Physics of agarose fluid gels: Rheological properties and microstructure

Agarose, a strongly gelling polysaccharide, is a common ingredient used to optimize the viscoelastic properties of a multitude of food products. Through aggregation of double helices via hydrogen bonds while cooling under quiescent conditions it forms firm and brittle gels. However, this behavior can be altered by manipulating the processing conditions viz shear. For example, gelation under shear leads to microgel particles with large surface area, which in turn leads to completely different rheological properties and texture. Such fluid gels are shown to play an important role in texture modification of foods and beverages for dysphagia patients. In this study, different concentration of agarose fluid gel (0.5 % wt, 1 % wt and 2 % wt) were considered. Rheological measurements of the microgel particles showed an increase of storage and loss modulus with increasing concentration. However, 1 % wt fluid gel exhibited the lowest viscosity in the low shear range and the shortest LVE range. Furthermore, the effect on the microstructure and size of gel particles were also investigated by using light microscopy and particle size analysis. It was observed that as the concentration of agarose increased the particle size and unordered chains present at the particle surface decreases. Based on our results, we propose specific models suggesting the impact of the particle size, the concentration and the hairy projections on the rheological and tribological properties that could help in understanding the differences in characteristics of fluid gels.

Automated summary

Agarose, a strongly gelling polysaccharide commonly used in food products, can form firm and brittle gels through hydrogen bond aggregation of double helices while cooling. The behavior of these gels can be altered by shear processing conditions, leading to microgel particles with different rheological properties. Rheological measurements showed that increasing agarose concentration resulted in higher storage and loss modulus, with the 1% wt fluid gel exhibiting the lowest viscosity in the low shear range. Light microscopy and particle size analysis revealed that higher agarose concentration led to smaller particle size and decreased unordered chains on the particle surface. These findings suggest that factors like particle size, concentration, and hairy projections impact the rheological and tribological properties of fluid gels.