13 Principles of moisture transfer in multi-domain cereal systems.

Dr. Ted Labuza. Department of Food Science and Nturtion, Univ. of Minnesota, St Paul, MN 55108.

Multi-domain systems are systems that can be defined as those with non-equilibrium conditions where the thermodynamic driving force is such to cause exchange of water from the high chemical potential (aw) region to the low one. This paper will review several of those systems and illustrate some physico-chemical approaches that might be used to maintain non-equilibrium conditions and thus maintain consumer acceptability. As examples, these include migration of water from the sauce of a frozen pizza to the crust making it soggy, migration of water from a high aw cheese into crackers for a vending machine cheese- cracker snack causing loss of desired crispness in the cracker, migration of water from ice cream into a cone during frozen storage of the composite system making it mushy, and loss of moisture from fruit pieces mixed in with cereals, causing the fruits to be hard and brittle and the cereal to soften. These represent composite cereal with filling type systems where shelf life is shortened because of water migration. Solutions include separate packaging which is expensive, use of edible barriers between the layers, using colligative property principles such as manifested in Raoult’s Law to minimize chemical potential differences between domains and thus reduce the thermodynamic driving force, controlling the diffusion rate of moisture in the higher aw product, and raising the lower aw Tg which is usually the cereal product. This can be done with ingredient selection or modification inducing retrogradation, gelatinization and/or enzymatic protein aggregation.