Study On Rheological Properties Of Semi-solid Food And Their Determination Method

The paper aimed to investigate the semi-fluid food with complex characteristics anddifficult to determine, such as mayonnaise, jams, cheeses, chocolates. The foods ofdifferent types and under various processing conditions, were tested by MCR101toacquire the rheological properties which can provide the theoretical basis andexperimental data for the processing and quality control. The following researcheswere carried out.Firstly, the rheological properties of semi-fluid food were studied. It was focusedon the mayonnaises of different types and several kinds of jams. The static anddymatic rheological properties of these foods were studied. The results suggested thatthey were pseudoplastic fluid and exhibited thixotropic. The viscosity of the samplesdecreased with the increasing of temperature. The dymatic rheology showed that thekind of food are viscoelastic, with weak gel-like property. The change of internalstructure affected by the temperate from4℃to25℃is little. The concentrationprocessing made the viscosity and the stability increased. While the heating made theyield stress decreased and tanδ increased. During the heating processing, theincreasing of viscous components caused the fluidity improving. The yield stress,viscosity, G’ and G’’ increased as the solid content increased which showed thestructures were improved. Compared with mayonnaise, the yield stress and viscosityof jams were higher, which indicated the jams were difficult to flow. The G*of jamsabove that of mayonnaise suggested that the anti-deformation capability of the formerone was greater.Sencondly, the rheological properties of semi-solid food containing chocolatesand cheeses were studied. It demonstrated that melt samples exhibited shear thinningbehavior and thixotropic. As the temperate increased, their viscosity decreased. Theflow of melt chocolates followed Casson equation. The whole tanδ of chocolate weregreater than1, which indicated the viscous composition were more than the elastic elements. However, all the tanδ of cheese were less than1, revealing that the elasticitywas dominant. Compared with the chocolates, the yield stress and viscosity of cheeseswere greater. So the cheeses were more difficult to flow than chocolates. The Ea ofcheeses were greater, which showed the changes of temperature of cheese weregreater. The weak gel and anti-deformation capability of cheeses were better than thechocolates.Finally, the parameters of rheology were determined. The rheological propertiesincluded viscosity, yield stress, flow activation energy(Ea), the flow pattern, phaseangel(δ) and complex modulus(G*). The viscosity of semi-fluid were0.6-120Pa, theyield stress values were from20Pa to160Pa, the flow activation energy values(Ea)of semi-liquid were from10kJ to25kJ, while the semi-solid were0.6Pa to900Pa,1.9Pa to500Pa, Ea were20to75kJ. Food of this type followed pseudoplastic flow.The parameters of dymatic rheology included phase angel(δ) and complexmodulus(G*). The tanδ values of semi-liquid was between0.1and0.5, while thesemi-solid was between0.5to16. The G*values of semi-liquid were500Pa to25000Pa, the semi-solid were450Pa to7000Pa. Compared with the semi-solid, the yieldstress and viscocity of the semi-liquid were less and apt to flow. The Ea of thesemi-liquid indicated that the viscocity affected by temperature was less. The weakgel and anti-deformation capability of cheeses were better than those of thesemi-liquid, moreover, those in the latter one were better than the semi-solid. The sixparameters were the characterization of the rheological properties.