The Mechanical Properties And Rheological Behaviors Of Machine-made Noodle Dough Sheets

The machine-made noodle dough sheet is the intermediate product of noodle processing,of which the mechanical properties and rheological behaviors of the noodle dough sheets could reflect the processing quality of noodles.However,it is short of systematic evaluation criteria for mechanical properties and rheological behaviors of dough sheets with lower water contents.And the influences of wheat flour quality and processing parameters on the viscoelasticity of dough sheets are not clear.Therefore,the mechanical properties and rheological behaviors of the dough sheets were studied by loading-unloading,stress relaxation and creep-recovery tests,and the rheological models of the dough sheets were determined.Based on this,the rheological models were used to characterize the varieties of viscoelasticity of the dough sheets prepared with the conditions of various wheat flours,mixing times,mixing vacuum degrees and rolling speeds.And the effects of wheat flour quality and processing parameters on the processing properties of dough sheets were analyzed.The main conclusions were as follows:(1)Study the mechanical properties and rheological models of the noodle dough sheets.Loading-unloading,stress relaxation and creep-recovery trials were carried out with different test parameters,and the stress relaxation and creep-recovery behaviors of the dough sheets were characterized by generalized Maxwell models with various number of elements and Burgers model.Then the effects of test parameters on the mechanical properties and rheological behaviors of the dough sheets were studied,and the optimum rheological models were determined.The results showed that the elasticity of dough sheets decreased with the decrease of loading(unloading)speeds,and the viscoelastic parameters increased with the amplification of loading amount and speed.The stress relaxation and creep-recovery behaviors of dough sheets can be fitted by 5-elements generalized Maxwell models and Burgers model respectively,of which the coefficients of determination were greater than 0.99 and 0.96 respectively.Therefore,the optimum test parameters are: loading(unloading)speed is 1 mm/s,compression strains range from 25% to 55%,compression loads range from 30 to 50 N,and stress relaxation and creep-recovery behaviors of dough sheets can be characterized by 5-elements generalized Maxwell model and Burgers model respectively.(2)Study the influence of wheat flour quality on the mechanical properties and rheological behaviors of the dough sheets.The five varieties of wheat flour were mixed in proportion by two wheat flour with a great difference in quality.The mechanical properties and rheological behaviors of dough sheets prepared with different moisture contents were examined by loading-unloading,stress relaxation and creep-recovery tests,and the viscoelasticity was characterized by rheological models.The results indicated that the hardness,elasticity and viscoelasticity of dough sheets increased gradually with the increase of the gluten content and quality,but when the moisture content was at 38%,the hardness,elasticity and viscoelasticity of the various quality dough sheets had the largest difference.Therefore,for machine-made noodles,the quality difference of wheat flour was reflected clearly by the higher water addition.(3)Study the influence of mixing time on the mechanical properties and rheological behaviors of the dough sheets.The mechanical properties and rheological behaviors of dough sheets prepared with various moisture contents and mixing times were studied by loading-unloading,stress relaxation and creep recovery tests,and the viscoelasticity was characterized by rheological models.The results showed that the highest hardness and elasticity among dough sheets with different moisture contents presented when the dough was mixed for 10 min.At the moisture content of 34%,the viscoelasticity of dough sheets first increased and then decreased with the mixing time increasing,and the maximum viscoelastic parameters presented at mixing 15 min.At the moisture content of 36% and 38% respectively,the viscoelastic parameters of dough sheets increased until 10 min and then remained.Therefore,the mixing time should not last for too long during the machine-made noodles processing.Mixing time could take10～15 min with lower moisture content,and 10 min with higher moisture content.(4)Study the influence of mixing vacuum degrees on the mechanical properties and rheological behaviors of the dough sheets.The mechanical properties and rheological behavior of the dough sheets with various moisture contents and mixing vacuum degrees were studied by loading-unloading,stress relaxation and creeprecovery tests,and the viscoelasticity of the dough sheets was characterized by rheological models.The results showed that the hardness and elasticity of the dough sheets were significantly improved when the vacuum degrees reached-0.06 MPa.For the dough sheets with moisture content of 34%,the viscoelastic parameters increased significantly at vacuum degrees-0.04 MPa.And for the dough sheets with moisture contents of 36% and 38% respectively,the viscoelastic parameters increased only when the vacuum degrees reached-0.06 MPa.Meanwhile,the higher the moisture content,the smaller effect of vacuum on dough sheet viscoelasticity.Therefore,with the lower moisture,the vacuum degrees of mixing could be-0.04 MPa,while the water addition increased,the vacuum degree could be-0.06 MPa.(5)Study the influence of rolling speeds(roller linear speeds)on the mechanical properties and rheological behaviors of the dough sheets.The mechanical properties and rheological behaviors of the dough sheets with various moisture content and rolling speeds were studied by loading-unloading,stress relaxation and creep-recovery tests respectively.The results suggested that the hardness,elasticity and viscoelasticity of dough sheets decreased with the rolling speeds increasing.However,with the rolling speed greater than 5.0 mm/s,the hardness,elasticity and viscoelasticity of dough sheets with 36% and 38% moisture content respectively showed no significant change.Therefore,for lower moisture content of dough sheets,the rolling speeds should not be too fast.By contrast,with higher moisture contents,the rolling speeds can be increased appropriately.