Conjugation of soy protein isolate (SPI) with pectin: effects of structural modification of the grafting polysaccharide

Recently, there has been a great interest in enhancing the emulsifying properties of soy protein isolate (SPI) by Maillard reaction. As a commonly-used grafting polysaccharide, pectin has proved useful in modifying proteins. However, effects of its structural characteristics on conjugation are still not fully understood. To address this problem, we employed alkaline or/and enzymatic treatments to modify pectin and obtained three modified samples. Structural characteristics of pectin, including the molecular weight, degree of methoxylation and acetylation, and monosaccharide compositions were measured. When conjugated with SPI, pectin with lower molecular weight and less main chains induced higher conjugate yield. Fluorescence intensity and surface hydrophobicity of all conjugates markedly reduced compared to the original SPI, suggesting a more loosened protein structure after Maillard reaction. In this study, the enzymolysis pectin proved an optimum grafting polysaccharide considering the simple preparation procedures and the highest emulsifying properties of its resulting conjugates.