4. Relaxations, Glass Transition and Engineering Properties of Food Solids

The glass transition of food solids has received considerable attention and its relationships with the behaviour of food solids in various processes and food storage are well established. The glass transition properties for food components have been obtained primarily from calorimetric measurements, and their limit has been in identifying a transition temperature range with no particular information on the kinetics of changes associated with the transition. On the other hand, theories on the fragility of glass-forming materials have advanced with some reference to food and pharmaceutical applications. Information on enthalpy relaxations and their use to derive the fragility of glass formers in food is also available. Understanding glass-transition-related relaxations and their coupling with the engineering properties of food materials is a challenging and developing area of food materials science. The glass formation of complex solid food systems and their stability is of the utmost importance in the development of advanced nutrient delivery systems. Our studies have shown that knowledge of the macroscopic glass-transition behaviour of food systems may often be misleading in the prediction of characteristics of food components and their storage stability. For example, the glass transition and relaxation times determined for mixtures of carbohydrates and proteins vary and need to be interpreted carefully when coupled with measurements of the flow properties of powders or reaction kinetics. We have found that the contact time of particles for liquid bridging in stickiness measurements may be governed by the mobility of selected molecular species forming food solids. This has shown varying relaxation times of reactive components which may affect physicochemical properties and kinetics in food processing and storage. The new information can advance innovations in food formulation by mapping the engineering properties of food components and their mixes and the engineering of novel nutrient delivery systems.