Kefiran improves rheological properties of glucono-δ-lactone induced skim milk gels

The effects of addition of kefiran, the exopolysaccharide found in kefir grains, on apparent viscosity (ηappηapp) and dynamic rheological properties of chemically acidified skim-milk gels were investigated. The effect of a heat treatment on kefiran–skim milk mixture was also evaluated. Gels without kefiran showed a pseudoplastic thixotropic behaviour with a small area enclosed between the up and down curves. The addition of kefiran significantly (P⩽0.05) increased the hysteresis loop and the viscosity of the gels. Apparent viscosity of gels increased with kefiran concentration up to 300 mg L−1. Further addition did not modify significantly (P  ⩽0.05) the apparent viscosity of gels. Gels prepared from heat treated milk–kefiran mixtures showed a significantly higher ηappηapp than the ones that were prepared without a heat treatment at all kefiran concentrations assayed. The elastic modulus (G′) and the viscous modulus (G′′) of gels prepared with heat treated milk mixes increased with increasing kefiran concentration, without influencing the loss tangent (G′′/G′). The present results demonstrate that viscosity and viscoelastic properties of acid gels were improved by kefiran addition suggesting a possible application of this natural polysaccharide as an alternative thickening agent in dairy products.