Answer to Question 1
Bacteria, yeast, mold, and enzymatic reactions need water. Drying removes the water from the food so bacteria, yeast, and mold cannot grow and spoil the food. Drying also slows down the action of enzymes.
Water activity (Aw) is used in many cases as a critical control point for Hazard Analysis and Critical Control Points (HACCP) programs. Samples of the food product are periodically taken from the production area and tested to ensure water activity values are within a specified range for food quality and safety. Higher Aw substances tend to support more microorganisms. Bacteria usually require at least 0.91, and fungi at least 0.7 . Dehydration lowers the Aw.
Answer to Question 2
Depending on the database used the total carbohydrates or sugars for a food can used to guide a selection of food least likely to cause blood glucose to rapidly rise after consumption.