Study On Quality Deterioration Mechanism And Improvement Of Frozen Dough Youtiao

As a breakfast food,youtiao is popular with consumers because of its unique flavor and texture.However,the preparation process of traditional youtiao is very complicated,the degree of industrialization is low,and it is difficult to guarantee hygiene and safety issues.Frozen dough youtiao is a new type of frozen dough product,which can be eaten directly by frying without thawing.It has a broad prospect for development.Nowadays,the demand for frozen dough youtiao in the market is growing.However,its quality is affected by frozen storage and freeze-thaw cycles.Therefore,this subject studied the quality changes and underlying mechanism of frozen dough youtiao during frozen storage and freeze-thaw cycles,and then improved them on this basis.Firstly,the quality changes of frozen dough youtiao during frozen storage were studied,and its mechanism was explored.The results showed that after 27 weeks of frozen storage,the specific volume of frozen dough youtiao decreased by 35.43%compared with 0 weeks.The internal structure of youtiao became denser.The hardness and chewiness increased,while the elasticity decreased.As storage time prolonged,the brightness of the skin of frozen dough youtiao decreased.The water content increased,while the oil content decreased.The sensory quality of frozen dough youtiao deteriorated.While during 27 weeks of frozen storage,the total score remained above 60.During frozen storage,the freezable water content of frozen youtiao dough increased.The elastic modulus（G′）and viscous modulus（G′′）decreased,while the loss factor（tanδ）increased.High-performance liquid chromatography（SE-HPLC）showed that the content of SDS extractable protein（SDSEP）increased.Meanwhile,the free sulfhydryl content increased.The microstructure found that more starch granules in the frozen youtiao dough were exposed,and the integrity of the protein network structure was lost.Secondly,the effect of freeze-thaw cycles on the quality of frozen dough youtiao and underlying mechanism were studied.After 4 freeze-thaw cycles,the specific volume of frozen dough youtiao decreased by 59.05%compared with 0 freeze-thaw cycles,the internal fibrous structure weakened.The hardness increased significantly（P<0.05）.After freeze-thaw cycles,the color of frozen dough youtiao deepened.The moisture content increased significantly（P<0.05）,while the oil content decreased significantly（P<0.05）.After 2 freeze-thaw cycles,the sensory quality has exceeded the acceptable range of consumers.Differential scanning calorimetry（DSC）found that the frozen youtiao dough had an increase in the freezable water content.The rheological properties showed a decrease in tensile resistance,G′,G′′,an increase in tanδand creep compliance.The strength of the dough was decreased.During freeze-thaw cycles,SDSEP and free sulfhydryl content increased.The microstructure observed frozen youtiao dough became loose and the protein network ruptured.Thirdly,the quality of frozen dough youtiao was improved by using fresh egg white during freeze-thaw cycles.It was found that the fresh egg white significantly（P<0.05）increased the specific volume of frozen dough youtiao.The addition of 15%fresh egg white increased the specific volume by 31.81%compared to the blank group at 4 freeze-thaw cycles,and the internal pore structure was larger.However,it increased the hardness.DSC detected that the fresh egg white slowed the increasing trend of the freezable water content of frozen youtiao dough.SE-HPLC showed that fresh egg white could increase the degree of protein cross-linking and decrease SDSEP.SDS-polyacrylamide gel electrophoresis（SDS-PAGE）and the free sulfhydryl content showed that gluten and fresh egg white protein were cross-linked through disulfide bonds.Scanning electron microscopy（SEM）showed that fresh egg white could reduce the number and size of pores in the skin of frozen dough youtiao and maintain the integrity of the surface structure.Finally,the effect of Na₂CO₃ on the quality of frozen dough youtiao during freeze-thaw cycles was investigated.The results showed that the addition of Na₂CO₃ could significantly（P<0.05）increase the specific volume of frozen dough youtiao and obtain youtiao with less hardness and fuller internal structure.Na₂CO₃ could reduce the freezable water content of frozen youtiao dough and increase G′and G′′.SE-HPLC and SDS-PAGE showed that Na₂CO₃promoted the cross-linking between proteins through disulfide and non-disulfide bonds.SEM observed that Na₂CO₃ made the surface structure of frozen dough youtiao more continuous and the pores were reduced obviously.Na₂CO₃ had a good improvement effect on the freeze-thaw quality of frozen dough youtiao.