Avenanthramides are phenolic compounds characteristic to oats. They consist of anthranilic and hydroanthranilic acid linked to one of several hydroxycinnamic acids through an amide bond (Peterson 2004). The concentration of avenanthramides cultivar related and dependent on the location and harvest year. High concentration can be a result of attack of certain plant pathogens. Also unfavourable environmental conditions leading to sprouting prior harvest can increase the amount of avenanthramides. The concentrations in grains vary between 2 mg/kg - 53 mg/kg (Pihlava et al. 2004).
Tocols (tocopherols and tocotrienols) are natural antioxidants in grains that may benefit human and animal health. They exist as lipid-soluble compounds and are unevenly distributed within the grain (α-tocotrienol primarily in the endosperm, whereas α-tocopherol in the germ). Tocols are known as vitamin E (Peterson 2004). Their biological activity results from their ability to donate phenolic hydrogen atoms to free radicals, thus breaking destructive chain reactions (Kamal-Eldin and Appelqvist 1996). Other beneficial therapeutic properties of tocols include the ability to reduce serum cholesterol concentration and to inhibit the growth of certain cancer cells (Peterson 2004).
The tocotrienols are stronger free radical scavengers than tocopherols (Peterson 2004). α-Tocotrienol is the major homologue of the tocols in oats, followed by α-tocopherol. Various other homologues are found in minor or trace amounts (Peterson et al. 2007). A survey of 12 genotypes grown in three locations in the USA found a range of 9 - 19 mg/kg for the concentration of α-tocotrienol, and 7 - 10 mg/kg for α-tocopherol (Peterson and Qureshi 1993). Mannerstedt-Fogelfors et al. (2004) examined the effect of N fertiliser on the concentrations of avenanthramides and tocols. The cultivar x N-level interaction was significant for content of α-tocopherol, α-tocotrienol and total tocols.
Compounds occurring in trace amounts
Phenolic compounds, flavonoids, saponins, lignans and sterols are found in oat grain, but in minor quantities. Their concentrations are very low compared to avenantramides and tocols (Peterson 2004). These compounds have antioxidant and other bioactivities.
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