Rheology of individual chitosan and polyphenol/chitosan microparticles for food engineering

Encapsulation of perishable bioactive molecules has become a standard process in the food industry. Beads in the millimeter size range may offer technological advantage over smaller particles and nano-structured materials for encapsulation purposes because of higher volume to surface ratios, but their size might seriously affect the sensory properties of the final edible products. We investigated the rheological properties of individual beads composed of chitosan (CTS) cross-linked with sodium tripolyphosphate (TTP). We produced the beads by the external gelation method using different combinations of CTS and TTP concentrations. Analysis of raw data showed that CTS and TTP affected both the morphology and the response of the particles to mechanical load in a non proportional way. The data indicated that the mechanical properties of the beads could not be explained with the aid of standard linear viscoelastic models. We therefore exploited a recently-developed nonlinear model to analyse mechanical data collected during the stress phase and estimate viscoelastic parameters. We found a clear synergic effect of CTS and TTP concentrations on particles' stiffness and a crossover effect on their viscosity. Two representative bioactive food phenolic compounds, i.e. chlorogenic acid and catechin, were then encapsulated into the beads. Encapsulation of chlorogenic acid and catechin dramatically altered the viscoelastic behaviour of the particles in a similar way. The particles became less stiff and viscous and more fluid-like compared to empty beads with the same CTS and TTP composition. Our results pave the way for a more accurate evaluation of sensory characteristics of novel functional foods incorporating particle carriers for bioactive molecules.

Automated summary

Encapsulation of perishable bioactive molecules has become a standard process in the food industry. In this study, we investigated the rheological properties of chitosan cross-linked with sodium tripolyphosphate beads and found that their mechanical properties could not be explained with standard linear viscoelastic models. Encapsulation of phenolic compounds also altered the viscoelastic behavior of the beads.