Water sorption and crispness of fat-free apple chips

Equilibration of fat-free apple chips to predetermined moisture level was achieved by keeping samples over saturated salt solutions. The sorption isotherm obtained indicated absence of a monolayer and was typical for type III according to the Brunauer classification. At water activity below 0.12 apple chips demonstrated excellent crispness and were highly acceptable as a snack food item. They were extremely hygroscopic and lost crispness easily. The critical water activity was found to be a(c) = 0.18 which corresponds to a water content of 3.5 g H2O/100 g solids. These values were much lower than those found for other crispy snack foods.