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Some grapes have marked antioxidant activity.

Pedro Ximenez, also known as PX, is the name of a white grape grown in certain regions of Spain. It is used to create a varietal wine--an intensely sweet, dark dessert sherry. Musts from sun-dried grapes of Pedro Ximenez are rich in polyphenols and sugars, and interactions occur between them.

The autoxidation of catechin, a polyphenolic antioxidant plant secondary metabolite, is caused by ferrous iron. But the oxidation process is inhibited by a mixture of glucose and fructose compounds similar to those found in the musts of dried grapes. Spanish scientists extracted the phenolic fraction of musts from these dried grapes and then identified and quantified the phenolic compounds using high-performance liquid chromatography.

The evolution of the phenolic content from the musts helped to explain to the researchers that there was a fourfold increase in most of the phenolics they identified. Catechin was the most abundant phenolic. The musts and the phenolic fractions exhibited high antioxidant activity when analyzed using various established assays. This high antioxidant activity found in the assays involved the formation of hydroxyl radicals, deoxyribose degradation, and DNA oxidation processes. The antioxidant activity was partially due to the presence of sugars in the musts.

The researchers also studied the glycation of albumin by incubating bovine serum albumin with a concentration of glucose and fructose, similar to that found in the musts. Under these conditions, the phenolic fraction from must inhibited, by 76%, the formation of advanced glycation end products (AGEs). These compounds are the result of a chain of chemical reactions that occur after an initial glycation reaction. A similar inhibition of the AGEs was observed when the musts were directly incubated with albumin. The results indicate that the musts and the phenolic fraction of sun-dried Pedro Ximenez grapes possess marked antioxidant activity.

Food manufacturers have added AGEs to foods, especially in the last 50 years, as flavor enhancers and colorants to improve appearance. Foods with significant browning or caramelization activity or those products to which preformed AGEs have been added can be exceptionally high in proinflammatory compounds. Glycation may also contribute to the formation of acrylamide, a potential carcinogen, during cooking.

Further information. J. Peinado, Department of Biochemistry and Molecular Biology, Building Severo Ochoa, University of Cordoba, Campus Rabanales, 14014 Cordoba, Spain; phone: +34 957 21 85 90; email:
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Publication:Emerging Food R&D Report
Date:Sep 1, 2010
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