Processing berries may eliminate as much as 67% of the berries’ antioxidant capacity, according to research from the University of Arkansas. Potential ways to limit antioxidant loss include extracting antioxidants due to pressing, inactivating one specific enzyme and reducing the amount of water or syrup used in canned products.
The research in Arkansas has involved blueberries, blackberries and black raspberries. They all contain antioxidants, which research has shown may help prevent heart disease, cancer and other illnesses.
Eight to 10 scientific papers on antioxidants in foods and beverages should come out within the next year, said Luke Howard, a food science professor at the University of Arkansas. Mr. Howard and Ron Prior, a scientist with the Agricultural Research Service of the U.S. Department of Agriculture, will be co-authors of the papers.
"We’ve certainly identified where some of the major losses occur," Mr. Howard said.
The pilot plant used in the University of Arkansas studies is not able to simulate commercial processing, Mr. Howard said. Because it’s more efficient, commercial processing might reduce antioxidant capacity in a less drastic manner, he said.
In the Arkansas studies, blanching and enzymatic treatment used in juice processing caused antioxidant loss, including as much as 34% for blackberries. A 14% loss in antioxidant capacity occurred when juice was pressed. Anthocyanins, which are antioxidants and pigments that give berries their color, stuck to the press, which signals a need for technology that may extract the anthocyanins and add them back to the juice, Mr. Howard said.
During the pasteurization process in juice production, heat may result in another 18% loss in antioxidant capacity. Also, once fruit is macerated in the production of juices or purees, the polyphenol oxidase enzyme causes rapid destruction of antioxidant compounds, Mr. Howard said. Processors need to find out how to inactivate the enzyme rapidly without destroying the antioxidant compounds.
In canned fruit, 30% to 50% of antioxidants called polyphenols may leach out of the fruit and into the water or syrup inside the can. Reducing the use of water or syrup may cut down on the amount of leaching, Mr. Howard said. In baked foods, Arkansas researchers made blueberry cobblers from both frozen berries and canned berries. Baking caused about a 50% loss in antioxidant capacity, Mr. Howard said.
More losses in antioxidant capacity may take place during storage at ambient temperatures because of instability of anthocyanin pigments.
"There is a great need for methods to increase the stability of anthocyanins during storage," Mr. Howard said.
Some studies have examined using other antioxidants, or co-pigments, to protect anthocyanins during storage, he said.
Melatonin takes the heat
Studies have shown melatonin, an antioxidant, to be heat stable, said Dr. Russel J. Reiter, Ph.D., editor-in-chief of the Journal of Pineal Research and based at the University of Texas Health Science Center in San Antonio. The heat involved in pasteurization thus may have no effect on a food’s melatonin capacity during juice production. The same may be true of baking foods.
"Melatonin in foods is relatively new," Mr. Reiter said. "Very few foods have been tested for melatonin content."
Tart cherries and walnuts are two foods boasting a high level of melatonin, an antioxidant first discovered by researchers in 1993 and first found in foods about five years ago, Mr. Reiter said. Besides its sleep-promoting qualities, melatonin may prove beneficial in preventing cancer, including leukemia, according to ongoing studies led by Mr. Reiter.
Heat affects many other antioxidants. For example, tart cherries also contain a high level of antioxidants called anthocyanins, or pigments that provide color. Anthocyanins are heat-sensitive, which explains why fruit may lose color during processing that involves heat, Mr. Reiter said.
This article can also be found in the digital edition of Food Business News, May 1, 2007, starting on Page 46. Click