Total Phenolic Content And Antioxidant Potential Of Commercial Grape Juice

Abstract

LEARNING OUTCOME: antioxidant potential of commercial grape juice to that of red wine.The phenolic antioxidants in red wine have been proposed as an explanation for the lower death rate from coronary heart disease (CHD) in France. The death rate is lower even though the French consume saturated fat and cholesterol in amounts comparable to those consumed by Americans. The oxidative modification of low-density lipoprotein (LDL) has been linked to the development of atherosclerosis, the principle cause of CHD. The phenolics in red wine and grapes have been shown to prevent the oxidation of human LDL in vitro. The purpose of the present study was to determine the phenolic content and antioxidant potential of commercial grape juice. The phenolic content of six samples of red (Concord) grape juice and three samples of white grape juice (Welch, Inc.) and a sample of red wine (Petite Sirah without added sulfite) was determined with the Folin-Ciocalteu colorimetric assay using gallic acid as the standard. The antioxidant potential of these samples was also determined by measuring the hexanal formed by the copper mediated peroxidation of freshly prepared LDL, which had been isolated from normolipidemic males, using headspace gas chromatography. All samples were measured in duplicate. The concentration of total phenolics in the white and red grape juice samples varied from 254 to 389 mg/L gallic acid equivalents (GAE) (mean=324) and 1407 to 2246 mg/L GAE (mean=1760), respectively. The red wine contained 3630 mg/L GAE. Based on hexanal formation, when samples of juice and red wine were diluted to contain the equivalent of 10 μM gallic acid, white and red grape juice inhibited the oxidation of LDL on average by 72 and 62%, respectively. Petite Sirah inhibited LDL oxidation by only 52%. However, when inhibition was based on the concenttration of total phenolics concentration the antioxidant activity of the white juice was 15% that of red wine, whereas red grape juice was 60% that of red wine. Thus, our results confirm that grape juice, especially red grape juice, is a significant source of phenolic antioxidants that protect against CHD.