The Effect Of Freezing On The Water State And Ice Crystal Morphology Of Non-fermented Dough

Frozen dough technology is widely used in the pasta manufacturing industry,which creates conditions for the industrialization,standardization and large-scale production of pasta products and staple foods.Moisture is an indispensable part of the dough,and its binding state and ice crystal shape formed during the production and processing of frozen dough will affect the quality of the final product.In this study,Xiaoyan 22 wheat grains were used as test materials.After milling,flour was used for making dough with farinograph,using low-field nuclear magnetic resonance(LF–NMR),differential scanning calorimetry(DSC)and scanning electron microscope(SEM)and other technologies,systematically studied the influence of different mixing degree,freezing temperature,frozen storage time and thawing method on the moisture binding state and ice crystal form of non-fermented frozen dough,and analyzed the changes in moisture state during the dough processing,which can be used for the frozen dough production provides theoretical basis.The main conclusions are as follows:(1)The mixing degree has a significant effect on the moisture binding state and ice crystal shape of the dough.In the dough with different mixing degree,the ratio of strongly bound water(A₂₁)is the highest when the dough just leaves 500 BU,and the ratio of weakly bound water(A₂₂)is the lowest.Meanwhile,the internal structure of the dough is dense,and the average pore area,pore number and porosity are the lowest.After a certain period of frozen storage,part of the strongly bound water in the dough is transformed into weakly bound water and free water.Small ice crystals gradually form large ice crystals,and the average ice crystal area and porosity increase.The frozen dough just leaves 500 BU is compared with the other 4 dough with different mixing degrees still has the higher A₂₁,the average area and porosity of ice crystals are the lowest,and the number of ice crystals is small.It can be seen that the water molecules of the dough that have just left 500 BU have the least fluidity,the most fully hydrated gluten,the formation of protein network structure is better,and the internal moisture state is still relatively stable after freezing.(2)The freezing temperature has a significant impact on the water binding state and ice crystal morphology of dough.After freezing at-40?,the water binding state and freezing water content of the non-fermented dough is closer to that of the control group,and the degree of change is smaller,and the mean area and percent of ice crystals formed are also the smallest,resulting in the least damage to the dough.During the storage process,as the freezing temperature decreases,the relaxation time and ratio of weakly bound water and free water(T₂₂,T₂₃,A₂₂,A₂₃),average ice crystal area and porosity all show a downward trend,while A₂₁shows an increasing trend.Higher freezing temperature has the greatest negative impact on the water and ice crystals of the dough,thereby affecting the stability of the water molecules in the dough.(3)Frozen storage time has a significant effect on the water state of non-fermented dough.During the storage process,A₂₁in the dough showed a decreasing trend,while T₂₂,T₂₃,A₂₂and A₂₃all showed an increasing trend.The pores where ice crystals are formed inside are getting bigger and bigger,the average ice crystal area increases fluctuatingly,and the number of ice crystals decreases.The surface structure also began to become rough.The gluten fiber bundles gradually became thinner,elongated,and broken,and the protein structure became loose.The starch granules began to be exposed.Especially when the dough was frozen for 1-60 d,the water binding state and ice crystal form in the dough change most significantly,indicating that the frozen storage time has the greatest negative impact on the moisture state of the dough at this time.(4)Different thawing methods have a significant impact on the moisture state and pore shape of the dough.Among the three thawing methods,4?low-temperature thawing and 25?room temperature have the least influence on the moisture state of the dough,and microwave thawing has the greatest influence on the moisture state of the dough.During the frozen storage,the dough after thawing at 4?and room temperature at 25?contains lower T₂₁,A₂₃,freezing water content,average pore area and porosity,and higher T₂₂,A₂₁and number of pores.The dough after microwave thawing contains high A₂₃,freezing water content,average pore area and porosity,and does not contain strongly bound water.Therefore,microwave thawing has the most significant negative effect on the moisture state of non-fermented dough.