Broccoli Varieties Differ in Potential Anticarcinogenic Activity

In a ground-breaking study, Agricultural Research Service scientists have screened broccoli varieties to see if they induce activity of a key enzyme in mammals that may protect against certain cancers.

Agricultural Research Service plant geneticist Mark W. Farnham at ARS’ U.S. Vegetable Laboratory in Charleston, S.C., worked with scientists in the Brassica Chemoprotection Laboratory at Johns Hopkins University’s School of Medicine, Baltimore, Md. The scientists evaluated a diverse collection of broccoli (Brassica oleracea) varieties for their ability to stimulate what’s called a mammalian detoxification enzyme--which helps protect mammals against development of cancer.

In 1996 and 1997, Farnham grew 71 USDA broccoli varieties and five commercial hybrids in the field, and then took extracts from each one. In these extracts, the scientists looked for a chemoprotective compound called glucoraphanin. A derivative of glucoraphanin spurs mammals to induce activity of detoxification enzymes. The scientists found a 30-fold variation in glucoraphanin and the activity of these enzymes among the broccoli tested. In the future, scientists could use the enzyme activity to gauge a broccoli variety’s anti-cancer potential.

Data from several previously published studies have shown that people who eat cruciferous vegetables like broccoli have a lower incidence of colon and rectal cancers. Occurring in two out of 1,000 people, these account for 15 percent of all cancer deaths.

Broccoli florets and young seedlings are rich sources of glucoraphanin and its breakdown product, sulforaphane. Sulforaphane is a potent inducer of mammalian detoxification enzyme activity and inhibits early tumor growth in rodent models.

Scientists know little about variations of glucoraphanin and sulforaphane in broccoli varieties. If genetic variation among varieties does exist, then breeders could exploit it to develop new varieties with greater levels of the protective compounds. And eating such improved broccoli might stimulate an enhanced chemoprotective response against cancer.

ARS is the chief scientific research agency of the U.S. Department of Agriculture.

Scientific contact: Mark Farnham, ARS’ U.S. Vegetable Laboratory, Charleston, S.C., phone (843) 556- 0840, fax (843) 763-7013, mfarnham@awod.com