Effects of deamidation on structure and functional properties of barley hordein

Deamidated hordeins of various deamidation degree (DD) ranging from 0.7 to 40% were prepared using an alkaline method. The hordein peptide bond cleavage, secondary structure, surface charge and hydrophobicity as well as their solubility, emusifying and foaming properties were studied as a function of DD value. SDS-PAGE, size exclusion chromatography (SEC) and Fourier transform infrared (FTIR) results suggest that limited deamidation (≤ 4.7%) could dissociate hordein aggregates, leading to great increase of the protein solubility and surface hydrophobicty. A further increase of the DD value greater than 4.7% resulted in extensive protein hydrolysis and a marked change of protein secondary structure. The optimal functionalities were obtained at a narrow DD range (2.4-4.7%), where hordein samples demonstrated significantly improved solubility and the emulsifying and foaming properties at both acidic and neutral pHs. These results suggest that deamidated hordein would be an excellent candidate to be developed as an emulsifying and foaming ingredient.