LITERATURE REVIEW

Effects of Antioxidants in Wheat on Lipid Peroxidation

Effects of Antioxidants in Wheat on Lipid Peroxidation

Literature Review

Ferulic acid (4-hydroxy-3-methoxy cinnamic acid ) is present at relatively high concentrations in the cell walls of several plants, including Graminaceae among Monocots (Hartley and Ford, 1989: 136) and Solanaceae (Fry, 1982: 164) and Chenopodiaceae (Rombouts and Thibault, 1986: 244) among Dicots (Fry, 1979; Hartley and Harris, 1981: 106). They are derived from the general phenylpropanoid pathway that is ubiquitous in plants. In cereal grains, ferulic acid is essentially found in the bran (Wetzel, Pussayanawin and Fulcher, 1988: 209; Seitz, 1989: 188) and hence it is a suitable raw material for the production of ferulic acid (Ralet, Thibault and Della Valle, 1990: 136). Ferulic acid is also found esterified to the glucuronoarabinoxylans in pineapple cell walls (Smith and Harris, 2001: 265). In dicots, ferulic acid is present in high amounts in sugar beet pulp, another potential raw material for the production of ferulic acid (Rombouts and Thibault, 1986: 166) and in the cell walls of spinach (Spinacia oleraced) (Fry, 1982), glass wort (Salicornia ramosissima) (Renard, Champenois and Thibault, 1993), Chinese water chestnut (Eleocharis dulcis) (Parr et al., 1996-:35-37: 133), pine hypocotyls (Pinus pinaster) (Sanchez et al., 1996-:35-37: 106) and carrot (Daucus carota) (Massiot, Rouau and Thibault, 1988: 98).

Ferulic acid constitutes about 0.14% (w/w, dry weight) in barley grains (Nordkvisk, Salomonsson and Amar, 1984), 0.66% in wheat bran (Smith and Hartley, 1983), 0.8% in sugar beet pulp (Micard, Renard and Thibault, 1994:40-42: 133), 0.9% in rice endosperm cell wall (Shibuya, 1984: 85) and 3.1% in maize bran (Saulnier, Vigouroux and Thibault, 1995-:45-65: 177). Among the agricultural byproducts that are potential sources of ferulic acid , maize bran is one of the most promising sources. In barley and wheat , ferulic acid is concentrated mainly in the aleurone layer of the bran (Pussayanawin and Wetzel, 1987: 136). Wheat straw contains approximately 30% more ester-linked cinnamic acid sthan wheat bran and contains approximately equal amounts of ferulic acid and p-coumaric acid . In contrast, wheat bran contains a very small amount of p-coumaric acid (Lequart et al., 1999: 130). Ferulic acid dominates the monomeric phenolic fraction (7.2 mg g^sup -1^) of cold alkali treated cell walls of Chinese water chestnut (Parr et al., 1996-:35-37).

Maize bran and wheat bran are rich in heteroxylans in which [beta]-(1-4) linked xylose residues form the backbone (xylans), and arabinose residues or glucuronic acid are attached at O-2 and/or O-3. The ferulic acid is found linked to the O-5 of these arabinose residues (Wende and Fry, 1997:38-40: 166). The maize bran cell walls are very resistant to enzymatic degradation, probably due to the highly branched character of the heteroxylan, high level of cross linking and high levels of esterified ferulic acid , which in fact restrict enzyme accessibility (Faulds et al., 1995-:45-65: 42).

Feruloyl esterases can be isolated from a wide range of microorganisms (Kroon and Williamson, 1996-:35-37: 265; Donaghy and McKay, 1997:38-40: 41) when they are grown on complex substrates such ...