Features Production Research
Improving safety, quality of organic leafy greens

November 15, 2010,
Tuscon, AZ – A USDA-funded project at the University of Arizona aims to
increase the safety and quality of organic leafy greens and profitability for
farmers. The endeavor includes outreach and an education program.

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Tuscon, AZ – A USDA-funded project at the University of Arizona aims to
increase the safety and quality of organic leafy greens and profitability for
farmers. The endeavor includes outreach and an education program. 

The U.S. Department of
Agriculture has provided $2.9 million for the University of Arizona to improve
the safety and post-harvest quality of field-grown organic leafy greens.

“This is a very
comprehensive project covering all aspects of leafy green production, from
field to fork,” said principal investigator Sadhana Ravishankar, an assistant
professor in the UA’s department of veterinary science and microbiology in the
College of Agriculture and Life Sciences.

“The goal is to provide
safer and better-quality organic leafy green products for consumers and to
increase profitability for growers of organic produce.”

U.S. producers are
turning to certified organic farming systems as a way to lower input costs,
decrease reliance on nonrenewable resources, capture high-value markets and
boost farm income. Since the late 1990s, U.S. organic production has grown
steadily.

Leafy greens include
spinach, lettuce, arugula, cabbage and radicchio, all of which are part of the
grant in one way or another.

“The large foodborne
outbreak affecting mostly organic spinach in 2006 was a reminder of how
important it is to ensure safety of leafy greens,” Ravishankar said. “The two
most common disease-causing pathogens in leafy greens are Escherichia coli O157:H7 and Salmonella enterica. Contamination can come from human or
animal excrement, for example from runoff from nearby farms, communities or
from contaminated irrigation water.”

While cooking eliminates
both E. coli and Salmonella, consuming raw leafy greens can pose a risk.

The researchers are
going to look at ways to eliminate bacterial contamination in bagged leafy
greens using organic methods. In previous studies, Ravishankar’s team tested
edible films made from apples, carrots, or hibiscus, which contained essential
oils and other plant extracts. These antimicrobial edible films effectively
inactivated E. coli and Salmonella on various foods.

“We are going to test
whether these plant extracts and essential oils inactivate bacteria if
incorporated into an edible film lining the insides of the bags in which leafy
greens are sold or as pieces of edible film mixed into the salad,” she said.
“Since the films are made of edible plant parts, they can be consumed as part
of the salad.”

“At the field level, we
want to look at various production practices as well as environmental factors
affecting the quality and safety of leafy greens,” she added. “We will study
organic fertilizers, mainly compost teas, and see how the microbes survive in them.”

Those studies will
involve growing organic leafy greens on an experimental parcel and fertilizing
them with compost teas inoculated with harmless strains of E. coli. The
benefits of compost teas and organic nutrients on plant growth will also be evaluated,
through Jorge Fonseca at the Yuma Agriculture Center, part of the UA’s College
of Agriculture and Life Sciences.

In collaboration with
Kelly Bright and Charles Gerba in the UA’s department of soil, water and
environmental science, the team plans to monitor irrigation water by sampling
water from different areas in Arizona for contamination with E. coli O157:H7,
Salmonella and viruses at different times of the year.

“In addition to taking
seasonal samples, we are going to sample right after a rainfall to see whether
that affects the contamination risk,” she said. “If it turns out that rainfall
is causing a hazard, then we’ll advise farmers to not irrigate fields or
harvest after rain.”

“Some researchers say
the bacteria are only on the surface and there is no way for them to get inside
the fruit," Ravishankar said. “Others say they can. We are going to study
how the microbes attach to the plants and whether they get inside. Limited
research has been done with regard to these issues in organically grown leafy
greens. We hope to be able to find an answer.”

Vegetable surfaces are
not the only areas that could breed foodborne bacteria. Contaminated harvesting
tools are likely to spread bacteria further.

“Commonly, the growers
sanitize the harvesting tool but then use it for harvesting numerous lettuce
heads before they sanitize it again,” Ravishankar said. “All it takes is one
bad apple in the row for the harvester to spread the microbes to other plants.”

“We will artificially
inoculate tools used for harvesting and for coring lettuce with harmless
strains of E. coli and put them to the test: How many lettuce heads can they
contaminate along the way?”

How effective is washing
at removing bacteria from produce? The researchers will take a closer look at
that, too. “We will be looking at about a dozen plant extracts, essential oils
and organic sanitizers for their effectiveness against bacteria as well as
viruses,” Ravishankar said. “The most effective ones can potentially be applied
in the rinse water used for washing leafy greens after harvest.”

To ensure that the
recommendations are economically viable, the grant includes commercial scale
validation of the results. The team plans to assess the efficacy of the most
effective organic sanitizers, plant extracts and essential oils by applying
them in the flume washers used to clean the harvested produce in Yuma, Ariz.

Organic leafy greens
treated with the most effective organic sanitizers, plant extracts, essential
oils as well as antimicrobial edible films will be evaluated for their sensory
acceptability using a panel of consumers.

“We will communicate our
results through workshops for people in the industry to make it easy for them
to adopt safe practices,” Ravishankar added. “There will be training workshops,
field days, presentations to extension agents and media outreach to raise
public awareness.” Kurt Nolte, director of Yuma County Extension, will be
responsible for this effort.