ABSTRACT
Phenolic compounds are ubiquitous in cereals, legumes, and nuts. Different phenolics belonging to the benzoic acid, cinnamic acid, flavonoid and tannin class of compounds may be present in free, esterified/etherified or insoluble bound forms (Ribereau-Gayon, 1972; Salunkhe et al., 1982). Thus, ferulic acid may be linked to polysaccharides (Faulds and Williamson, 1999; Hartley et al., 1976; Hatfield et al., 1999; Iiyama et al., 1990; Ishii, 1997; Ishii and Hiroi, 1990; Markwalder and Neukom, 1976), lignins (Higuchi et al., 1967; Iiyama et al., 1990) and suberin (Riley and Kolattukudy, 1975);
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-coumaric acid may be linked to polysaccharides (Hartley et al., 1976), lignins (Grabber et al., 2000; Nakamura and Higuchi, 1978), and cutin (Kolattukudy et al., 1981). In aleurone layer of cereal grains, ferulic acid is mainly linked to polysaccharides via an ester bond at the
O
-5 position of arabinofuranose (Ishii, 1997). Ferulic acid may also undergo dimerization by oxidative coupling catalyzed by peroxidase (Brett et al., 1999; Geissmann and Neukom, 1973). Dehydrodimers of ferulic acid have been proposed to form cross links between arabinoxylan chains (Markwalder and Neukom, 1976; Waldron et al., 1996). The main dehydrodimers identified in plant material are shown in Figure 2.1.
