A substantial research effort is being devoted to better understand the protection against various diseases that epidemiological studies have shown to be provided by certain fruits and vegetables. Researchers generally believe that this protection comes from the activity of antioxidant compounds, particularly polyphenols, found in abundance in many fruits and vegetables.
Explore this issueDecember/January 2007
Polyphenols are a group of chemical substances that are characterized by the presence of more than one phenol group per molecule. These compounds are responsible for providing the coloring of many plants. Various polyphenols have been shown in epidemiological studies to prevent cancers of the colon, esophagus, liver, stomach, lung, breast, pancreas and skin. The result is that a considerable amount of attention is now being focused on polyphenols, and particularly the category of polyphenols known as flavonoids which have been demonstrated in a number of studies to be powerful antioxidants.
Antioxidants are believed to help prevent disease by binding with and destroying free radicals, reducing oxidative damage to cells and biochemicals. (For example, oxidation by free radicals is a precursor to cardiovascular disease.) Therefore, it is becoming increasingly important to identify antioxidant compounds in foods, as well as in urine, tissue and plasma samples, in order to develop disease models and improve the design of epidemiological studies.
One of the more challenging aspects of this research is the identification and accurate measurement of these antioxidants amid the many types and varieties of fruits and vegetables where the compounds can be present in different quantities. For example, Dr. Ronald L. Prior of USDA has determined that the total antioxidant activity of a strawberry is 16 times that of a honeydew melon.
The standard approach for the identification of flavonoids combines the separation capabilities of high-performance liquid chromatography (HPLC) with the pinpoint molecular identification capabilities of mass spectroscopy (MS). This approach has been involved in the discovery of many polyphenols and provides the gold standard of positive identification. On other hand, the large number of polyphenols found in many fruits and vegetables and the large universe of potential plants whose antioxidant activity is of interest create the need for a method of quickly screening food, tissue and plasma samples for a large number of potential antioxidants in a minimal amount of time.
Investigation of Coulometric Array Detection
HPLC/MS is not well suited for this task because of the limited ability of HPLC to separate closely related antioxidants and the relatively large amount of time required for MS analysis.