Characterization of the extreme pH-induced molten globule state of soy protein isolate and its influence on functional properties

The molten globule (MG) state of soy protein isolate (SPI) is an intermediate stage between the natural and denatured states, where the protein is undergoing unfolding. In this study, we investigated the conformational changes of SPI induced to form the MG state using polar acid (pH 1.0–3.0) and polar alkaline (pH 10.0–12.0) solutions. Our findings indicate that extreme pH treatment can induce the transformation of SPI into the MG state, resulting in a series of structural changes. Compared to SPI, the foaming capacity of the MG state improved by 77–113%, and foam stability improved by 60–124%, resulting in noticeably improved foaming characteristics. Similarly, the emulsification property and emulsification activity of MG state were remarkably enhanced. This study offers new understanding of the MG state of SPI and offers a theoretical basis for developing food, pharmaceutical, and cosmetic products with excellent foaming and emulsifying properties.