Singlet oxygen quenching activities of various fruit and vegetable juices and protective effects of apple and pear juices against hematolysis and protein oxidation induced by methylene blue photosensitization

Effects of various fruit and vegetable juices on rubrene oxidation induced by a chemical source of singlet oxygen in a microemulsion system has been studied. The singlet oxygen quenching activities of fruit and vegetable juices were greatly different juices. The apple and pear juices exhibited the highest antioxidative activity among the tested juices in singlet oxygen-induced rubrene oxidation, showing 56.69% and 59.34% inhibition, respectively, The grape, kumquat, red cabbage, and spinach juices also showed relatively strong antioxidative activity against singlet oxygen induced rubrene oxidation. Lemon juice showed the least activity, resulting in 0.63% inhibition of rubrene oxidation. The singlet oxygen quenching activities of 1 mL of apple and pear juices were equivalent to 33.97 and 34.46 mg ascorbate, respectively. Singlet oxygen quenching activities of juices had very low correlation with ABTS radical scavenging activity (R-2 = 0.11) and total phenolic contents (R-2 < 0.1). However, a high correlation (R-2 = 0.66) was found between the ABTS radical scavenging activities and total phenolic contents of juices. The apple and pear juices also significantly inhibited both erythrocyte lysis and protein oxidation induced by fluorescence light illumination in the presence of methylene blue. Electron spin resonance (ESR) spectroscopy data showed that the protective activities of these juices against biological damages induced by photodynamic ways were, to at least some extent, due to their singlet oxygen quenching abilities. This represents first report on the singlet oxygen quenching activities of the apple and pear juices, and their protective activities against photodynamically induced biological damages.