Effects Of Purple Sweet Potato Flour On The Physicochemical Properties Of Wheat Flour And The Compatibilities Of Both Of Starches

China is a big country of purple sweet potato cultivation and production,and purple sweet potato is rich in nutrients and contains many biologically active components.In order to expand the application of purple sweet potato in flour products,purple sweet potato flour and wheat flour were used as raw materials in this paper,the effects of purple sweet potato flour on the physicochemical properties of wheat flour,the compatibility between purple sweet potato starch and wheat starch,and the effect of purple sweet potato starch on gel properties of wheat starch were studied.The main results are as follows:1.The effect of different amount of purple sweet potato flour on physicochemical properties of wheat flour was studied by adding 0%,5%,10%,15% and 20% purple sweet potato flour to wheat flour in order.The results showed that with the increase of the content of purple sweet potato flour,the water absorption and degree of softening of the mixed flour are increasing,while the development time,stability time and farinograph quality number are decreasing.The addition of purple sweet potato flour significantly increased the peak viscosity,trough viscosity and final viscosity of wheat flour,and decreased the value of breakdown and setback.The rheological results show that with the addition of purple sweet potato flour,the shear thinning phenomenon of wheat flour gradually weakens,and the elastic modulus(G’)and viscous modulus(G’’)gradually increase,starch gel network structure was enhanced in mixed systems.Moreover,the addition of purple potato flour made the gelatinization temperature of the wheat flour drift toward high temperature,which improved the thermal stability of the wheat flour.2.The shapes and particle size of wheat starch and purple sweet potato starch are similar.The two starches were both spherical or oval in shape and the distribution is uneven.The average particle diameter of wheat starch is 21.770 μm,and the average particle diameter of purple potato starch is 19.265 μm.The crystal form of wheat starch is A type,the crystal form of purple sweet potato starch is C type.3.The compatibility of purple sweet potato starch and wheat starch was characterised by measuring glass transition temperature,equilibrium melting temperature and interaction parameter at water contents of 40% and 60% respectively.It was found that the addition of purple sweet potato starch could effectly enhance the glass transition temperature of wheat starch and the glass transition temperature of all mixed starches has a single peak.The equilibrium melting temperature of mixed starch decreased slightly with the increase inpurple sweet potato starch content.And when the addition amount of purple sweet potato starch was 10%,the change was most obvious.Moreover,the interaction parameter values of all mixed starches were negative by adding purple sweet potato starch.The above results showed that wheat starch and purple sweet potato starch have good compatibility.4.The results of the study on the gelling properties of wheat starch with different amounts of purple sweet potato starch showed that with the increase of purple sweet potato starch content,the solubility,swelling power and transparency of wheat starch gradually increased,and the retrogradation decreased.Moreover,the addition of purple sweet potato starch improved the hardness,gummingness,springness and cohesiveness of wheat starch gel.The peak viscosity,trough viscosity and final viscosity showed an upward trend,while the setback value showed a downward trend.The addition of purple sweet potato starch increased the elastic modulus(G’)and viscosity modulus(G’’),reduced the loss tangent value,the value of synerisis was reduced,improving the freeze-thaw stability of wheat starch gel,the free water content was reduced,and the weakly bound water content was increased,and the change is most obvious when the addition amount of purple sweet potato starch is 10%.The comprehensive results showed that purple sweet potato starch enhanced the wheat starch gel network structure.