Hydrophobic interaction driving the binding of soybean protein isolate and chlorophyll: Improvements to the thermal stability of chlorophyll

Abstract Achieving the right color is a very important aspect to obtain a favorable appearance during the processing of soy-based products. Chlorophyll (Chl) presents a bright green color, however, it is not stable during processing and storage, which is a major problem that Chl-rich food has not yet overcome. Whether the addition of protein can improve Chl stability is unclear. This study investigated the effects of soybean protein isolate (SPI) on the thermal stability of Chl and interactions between SPI and Chl were investigated. Fluorescence spectra presented a static quenching in the binding of them with strong affinity of 6.3972 × 104 L/mol, and the hydrophobic interactions between SPI and Chl were predominant. Both the polydispersity index (PDI) values and particle size of the Chl-SPI mixtures were lower than SPI alone, indicating that the molecular weight distribution was more uniform and stable. The fluorescence distribution demonstrated that the addition of SPI caused a significant change in the distribution of Chl fluorescence. Moreover, molecular modeling displayed the conformation of Chl-SPI complex, and revealed the important role of Mg2+ and the phytol residue from Chl in binding with SPI. The present study enriched our understanding of interaction mechanisms involving SPI and Chl, providing some significant and interesting information for the development of novel plant-derived proteins products with stable green color.