Sunlight-Induced Lipid Oxidation and Degradation of Edible Oil Mediated by Hemoglobin: Implications for Food System Sustainability.

Lipid oxidation is one of the major factors affecting the quality, safety, and shelf life of edible oils. In this study, sunlight-induced oxidation of edible oil was investigated in an aqueous system using erythrocyte-derived hemoglobin (Hb) as a natural biocatalyst. Significant oxidation was observed only under visible-light irradiation in the presence of Hb and oxygen. The peroxide value (PV) increased rapidly, reaching 9.7 meq O2/kg within 2.5 h, followed by the degradation of unsaturated fatty acids, indicating the occurrence of secondary oxidation reactions. Proton nuclear magnetic resonance (1H NMR) analysis showed a 31.2% decrease in vinylic protons and a 36.9% decrease in bis-allylic protons, together with the appearance of an aldehydic signal at δ 9.5 ppm, confirming the formation of malondialdehyde (MDA). The generation of singlet oxygen (1O2) was supported by anthracene bleaching (33%) and its inhibition by sodium azide (NaN3), while the inhibitory effect of butylated hydroxytoluene (BHT) suggested the simultaneous involvement of radical-mediated oxidation pathways. Compared with Rose Bengal and potassium permanganate (KMnO4), Hb showed higher photodegradation activity, likely due to the combined contribution of singlet oxygen generation and ferryl-mediated (HbFe(IV)═O) hydrogen abstraction. Beyond advancing our understanding of the still underexplored mechanism of hemoglobin-mediated photooxidation, these findings provide a scientific basis for exploring food-derived hemoproteins as naturally abundant photosensitizers for the treatment of lipid-rich wastewater.