Natural Pesticides Could Keep Fruit Fresh Longer

The potential of natural fruit "volatiles" to improve the storage qualities of fresh fruit is being examined by Lisa Skog and Prof. Dennis Murr, from the Department of Plant Agriculture'sVineland Research Station, and Brian McGarvey of Agriculture and Agri-Food Canada.

Volatiles are natural compounds that contribute to the aroma and flavour of fruit. But in high concentrations, some are antimicrobial agents that can protect against fungal organisms and damage.

"If natural fruit volatiles prove effective, then growers, distributors and consumers will all benefit," says Skog. "It could lead to a healthier product, less storage decay, longer shelf life and decreased losses during shipping."

Fruit boosts its production of certain volatiles in response to injury, microbial attack or environmental stress. There are many fruit volatiles —which include aldehydes, ketones and alcohols — that are commercially available for flavour additives in some foods. But they don't all act as antimicrobial agents.

Skog is evaluating the effectiveness of 20 different volatiles on Ontario peaches and pears in decreasing brown rot and blue mould microbial diseases. A pear processor collaborating on the project estimates that a 75 per cent decrease in the incidence of blue mould alone could save $30,000 per year.

Fruit losses from spoilage are partly due to a recent push to use fewer conventional post- harvest pesticides. This has decreased pesticide residues and risks to consumers, but has also increased post-harvest decay during long distance shipping and storage of fresh fruit, says Skog. Reduced pesticides allow latent infections -- which originate in the field but show no immediate and visible symptoms -- to become active. And fruit processors and growers pay the price in product losses and longer processing times required to remove spoiled fruit.

Skog hopes the low-risk natural volatiles can be an effective substitute for conventional post-harvest pesticides.

"The application of antimicrobial volatiles against post-harvest decay is advantageous because the volatiles quickly dissipate and little residue remains," says Skog. "Also, because the compounds occur naturally in the plant, they may actually enhance flavour."

Results so far indicate that five of the 20 volatiles being investigated are effective antimicrobial agents. Laboratory trials have shown they protect fruit against latent infections, spores and active (already growing) infections. Skog predicts volatiles will be very effective in preventing latent infections from becoming active because they can penetrate the fruit surface.

Future projects include determining the mode of action of natural volatiles, finding the best methods of application, and the precise concentration of volatiles required to protect the fruit.

This research is sponsored by the Vineland Growers Cooperative, Nabisco Ltd., and Agriculture and Agri-Food Canada through the Ontario Research Enhancement Program, a $4- million federally funded research initiative administered by the Research Branch of AAFC with input from the agriculture and agri-food sector, universities and the province. OREP supports 25 research projects in universities and research centres across the province, with the University of Guelph as a major participant. Projects focus on two key areas identified by the agriculture and agri-food community: consumer demand for higher quality safe products and ensuring crop production management systems that are environmentally sustainable.