Rheological influence of non-gelling amylopectins on β-lactoglobulin gel structures

The effect of non-gelling potato amylopectin on the gel properties of a particulate beta-lactoglobulin gel was studied by small and large deformation rheology and by Light microscopy. Two different techniques using small deformations, one measuring the modulus in shear and the other measuring the modulus in compression, have been compared. The fracture tests of the gels were performed in tension. The concentration of beta-lactoglobulin was kept constant at 6 wt%, and the amount of potato amylopectin was varied from 0 to 2 wt%. Two preparations of potato amylopectin, with different rheological behaviour, were used. The results illustrate the importance of a full rheological characterisation, since small and large deformation tests responded different to the structure. Both the viscoelastic and the failure properties of beta-lactoglobulin gels changed on addition of potato amylopectin even at low concentrations. The effect of the potato amylopectin concentration on the rheological properties of the mixed system varied with the properties of the potato amylopectin. The higher viscosity (HV) potato amylopectin had a shear-thinning behaviour and a small yield stress, while the lower viscosity (LV) potato amylopectin had a lower viscosity with a Newtonian behaviour. The gels containing the LV potato amylopectin increased in the modulus of small deformations with increasing potato amylopectin concentration, while the stress at fracture was constant up to a concentration of 0.5 wt% potato amylopectin and then increased with increasing potato amylopectin concentration. For the gels containing the HV potato amylopectin the modulus of small deformations reached a maximum at 0.25 wt% potato amylopectin and then decreased with increasing potato amylopectin concentration. The stress at fracture was constant up to 0.5 wt% potato amylopectin and decreased at higher concentrations. The state of aggregation of beta-lactoglobulin was influenced both by concentration and properties of potato amylopectin. The higher the potato amylopectin concentration the larger the pores in the beta-lactoglobulin gel. (C) 2000 Elsevier Science Ltd. All rights reserved.