| A Clean Break
Whatever the source of contamination, more than one solution may be needed.
One area of concern is that conventional washing methods remove or kill only
between 90 and 99 percent of bacteria attached to the surfaces of produce.
Scientists at the Eastern Regional Research Center (ERRC) in Wyndmoor,
Pennsylvania, are searching for practical ways to overcome these current
The scientists are conducting experiments on commercial-type produce washing
and sanitizing equipment to reduce bacterial populations on fresh and minimally
processed fruits and vegetables. The tests use produce artificially
contaminated with harmless bacteria similar in behavior to disease-causing
organisms. This research is being conducted in a unique BSL-2 (short for
biosafety level 2) pilot plant at the ERRC, says Gerald M. Sapers, a food
technologist with ERRC's Food Safety Interventions Research Unit.
Future studies will be carried out on produce contaminated with actual
disease-causing organisms within a containment structure equipped with its own
steam decontamination system. A small-scale prototype was designed, built, and
validated by a team of scientists and engineers from Pennsylvania State
University and ERRC.
"Early tests with the prototype containment system have been very
successful, and installation of a full-scale unit at ERRC is nearing
completion," Sapers says.
Paul Walker, a professor of agricultural and biological engineering at Penn
State, came to ERRC on a 15-month sabbatical to design, build, and evaluate
research-grade produce-washing equipment for the BSL-2 pilot plant as part of a
joint venture between Penn State and ARS, says Sapers. Walker oversaw the design
and construction of the prototype and full-scale containment systems as well as
the newly designed, commercial-scale washing equipment the lab received from
Penn State. This equipment is operated by computer and permits precise control
of all experimental variables. Joseph Sites, an ERRC mechanical engineer,
manages the pilot plant, designs equipment, and conducts experiments.
Sapers and food microbiologist Bassam Annous are developing new washing and
sanitizing treatments in the laboratory and then testing them in the pilot
plant. Current trials are performed primarily with apples and cantaloupes,
using nonpathogenic surrogates for human pathogens.
Denise Riordan, a former research associate, and Annous compared
nonpathogenic strains of E. coli with harmful strains to find surrogates
with similar traits.
ARS uses pilot plant programs to serve as a bridge between invention and
commercialization. Industries form partnerships with ARS scientists to further
evaluate research that shows promise in the laboratory. Effective technology
can then be transferred to produce packing and processing industries.
Sapers says that the one-of-a-kind equipment developed in this program
allows improvements in conventional methods as well as novel approaches.
"The equipment must be suitable for use in a commercial produce packing
or processing facility," he explains.
One of the major problems that the ERRC team is addressing is the ability of
bacteria to attach firmly to produce surfaces, often in inaccessible locations,
and survive conventional washing and sanitizing methods.
Packinghouses use chlorine and other sanitizers to reduce microbe levels,
but conventional sanitizers are not able to penetrate skin crevices, creases,
or pockets to destroy pathogens very effectively. The trick is to find an agent
that will reach the pathogens without damaging the appearance and texture of
Is the Solution in the Solution?
Scientists at ERRC have confirmed the limited capabilities of conventional
washing methods, and are now looking for methods that increase the safety of
produce while keeping the sensory qualities consumers expect in their fruits
and vegetables. Their results with experimental sanitizing treatments have been
Washing apples in a brush washer, even when the apples were sprayed with
very hot water, was found to be ineffective. Sapers says that total immersion
in a sanitizing solution is superior to brush washing. However, he cautions
that improper use of this "dump tank" method for washing can lead to
cross-contamination of the submerged produce.
Experimental hydrogen peroxide and hot water treatments were applied to
apples in a dip tank at different temperatures. Temperatures exceeding 60°C
could not be used without causing discoloration. While such treatments were
able to eliminate up to 99.9 percent of the bacteria, they still did not
achieve the total kill (99.999 percent) desired by the Food and Drug
Sapers says other experimental methods being studied involve steam
treatments or application of sanitizer solutions under vacuumfor better
"This would be a new approach for commercial facilities," he said.
"One challenge for researchers is to find ways to keep the speed of the
processing line up to par, even when new sanitizing operations have been
incorporated into the process."
Another method they are trying in Wyndmoor involves treating apples and
other produce with acetic acid and hydrogen peroxide vapors. Sapers said there
were large population reductions in inoculated apples with some vapor
treatments but also some product discoloration. Work in this area is
Yet another approach involves the use of an abrasive paste to grind
pathogens off produce surfaces while being careful not to bruise or puncture
The pilot plant program will become fully operational when the larger
containment structure is in place, permitting the scientists to experiment with
real pathogens.By Jim Core,
Agricultural Research Service Information Staff.
This research is part of Food Safety (Animal and Plant Products), an ARS
National Program (#108) described on the World Wide Web at
Gerald M. Sapers is in the
USDA-ARS Food Safety Interventions Research Unit,
Eastern Regional Research Center, 600
East Mermaid Lane, Wyndmoor, PA 19038-8598; phone (215) 233-6417, fax, (215)