Not a ton of preservatives......  but thinking about it here..... generally some vegetables need to be blanched before putting in a freezer. Corn is one of them.  So, a commercial operation could be set up to blanch this sweet corn before packaging it.  Blanching , if you are not familiar, is placing the corn in boiling water for a couple of minutes, and then plunging into cold water. It breaks down the enzymes in the sweet corn (and other vegetables) to stop the aging process.I'm guessing that is what they did.