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Less stressed spuds are best.

A potato grown for processing stands many chances of getting bumped and bruised between the time it's harvested until it's made into fries or chips.

But in a vat of hot cooking oil, even the slightest internal bruise from the spud's past may be exposed. The heat turns damaged potato tissue - which has converted much of its starch into sugars - to an unattractive dark brown.

"Most people prefer light-colored chips and fries made from undamaged potatoes," says Paul H. Orr, director of the Red River Valley Potato Research Laboratory, East Grand Forks, Minnesota. "So our biochemical and agricultural engineering studies are aimed at both improving potato product quality and reducing costly handling and storage problems."

The research is financed, in part, by the Red River Valley Potato Growers Association.

Breeding Splendid Spuds

Working with researchers at North Dakota State University and the University of Minnesota, ARS scientists have developed standardized tests to rate processing qualities of potatoes that are showing promise in state and federal vegetable breeding programs.

For example, University of Minnesota biochemist Joe R. Sowokinos, stationed at the ARS potato research lab, has shown that cultivars considered ideal for chipping must be low in sucrose content at harvest time and convert minimal amounts of starch to reducing sugars (glucose and fructose) during storage.

Orr coordinates annual testing of processed products made from potatoes sent to the laboratory from several state breeding programs. These products must pass tests for flavor, color, and texture by a trained sensory/taste panel under the direction of North Dakota State University food scientist Edna T. Holm.

One new cultivar judged especially good for fries - if not bruised - is Ranger Russet, developed by ARS scientists Joseph J. Pavek and Dennis L. Corsini of Aberdeen, Idaho, and by university, Cooperative Extension, and industry researchers in Washington, Oregon, Idaho, and Colorado.

Into some experimental potatoes, biochemist William R. Belknap of the ARS Western Regional Research Center, Albany, California, has introduced a gene from a wax moth that might help prevent ugly black spots from forming in bruised tubers. Corsini, Pavek, and researchers in North Dakota, Minnesota, and Maine are field-testing these potatoes' production qualities and bruise resistance.

Better Bin Management

In East Grand Forks, scientists are trying to find out when and how bruising occurs so as to better prevent such damage. To measure the impact of handling jolts, Orr's research team puts an artificial potato - a battery - powered instrumented sphere just 3-1/2 inches in diameter - amid potato samples.

Developed by ARS and scientists at Michigan State University, East Lansing, the beeswax sphere encases impact-detecting devices called accelerometers, along with computer circuitry that records the data.

But bruises are not the only injuries that concern these researchers. Potatoes with cuts and scrapes from handling equipment - especially at harvest time - are highly vulnerable to moisture loss and serious storage diseases.

These all end up costing the industry dearly - perhaps a quarter-billion dollars by the time 27.5 billion pounds of potatoes have come out of storage, some 10 months after harvest. Obviously, says Orr, most potatoes grown for processing have to be stored until they can be fried, flaked, or granulated.

Keeping damaged spuds from rotting and spoiling other healthy potatoes in the bin is a challenge. Growers carefully try to help the still living and breathing tubers heal during the first week or two of storage. Throughout this critical time, warmth and moisture regulated by minimal ventilation enhance suberization - the process that forms potato skins and scar tissue over wounds.

Considering the size of a typical 20-foot-high storage bin, any mistakes in bin management could be hazardous to a grower's financial health. Larger than the volume of the average American home, each bin holds about 1,300,000 pounds of potatoes worth perhaps $65,000.

Research at East Grand Forks may help storage managers make the best decisions on bin and equipment use during hectic days of harvest and suberization. ARS agricultural engineer Lewis Schaper led the development of SUBERMAX, a computerized expert system, to assist in making decisions for managing potatoes do are either healthy or stressed.

Schaper says SUBERMAX may be revised as often as every 2 years, as new information is gleaned from research and from commercial practices. Soon the system may include data from automated sampling of various gases, as well as temperature and humidity measurements, taken from various sites throughout the bin.

Sudden changes in these gases might signal developing disease problems. Rather than risk large- scale damage, managers may then decide to sell the potatoes for immediate processing rather than hold them for anticipated higher prices.

About Sprouting...

Other unfavorable changes that affect processing qualities of potatoes in storage result from sprouting. Sprouting tubers quickly lose weight and soften. Much of their starch turns into reducing sugars that, when cooked, react with amino acids - the Maillard reaction - making undesirably browncolored chips and fries.

ARS plant physiologist Jeffrey C. Suttle, Fargo, North Dakota, is conducting research on potato sprouting at the cellular and subcellular level. Such studies may help breeders develop potato varieties that will sprout well at planting time but not in storage environments.

For more than three decades, storage managers have had to rely on one synthetic chemical to inhibit sprouting of stored potatoes. While a crop breeding approach is being pursued as an alternative, another natural inhibitor may fill in.

ARS plant physiologist Steven F. Vaughn and his colleagues at the National Center for Agricultural Utilization Research, Peoria, Illinois, have been issued two patents on the use of sprout inhibitors derived from volatiles, such as some major flavor components found in almonds, cinnamon, curnin, and thyme.

At East Grand Forks, scientists are researching these and other compounds to test sprouting inhibition under longterm, controlled storage conditions.

In still other research, ARS molecular biologist Yannis Gounaris and Sowokinos are studying biochemistry as related to cold-resistance in potatoes. Some cultivars - in response to cold temperatures in storage - readily develop the unwanted sugars that interfere with processing.

Some wild potatoes have genes that impart resistance to cold-induced sweetening. But transferring these genes to commercially acceptable cultivars may require the use of biotechnological techniques, rather than conventional plant breeding.

Gounaris has found that potatoes' sucrose content or cold-resistance is related to the density of mitochondria - energy-processing bodies within cells. In the mitochondria of potatoes sensitive to cold, he has found greater amounts of a certain protein that may help explain cold sensitivity. These discoveries may be stepping stones to identifying a cold-resistance gene.

Enhancing the Wound-healing Process

Apart from handling, storage management, and marketing decisions, one way to minimize spoilage and reduce unsightly blemishes is to increase the resistance of potatoes to harvest damage and assure that potatoes wounded during harvest heal rapidly.

Toward that end, ARS biochemist Edward C. Lulai of the Red River Valley Potato Research Laboratory has refined techniques to measure the effect of potato storage environment and treatments on wound-healing rates.

To study the biochemistry of suberin, a wound-healing substance found in injured potato skins, Lulai and coworkers developed a technique to make its components fluoresce for microscopic examination. Such detailed study may enable researchers to relate various suberin components to the activation of specific potato genes.

And Lulai says damages may also be significantly reduced by breeding potatoes to resist skinning injury.

Using an experimental device developed by agricultural engineer James L. Halderson of the University of Idaho, Moscow, Lulai is testing the skin toughness of various genetic crosses as they mature in the field.

He and his colleagues hope to physiologically improve and identify breeding selections that will not only resist skinning but also have the biological mechanisms to resist disease if they are damaged.
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Title Annotation:creating a hardier potato
Author:Hardin, Ben
Publication:Agricultural Research
Date:Nov 1, 1992
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