Effects of Folic Acid and Caffeic Acid on Indirect Photo-oxidation of Proteins and Their Costabilization under Irradiation

Proteins, vitamins, and phenols are often present together in foods, but they are sensitive to environmental factors. Folic acid (FA), a synthetic form of folate, decomposes under light, leading to protein oxidation. Caffeic acid (CA), a phenolic acid, exhibits remarkable activity for scavenging reactive molecules. The exploitation of their interactions offers opportunities for designing the stabilizing system. In this study, FA-photodecomposition-induced protein (β-lactoglobulin, α-lactalbumin, bovine serum albumin, and β-casein) damage and its inhibition by CA were investigated in terms of protein composition and structural change. The results indicated that FA photoproducts oxidized the proteins via the electron transfer pathway, leading to degradation, aggregation, and unfolding. At the same time, photostability of FA, CA, and proteins in the tertiary mixture was better than that of any individual components. The antioxidant activity of the proteins contributed to their protection for FA. CA and its products inhibited FA photodecomposition and the photodecomposition-induced protein oxidation by trapping excited states.