Fluorescence due to interactions of oxidizing soybean oil and soy proteins

Soy proteins with soybean oil (9:1,w/w) were stored at 60°C to investigate the changes in intrinsic fluorescence during oxidation. The front-surface fluorescence of the oxidized samples showed excitation and emission maxima at 355 and 440 nm respectively. The fluorescent compounds were soluble in the organic layer of the chloroform–methanol (2:1,v/v). The solution fluorescence showed an excitation maximum at 365 nm and an emission maximum at 450 nm, and the intensity increased during storage. The interactions of oxidizing soybean oil and soy proteins also resulted in decreases of protein solubility, soluble protein hydrophobicity, and free amino groups of proteins. With an antioxidant (BHT) addition, the changes in fluorescence and in protein properties were inhibited. The intensity of the solution fluorescence showed high correlation with TBA value (r=0.968) and protein solubility (r=−0.979), which could serve as an indicator for oxidative deterioration of soy proteins and soybean oil systems.