Study On The Effects Of Different Heat Treatment On Wheat Flour Characteristics

Physicochemical and digestive properties of wheat flour modified by heat-moisture treatment(HMT) were investigated. The Jin Yuan medium hard wheat flour was used as raw material to prepare HMT samples at varying conditions, exploring the optimize HMT modification conditions. Using isolated wheat starch(WS) as control, the wheat flour(WF) was modified by HMT in a high pressure reactor with the optimize conditions. Components in wheat flour other than starch and starch interactions during HMT were investigated. In vitro digestibility of native and HMT wheat flours was discussed. And then, the effects of Spray Drying and Extrusion treatment on properties of wheat flour and starch were explored. Finally, this article also discusses the application of different heat modification on flour quality. The analyzed results are shown as follows.The effect of Heat-moisture Treatment on flour characteristics was explored. It was found that, after Heat-moisture Treatment, wheat flour’s whiteness, color and lustre was poor; gelatinization degree increased, the pasting viscosity was reduced, gelatinization temperature was increased; the solubility enhanced dramatically and then slowly with processing temperature, swelling power decreased at 90℃ while increased at 80℃, The processing temperature and the duration time have a positive correlation(p<0.05) with whiteness, color, gelatinization degree, pasting characteristics of wheat flour. However, the processing time was not significantly correlated with these indicators(p>0.05). So, the conditions with 100,120℃, water content of 25%, 30% and duration time of 0.5h were the optimum technological conditions for modification by HMT.The wheat flour(WF) and wheat starch(WS) were modified by HMT in a high pressure reactor with the optimization process. Results indicate that moisture had greater influences on the properties of HMT samples than temperature. When compared to native samples, decreases in peak viscosity, enthalpy change, swelling power and relative crystallinity, and increases in gelatinization temperature were found in both WF and WS after HMT treated at moisture of 25% and 30%, but an opposite trend was found for those treated at 8% moisture. A decrease in rapidly digestible starch(RDS) and slowly digestible starch(SDS) content while increase in solubility and resistant starch(RS) content were found for all moisture levels. In most case, more significant changes were found for higher moisture content. There were some remarkable differences between WF and WS after HMT. The solubility of WF was higher than that of WS after HMT. The effects of temperature and moisture on relative crystallinity of WF followed a similar tendency to WS, but with less amplitude. This may be due to other components such as protein inhibited chain mobility of starch molecular during HMT.When the effects of Spray Drying on characteristics of wheat flour. Results showed that when compared to native samples, increased in damage starch, amylase content, gelatinization temperature and solubility, and decreased in peak viscosity, enthalpy change were found in both WF and WS after Spray Drying Treatment. Compared with the WS, damage starch and amylase content of wheat flour increase rate was lower. Compared with HMT, the Spray samples of crystallinity and crystal integrity was basically consistent with the moisture content of 8%; The enthalpy change of WF was higher than that of WS after Spray processing; Compared with WS after HMT, elastic modulus G ’ of starches was higher than the former after Spray treatment. Increase in resistance starch was found during Spray processing, but with less amplitude.The results of extrusion treatment on flour characteristics were shown as follow. Compared with the previous two, the modification of extrusion treatment on wheat flour was more intense. Decreases in peak viscosity, breakdown value and setback value, and increases in damaged starch, gelatinization temperature and solubility were found in WF after Extrusion treatment. Extrusion treatment significantly changed the crystal structure and pattern. Protein which formed a barrier surrounding starch granules was denatured, accelerating access to amylases and increasing starch digestibility. And then, the rheological properties were studied. Results showed that elastic modulus G ’ of flour increased and the viscous modulus decreased after Spray treatment, so it was easy to deformation under the action of external force.Some kinds of wheat flour of higher resistant starch by different heat treatment were used to make noodles. Results showed that two kinds of flours of highest resistant starch content were made noodles and the luster was worst. However, the heat treatment starch was added to the flour for making noodle and the luster was better, and it can improve the noodle quality. Wheat flour noodles quality was poor after HMT. The sensory evaluation of heat treatment noodles was higher than the native flour noodles. The rate of cooking lose : HMT > Extrusion > Spray treatment.