Impact of roasted oat flour on the gas cell structure of steamed oat cake and its underlying mechanism

Abstract

Roasting (or called stir-frying) can modify the properties of oat flour and improve the poor quality of steamed oat cake, especially uneven gas cell and high hardness, but the underlying mechanism remains unclear. The properties of protein-starch network matrix of oat dough (made by roasted oat flours with gelatinization degrees of 30%, 50% 70% and 90%) before and after steaming were investigated, as well as the air/water interfacial characteristics of oat dough liquor. Results revealed that adding roasted oat flour with moderate gelatinization degree to the raw oat flour (ROF) could significantly improve the quality of steamed oat cakes, and their average pore size and specific volume reached the corresponded maximum values when roasted oat flour with gelatinization degree of 50% (G50) was added, which were 1.97 mm and 2.56 mL/g, respectively. Roasted oat flour with moderately gelatinization could not only facilitate the formation of protein polymers by promoting disulfide cross-linking of larger monomer proteins in both raw and steamed oat dough, but also induce the conversion of random coil to α-helix and β-sheets structure, resulting in an ordered protein secondary structure. Meanwhile, the improvement of short-range molecular order structure of starch in oat dough was observed for ROF/G50（w/w = 1:1）sample (RG50). Additionally, compared to ROF, RG50 sample possessed the strongest foaming stability, which increased from 32.70% to 61.43%. In conclusion, the quality enhancement of steamed oat cake can be attributed to the combined effects of changes in the protein-starch matrix and the thin liquid film induced by moderately roasted oat flour.