The Significance of Glass Transition Temperature in Processing of Selected Fried Food Products: A Review

Abstract

This paper emphasized the significance of the glass transition temperature (Tg) by highliting its applications in drying (hot air and freeze drying) for various food systems such as skim milk powders, rice kernels, starch and sugar products and some freeze-dried products such as strawberries and surimi. The study revealed that the major components of the specified foods (which consist of mixture of ingredients), for example lactose in skim milk powder and sucrose in sugar mixtures, will influence the glass transition temperature of the food. Moreover, Tg is an important parameters for determining the optimum processing conditions of dried products. Thus, it is used in designing drying equipment to meet the purpose. In general, Tg affects the physical properties of food such as stickiness, caking and agglomeration. The effect of moisture content on Tg was covered by almost all studies focusing on Tg of foods. Meanwhile, the effect of pressure on Tg was not well covered due to its scarce availability in the existing literature. In term of test methods for determining the Tg of foods, it seems that not all test methods are suitable for certain type of foods, accordingly, more study on the recommended test methods should be carried out.

A Polymer Science Approach to Physico-Chemical Characterization and Processing of Pulse Seeds

“…As noted, amorphous food materials are in a non-equilibrium state, which can be greatly affected during processing and storage conditions (Abbas et al, 2010;Campanella et al, 2002;Rhaman, 2006;Roos, 1991;Roos, 2010). The state of an amorphous material depends on its composition, temperature, and time.…”

“…The control of moisture content or water activity and temperature of glassy foods is of great importance as the concept of the glass transition helps to explain changes which occur during food processing and storage. Typical changes in amorphous food materials above the Tg include stickiness, caking, collapse, and crystallization, textural changes such as softening and hardening, as well as chemical changes, such as enzymatic reactions and oxidation (Abbas et al, 2010;Li, 2010;Roos, 2010,). Furthermore textural changes, which are manifested as changes in mechanical properties, occurring over the glass transition, are characterized as a function of temperature, moisture content or water activity (Peleg, 1993;Roos, 2010).…”

“…The glass transition theory from polymer science has been studied from a food science perspective since the pioneering work of Slade and Levine in the 1980's as many phenomena related to food processing and stability can be systematically explained by the concept of glass transition (Abbas et al, 2010;Campanella et al, 2002;Kumagai & Kumaga, 2009;Lemeste et al, 2002;Rhaman, 2006;Roos, 2010). A material typically forms an amorphous glass if crystallisation is inhibited by steric hindrance and kinetic constraints (Norton, 1998).…”

“…A state diagram, which reflects the relationship between Tg and moisture content (or water activity) and temperature, is a valuable tool to manipulate both Tg and material behavior under various storage and processing conditions (Roos 1993). Explicitly, a state diagram can be used to explain physical state changes of foods as a function of moisture content during water removal processes such as drying, baking, extrusion, evaporation, freezing, or water uptake processes such as agglomeration or tempering and flaking (Abbas et al, 2010;Campanella et al, 2002;Roos, 2010). Therefore application of the Tg as a processing parameter in the food industry is immense and is of relevance to the pulse processing industry.…”

“…The importance of the glass transition with respect to the processing and the stability of foods has long been recognized in food processing unit operations such as agglomeration, freezing, dehydration, flaking, sheeting, baking, and extrusion (Abbas et al, 2010;Campanella et al, 2002;Rhaman, 2006;Roos, 2010). However, the concept of the glass transition with respect to the processing of pulse seeds has been largely ignored.…”