Most low water content or frozen food products are partly or fully amorphous This review will discuss the extent to which it is possible to understand and predict their behavior during processing and storage, on the basis of glass transition temperature values (Tg) and phenomena related to glass transition Two main conclusions are provisionally proposed Firstly, glass transition cannot be considered as an absolute threshold for molecular mobility Transport of water and other small molecules takes place even in the glassy state at a significant rate, resulting in effective exchange of water in multi-domains foods or sensitivity to oxidation of encapsulated materials Texture properties (crispness) also appear to be greatly affected by sub-Tg relaxations and aging below Tg Secondly, glass transition is only one among the various factors controlling the kinetics of evolution of products during storage and processing For processes such as collapse, caking, crystallization, and operations like drying, extrusion, flaking, Tg data and WLF kinetics have good predictive value as regards the effects of temperature and water content On the contrary, chemical/biochemical reactions are frequently observed at temperature below Tg, albeit at a reduced rate, and WLF kinetics may be obscured by other factors

Glass Transition and Food Technology: A Critical Appraisal

Thermophysical properties of chitosan, chitosan–starch and chitosan–pullulan films near the glass transition

State diagram is a map of the different states of a food as a function of water or solids content and temperature. The main advantage of drawing map is in identifying different states of a food, such as freezing point and glass transition, which helps in understanding the complex changes when food's water content and temperature are changed. It also assists in identifying food's stability during storage as well as selecting suitable conditions of temperature and moisture content for processing. This paper provides an overview and critical assessment on the basic concepts of the state diagram with their terminologies, selected measurement techniques, and their use. Glass transition alone could not be considered as generic rules for food stability criteria since numbers of instances, such as pore formation, diffusion, microbial stability, non-enzymatic browning, other factors or mechanisms play important role. However, it is definitely one of the factors affecting the stability, and a future challenge to combine the glass concept with other mechanisms or factors.

http://depa.fquim.unam.mx/amyd//archivero/26TVDiagramasdeestado_14242.pdf

State diagram of foods: Its potential use in food processing and product stability

The plasticizing effect of water on proteins, polysaccharides and their mixtures. Glassy state of biopolymers, food and seeds

Many texture studies have been published on crispness because of the great interest of consumers towards crispy foods. This work reviews the existing literature on the topic, and especially the different approaches, instrumental and sensory, applied to study crispness. These studies result in a wide range of data but, because crispness is not a clearly defined sensory attribute, the conclusions that can be drawn from these studies should be carefully examined. The physical basis for crispness are discussed and the role of structure, hydration and ingredients on crispness and its stability are presented.

I.A.M. Appelqvist

Papers

Glass transitions and the fracture behaviour of gluten and starches within the glassy state