Influence of Nongelling Hydrocolloids on the Gelation of Agarose

Abstract

The combination of different gelling and nongelling hydrocolloids is known to yield complex systems with a wide range of mechanical properties. Here, the influence of the nongelling hydrocolloids sodium-alginate and xanthan on the gelation of agarose is investigated. The two polyelectrolytes differ significantly in their flexibility, leading to opposing effects on the thermomechanical properties of the resulting composite gels. The network structure of the agarose as well as viscoelasticity, gelling temperature, and thermal stability of the gels are altered. These properties are investigated by strain and temperature dependent oscillatory rheological measurements as well as confocal laser scanning microscopy. A phenomenological model to describe the network formation of agarose in the presence of alginate or xanthan respectively is presented.

Gels: model systems for soft matter food physics

“…For the interpretation it is important to note that neither xanthan nor alginate show a significant temperature dependence [50]. In addition the xanthan jamming state is formed before the gelling of the agarose network.…”

“…In between the junction zones of this network, meshes are established that enables the bind water by forming hydrogen bonds with the hydroxyl groups of the agarobiose units facing outward [43 ]. The gelation process [50] and the increase of the real part of the complex modulus at lowering of the temperature is shown in Figure 5. The hysteresis of the modulus between the cooling and the heating curve which indicates the nonequilibrium nature if the gelation process [51,52].…”

“…The figures allow the evaluation of the mesh sizes by imaging evaluation [50]. The result for the different concentration is shown in Figure 7 in the lower curve.…”

“…There are many possibilities in the landscape of gelling and thickening agents to produce food relevant mixtures, but so far no systematic investigations which allow some insight to the influence of the physical parameters. Recently [50] had studied the influence of chain flexibility of added hydrocolloids on agarose gel formation. As examples two polyelectrolytes, xanthan and alginate [54 ] have been chosen.…”

“…The macromolecules are water soluble and are in most cases used to form with bivalent ions (calcium and magnesium) ionic networks of considerable strength [55,1 ,56] with many applications in controlled drug release [57,58] and physically and culinary aspects [59,60,13]. Without the combination with bivalent ions alginate can be used as a thickening agent due to its flexibility provides very different viscoelastic properties compared to xanthan [61,50].…”