Effects Of Different Veasts On The Quality Of Frozen Dough And Protein Changes During Freezing And Storage

In this study,the yeast was cultured by controlling the glucose concentration in the medium to 5%,10%,13%,16%,18%,20%,and 22%,and growing simultaneously with the commonly used Angel Yeast and Barbie yeast.The experiment of the rate and the survival rate in the dough was carried out by selecting the yeast having excellent freeze resistance in the hypertonic culture to culture the yeast at a sugar concentration of 20%.Yeast,Babi yeast and 20%sugar concentration yeast were used as research objects.The effects of different antifreeze yeasts on the rheological properties,starch properties,rheological properties,moisture state and quality of steamed bread were studied.Yeast was cultured in a glucose-simulated in yeast protein structure and ultrastructural properties under different freezing conditions were studied.The main conclusions of the research are as follows:(1)The effects of antifreeze yeast on fermentation rheology,starch properties and steamed bread quality in pre-fermented frozen dough were studied.The results indicate that:With the extension of the freezing time,the Hm value of the frozen dough,the V total gas holding rate showed a downward trend.The peak viscosity,valley viscosity,termination viscosity and the setback of the three groups showed an upward trend.The hardness,gluttony and chewability of frozen dough steamed bread increased obviously,the specific volume and elasticity are reduced.It indicates that freezing storage will decrease the quality and starch characteristics of frozen dough steamed bread.But the change of these indexes of the yeast with good frost resistance is small.It was proved that antifreedough medium to extract yeast proteins from different frozen periods,and the changes ze yeast could slow down the damage caused by freezing storage,stabilize the gas production and gas holdup of dough,improve the stability of frozen dough starch paste,and slow down the aging rate of starch.(2)The effects of antifreeze yeast on the dynamic rheological properties and water state of pre-fermented frozen dough were studied by using dynamic rheometer and NMR,The results indicate that:With the extension of freezing storage time,the elastic modulus and water loss rate of frozen dough showed a decreasing trend,and T21 and T22 showed an increasing trend with the extension of freezing storage time.The bound water content of dough decreased,while the semi-bound water content increased.The frozen dough prepared by yeast with better freeze resistance has relatively good stability of dough strength,and the gluten network structure suffers less damage during the freezing process.The content of bound water and semi-bound water in the frozen dough changes little.Maintain the rate of moisture migration in the dough.(3)Yeast was cultured in simulated dough medium with glucose liquid,and yeast protein was extracted in different frozen storage periods,Ellman's colorimetric method,SDS-PAGE electrophoresis,Fourier transform infrared spectroscopy and scanning electron microscopy were used to study the changes of free mercapto and disulfide bonds,subunits,secondary structures and ultrastructural properties of yeast protein under freezing storage conditions.The results indicate that:With the extension of freezing storage time,The disulfide bond in the yeast protein is reduced,the free sulfhydryl content is increased,and the a-helix and random coil content in the secondary structure of the yeast protein have small fluctuations,?-sheet content increased,?-turn content to reduce.During the same freezing period,the disulfide bond and free sulfhydryl group of Babi and Hypertonic culture of yeast yeasts changed less than that of Angel yeasts.SDS-PAGE electrophoresis showed that the content of yeast protein Angel decreased with the extension of freezing storage time,but the content of yeast protein Babi and Hypertonic culture of yeast didn't decrease obviously,and the expression was complete.The microstructure of yeast protein was observed under scanning electron microscope.After 30 days of freezing,Angel yeast cells showed depression,rupture and some cell morphology changed,while the morphology of Babi and Hypertonic culture of yeast cells in the same frozen period was intact.Smooth,no large-scale depressions and breakages.