Lactose crystallization delay in model infant foods made with lactose, beta-lactoglobulin, and starch.

Handling and storage alter infant food powders due to lactose crystallization and interactions among components. Model infant foods were prepared by colyophilization of lactose, beta-lactoglobulin (beta-LG), and gelatinized starch. A mixture design was used to define the percentage of each mixture component to simulate a wide range of infant food powders. The kinetics of crystallization was studied by a gravimetric method (dynamic vapor sorption) at 70% relative humidity (RH). After freeze-drying, lactose was amorphous and crystallized at 70% RH. The delay before crystallization depends on the contents of beta-LG and starch in the formulations. A mathematical model was proposed to predict crystallization time (delay) at 70% RH. For the formulation containing 50% lactose, 25% beta-LG, and 25% starch, lactose was still amorphous after 42 h at 70% RH, whereas pure amorphous lactose crystallized after approximately 70 min. Calculated and experimental results of adsorbed moisture from the formulations were compared. Adsorbed water of formulation containing lactose could not be calculated from moisture sorption properties of each component at a given RH because beta-LG and gelatinized starch prevented lactose crystal growth.