The Research of Combined Emulsifiers on Enhancing Frost Resistance of Yeast and Improving Frozen Dough’s Quality
|Course||Of Food Science|
|Keywords||Emulsifiers Frozen yeast Flour items Frozen dough Differential scanning calorimetry DSC Dynamic rheological properties Scanning electron microscopy (SEM) Bread quality|
In this thesis, the emulsifiers - sucrose ester and soybean phospholipids survival and growth rate of frozen yeast, the water content and glass transition temperature, frozen dough the silty and tensile properties of wheat flour, frozen dough can be frozen dynamic rheological properties, as well as frozen dough bread quality produced. The frozen yeast experiments show that the add emulsifiers to the yeast extract powder peptone dextrose medium (YPD) can improve the survival rate and growth rate of the yeast in frozen, multiplexed with the emulsifying agent may be to reduce the damage the yeast cells in the freezing process. ADD 4% of the mass fraction of emulsifiers into the yeast YPD medium and frozen at -30 ℃ and refrigerated for 5 days, the survival rate of the yeast is increased to 80% from 50%. The growth adaptation period reduced from 15 hours to six hours after to add emulsifiers yeast frozen, and frozen plate culture colonies significantly larger. Scanning electron microscope (SEM) observation showed that the emulsifiers of the yeast freezing capacity increase may be related to the aggregation of the same yeast and the emulsifier. The silty experiments show that the emulsifiers can improve the flour silty characteristics, purpose flour, add the flour mass fraction of 2% and 3% water absorption the emulsifier behind group and the formation of the time did not change significantly, settling time 7.6min liter high to 13.4min and 14.8min, the softening degree by 48FU reducing the 16FU and 10FU, silty mass index increased from 43 to 136 and 154. The stretch experiments show that the added emulsifier stretch behind the group's energy becomes larger, gluten strength enhancement, increased elongation, is conducive to the processing properties of dough, add 3% mass fraction of emulsifier is better than adding 2% mass fraction emulsifier. Differential scanning calorimetry (DSC) and experimental results show that the emulsifiers to reduce the the frozen stored procedure, the dough freeze the trend of increase in the water content, enhanced water-holding capacity of the gluten protein. The same frozen storage time, add the dough can be frozen water content is less than the blank dough emulsifiers. To add the fresh dough emulsifiers melting enthalpy by 22.35J / g reduced to 15.08J / g, and the melting enthalpy of the blank after two months frozen storage of dough increased 29.18J / g, an increase of 31.14% compared not frozen. the added emulsifier dough melting enthalpy increased 16.08J / g, an increase of only 6.63% compared to non-frozen. And after two months of frozen storage, dough add emulsifiers glass transition temperature increases from -38 ℃ -28 ℃. Add emulsifier is conducive to maintaining the stability of the dough frozen storage process quality. The dynamic rheological properties of the frozen dough studies show that different frozen storage time, adding multiplexing dough emulsifiers having a greater modulus of elasticity and a higher average molecular mass, i.e. the more complete structure of its network. Dough frozen storage after two months, within the range of 0-100Hz frequency sweep, add the emulsifier of the dough have a greater modulus of elasticity, and its elastic modulus and the viscous modulus curves intersect increased from 14.67Hz to 32.04Hz, i.e., after adding an emulsifier, the frequency scanning process dough elastic modulus greater proportion of the point of intersection of the scan curves attributable to moving to the high-frequency direction, the increase in the average molecular mass of the dough, the network structure is more complete. Baked experimental results show that the add emulsifiers is beneficial for increasing the specific volume of the frozen dough of bread obtained and improve the organoleptic properties of bread, to reduce hardening speed. Unfrozen blank, the blank and the freezing of frozen two months two months to add dough emulsifier produced bread hematocrit to 4.65cm3 / g, 3.78cm3 / g and 4.55cm3 / g and, and add emulsifier frozen dough bread Cored soft, uniform pore distribution. In the storage time of the week, frozen two months blank, adding 2% and 3% of an emulsifier The dough resulting bread 4 ° C under the the average curing speed 157.1g / day, 114.3g / day and 100.0g / day, 20 ℃ The The Average hardening speed 121.4g / day 74.3 g / day and 60.0g / day.