidase activity. Cereal Chem., 74, 337, 1997. 

Nuts, seeds, and grains are not considered as sources of organic acids. Other than amino acids and fatty acids, they contain phenolic acids and phytic acid. Phytic acid and its salts, phytats, are regarded as the primary storage form of both phosphate and inositol in seeds, mostly within the hulls. The phytic acid content of cereals (whole grain) varies from 0.5% to 2.0% [21],... 

Weidner, S., Amarowicz, R., Karamac, M., and Fraczek, E., Changes in endogenous phenolic acids during development of Secale cereale caryopses and after dehydration treatment unripe rye grains. Plant Physiol. Biochem., 38, 595-602, 2000. 

Other plants (cereals, seeds, rye, nuts, barley, malt) can also be extracted with organic solvents or their mixtures with water, but, in many cases, less polar solvents are also used for the elimination of pigments, oils, non-polar and macromolecular compounds. Many of these assays have also included acidic and/or alkaline hydrolysis steps, column liquid clean-up procedures, or SPE. The simultaneous separation of phenolic acids and other phenolic compounds in these samples also complicates the preparation step. Very often, multi-step liquid extraction and sample clean-up assays are recommended. It is necessary to select extraction solvents according to the polarities of the analytes and the form of their bonding to the sample matrix. Very often, both free and bound phenolic acids are separated in plant samples, and hydrolyzed and non-hydrolyzed materials are analyzed separately. In some cases, two or more hydrolysis methods are applied for the analyses of cereals and nuts. ... 

Phenolics reported in cereals and cereal products include 29 phenolic acids, 33 flavonoids, 6 lignans, and 2 other polyphenols [9]. The major phenolics in cereals and cereal products are summarized in Table 81.2. 

The major phenolic acids (mg 100 g FW) in the above cereals and cereal products with high maximum SIPA (>10 mg 100 g FW) were ferulic acid in hard wheat whole grain flour (72.2) oat whole grain flour (35.8) hard wheat reflned flour (14.1) and avenanthramide 2c (3.8-3.9), avenanthramide 2p (1.4-3.1), avenanthramide 2f (2.6-2.7), and avenanthramide K (1.2-2.7) in oat whole grain flour without conducting a hydrolysis step. 

After hydrolysis, the major phenolic acids in cereals and cereal products with high maximum SIPA (>100 mg 100 g FW) were identified as ferulic (90.6-255.3),... 

Variations in the phenolic acid levels during growth and development of vegetables and cereals are not so homogeneous as those reported for fleshy fruits. It depends mainly on two parameters the nature of the plant organ (leaves, tubers, grains, etc.) and the subcellular localization of the phenolic conjugates that accumulate either as soluble forms in the vacuole or linked to the cell wall. 

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