A Review on Methods and Theories to Describe the Glass Transition Phenomenon: Applications in Food and Pharmaceutical Products

Abstract

Given the complexity in composition and the various environmental conditions to which foods and pharmaceuticals are exposed during processing and storage, stability, functionality, and quality are key attributes that deserve careful attention. Quality and stability of foods and pharmaceuticals are mainly affected by environmental conditions such as temperature, humidity, and time, and for processing conditions (e.g., shear, pressure) under which they may undergo physical and chemical transformations. Glass transition is a key phenomenon which is useful to understand how external conditions affect physical changes on materials. Consequently, theories that predict and describe the glass transition phenomenon are of a great interest not only for the food industry but also it extends to the pharmaceutical and polymer industries. It is important to emphasize that the materials of relevance in these industries are interchangeably sharing similar issues on functionality and their association with the glass transition phenomenon. Development of new materials and understanding the physicochemical behavior of existing ones require a scientific foundation that translates into safe and high-quality foods, improved quality of pharmaceuticals and nutraceuticals with lower risk to patients, and functional efficacy of polymers used in food and medicinal products. This review addresses the glass transition phenomenon from a kinetics and thermodynamics standpoint by presenting existing models that are able to estimate the glass transition temperature. It also explores traditional and novel methods used for the characterization of the glass transition phenomenon.

Thermomechanical characterization of an amylose-free starch extracted from cassava (Manihot esculenta, Crantz)

“…Other techniques (like nuclear magnetic resonance, electric spectroscopy spin resonance dielectric spectroscopy, dynamic rheometry, inverse gas chromatography, among others) are available but were not used here (Abiad, Carvajal, & Campanella, 2009;Blanshard, 1995).…”

Brewing with fractionated barley

“…The reason for this might be the difference in the heating rate; it is known that the glass transition depends on the rate of heating or cooling. A lower heating rate would result in a lower measured glass transition temperature (Abiad, Carvajal, & Campanella, 2009). …”

“…The values for the parameters from the GAB equation are shown in Table 2. We used the isotherms to adapt the state diagram; this extends the methodology (Abiad et al, 2009). The isotherms showed that proteins take up less water than the starch granules, which causes the protein to be dryer than expected from the moisture content of the endosperm.…”

“…The glassy state is a nonequilibrium solid state, in which the molecules have no ordered structure, leading to a larger volume to be occupied than when in crystalline state (Roos, 2007;Slade et al, 1995). The glass transition is a second-order reaction and the glass transition temperature (Stuart et al) is influenced by the water content and the temperature (Abiad, Carvajal, & Campanella, 2009). It can be reasoned that when one material, for example the protein matrix of barley, is in the rubbery state and one material, for example barley starch, is in the glassy state, milling could be more effective in separating these two components.…”

“…Diff erent methods for measuring glass transitions are described in the literature but diff erential scanning calorimetry (DSC) is the most widely used method (Abiad et al, 2009). DSC measures the heat fl ow and heat capacity in heating and cooling to identify the temperature of the transitions.…”