Levels of the antioxidant glutathione in edible fruit species and the effect of irradiation quarantine treatment on glutathione levels in papaya

Glutathione (GSH) is a direct antioxidant found in all aerobic life forms. The glutathione molecule is a key player in the detoxification of xenobiotics and reactive metabolic species. The ubiquity of this compound enables humans to increase their plasma GSH levels by incorporating fresh fruits, vegetables and freshly cooked meats in their diet. Eighteen scientifically verified fruit varieties were selected for study and include many tropical and subtropical species for which their glutathione content has yet to be documented. Low-dose irradiation is approved by the United States Food and Drug Administration (FDA) to reduce pest populations in fruits and vegetables and increase their shelf life. A collaborative study was instituted with the Hawaii USDA to determine how irradiation of papaya fruit affects glutathione concentrations. Fresh, frozen fruit samples were processed down to a dry powder and subject to several extraction procedures to remove protein and retrieve glutathione. GSH analysis was conducted using a 96-well plate spectrophotometric endpoint assay that relies on an enzymatic recycling reaction mediated by glutathione reductase. This work identified several fruit varieties that contain high concentrations of glutathione: blueberry ‘Rubel,’ ‘Sprite’ melon, guava ‘Pink Acid,’ litchi ‘Kaimana,’ and yellow passion fruit. Data evaluating papaya ‘Rainbow’ treated with 0–1000 Grays of irradiation indicated that the glutathione concentration in papaya is not significantly affected by irradiation practices. Diets high in fruits and vegetables are associated with reduced disease risk and greater longevity. GSH is an anticarcinogenic compound; this research identified specific fruit varieties that are high in glutathione and may further warrant their incorporation in the American diet.