Avenanthramides

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

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.

References

Bryngelsson, S., Mannerstedt-Fogelfors, B., Kamal-Eldin, A., Andersson, R., Dimberg, L.H. (2002) Lipids and antioxidants in groats and hulls of Swedish oats (Avena sativa L). J Sci Food Agric 82, pp. 606-614.

Kamal-Eldin, A., Appelqvist, L.-Å. (1996) The chemistry and antioxidant properties of tocopherols and tocotrienols. Lipids 31, pp. 671-701.

Mannerstedt-Fogelfors, B., Sohl, J., Alström, S., Peterson, D.M. (2004) Antioxidant and β-glucan content in oats as affected by soil type and N-level. In: Proceedings of the 7th International Oat Conference. Helsinki, Finland. Peltonen-Sainio, P., Topi-Hulmi, M. (eds.) Jokioinen: MTT Agrifood Research Finland, Agrifood Research Reports 51, p. 220.

Peterson, D.M., Dimberg, L.H. (2008) Avenanthramide concentrations and hydroxycinnamoyl-CoA: hydroxyanthranilate N-hydroxycinnamoyltransferase activities in developing oats. J Cereal Sci 47, pp. 101-108.

Peterson, D.M., Jensen, C.M., Hoffman, D.L., Mannerstedt-Fogelforsl, B. (2007) Oat tocols: saponification vs. direct extraction and analysis in high-oil genotypes. Cereal Chem 84, pp. 56-60.

Peterson, D.M. (2004) Oat - a multifunctional grain. In: Proceedings of the 7th International Oat Conference. Helsinki, Finland. Peltonen-Sainio, P., Topi-Hulmi, M. (eds.) Jokioinen: MTT Agrifood Research Finland, Agrifood Research Reports 51, pp. 21-25.

Peterson, D. M., Hahn. M.J., Emmons, C.L. (2002) Oat avenanthramides exhibit antioxidant activities in vitro. Food Chem 79, pp. 473-478.

Peterson, D. M. (2001) Oat antioxidants. J Cereal Sci 33, pp. 115-129.

Peterson, D. M., Qureshi, A. (1993) Genotype and environmental effects on tocols of barley and oats. Cereal Chem 70, pp. 157-162.

Pihlava, J.-M., Eurola, M., Hietaniemi, V., Kontturi, M., Vuorinen, M. (2004) Factors affecting the concentration of avenanthramides in oats. In: Proceedings of the 7th International Oat Conference. Helsinki, Finland. Peltonen-Sainio, P., Topi-Hulmi, M. (eds.) Jokioinen: MTT Agrifood Research Finland, Agrifood Research Reports 51, p. 119.

Skoglund, M., Peterson, D.M., Andersson, R., Nilsson, J., Dimberg, L.H. (2007) Avenanthramide content and related enzyme activities in oats as affected by steeping and germination. J Cereal Sci, in Press.