URBANA, Ill. There was bad news, then good news from University of Illinois broccoli researchers this month. In the first study, they learned that frozen broccoli lacks the ability to form sulforaphane, the cancer-fighting phytochemical in fresh broccoli. But a second study demonstrated how the food industry can act to restore the frozen vegetable's health benefits.
"We discovered a technique that companies can use to make frozen broccoli as nutritious as fresh. That matters because many people choose frozen veggies for their convenience and because they're less expensive," said Elizabeth Jeffery, a U of I professor of nutrition.
"Whenever I've told people that frozen broccoli may not be as nutritious as fresh broccoli, they look so downcast," she added.
As little as three to five servings of broccoli a week provides a cancer-protective benefit, but that isn't true for bags of broccoli that you pluck out of your grocery's freezer, she noted.
The problem begins when soon-to-be-frozen broccoli is blanched, or heated to high temperatures, to inactivate enzymes that can cause off-colors, tastes, and aromas during the product's 18-month shelf life, she explained.
The extreme heat destroys the enzyme myrosinase, which is necessary to form sulforaphane, the powerful cancer-preventive compound in broccoli, she said.
"We know this important enzyme is gone because in our first study we tested three commercially frozen broccoli samples before and after cooking. There was very little potential to form sulforaphane before the frozen broccoli was cooked and essentially none after it was cooked as recommended," said Edward B. Dosz, a graduate student in Jeffery's laboratory.
In the second study, the researchers experimented with blanching broccoli at slightly lower temperatures instead of at 86C, the current industry standard. When they used a temperature of 76C, 82 percent of the enzyme myrosinase was preserved
|Contact: Phyllis Picklesimer|
University of Illinois College of Agricultural, Consumer and Environmental Sciences