Health & Horticultural Research at UNH: Leafy Greens at the Leading Edge
Research scientists in the University of New Hampshire Departments of
Plant Biology and Human and Animal Nutrition have teamed with Extension
educators and New Hampshire vegetable growers to conduct research into
the health-promoting benefits of plant compounds known as phytonutrients.
The UNH Carotenoid Project focuses on compounds called xanthopyll carotenoids, found in high concentrations in leafy green vegetables like kale and spinach. Health researchers believe that eating plant foods rich in these carotenoids may help protect people against macular degeneration, a leading cause of blindness in older adults.
The Carotenoid Project
Funded by an $800,000 grant from the U.S. Department of Agriculture’s
Initiative for Future Agriculture and Food Systems, the four-year Carotenoid
Project features an interdisciplinary collaboration between assistant professor
of plant biology Dr. Dean Kopsell and Dr. Joanne Curran-Celentano, an associate
professor of animal and nutritional sciences with a longstanding interest
in the role of carotenoids in human health.
Curran-Celentano’s team is studying how well humans who eat lutein-rich food or take lutein supplements absorb the carotenoids and deposit them into the macula lutea of their eyes.
Kopsell and his team have examined the genetic, cultural and environmental factors that maximize the concentration of xanthopyll carotenoids lutein and zeaxanthin in leafy greens like kale and spinach. They’ve modified the sulfur content of soils to moderate the strong flavors in kale that some people don’t like. Kopsell has also sampled and analyzed a wide range of vegetable crops grown at six New Hampshire farms for their carotenoid content.
The field research has focused primarily on kale.
More than just a pretty garnish
Although many people know kale primarily as that coarse ruffled leaf
placed alongside the “real food” on a restaurant plate, nutritionists
have long recognized the superior food value of this leafy crop. A rich
source of vitamins A and C, dietary fiber, iron, potassium and manganese,
kale also rivals dairy products as a source of calcium. And new research
findings suggest that kale may also deliver a host of health benefits through
its high levels of phytonutrients.
Among all vegetables, kale ranks highest in its concentration of the xanthophyll carotenoids lutein and zeaxanthin, the yellow-orange pigments plants evolved to help protect their tissues against the harmful effects of excess solar radiation. Lutein and zeaxanthin concentrate in the macula lutea of the human retina, where scientists believe the phytocompounds may serve a similar function, absorbing and dispersing ultraviolet radiation to help protect against cataracts and macular degeneration.
Growing carotenoid-rich crops with improved flavor
Kopsell’s research involves studying the genetic, vegetable cultural
and environmental factors that that favor high concentrations of carotenoids,
and manipulating soil fertility factors to make these nutrient-dense crops
taste better.
According to Kopsell, plants evolved carotenoids as “accessory pigments” for self-protective purposes. “Plants use only about one or two percent of the light energy falling on the leaf surface for photosynthesis,” Kopsell says. “In plants, lutein and zeaxanthin play a role in absorbing light outside the red and blue range and funneling it away, in essence acting as a chemical “sun black” that helps protect the pant from excessive radiation.” Medical researchers theorize that carotenoids play a similar role when they concentrate in the macula lutea, the region of highest visual acuity in the human eye.
Kopsell analyzed the carotenoid content of dozens of kale varieties, discovering the varieties with the highest concentrations had two and a half times the carotenoid levels of those with the lowest concentrations.
In greenhouse research, Kopsell found that manipulating the amount of sulfur in the soil could alter the flavor of kale without affecting its carotenoid content. “We thought if we could grow kale with a milder, less bitter, less acrid flavor, it would make it more acceptable to consumers,” Kopsell said. He found that soils with less sulfur produce greens with a milder, less pungent flavor, but no loss of carotenoids.
Last summer, Kopsell worked with Extension educators Steve Turaj in Coos County and George Hamilton in Hillsborough to bring his greenhouse research into the field. Three vegetable farmers agreed to plant three different kale varieties in test plots with three levels of sulfur added to the soil. Participants at well-attended twilight meetings in both counties heard about the research and sampled three different high-carotenoid kale varieties grown under three different levels of sulfur fertility.
“At one of our twilight meetings we had 150 people and more than half of them tasted the kale samples from the three different plots,” said Hamilton . “They couldn’t believe the difference between the high-, medium- and low-sulfur treatments.”
“People derive benefits from only those vegetables they’re willing to eat,” says Turaj with a laugh. However, Kopsell noted that some kale tasters in each group actually prefer the stronger-tasting kales grown in high-sulfur soil.
Human feeding trials
Last summer, co-investigator Dr. Joanne Curran-Celentano began
work on the human
nutrition component of
the study, in which human volunteers will either consume spinach or lutein
supplements over several months, then measure how much lutein gets absorbed
into their bloodstreams and deposited into the macula lutea of their eyes.
Celentano’s team recruited 50 test subjects, divided into five groups. The control group receives a placebo. Two groups received lutein supplements, one with a higher, the other with a lower dose of lutein. The other two groups eat a prepared dish five days a week containing spinach grown at the UNH research farm. One group of spinach eaters gets the high-lutein 'Spinner' spinach variety; the other eats 'Springer' spinach, a variety containing 33 percent less lutein.
Curran-Celentano says the project used spinach instead of kale to make it easier to recruit volunteers, since more Americans eat spinach than kale. She and her team hope to complete the feeding trial and analyze the data this fall.
Kopsell recently accepted a position at the University of Tennessee in Knoxville and will continue his carotenoid research there. “A lot of Americans look to professional health care to cure diseases. [Research like ours] is approaching health from the preventative side,” says Kopsell. “Some day not too far into the future, [nutritionists] may establish an RDA for lutein and other phytonutrients. As a plant physiologist, I want to know what genetic and cultural factors contribute to increasing the levels of those phytonutrients in food crops.”
A boost for local growers?
All this knowledge may translate into a little home-team advantage
for local farms,” says Coos County Extension educator Steve Turaj. “Perhaps
you’ve heard about the Country-of-Origin
labeling law (COOL)
passed by Congress as part of the 2002 Farm Bill. [Still working its way
through the rulemaking process], the law will eventually require that fruits,
vegetables, meat and fish sold in the U.S. include a label identifying
the country where the food originated.”
“University studies show consumers favor the idea,” Turaj says. “ Wouldn’t it be terrific to say, ‘Yes it’s grown here and it’s superior to food from somewhere else. Here’s why.’”
by Peg Boyles, UNH Extension writer/editor, with help from Coos County Extension educator Steve Turaj
For more information
- About phytonutrients
- About carotenoids
- Descriptions of the various threads of carotenoid research at UNH
- USDA Nutrient Database - Learn about the nutritional value of the foods you eat by typing the name of the food in the “keyword” box.