The effect of extreme acid-induced soybean glycinin molten globules state on foaming ability

The molten globule (MG) state of soybean glycinin (11S), which is an unfolding quasi-intermediate state, has been achieved in an extremely acidic pH range (pH 0.5-3.0). By endogenous fluorescence, near and far ultraviolet circular dichroism, it was found that the secondary structure of soybean 11S protein was retained but the tertiary structure was stretched at pH 1.0. The-1-anilino-8-naphthalene sulfonate (ANS) fluorescence spectrum and particle size measurement revealed that soybean 11S protein at pH 1.0 had greater hydrophobicity, and the particle size was between native state and fully denatured state. Taken together, the results show that soybean 11S protein could exist in a molten globule state at pH 1.0. The foaming characteristics of this state were analyzed according to foaming overrun and the foam microstructure. Relative to the native state, the foaming properties and foaming stability of MG-11S at pH 1.0 were significantly improved by 3.4 times and 3.1 times, respectively, and the mean life index of foam was significantly improved and the sizes of the bubbles generated were smaller by a polarizing microscope. Moreover, the zeta potential results show that the MG-11S system was relatively stable, with greater viscosity and lower surface tension. This study advances the understanding of the acid-induced MG state of soybean 11S protein and provides a theoretical basis to produce proteins with excellent foaming properties, which is helpful for applications in the food, biomedical and non-food fields.