Inhibitory effect of whole strawberries, garlic juice or kale juice on endogenous formation of N-nitrosodimethylamine in humans

In vitro and in vivo experiments were performed on inhibition of nitrosation by strawberry, garlic, and kale extracts. Strawberry, garlic, and kale extracts inhibited nitrosation in vitro. However, garlic extract has a greater ability to inhibit the chemical nitrosation in vitro than strawberry and kale extracts. The garlic methanol-soluble fraction of the garlic extract was fractionated into G1-G4 fractions by Prep-l-C. Fraction G1 inhibited N-nitrosodimethylamine (NDMA) formation by 84 +/- 1%. We studied the formation of the carcinogen NDMA in humans after administration of nitrate (400 mg/day) in combination with an amine-rich diet and its possible inhibition by administration of whole strawberries (300 g), garlic juice (200 g: 75 g garlic juice in drinking water), or kale juice (200 g) in 27 males and 13 females (ten healthy volunteers in each group) of age 24 +/- 3 years. Nitrate intake resulted in a significant rise in mean salivary nitrate and nitrite concentrations. Also, nitrate excretion in urine during the experimental day was significantly increased compared with the control days. When whole strawberries, garlic juice, or kale juice was provided immediately after an amine-rich diet with a nitrate, NDMA excretion was decreased by 70, 71, and 44%, respectively, compared with NDMA excretion after ingestion of an amine-rich diet with a nitrate. These results suggest that consumption of whole strawberries, garlic juice, or kale juice can reduce endogenous NDMA formation. (C) 2002 Published by Elsevier Science Ireland Ltd.