Preserving fruit with a chitin coat.

Preserving fruit with a chitin coat

Chitin is second only to cellulose as the most abundant natural polymer (long-chain molecule). Made from a series of linked glucose-based units, it is the primary structural ingredient in the exoskeleton of insects, in the shells of crustaceans and in the cell walls of fungi and yeasts. One reason behind the slow commercial development of this strong, biodegradable and nonallergenic material, Ernest R. Hayes believes, has been its insolubility "in practical solvents" -- especially water. But the chemist from Acadia University in Wolfville, Nova Scotia, has eliminated that obstacle with a two-step process that transforms chitin into a water-soluble compound. Its first application, scheduled for commercial introduction within a year or two, is a semipermeable film to coat fruit.

Because oxygen and warmth promote ripening, the fresh-fruit industry often uses low-oxygen vaults kept near 0[deg.]C to extend the useful life of picked fruit. But this storage is costly, Hayes says. And as soon as the fruit is removed from the low-oxygen environment, it begins ripening quickly. The NOCC (N,O-carboxymethylchitosan) Hayes developed replaces low-oxygen storage by providing treated fruit -- including pears, peaches and plums -- a gas-permeable coating that largely excludes oxygen. Moreover, it tends to retain the fruit's carbon dioxide, which can retard ripening. This coating stays on the fruit until washed off in warm water. Preliminary data indicate it is nontoxic.

Hayes' patented NOCC-forming process treats chitin with heat and a caustic chemical such as lye or sodium hydroxide, then reacts the product it forms with monochloroacetic acid. The Canadian government already has approved NOCC's use as a preservative film for apples that will be washed and peeled before use--about one-third of Canada's apple market. The fruit will be sprayed or dipped in an aqueous solution containing 0.7 to 2 percent NOCC. Hayes and two chemistry professors from St. Mary's College in Halifax, Nova Scotia, have incorporated as Nova Chem Ltd. to produce the preservative.