Maltodextrin

Maltodextrin is used in enzyme formulations as a substrate, which allows enzymes to readily access and breakdown larger starch molecules into smaller more usable sugar units; this is due to its easy digestible nature and ability to be broken down by specific enzymes such as amylase.  It essentially act as a source of carbohydrate for the enzymes to work on.  It also helps to stabilize enzyme formulas, preventing them from degrading too quickly.