FORCE-DEFORMATION AND TEXTURE PROFILE BEHAVIOUR OF AQUEOUS SUGAR GLASSES

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.