Effects of heating on the interaction of lipid and zein in a dry powder system.

The effects of heat treatment on the interaction of lipid and zein in a dry powder system were investigated. Linolenic acid ethyl ester (LAE) was mixed with the zein powder. The glass transition temperature (T(g)) for the dry powder zein was shown to be approximately 107 degrees C by differential scanning calorimetry. The thermogram of the zein-LAE mixed powder showed an exothermic transition near the T(g) of zein. Fourier transform infrared (FT-IR) spectroscopy was used for detecting the structural changes in zein by heat treatment, that is, elevating the temperature from 25 to 160 degrees C. The heat treatment of the powdery zein with and without LAE caused increases in the alpha-helix, beta-turn, and beta-sheet, concomitant with decreases in the intermolecular hydrogen-bonded beta-sheet and random coil. Such changes in the secondary structure were more drastic for the powder with LAE. The heating of the zein-LAE mixed powder also caused decreases in the peaks originating from LAE in the FT-IR spectra. These results suggest that the heat treatment induced the interaction of the zein and LAE in the powdery system. The influence of heating on the antioxidative activity of dry powder zein was studied by measurements of the peroxide value. When zein-LAE mixed powder was heated before storage, the oxidation of LAE was inhibited for 7 days, whereas LAE was oxidized within 1 day in the absence of heat treatment.