Subject - Darkeing of canned corn
QUESTION - Is there anything you can do to prevent the darkening of home canned corn?
ANSWER - There are two ways for corn to darken; 1) by the enzyme polyphenoloxidase which acts before the corn is blanched and processed, or 2) by non-enzymatic oxidation reactions involving phenolic compounds in the corn with air to form dark pigments after processing (and often especially after the lid is removed). The non-enzyme reaction is catalyzed by the presence of harmless metal ions (like iron) that are normally present in corn tissue or in blanching or fill water.
Blanching the corn in boiling water according to directions in "Let's Preserve Corn" should prevent the enzyme reaction so if those directions are followed, then the non-enzyme post-processing reaction is probably the culprit.
Let's Preserve states that sweet and white corn varieties tend to darken after canning more so than other varieties but switching varieties is not usually an option. The non-enzyme reaction can be inhibited by adding substances that are anti-oxidants (such as vitamin C) which binds metals so they cannot participate in the reaction (such as citric acid) The product "Fruit Fresh" contains these substances. The Fruit Fresh web site (http://www.fruit-fresh.com) recommends sprinkling some in each jar before sealing. An alternative might be to follow the directions on the label for preparing an anti-browning solution and soak or blanch the corn in that. Some experimentation might be needed to determine the best way to add it. Because Fruit Fresh is composed of acids, it is safe to use since if it affects the pH at all, it will be to drop it and thus not result in an under processing situation. But use only the minimal amount needed to prevent discoloration since it might affect the taste of the final product.
Let's Preserve Sweet Corn
