Researchers at the University of Warwick in the UK found that boiling, shredding and freezing cruciferous vegetables can destroy much of their acclaimed cancer fighting properties.
A study carried out at the University of Warwick, in the UK, shows that simple boiling can destroy most of the cancer-fighting phytochemicals in cruciferous plants like broccoli, cauliflower, Brussel sprouts and kale. Boiling is one of the most widespread forms of preparing vegetables and traditionally considered more healthful than other cooking methods.
Cruciferous vegetables are natural cancer-fighters
Over the last decades, research and clinical trials have revealed that cruciferous vegetables are laden with healthy substances that can significantly decrease the risk of cancer. Glucosinolates are secondary plant metabolites that can be turned into cancer-fighting substances known as isothiocyanates. For a long time, scientists were not sure what the impact of cooking is on the curative potential of these precious phytochemicals.
The UK research team, led by professors Paul Thornalley and Lijiang Song from the University of Warwick, carried out a series of tests to see how the cooking, storing and handling of broccoli and similar vegetables affects their glucosinolate levels. They went to the local organic market and purchased a generous sample of broccoli, cauliflower, Brussel sprouts and kale. The idea behind getting vegetables as fresh as possible was that the scientists could look at how fast their glucosinolate content decreased, depending on the different storage and cooking methods used. Thornalley and Song investigated four popular cooking methods, namely boiling, steaming, microwaving and stir-frying.
Green veggies are best served fresh and raw
Surprisingly, boiling had the most devastating effect on the nutrient content of the vegetables. After just 30 minutes of boiling, the glucosinolate content dropped by 77% in broccoli, 75% in cauliflower, 58% in Brussels sprouts and 65% in kale. Storing the vegetables at room temperature or in a refrigerator for 7 days did not lead to any significant losses in cancer-fighting substances, although the vitamin content of fruits and vegetables is known to decrease as they lose freshness.
The scientists were also curious about what happens to cruciferous plants when they exposed to other popular treatments, such as freezing and shredding. Consequently, they found that freezing causes a significant loss of cancer-fighting substances, and may result in massive fractures of plant cell walls during thawing. Shredding was found to lead to a loss in glucosinolates of up to 75% over just several hours.
Fresh broccoli and cauliflower are rich in vitamin C, carotenoids, dietary fiber, folate and vitamin K. Brussel sprouts can provide B complex vitamins, iron, phosphorus and potassium, while kale is an exceptional source of lutein, zeaxanthin (which promotes eye health), as well as a good vegan source of calcium.
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