Insect Protein May Prevent Fruits And Vegetables From Turning Brown

November 16, 2001

GAINESVILLE, Fla. — A small protein derived from the common housefly may offer Third World countries a cheap way to preserve cut fruits and vegetables, said a University of Florida food science researcher.

Marty Marshall, a professor with UF’s Institute of Food and Agricultural Sciences, said some developing nations cannot afford preservatives commonly used in the United States, and that millions of dollars of edible produce is discarded each year because of brown discoloration.

“Brown spots on the inner flesh of fruits or vegetables after they are cut is simply a result of oxygen reacting with the fruit,” Marshall said. “The brown spots are harmless, and there’s no reason not to eat such produce, but many people throw it away.”

Rosa Rolle, an officer with the Food and Agricultural Organization of the United Nations, developed the idea for the preservative while researching fruit flies. Later, she read a Japanese study that validated her hypothesis. The report showed how a certain protein in a fly’s body was able to turn on and off an enzyme that hardens the fly’s shell and turns it brown.

“The enzyme, called polyphenol oxidase, is the same one in fruits and vegetables that causes them to turn brown,” Rolle said. “I wondered if we could somehow extract the protein from the fly and use it to turn off the browning effect in produce, so I called Marty Marshall for help on that aspect of the study.”

Marshall said results came quickly.

“Right away, it was obvious that a small protein, which is actually called a peptide, was affecting the polyphenol oxidase enzyme in the fly,” Marshall said. “We thought if we could isolate the peptide, it could be used to prevent the browning in fruits, vegetables and also in shrimp.”

Marshall asked the U.S. Department of Agriculture to provide him with large batches of flies from which he could extract the peptide. Marshall obtained about 100,000 flies from the Gainesville, Fla.-based Center for Medical, Agricultural and Veterinary Entomology, where UF adjunct Professor Jerry Hogsette regularly breeds colonies of flies for biological experiments.

In Marshall’s lab, doctoral student Ruhiye Yoruk took the flies, which were in the third pupal stage and had not emerged as adults yet, and washed them in ionized water. She then froze them with liquid nitrogen at 38 degrees Fahrenheit and ground them into a powder.

To extract the “anti-browning” peptide, she mixed the powder with a buffered solution, which contains a chemical that kills any bacteria that may be on the fly pupae. She then extracted the polyphenol oxidase “browning” enzyme from a batch of Red Delicious apples.

Now ready to test the theory, Marshall and Yoruk mixed the two extracts in a test tube.

“The reaction between the peptide inhibitor from the insects and the enzyme was instantaneous,” Marshall said. “We saw good results, with about 60 percent of the browning enzyme neutralized, indicating this is a potent extract.”

Marshall said the next step will be to purify the inhibitor so researchers can determine how much is needed to be effective. He also said the long-term safety of the procedure needs to be determined.

Eventually, the end result would be a commercial spray or dip, Marshall said. Future plans include using cockroaches to produce a spray, because they seem to have a substance in their bodies that is similar to the peptide in flies. Marshall said additional research and the purification process should be complete within a year.

To date, Agro-Industries and Post-Harvest Management Service of the Food and Agriculture Organization has provided $18,000 in support of the research.

Hogsette said poor nations could breed flies and cockroaches very inexpensively.

“You basically put the insects in large trays and feed them with low-cost nutrient materials,” Hogsette said. “Nature does the rest, which allows for endless production of flies and cockroaches.”

Looking beyond the current experiments, Marshall said foods in the future could be modified so they don’t turn brown after cutting.

“We may be able to take the gene for this peptide and use it to engineer foods that have an internal control,” Marshall said. “Then, they would not turn brown after cutting, and you wouldn’t have to spray anything on them.”