Effects of Different Processing Methods on Induction of Quinone Reductase by Dietary Broccoli in Rats

Broccoli belongs to a group of cruciferous vegetables characterized by its content of glucosinolates, secondary metabolites that, upon hydrolysis, release bioactive isothiocyanates (ITCs). Sulforaphane, the major ITC from broccoli, is believed to protect the body from cancer by induction of detoxification enzymes such as quinone reductase (QR). Sulforaphane provides powerful protection against carcinogenesis, mutagenesis, and other forms of toxicity by electrophiles and reactive forms of oxygen. The purpose of this study was to investigate the effects of processing methods on the ability of broccoli to induce QR in various rat tissues. Male F344 rats (four per group) received an AIN 76B-40 diet containing either 0% or 20% broccoli processed by different methods (dehydrated, freeze-dried, or freeze-dried and hydrolyzed) for 5 days. Colon tissues of rats receiving dehydrated, freeze-dried, and hydrolyzed broccoli diets showed QR induction of 9.1-, 10.5-, and 6.4-fold, respectively. Induction of QR by dehydrated broccoli in the liver and kidney was significantly less robust than in colon, being 2.3- and 1.6-fold over control, respectively. These results suggest that freeze-drying and dehydration are promising approaches for providing the public with the functional benefits of broccoli consumption.