I have a bakery and have been selling retail to customers for awhile now but my business is expanding and several grocery stores and other distributors will be carrying my banana bread. I need to extend the shelf life of the banana bread SIGNIFICANTLY. Ideally we need to get to 3 weeks or more. I am already working on a new heat sealed package (which will help) but I need advice on what preservatives to try, where to get the preservatives (buy online) and how to go about testing the preservatives (any professional tasters or testers?).