It probably won’t get you off the hook with mom, but researchers say that the nutritional content of broccoli tends to fluctuate wildly. While a single serving from one head could pack enough antioxidants and cancer fighters to keep you going for a few days, eating an entire other head could do bupkus.
From the University of Illinois at Urbana-Champaign
Broccoli may not always carry high nutritional content, researchers find
10/7/02
CHAMPAIGN, Ill. — Broccoli packs a healthy punch, but not necessarily every time you eat it, say researchers at the University of Illinois at Urbana-Champaign.
Such is the picture coming into focus amid a lengthy series of experiments that someday may result in broccoli with consistent health benefits that growers can produce, store operators can stock and consumers can demand.
The healthiest broccoli contains high levels of antioxidants ? carotenoids, tocopherols, ascorbic acid and flavonoids ? that inhibit free radical reactions in the body, reducing oxidative damage and promoting cardiac health. The carotenoids lutein and zeaxanthin also have been associated with a reduced risk of macular degeneration. Other component glucosinolates called glucoraphanin and glucobrassicin protect against cancer.
“You can buy a head of broccoli, cook it and get a good dose of compounds that can reduce the oxidative stress on your cells or contain a high level of glucosinolates that can reduce the incidence of cancer,” said John A. Juvik, a plant breeder in the department of natural resources and environmental sciences. “A good single serving may protect you for a few days. Then you can go to the store a week later and buy another head that has almost none of these beneficial compounds.”
For a recent study in the Journal of Agricultural and Food Chemistry reported by five Illinois scientists, eight genotypes of broccoli were analyzed. The genotypes represented commonly grown varieties in the Midwest which, based on previous findings, contain a wide range of antioxidant compounds. Researchers found that carotenoids (both lutein and zeaxanthin) accounted for often far-ranging variability within broccoli?s fat-soluble compounds, but they could not account for variations of the water-soluble ones.
“We can see that there are differences among the broccoli genotypes,” said Barbara P. Klein, a professor in the department of food science and human nutrition. “We cannot yet say that the overall differences are due to any specific compound, but the carotenoids are definitely responsible for one part of the variability.”
Anne Kurilich, now a research scientist with the USDA Phytonutrient Laboratory in Maryland, used the oxygen radical absorbance capacity (ORAC) assay, a tool that for the past decade has been widely used to analyze antioxidants and other components in fruits, vegetables and wines. The Illinois researchers measured the antioxidant capacities of the fat and water-soluble extracts taken of broccoli plants.
“Broccoli differs,” Klein said. “Some cultivars have more positive health-promoting compounds in them. Broccoli is not just broccoli. Some varieties are higher in antioxidant content, in vitamin content and in nutrients. This most recent study tells us that we are still missing some information. There may be some contributing compounds that we are not measuring or it may be that several components have a synergistic effect.”
The researchers have since used a cell-culture technique that mimics what happens in an actual living human liver cell to see how well the various antioxidant compounds prevent oxidation. That study is being prepared for publication.
In previous research, they created a database of 50 broccoli varieties and their amounts of antioxidants and cancer-fighting compounds. Some varieties had 10 times the vitamin E, twice the vitamin C and eight times the beta-carotene. The broccoli varieties also ranged widely in their amounts of glucosinolates, which break down carcinogens and suppress the growth of cancer tumors.
Environment, as well as plant genetics, appear to affect broccoli?s contents. In particular, the amount of glucobrassicin varies greatly, said Elizabeth Jeffery, a professor in the department of food science and human nutrition and of pharmacology in the College of Medicine at Urbana-Champaign. “This compound is produced when insects or animals bite the plant. More than 50 percent of the variation in glucobrassicin content in broccoli is determined by the environment in which the crop is grown,” she said.
Juvik?s lab now is evaluating data on the antioxidant vitamin levels that were found in 12 genotypes of broccoli grown over four years in four different environments. While the study is not ready for publication, Juvik said, “we are seeing genetic variation, for instance, in beta carotene ? vitamin A ? ranging five- to eight-fold, from trace levels to a healthy dose.”
Those findings, he said, eventually may help determine if plant scientists should be focusing their attention on environmental or genetic adjustments in their approach to improving broccoli plants.
Understanding the mechanisms that trigger the release of important compounds may open the door to genetically regulating the amounts of health-promoting compounds that crop plants produce, Jeffery said. “More work is needed to get to that point, but one day we might breed broccoli plants that produce more of these compounds.”
At present, consumers usually cannot know what kind of broccoli they buy at a grocery store, and often store managers may not know what varieties they carry at any given time, Juvik and Klein said.
Co-authors of the Agricultural and Food Chemistry paper were Jeffery, Juvik, Klein; Matthew Wallig, a professor of veterinary pathobiology; and Kurilich, who did graduate and doctoral research with Juvik, Jeffery and Klein.
The U.S. Department of Agriculture and the Illinois Council on Food and Agricultural Research funded the research.
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