THE ANTIOXIDANT PROPERTIES OF PHENOLIC MOLECULES IN RELATIONSHIP WITH THE pH OF ENVIRONMENT REACTION

Abstract

THE ANTIOXIDANT PROPERTIES OF PHENOLIC MOLECULES IN RELATIONSHIP WITH THE pH OF ENVIRONMENT REACTION Some epidemiological evidence suggests beneficial effects on human health from a diet rich in fruit, vegetables and certain types of beverages such as tea and wine (1,2). These compounds do not have nutritive properties but they have a functional role in the human organism. Some studies have investigated the effect of pH on the antioxidant properties of polyphenols (3,4) and have reported that the pH-dependent behaviour is related to hydroxyl deprotonation. However, these studies did not compare the antioxidant activity of various classes of polyphenols and did not take into account the acidic pH. The aim of this study was toevaluate either the antioxidant or pro- oxidant behaviors of various polyphenol compounds by the crocin bleaching assay (5-7) in order to investigate the influence of two different pH levels. Thirteen polyphenols were analysed. They were used at 1 mmol/L in a phosphate buffer (pH7.4) and in synthetic wine (pH3.5). The myricetin, quercetin and kaempferol were prepared at concentrations of 0.5mmol/L in both pH, because with an increasing concentration of these compounds, a decreased sensitivity of the method was observed .The behavior of these molecules were analysed at pH 3.5 to simulate the food source; on the other hand, the same compounds were evaluated in a reaction mixture at pH 7.4 to simulate the in vivo condition. The position and the total number of hydroxyl and methoxy groups influence the magnitude and mechanism of the antioxidant activity. The flavonols and flavan-3-ols reveal differences in antioxidant property only at physiological pH, whereas for phenolic acids, both pH 3.5 and 7.4 determine a diversification in antioxidant potential in relationship to their chemical structure. The cinnamic acids are more active than the respective benzoic acids at both pH levels. Data produced indicate that the antioxidant properties of polyphenol compounds are strongly influenced by pH level. The polyphenolic compounds are more sensitive to pH change than to the number and position of substitution groups. Reference 1 Lotito, S.B., Frei, B., 2006, Free Radical Biology & Medicine ,41, 1727–46. 2Fernandez-Pachon´, M.S.,Villaño,D.,Garcıa-Parrilla, M.C.,Troncoso, A.M., 2004. Analıtica Chimica Acta 513, 113–8. 3Tyrakowska, B., Soffers, A. E. M. F., Szymusiak, H., Boeren, S., Boersma, M.G., Lemanska, K., Zielinski, R., Vervoort, J., Rietjens, I.M.C.M., 1999, Free Radical Biology & Medicine 27, 1427– 36 4 Lemanska, K., Szymusiak, H., Tyrakowska, B., Zielinski, R., Soffers, A.E.M.F., Rietjens, I.M.C.M., 2001, Free Radical Biology &Medicine 31, 869–81. 5Tubaro F, Micossi E,Ursini F. Journal American Oil Chemical Society 1996, 73, 173–9 6Ordoudi, S. A., & Tsimidou, M. Z. 2006, Journal of Agricultural Food Chemistry, 54, 1663–71. 7Di Majo D,La Guardia M,Giammanco S,La Neve L,Giammanco M. Food Chemistry 2008,111,45-9