Force‐deformation and Texture Profile Behaviour of Aqueous Sugar Glasses

Abstract

Aqueous sugar glasses, simulating the structure of commercial boiled sweets, were investigated in their temperature transition range by force deformation and texture profile tests using the Instron Universal Testing Machine. Cylindrically cast and thermally equilibrated aqueous glucose‐sucrose model systems having 2—2.3% moisture (w/w) and containing glucose to sucrose ratios (%w/w) of 100/0, 70/30, 55/45 and 35/65 were used. Force‐deformation tests revealed that the Young's modulus was independent of the glucose‐sucrose ratio and decreased drastically with temperature from 820 MN/m2 at 3°C to 30MJV/m2 at 30°C. Texture profile tests were carried out on a model system (35/65 glucose‐sucrose blend) and on a commercial hard boiled sweet. Experimental profiles for both systems were largely similar and permitted evaluation of the textural parameters of hardness and cohesiveness. Composite force‐strain or force‐penetration curves were constructed from series profile tests on the same sample and demonstrated that (a) high values of hardness were found with a flat probe and low temperatures; (b) low values of hardness were found with cone and wedge probes and high temperatures. Cohesiveness generally decreased as the initial applied strain increased, because higher strains resulted in greater sample fracture and/or plastic flow. On the other hand, temperature and probe type had little effect on cohesiveness. The difficulties experienced in bridging the gap between the empirical and the fundamental approaches to texture profiling of food are discussed.

Physico‐chemical studies on sugar glasses.

“…Our observations that the glass transition temperature is independent of the sucrose to dextrose ratio is in agreement with the work of McNulty & Flynn (1977). They studied aqueous sucrose glasses containing 35, 55, 70 and 100% w/w dextrose and 2.0-2.3% w/w water.…”

Dimensions of food texture: A conceptual discussion

“…Several authors working on a diverse range of foods have described brittleness as characteristic of hard foods. Yet in absolute terms, the scale of hardness for foods is large (e.g., boiled sweets $1 kN [McNulty & Flynn, 1977] to 1 N for yoghurt [Zhao et al, 2020]) suggesting that brittleness can occur throughout the low strain domain. Similarly, and perhaps by definition a material that exhibits plastic failure when deformed is undergoing a high level of strain, yet strain alone is not a measure of plastic failure as many semi-solid foods exhibit recoverable elasticity and will regain some of their former shape when the force is removed.…”

Effect of glass transitions on the rheological properties of food polymers

“…The figure also shows that higher molecular weight compound gives higher T,' . Annular shear test for amorphous sorbitol: (A) storage modulus G', (+) loss modulus G", and (*) loss tangent (From Ref 15…”