A comparative study of thermally induced conformational changes occurring in food-grade seed proteins

The conformational properties of the purified amaranth and soybean 11S seed storage globulins were comparatively studied as a function of temperature i.e., 20 to 85 degrees C (up to the onset of denaturation). At temperatures investigated between 20 degrees to 60 degrees C both globulins experienced little change in secondary structure as a function of change in temperature being characterized by low levels of a-helical and high beta-sheet structure content. Above 80 degrees C the soybean globulin underwent major conformational changes as evidenced by major decreases in beta-sheet and corresponding increases in random coil. In contrast, the amaranthglobulin exhibited little change in secondary structure with change in temperature over the entire temperature range (20 degrees-85 degrees C) investigated in this study. Above the temperatures of 70 degrees and 60 degrees C for the amaranth and soybean globulins, respectively, both globulins were observed to experience a progressive loss of tertiary structure upon further heating. In the case of the amaranth globulin, the observed lack of secondary structure alteration combined with the loss of tertiary structure would support the notion of the formation of a molten globule-type structure at elevated temperatures prior to denaturation. On the other hand, a molten globule state was not found to occur in the soybean globulin and may be a reason for the previously reported differences in their thermal functional properties.