Processing, storage affect antioxidant content of fruit
June 26, 2008Contact Information:
Dr. Luke Howard, Professor, Food Science
479-575-2978 / lukeh@uark.edu
Dr. Ron Prior, Research Chemist, Arkansas Children’s Nutrition Center
501-364-2747 / priorronaldl@uams.edu
By Fred Miller, Science Editor
479-575-5647 / fmiller@uark.edu
Ph.D. student Jeana Monrad examines anthrocyanin and Procyanidin compounds extracted from dried red grape pomace with “green” technologies. She is studying new technologies that extract the phytochemicals with pressurized hot water or ethanol instead of the conventional methods using chemical solvents.
Lab technician Cindi Brownmiller analyzes phytochemicals extracted from fruit pomace — the waste solids left after fruit juices have have been squeezed out.
FAYETTEVILLE, Ark. – Blueberries, grapes and other pigment-rich fruits contain high levels of antioxidant compounds that offer significant defenses against cancer, heart disease and other ailments. But antioxidant levels decline when the foods are processed for juices and other products, or when stored without refrigeration.
Scientists at the University of Arkansas System’s Division of Agriculture and the U.S. Department of Agriculture are studying the phytochemical makeup of these foods, how they enter and work in the body and how food processing and storage affect them.
Division of Agriculture food scientist Luke Howard said anthocyanins tend to concentrate in fruit skins. Procyanidins and another type of phytochemical, ellegitannins, concentrate in the seeds. When fruits are pressed to make juices, most of these antioxidant compounds are left behind.
“We lose up to half of these compounds in the pomace, the solid material left behind as waste,” Howard said.
In contrast, chlorogenic acid, which is present in the blueberry pulp, carries through to the final product.
Howard and University of Arkansas chemical engineer Jerry King are working on means to reclaim the phytochemicals from the pomace using green technology. Howard said the grape industry commonly reclaims the compounds using chemical solvents. The Arkansas team is developing two means of reclaiming the antioxidants: pressurized hot water and ethanol, which have less impact on the environment and are safe for use in food products.
Howard said the reclaimed compounds can be used to fortify juices or as nutritional supplements.
During storage, Howard said, anthocyanin and procyanidin levels decline, often precipitously. Chlorogenic acid and other phytochemicals called flavonols hold up significantly better, he said.
Many of these products are stored at room temperature. Howard said refrigeration slows the loss of antioxidants.
“In general, fresh is best, frozen is still pretty good and processed fruit products, especially if stored for some time, have lost a lot of antioxidant and other health benefits,” Howard said.
Ron Prior of the USDA’s Arkansas Children’s Nutrition Center said some antioxidant compounds are not easily absorbed by the body. Nevertheless, in clinical studies, he’s found that test subjects who eat meals with antioxidant-rich foods show increased levels of antioxidants in their blood serum. Those who eat meals without such foods show decreased levels of antioxidants.
“Grapes and kiwis give a good dose of antioxidants,” Prior said. “However, you have to eat more blueberries or other food high in anthocyanins to show a similar response in antioxidant levels.”
Prior said, “There are many different compounds within the foods and we know considerable about what’s in these foods, but not enough is known about how these chemicals are absorbed or metabolized in the body.”
Extracting them individually for nutritional supplements may not provide as much benefit as eating the whole foods, Prior said.
“I’m sure there’s some sort of synergy between compounds that means they work better together than individually,” Prior said. “We have a lot of work left to do.”
Howard said antioxidant capacity is a measure of a chemical compound’s ability to neutralize oxygen free radicals, oxygen molecules that are missing one or more electrons. A proper balance of free radicals is necessary for such things as helping sustain the immune system and fight disease, but excess oxygen free radicals can damage cells and lead to cancer and other diseases.
Antioxidants — chemical compounds with names like anthocyanin, procyanidin and chlorogenic acid — neutralize free radicals. Howard said they have other health benefits as well. “Many of the compounds, for example, have anti-inflammatory ability,” he said.