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Foaming of Differently Processed Oats: Role of Nonpolar Lipids and Tryptophanin Proteins

¹University of Helsinki, Department of Food and Environmental Science, PO Box 66, FIN-00014 University of Helsinki, Finland. ²VTT Technical Research Centre of Finland, PO Box 1000, FIN-02044 VTT, Finland. ³Corresponding author. Phone: +358919158242. Fax: +358919158460. E-mail: jussi.loponen@helsinki.fi

The baking properties of oats are poor, mainly due to the lack of gluten matrix and hence the surface properties of the aqueous phase are crucial for the gas retention in oat dough. Our aim was to study the composition and foaming properties of the water-soluble fraction from differently processed oats. A water extract from kilned oats contained nonpolar triglycerides and had poor foaming properties, whereas removing lipids with hexane extraction improved the foaming capacity and foam stability. A water extract from supercritical carbon dioxide extracted oats (CO₂-oats) was free from nonpolar lipids and had good foam stability and excellent foaming capacity. Moreover, oat lipid-binding proteins, tryptophanins, were highly concentrated in the CO₂-oats-derived foam and apparently played an important role in the foam structure. Supplementing CO₂-oats extract with small quantities (<0.05%) of nonpolar lipids of oats destructed its foaming properties. In a preliminary baking trial, the addition of the nonpolar lipids to CO₂-oats and wheat-starch-based baking recipes resulted in baked goods with reduced volume. The study showed that nonpolar triglycerides were present in the aqueous phase of oat in a quantity that impaired foaming. Moreover, this was the first study showing that tryptophanins, lipid-binding proteins of oats, were highly concentrated in foams prepared of oats free of water-extractable nonpolar lipids. In conclusion, tryptophanins can be considered as the foam-active proteins of oats that prevent the lipid-induced destabilization of foam structures which could improve the baking properties of oats.