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Canned produce: mush no more.

Canned produce: Mush no more

Crunch. That's the sound of teeth biting into a canned green bean -- not just any green bean, but one canned by Malcolm Bourne, a food chemist with the New York State Agricultural Experiment Station in Geneva. A new treatment he developed can restore most of the firmness -- and crispness, if desired -- now lost during commercial food canning. It's resuscitating their polymers that puts the snap back, Bourne says.

Polymers are macromolecules formed by linking a chain of identical molecules such as pectins -- a class of water-soluble, gluey substances in plants. Cooked fruits and vegetables lose much of their original firmness as heating uncouples the links in polymeric pectin, explains Bourne. The reason so many canned goods end up mushy, he says, is that the temperatures used today to blanch and sterilize commercial canned goods far exceed what's needed to achieve the tenderness most consumers desire.

Bourne has discovered that by dropping canning temperatures from 220[degrees]F to just 142[degrees]F, an enzyme naturally present in the foods activates and begins binding pectin molecules back together by chemically crosslinking their calcium atoms. The longer the blanch, the more time the enzyme has to reestablish firming links between pectins. Supplementing the product with extra calcium "dramatically" enhances the process, Bourne says, allowing a restoration of crispness. Every food he's tested so far -- carrots, snap peas, zucchini, onions, bell peppers, apples, peaches, peas, cherries and potatoes -- Firms up under his processing. And because the calcium crosslinks resist thermal breakdown, cooks can reheat foods firmed up with them for hours without mushing. In fact, this process holds out the prospect for pies with fruit fillings even firmer than those Grandma baked from scratch.

The temperatures Bourne uses won't prevent growth of nontoxic "flat-sour" microbes that can spoil the flavor and appearance of foods. To prevent their growth during blanching, processors must change blanch waters more frequently, lower the pH of their product to less than 4.5 (Bourne adds a tangy bit of cirtric acid) or blanch with steam or microwaves.
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Title Annotation:food chemistry
Author:Raloff, J.
Publication:Science News
Date:Sep 23, 1989
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