The effect of heat treatments (65, 75, 85, and 95 ℃, 30 min) on the structure and the emulsifying properties of cumin protein isolates were investigated. The fluorescence spectra analysis showed that the conformations were remarkably influenced by heat treatments. An increase in the ratio of α-helix in the secondary structure of heated cumin protein isolates was observed from the result of circular dichroism. Thermal treatments at different temperatures led to an increase in the surface hydrophobicity ( Ho) and a decrease in zeta potential ( ζ) of cumin protein isolates. Emulsifying activity index and emulsion stability index of heated cumin protein isolates were reduced at different protein concentrations (0.1, 0.5, and 1.0%), while the protein absorption in emulsions stabilized by heated cumin protein isolates gradually increased with heating temperature increasing. Moreover, both emulsions stabilized by native and heated cumin protein isolates showed pseudo-plastic fluid behavior and exhibited a decrease in their viscosities with proteins concentration increasing. But thermal treatments produced different effects on the flow behavior of emulsions formed by various protein concentrations, the flow index for heated cumin protein isolates emulsions increased at protein concentrations of 0.5 and 1.0%, but decreased at a concentration of 0.1%. These results might provide reference for the cumin protein processing and its application in food industry.
Keywords: Cumin protein isolates; emulsifying property; heat treatment; rheological property; structure.