Loss of structure in freeze‐dried carbohydrates solutions: Effect of temperature, moisture content and composition

Abstract

During processing and storage, dehydrated food materials are subject to changes in their structure. Terms used to describe these changes, which are due to the same basic phenomena, vary from process to process. Thus, during freeze‐drying, loss of structure is called “collapse”, while during storage, phenomena related to viscous flow of the dried powder matrix are termed “stickiness”. This loss of initial structure often results in the loss of desirable product qualities, though in some cases controlled manipulation of these changes is used to produce improved products. In freeze‐drying, collapse of capillaries in the dry layer results in puffing and loss of desirable structure. In dehydrated powders “stickiness” leading to caking and other defects is also a result of collapse phenomena. The collapse temperature of freeze‐dried orange juice and carbohydrate solutions was investigated as a function of moisture content and sample composition. It was observed that collapse temperatures decreased as the sample moisture content increased. Mixtures of materials collapsed at a temperature intermediate to that of the individual components. The consequences of these observations to a number of food processes are discussed.