Comparative gelation characteristics of carrageenan via rheological and optical techniques: Glazing gels with different sweeteners

Abstract

Glazing gels used as decorative gels are most often applied by hot spraying of solutions based on fast-setting hydrocolloids. The formation of a non-sticky gel at room conditions is crucial for their use. Gel formation and gel melting of carrageenan-based glazing gels (CGGs) with various sweeteners (trehalose, erythritol with stevia, maltitol, oligofructose, and nutriose with sucralose and acesulfame) were monitored during cooling-heating cycles using both the oscillatory rheology and the multispeckle diffusing wave spectroscopy (MS-DWS). In addition, rheological properties (shear viscosity of sols, the viscoelastic properties of gels, gel breaking strain) and texture properties (gel strength, elasticity and rupture force) were evaluated. The 12% addition of sweeteners resulted in a significant increase in gelling and melting temperatures by 2–6 °C compared to the sugar-free control sample (42 °C and 57 °C, resp.). MS-DWS, as opposed to oscillatory rheology, allowed determining of the characteristic temperatures at the beginning, middle and end of the phase transitions. The rheology gelling temperatures correlated best with the end of the gelation process, while the melting temperatures corresponded to the middle point temperature of the MS-DWS. Mechanical properties showed CGGs create a continuous gel structure characterized by a viscoelastic solid with comparable hardness and strength at small deformation, and greater elasticity compared to the sugar-free control sample. CGGs containing small molecule sweeteners formed stronger gels against rupture at large deformation than those ones with macromolecular structure. Sols of all CGGs were clear dispersions at 70 °C with Newtonian fluids characteristics and low viscosity (in the range of 9.3–10.9 mPas). These findings prove CGGs with various sugar-replaced sweeteners could be applied by hot spraying method and indicate how MS-DWS can be used to monitor gelation processes.