Study On The Improvement Of Frozen Dough Quality By Antifreeze Polysaccharide Of Wheat Bran

Frozen dough technology is an important way to realize the industrialization of staple food and promote the development of the baking industry and the traditional pasta industry.The quality deterioration of the dough during the freezing storage process is the main factor restricting the promotion of frozen dough technology.Among them,the destruction of the dough structure by ice crystals is the main reason for the deterioration of the dough quality.As an important component of wheat dietary fiber,Wheat Bran Antifreeze Polysaccharides（WBAP）can act on key components of dough to improve the quality of frozen dough,but the mechanism of action is unknown.In this study,three kinds of antifreeze polysaccharides with different structures（BF30-40,BF40-50,BF50-60）were extracted from wheat bran,and their effects on the quality of frozen dough steamed bread were discussed.The mechanism of improving the quality of frozen dough by different structures of WBAP was elucidated from dough quality,yeast activity,water distribution,ice crystal morphology and gluten quality.The main results are as follows:（1）All three kinds of WBAP significantly improved the quality of frozen dough.BF30-40,BF40-50 and BF50-60 increased the specific volume of frozen dough steamed bread for 60 days by 9.90%,15.84%and 10.89%,the moisture content increased by 1.38%,3.37%and 1.54%,and the hardness decreased by 23.11%,28.19%and 25.21%,and the internal texture structure of the steamed bread is improved,the porosity and the average area of??pores are increased,and the pore distribution is more uniform.Among them,BF40-50 has the best effect.The rheometer was used to measure the viscoelasticity of the dough.It was found that the viscoelasticity of the frozen dough increased and the tanδdecreased.All three kinds of WBAP had positive impact on the rheological properties of the frozen dough,and BF40-50 had the most obvious effect.The results showed that three kinds of WBAP reduced the death rate of yeast in frozen dough,increased the activity of yeast,and increased the gas production of dough.The effects of BF30-40 and BF40-50were better than BF50-60.Differential scanning calorimeter（DSC）was used to measure the thermal properties of the dough.It was found that WBAP can reduce the starch gelatinization temperature and increase the gelatinization enthalpy of frozen dough,so that the dough has better stability during heating.There is no significant difference in the effect of WBAP.（2）DSC,time domain nuclear magnetic resonance,X-ray micro-computer tomography（Micro-CT）and cryo-scanning electron microscope（cryo-SEM）were used to explore the moisture distribution of frozen dough and the changes in ice crystal morphology.The results showed that:BF30-40,BF40-50 and BF50-60 reduced the freezeable water content of the frozen dough for 60 days by 7.25%,8.42%and 7.75%,respectively,and increased the T₂₁content by 24.34%,26.20%and 27.57%,T₂₂content decreased by 5.64%,5.62%and 4.95%.These indicate that WBAP can inhibit the conversion of strongly bound water to weakly bound water and free water caused by frozen storage,and reduce the content of freezeable water in the dough.After adding WBAP,the number and size of large pores in the frozen dough decreased obviously,indicating that WBAP effectively inhibits the recrystallization of ice,reduces the uneven distribution of moisture in the dough,and slows down the deterioration of the quality of the frozen dough,and the effect of BF40-50 and BF50-60 is more obvious.Using cryo-SEM to further observe the morphology of ice crystals in the dough,WBAP can inhibit the growth of ice crystals in the dough,and the ice crystals change from lumpy shape to acicular shape when they grow under the action of WBAP,which can reduce the damage to the dough structure.（3）For unheated frozen dough for 60 days,adding three kinds of WBAP significantly reduced the free sulfhydryl（SH）content of gluten protein in frozen dough,and BF50-60had the best reduction effect.Three kinds of WBAP can increase the surface hydrophobicity（H₀）of frozen gluten protein,indicating that WBAP can reduce the burying effect of hydrophobic groups under frozen storage conditions,among which BF40-50 and BF50-60have more obvious effects.The results of size exclusion chromatography（SE-HPLC）show that WBAP can significantly reduce the contents of SDS-P and SDS-M in frozen dough,and increase the content of insoluble protein（SDS-I）,indicating that WBAP can alleviate the depolymerization of GMP caused by frozen storage.In addition,through infrared spectroscopy（FITR）analysis,it was found that WBAP inhibited the decrease ofα-helix and the increase ofβ-structure of gluten protein induced by freezing,and improved the stability of gluten protein.Using a confocal laser scanning microscope（CLSM）to observe the microstructure,it can be found that three kinds of WBAP can enhance the gluten network structure in frozen dough.The above results indicate that WBAP can improve the stability of frozen gluten protein,inhibit the depolymerization of gluten protein caused by frozen storage,and improve the strength and elasticity of frozen dough.For the 60-day frozen dough heated to 95℃,adding BF30-40,BF40-50 and BF50-60reduced the SH content by 20.45%,30.30%and 28.03%,respectively.At 95°C,the gluten protein H₀of frozen dough with three kinds of WBAP was significantly lower than that of the control,which enabled the gluten to bury more hydrophobic groups at high temperature.Among them,the effect of BF40-50 was the most obvious,which was a decrease of 12.86%compared with the control.SE-HPLC results showed that all three kinds of WBAP significantly reduced the content of SDS-P and SDS-M and increased the content of SDS-I.Among them,BF30-40 and BF40-50 have similar effects and are better than BF50-60.Using reversed-phase chromatography to analyze the subunit distribution of gluten after heating,it was found that the content of almost all subunits of frozen dough added with three kinds of WBAP was not significantly different from that of fresh dough.It acts to weaken the thermal aggregation ability of gliadin subunits.Through FITR analysis of protein secondary structure changes,it was found that BF30-40,BF40-50 and BF50-60reduced theα-helix content from 33.02%of the control to 21.82%,22.97%and 23.51%,respectively,while theβ-structure content decreased.It was higher than the control and increased the intermolecularβ-sheet content from 1.67%of the control to 2.16%,2.21%and 2.12%.Observing the microstructure through CLSM,it can be found that the three kinds of WBAP promote the cross-linking of gliadin and glutenin when the frozen gluten protein is heated.The above results indicate that WBAP can promote the aggregation of gliadin and the cross-linking of gluten protein during the heating process of frozen dough,enhance the thermal aggregation ability of gluten protein,and make the frozen dough have good quality after being cooked.