"Spud Hub" Tests Potatoes' Fitness for Market
Technician Rebecca Lindlauf
measures potato chip color in
different potato breeding
lines submitted for evaluation.
Marty Glynn hasn't lost his taste for potatoeseven
though he and co-workers routinely process more of them into french
fries, chips, and dehydrated flakes each month than the average American
eats in a year (more than 140 pounds).
"We still nibble some chips every now and then, but
I prefer the kind you buy in a bag. Plus, ours aren't seasoned,"
says the food technologist with ARS'
Potato Research Worksite in East Grand Forks, Minnesota.
There, Glynn oversees the day-to-day operations of a cooperative
potato research program involving ARS and nine state universities. Researchers
evaluate the storage and processing characteristics of new, up-and-coming
potato germplasmfrom the tasty round reds sold as table stock
to the oblong Russets used for processing and baking.
For plant breeders who submit tuber samples, such testing helps ensure they're on track to developing a finished potato that will give good yields, store well, and satisfy industry's standards for product quality.
Pilot plant operator Dennis
Olson (right) and technologist
Marty Glynn prepare slices of
potatoes for frying and evaluation.
"A lot of new potato germplasm looks good in the
field but doesn't hold up in storage or processing. Or some may process
well at 45 °F but not at 42 °F," Glynn explains. That's
not to say such lines will be of little use to growers as a commercial
variety, though. The scientists are experimenting with new storage regimens
that cater to a particular tuber's storage and processing capabilities.
"If we know the potato's storage and processing characteristics," says Glynn, "we can determine new and better ways to store them and set up protocols for ensuring product quality."
Potatoes Put Through Their Paces
Fall is an especially busy time of year at the worksite, Glynn says. That's when breeders submit promising new tuber samples harvested from their breeding lines for analysis. The worksite boasts more than 46,000 cubic feet of temperature-controlled storage units. It also houses the latest in dehydration equipment and a french fry and chip processing line that's 1/20th the scale of a commercial operation. From the blanchers and cutters to the oil fryers, "everything is like industry," Glynn says.
Sprouting during storage
diminishes a potato's processing
and nutritional qualities and
means less profit for the
On arrival, new samples are placed into storage units cooled to one
of four temperatures: 38°, 42°, 45°, and 48 °F. "We
process some of the potatoes for chips, some for french fries, and others
for dehydrated products like instant potato flakes. We also evaluate
table stock potatoes for fresh market," Glynn says. "All samples
are stored, processed, and tested the same way so that the results are
comparable. The only variable is how the plant breeders treat the samples
before submitting them."
For one test, a device called a reflectometer is used to measure the
degree of whiteness in processed tuber samples destined to become chips.
"Right now, industry wants everything as white as a sheet of paper,"
Glynn notes, adding that the worksite's color rankings are based on
criteria set by the Snack Food Association.
Besides reflectometer tests, chemical analysis is also performed to measure concentrations of simple, or "reducing," sugars in the tubers' flesh. "The less reducing sugar you have, the whiter the potato chip you get," Glynn says.
For french fries, evaluations include color, length, and limpnesswhether or not the fries droop over. The job of tasting samples and checking their texture rests with a trained panel of sensory experts at North Dakota State University, in Fargo. Fresh-market testing includes checks for internal defects, like hollow heart, and external defects, such as deep-set eyes and bruising.
Physiologist Jeffrey Suttle
inspects microtubers for
signs of sprouting before he
analyzes their hormone content
by mass spectrometry.
A Unique Service
On average, the worksite's scientists and support staff conduct 14,000
to 15,000 quality tests annually, with about 1,000 new germplasm submissions
arriving each fall. "There's not a lot of downtime," says
Glynn. "If we get a sample in October, we'll test it immediately
and reevaluate it periodically thereafter until mid-June or July. Test
results are made public as soon as possible to help breeders make the
next year's selections."
Jeffrey Suttle, an ARS plant physiologist who collaborates with Glynn,
points out that the ARS worksite "is the only public facility in
the country where such comprehensive storage and processing evaluations
are done on a routine basis as a service to the potato industry."
A condition of such testing is that the results be made public through trade journals and other media, says Suttle, who is research leader of both the worksite and the Sugarbeet and Potato Research Unit at ARS' Red River Valley Agricultural Research Center, in Fargo.
Using fluorescence microscopy,
chemist Edward Lulai determines
cellular changes during wound
healing in a damaged potato.
NorValley, Snowden, Dakota Pearl, NorDonna, NorChip, and Dark Red Norland are a few notable graduates that have passed through the worksite's doors en route to commercial success.
Besides helping with evaluations, Suttle conducts potato postharvest
physiology studies with ARS chemist Edward Lulai to decipher the biochemical
mechanisms that regulate sprouting and wound healing in stored tubers.
"Our research objective is to identify key physiological processes
that can be manipulated to improve postharvest storage," Suttle
Along with rot diseases and physiological disorders, such as tuber
shrinkage and sugar-end defect, wounds and sprouting cost the U.S. potato
industry and consumers more than $300 million annually in postharvest
losses. Such problems can claim between 5 and 40 percent of a stored
"Unlike grains such as corn that are stored dry, potatoes are
stored in a fully hydrated and highly perishable form," Suttle
explains. "Plus, the potatoes are stored uncleaned and at temperatures
favorable to attack by disease organisms."
Storage managers can manipulate the warehouse environment to promote
wound healing, but there isn't a product available for treating the
tubers directly, notes Suttle, who cites a lack of earlier, in-depth
research on the topic.
One possible lead may come from recent discoveries at Lulai's lab.
He demonstrated that natural waxes in a tuber's skincalled phenolic
and aliphatic polymersare needed to form a chemical barrier around
wound sites. This shield seals water in but keeps disease organisms
"Once you know what you're looking for," says Suttle of tuber
physiology, "you can genetically select for it or design specific,
environmentally benign compounds to manipulate key biochemical processes."
The Fargo researchers also apply that mindset to controlling sprouting,
which is undesirable in stored potatoes because it results in the loss
of both nutritional and processing qualities and favors disease development.
A chemical known as CIPC (isopropyl-N-[3-chlorophenyl]-carbamate) is
widely used to control sprouting. About half the nation's roughly $2.5
billion crop is treated with the chemical to extend storage time and
improve marketability. Despite such widespread use, CIPC faces ever-tighter
In seeking more benign alternatives, the Fargo lab has devised a novel
tissue culture technique for identifying dormancy-controlling hormones
and determining their interactions that ultimately lead to sprout growth.
Thus far, three key hormones have been identified in these studies:
abscisic acid and ethylene, which usher in dormancy; and cytokinins,
which stop it so sprouting can begin.
In the lab, the technique involves snipping a leaf from a very young
potato plant and placing it in an agar growth medium. Chemicals that
either inhibit or stimulate synthesis of hormones are added to reveal
their effects on tuber dormancy. Suttle says compounds that increase
abscisic acid or ethylene levels lengthen dormancy, while chemicals
that block abscisic acid and ethylene synthesisor stimulate cytokinin
"With the tissue culture system, you can manipulate the chemical
and physiological environment as the potato plantlet or tuber grows,
right from the start, and see how that affects tuber dormancy,"
Suttle explains. "It's an experimental system that opens avenues
you just can't follow with field studies."
In other work, Suttle says, "We're pushing hard to develop our
program in the postharvest maintenance of value-added traits, such as
vitamins, nutraceuticals, and proteins, or medically important materials
such as antibodies. Postharvest storage deterioration affects all aspects
of potato composition, including these traits."By Jan
Suszkiw, Agricultural Research Service Information Staff.
This research is part of Quality and Utilization of Agricultural
Products, an ARS National Program (#306) described on the World Wide
Web at www.nps.ars.usda.gov.
"Spud Hub" Tests Potatoes' Fitness for Market" was published in the July 2003 issue of Agricultural Research magazine.