Relationship between Molecular Flexibility and Emulsifying Properties of Soy Protein Isolate-Glucose Conjugates

At present, the structure activity relationships of soy protein isolate are still not well understood. In this paper, the relationship between molecular flexibility and emulsifying properties of soy protein isolate and soy protein isolate glucose conjugates were investigated. The Maillard reaction was carried out at different temperature conditions (50 C, 60 C, 70 C, 80 degrees C, and 90 degrees C) under a specific wet condition. Meanwhile, structural properties including surface hydrophobicity (H0), molecular flexibility and secondary, tertiary, quaternary structures, and the free sulfhydryl group (-SH) content were measured. The results showed that there was a good correlation between molecular flexibility and emulsifying properties, and the correlation coefficients was 0.920 (P < 0.01) for emulsifying activity and 0.952 (P < 0.01) for emulsion stability. Compared with soy protein isolate, the Ho of samples at different temperatures first increased and then decreased reaching a maximum at 70 degrees C, a red shift occurred during the whole given reaction conditions shown by the intrinsic fluorescence spectrum, and the free sulthydryl content also displayed a marked increase (P < 0.05). At the same time, the particle size gradually became smaller as the degree of grafting increased. The contents of fi-turn and random coil increased at the cost of alpha-helix and fi-sheet contents, as evidenced by Fourier transform infrared results. The findings could provide a deep insight into the structure function relationship of soy protein isolate glucose conjugates, thus providing theoretical guidance for further research of soy proteins.