UpDate - Vol. 11, No. 39, Page 11
August 20, 1992
Market-fresh produce goal of agricultural researchers

     The stark steel of the laboratory contrasts with the rich soil in
her home garden. But to Margaret Sloan, her career as a food scientist
is an adventure that combines her two loves, plants and chemistry.
     "I like getting dirty," says the University assistant professor.
She recounts that she's had a garden for as long as she can remember.
     As a scientist, Sloan is interested in developing a better
vegetable for the outdoor market. That goal has led her to investigate
the keeping qualities, and in particular the textures, of commercially
grown potatoes, peppers, celery and carrots.
     "I'm interested in ways to help the fresh-food market," she says.
"People want to shop for local food in outdoor markets. They want food
that is fresher and that hasn't been in storage.
     "But fresh produce left out on a sunny day can deteriorate
rapidly," she adds. "Heat degrades food quality and having to keep
produce constantly refrigerated uses energy and money. I wondered if
there was anything we could to help maintain its quality."
     Unlocking the secret of keeping produce fresh is a matter of
biochemistry. Sloan is investigating callose synthase-the production
of cellulose-and researching the chemical structure of plant cell
membranes.
     Cellulose gives structure to the cell wall. And a sturdy wall
will help preserve the crisp texture of fresh produce. But creating
plants with more cellulose is not necessarily the answer, Sloan says,
because the resulting hardness could be unpalatable, especially in
such products as strawberries.
     Sloan has redirected her attention to another possible solution
to keeping quality texture in produce. She is investigating the
chemical structure of the plant cell membrane. Made up of proteins and
fatty acids, the membrane regulates water in the cell. Water imparts
the characteristic texture or crispness to fresh produce.
     "When the membrane becomes too solid due to a change in fatty
acids, which is the result of protein changes, it is more likely to
rupture," she says. "If the membrane is ruptured, the cell dies."
     High temperatures affect the proteins in the membrane, which
affect the fatty acids, making the membrane less permeable, more
brittle and subject to breakage. When the membrane breaks, water in
the cell is released and the vegetable becomes mushy, losing texture
and consumer appeal.
     Sloan has documented loss of protein in carrot cell membranes.
Because the ratio of fatty acid to protein controls the water in the
cell, when this changes, so does the texture.
     Sloan says the ultimate carrot, in terms of keeping quality, will
probably be a result of bioengineering-insertion of a gene to
manufacture a heat-stable protein in the vegetable's cell membrane.
     Sloan uses tissue culture to search for cells with desirable
characteristics. This breeding technique is much faster than
traditional breeding methods that require searching for plants with
desired characteristics through several complete generations. In
tissue culture, once a desired characteristic is found in a cell, the
cell can be encouraged to multiply, resulting in mature plants.
     "I'm looking at solutions from a biotech angle," Sloan says.
"Traditional methods of breeding would take months or years, but using
tissue culture and eventually using genetic engineering, the plants
with the keeping qualities we want can be produced quickly."
                                        -Claire McCabe