Effects of water activity and lipid addition on secondary structure of zein in powder systems.

The effects of water activity (Aw) and lipid addition on the secondary structure of powdery zein were investigated using Fourier transform infrared spectroscopy. Two fatty acid esters, i.e., the linolenic and eicosapentaenoic acid ethyl esters (LAE and EPE), were mixed with the zein powder. The powders were stored in the “dry” state (with silica gel) and the “humid” state (Aw = 0.9). The powdery zein without the lipids was shown to have a high content of the intermolecular hydrogen-bonded β-sheet in the “dry” state, indicating the presence of protein aggregates. An increase in Aw induced a decrease in this β-sheet, concomitant with increases in the α-helix and β-turn structures. The addition of LAE caused decreases in the α-helix and intermolecular hydrogen-bonded β-sheet of zein when the powder was stored in the “humid” state, suggesting the strong interaction of LAE and zein molecules. However, LAE did not affect the secondary structure of zein in the “dry” state. The addition of EPE hardly influenced t...