Plants produce a wide variety of compounds, some of which have demonstrated protective effects against degenerative diseases in man. For example, consumption of cruciferous vegetables such as cauliflower, kale, broccoli, brussel sprouts and cabbage is associated with a reduced incidence of cancer. These plants are a unique source of the dietary compounds isothiocyanates, which are thought to confer some of the protective effects against cancer. However, the biochemistry of plants is very complex, and when plant compounds interact with mammalian physiology the numerous biochemical interactions can create an interactive system that is not easy to understand. A myriad of enzymes within plants, mammals, mammalian gut bacteria as well as chemical changes during food preparation can cause changes to compounds present in plant foods which can result in an alteration in the bioavailability of many phytochemicals.
Isothiocyanates are thought to confer protection against cancers because they are able to induce the phase-II detoxification pathway that can eliminate potential carcinogens from the body before they initiate cancers. In addition, they may be able to inhibit carcinogenic-activating enzymes and regulate apoptosis and cancer cell proliferation. Isothyanates are produced from a group of sulphur and nitrogen containing glycosides called glucosinolates present in cruciferous vegetables. The enzyme myrosinase (β-thioglucoside glucohydrolase), present in the plants as well as gut bacteria, is necessary for this reaction to take place. Although the glucosinolate content of the original plant can vary depending on growing and storage conditions, the presence of myrosinase is an equally important factor in isothiocyanate bioavailability. Because myrosinase is heat sensitive, long boiling of cruciferous vegetables can result in decrease production of isothyonates by 30 to 60 %.
Those people who eat more of the cruciferous vegetables have been shown to be protected from the development of cancers. A healthy diet should contain a wide variety of cruciferous vegetables on a frequent basis. Although it is difficult to predict and control the glucosinolate content of these vegetables, correct preparation can be controlled and should be understood in order to maximise bioavailability of the isothiocyanates. Cooking is important because it breaks open the cell walls and releases the chemicals contained within. However, over cooking can denature the myrosinase enzyme and decrease the production of the isothiocyanates. Some intestinal bacteria are also able to convert glucosinolates to isothiocyanates because they possess the enzyme myrosinase. Regular consumption of cruciferous vegetables may be able to increase the populations of these specific bacteria responsible for this conversion.
RdB
