Effect Of Wheat Starch Structure On Noodle Quality

When starch is heated in water,the swelling of starch granules,the disappearance of birefringence and the destruction of crystal structure will occur.The process of starch structure from order to disorder is also called phase transition（gelation）.In this paper,four kinds of wheat starch were used as raw materials to prepare different phase transition samples by RVA simulated DSC heating.The phase transition process,microstructure,long-range orderliness,short-range orderliness and water migration mechanism of wheat starch were explored by differential scanning calorimetry,scanning electron microscopy,X-ray diffraction,Fourier transform infrared spectroscopy and low-field nuclear magnetic resonance technology,so as to explore the structural changes in the phase transition process of four kinds of wheat starch.Based on this,the influence of wheat starch structure on noodle quality was analyzed.The results are as follows :（1）The basic components of four wheat starches were determined by national standard method;（2）The phase transition states of the four wheat starches at different moisture contents（33.3 %,50 %,66.7 %,75 % and 80 %）were determined by DSC.It was found that the gelatinization enthalpy of the four wheat starches at 66.7 % moisture content was the highest,and the complete phase transition was achieved at this time.With the continuous increase of moisture content,the enthalpy decreased gradually and had no significant difference with the enthalpy of 66.7 % moisture content.The phase transition process of four wheat starch samples with different phase transitions was determined by DSC.It was found that the sample still had enthalpy when heated to the temperature of To-10,To and Tp.At this time,free water was detected by low field nuclear magnetic resonance,and there was no enthalpy and free water until heated to the temperature of Tc and Tc + 10,indicating that the sample did not undergo complete phase transition at the temperature of To-10,To and Tp,and complete phase transition occurred again when heated to a higher temperature;（3）The long-range order and short-range order of four wheat starch samples with different phase transitions were determined by X-ray diffraction and Fourier transform infrared spectroscopy.It was found that the crystal structures of the samples heated to To-10,To,Tp,Tc and Tc + 10 still exist.Although the diffraction peak of X-ray diffraction has almost disappeared at the temperature of Tc + 10,and the R1047 / 1022 value of Fourier transform infrared spectroscopy is very low,there are still some crystal structures,that is,the molecular structure of the sample is still changing when there is no endothermic peak measured by DSC and there is no free water measured by Low Field NMR;（4）The water migration mechanism of four wheat starch samples with different phase transitions was determined by low-field nuclear magnetic resonance technology,and it was found that at 33.3 % and50 % water contents,with the increase of heating temperature,the range of T2 gradually narrowed,the combination of water and starch was stronger,and the area of bound water and uneasy flowing water gradually increased.At 66.7 % moisture content,with the increase of heating temperature,the T2 range first decreases and then increases,but the bound water area gradually increases and the free water area gradually decreases to about 1 %.When the water content was 75 % and 80 %,the range of T2 gradually became smaller.When the temperature was heated to Tc and Tc + 10,the free water was fully combined with the starch sample,and all free water was converted into bound water and uneasy flowing water.The free water area was 0,and the sample had a complete phase transition,which was consistent with the DSC results;（5）The whiteness of four wheat noodles ranged from 84 to 84.8 by whiteness determination,cooking characteristics,sensory evaluation and texture determination.The water absorption rate of noodles ranged from 114.3 % to 115.2 %,cooking loss rate ranged from 1.4 % to 2.0 %,and broken rate was 0.Sense score reached more than 90 points;there were no significant differences in hardness and chewiness of four noodles,but there were significant differences in elasticity,cohesiveness and adhesiveness;（6）The correlation analysis showed that the gelatinization temperature of flour was significantly negatively correlated with the long-term order of starch,and the correlation coefficient r =-0.976,P < 0.05;noodle viscosity was significantly negatively correlated with the short-range order of starch,and the correlation coefficient r =-0.970,P < 0.05;noodle taste was positively correlated with amylose content（r= 0.967,P < 0.05）.The total score of noodle sensory evaluation was significantly positively correlated with protein content（r = 0.968,P < 0.05）,and significantly negatively correlated with long-term order（r =-0.988,P < 0.05）.Noodle cohesiveness was significantly positively correlated with amylopectin content（r= 0.967,P < 0.05）.Chewability and elasticity were significantly negatively correlated,with correlation coefficient r =-0.985,P<0.05.