复配乳化剂提高酵母抗冻性及改善冷冻面团品质的研究
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摘要
本论文主要研究了复配乳化剂—蔗糖酯和大豆磷脂对冷冻酵母的存活率和生长速率,小麦面粉的粉质和拉伸特性,冷冻面团中可冻结水的含量和玻璃态温度、冷冻面团的动态流变学性质,以及冷冻面团所制作的面包品质等的影响。
冷冻酵母实验表明添加复配乳化剂到酵母浸出粉胨葡萄糖培养基(YPD)中能够提高冷冻后酵母的存活率和生长速率,复配的乳化剂可以减少酵母细胞在冷冻过程中受到的损伤。添加4%质量分数的复配乳化剂到酵母YPD培养基中并在-30℃冷冻并冷藏5天后,酵母的存活率由50%升高到80%。添加乳化剂的酵母冷冻后生长适应期由15小时减少到6小时,且冷冻后平板培养菌落明显偏大。扫描电镜(SEM)观察表明复配乳化剂使酵母抗冻能力的提高可能同酵母与乳化剂的聚集作用有关。
粉质实验表明,复配乳化剂可以改善面粉的粉质特性,中筋粉中添加面粉质量分数2%和3%的乳化剂后面团的吸水率和形成时间没有显著变化,稳定时间由7.6min升高到13.4min和14.8min,弱化度由48FU减少到16FU和10FU,粉质质量指数由43提高到136和154。拉伸实验表明,添加乳化剂后面团的拉伸能量变大,筋力增强,延伸度增大,有利于面团的加工性质,其中添加3%质量分数的乳化剂效果优于添加2%质量分数的乳化剂。
差示扫描量热(DSC)实验结果表明,复配乳化剂能够降低冷冻存储过程中面团可冻结水含量增加的趋势,增强面筋蛋白的持水能力。相同的冷冻存储时间,添加复配乳化剂的面团可冻结水含量小于空白面团。添加复配乳化剂后新鲜面团融化焓由22.35J/g减少到15.08J/g,而冷冻储藏两个月后空白面团的融化焓增加到29.18J/g,相比未冷冻增加了31.14%,添加乳化剂的面团融化焓增加到16.08J/g,相比未冷冻仅增加了6.63%。并且冷冻储藏两月后,添加乳化剂的面团玻璃态温度由-38℃升高到-28℃左右。添加乳化剂有利于保持面团冷冻存储过程中品质的稳定。
冷冻面团的动态流变学性质研究表明,不同的冷冻储藏时间,添加复配乳化剂的面团具有较大的弹性模量和较高的平均分子质量,即其网络结构更加完整。面团冷冻储藏两月后在0—100Hz的频率扫范围内,添加乳化剂的面团有更大的弹性模量,并且其弹性模量和粘性模量曲线的交叉点由14.67Hz增加到32.04Hz,即添加乳化剂后,频率扫描过程中面团弹性模量所占比例更大,扫描曲线的交叉点向高频率方向移动,面团的平均分子质量增加,网络结构更加完整。
焙烤实验结果表明,添加复配乳化剂有利于增大冷冻面团所得面包的比容,提高面包的感官性质,降低其硬化速度。未冻空白,冷冻两月空白和冷冻两月添加乳化剂的面团所制作的面包比容分别为4.65cm3/g,3.78cm3/g和4.55cm3/g,并且添加乳化剂的冷冻面团所制面包包芯柔软,孔隙分布均匀。在一周的存储时间内,冷冻两月的空白、添加2%和3%乳化剂的面团所得面包4℃下的平均硬化速度为157.1g/天、114.3g/天和100.0g/天,20℃下的平均硬化速度为121.4g/天、74.3g/天和60.0g/天。
In this study, the effect of Combined Emulsifiers with Soybean Lecithins and Sucrose Esters on the survival ratio of frozen bake yeast and its develop speed & the quality of wheat flour & freezable water content and glass transition temperature, rheological properties of frozen dough & bread quality made from frozen dough were investigated.
The experiment of freezing yeast in Yeast Extract Peptone Dextrose Medium(YPD) culture medium showed that the yeast with combined emulsifiers had a relatively higher survival ratio and quicker growing speed. Combined emulsifiers could diminish the damage on yeast caused by freezing. The survival ratio of yeast cultivated for 48 hours after frozen at-30℃for 5days in a culture medium with 4% combined emulsifers increased from 50% to 80% compared with the control group, and the adaptive phase shortened by 9 hours. In addition,the image taken by scanning electron microscope (SEM) indicated that there might be some interaction effects existed between the two substances.
In farinograph, the results showed that the addition of combined emulsifiers could improve the quality of wheat flour. After the addition of combined emulsifiers, best stability time increased by 5.8min and 7.2min,weaken degree decreased from 48FU to 16FU and 10FU, the flour quality index upgraded from 43 to 136 and 154. Furthermore the tensile tests showed that tensile resistance of the dough was significantly enhanced by adding combined emulsifiers. The dough with emulsifiers had a higher extension energy which was propitious to process, and addition of 3% had a better effect than 2% emulsifiers.
Differential scanning calorimetry(DSC) showed that Combined Emulsifiers could slow down the growing of freezable water in frozen dough, enhance the water holding capacity of protein. With the same storage time, dough with emulsifiers had a lower freezable water content than the control group. The thaw enthalpy of fresh dough declined from 22.35J/g to 15.08J/g after the addition of emulsifiers, whereas the thaw enthalpy of dough without emulsifiers increased to 29.18J/g after two months'freezing, increased by 31.14% compared with unfrozen dough. The thaw enthalpy of dough with emulsifiers increased to 16.08 J/g, increased by 6.63% compared with unfrozen dough. The glass transition temperature of dough frozen for two months was enhanced from -3.8℃to -28℃by emulsifiers, which could make the dough quality more stable.
The dynamic rheological properties of frozen dough showed that at different storage time, the dough with emulsifiers had a higher storage module and average molecular weight. The dough frozen for two months with emulsifiers had a higher G'in the entire range of frequency sweeping, and it's cross point of storage module and loss module increased from 14.67Hz to 32.04Hz compared with dough without emulsifiers. The dough with emulsifiers was possessed of a bigger proportion of G'under the frequency sweeping, and the cross point moved to high frequency. The dough's average molecular weight was upgraded by emulsifiers.
The experiment of bread baking showed that emulsifiers could increase the loaf volume, improve sense properties, make the bread more softer and slow down the firming rate of bread crumb. The loaf volume of fresh dough without emulsifiers, dough without emulsifiers frozen for two months and dough with emulsifiers frozen for two months were 4.65 cm3/g,3.78 cm3/g and 4.55 cm3/g, and the bread crumb with emulsifiers was much softer, more uniform. Within one week storage, the bread made from control, with 2% and 3% emulsifier's dough had 157.1g/d、114.3g/d,100.0g/d firming rate at 4℃,121.4g/d、74.3g/d,60.0g/d at 20℃.
冷冻酵母实验表明添加复配乳化剂到酵母浸出粉胨葡萄糖培养基(YPD)中能够提高冷冻后酵母的存活率和生长速率,复配的乳化剂可以减少酵母细胞在冷冻过程中受到的损伤。添加4%质量分数的复配乳化剂到酵母YPD培养基中并在-30℃冷冻并冷藏5天后,酵母的存活率由50%升高到80%。添加乳化剂的酵母冷冻后生长适应期由15小时减少到6小时,且冷冻后平板培养菌落明显偏大。扫描电镜(SEM)观察表明复配乳化剂使酵母抗冻能力的提高可能同酵母与乳化剂的聚集作用有关。
粉质实验表明,复配乳化剂可以改善面粉的粉质特性,中筋粉中添加面粉质量分数2%和3%的乳化剂后面团的吸水率和形成时间没有显著变化,稳定时间由7.6min升高到13.4min和14.8min,弱化度由48FU减少到16FU和10FU,粉质质量指数由43提高到136和154。拉伸实验表明,添加乳化剂后面团的拉伸能量变大,筋力增强,延伸度增大,有利于面团的加工性质,其中添加3%质量分数的乳化剂效果优于添加2%质量分数的乳化剂。
差示扫描量热(DSC)实验结果表明,复配乳化剂能够降低冷冻存储过程中面团可冻结水含量增加的趋势,增强面筋蛋白的持水能力。相同的冷冻存储时间,添加复配乳化剂的面团可冻结水含量小于空白面团。添加复配乳化剂后新鲜面团融化焓由22.35J/g减少到15.08J/g,而冷冻储藏两个月后空白面团的融化焓增加到29.18J/g,相比未冷冻增加了31.14%,添加乳化剂的面团融化焓增加到16.08J/g,相比未冷冻仅增加了6.63%。并且冷冻储藏两月后,添加乳化剂的面团玻璃态温度由-38℃升高到-28℃左右。添加乳化剂有利于保持面团冷冻存储过程中品质的稳定。
冷冻面团的动态流变学性质研究表明,不同的冷冻储藏时间,添加复配乳化剂的面团具有较大的弹性模量和较高的平均分子质量,即其网络结构更加完整。面团冷冻储藏两月后在0—100Hz的频率扫范围内,添加乳化剂的面团有更大的弹性模量,并且其弹性模量和粘性模量曲线的交叉点由14.67Hz增加到32.04Hz,即添加乳化剂后,频率扫描过程中面团弹性模量所占比例更大,扫描曲线的交叉点向高频率方向移动,面团的平均分子质量增加,网络结构更加完整。
焙烤实验结果表明,添加复配乳化剂有利于增大冷冻面团所得面包的比容,提高面包的感官性质,降低其硬化速度。未冻空白,冷冻两月空白和冷冻两月添加乳化剂的面团所制作的面包比容分别为4.65cm3/g,3.78cm3/g和4.55cm3/g,并且添加乳化剂的冷冻面团所制面包包芯柔软,孔隙分布均匀。在一周的存储时间内,冷冻两月的空白、添加2%和3%乳化剂的面团所得面包4℃下的平均硬化速度为157.1g/天、114.3g/天和100.0g/天,20℃下的平均硬化速度为121.4g/天、74.3g/天和60.0g/天。
In this study, the effect of Combined Emulsifiers with Soybean Lecithins and Sucrose Esters on the survival ratio of frozen bake yeast and its develop speed & the quality of wheat flour & freezable water content and glass transition temperature, rheological properties of frozen dough & bread quality made from frozen dough were investigated.
The experiment of freezing yeast in Yeast Extract Peptone Dextrose Medium(YPD) culture medium showed that the yeast with combined emulsifiers had a relatively higher survival ratio and quicker growing speed. Combined emulsifiers could diminish the damage on yeast caused by freezing. The survival ratio of yeast cultivated for 48 hours after frozen at-30℃for 5days in a culture medium with 4% combined emulsifers increased from 50% to 80% compared with the control group, and the adaptive phase shortened by 9 hours. In addition,the image taken by scanning electron microscope (SEM) indicated that there might be some interaction effects existed between the two substances.
In farinograph, the results showed that the addition of combined emulsifiers could improve the quality of wheat flour. After the addition of combined emulsifiers, best stability time increased by 5.8min and 7.2min,weaken degree decreased from 48FU to 16FU and 10FU, the flour quality index upgraded from 43 to 136 and 154. Furthermore the tensile tests showed that tensile resistance of the dough was significantly enhanced by adding combined emulsifiers. The dough with emulsifiers had a higher extension energy which was propitious to process, and addition of 3% had a better effect than 2% emulsifiers.
Differential scanning calorimetry(DSC) showed that Combined Emulsifiers could slow down the growing of freezable water in frozen dough, enhance the water holding capacity of protein. With the same storage time, dough with emulsifiers had a lower freezable water content than the control group. The thaw enthalpy of fresh dough declined from 22.35J/g to 15.08J/g after the addition of emulsifiers, whereas the thaw enthalpy of dough without emulsifiers increased to 29.18J/g after two months'freezing, increased by 31.14% compared with unfrozen dough. The thaw enthalpy of dough with emulsifiers increased to 16.08 J/g, increased by 6.63% compared with unfrozen dough. The glass transition temperature of dough frozen for two months was enhanced from -3.8℃to -28℃by emulsifiers, which could make the dough quality more stable.
The dynamic rheological properties of frozen dough showed that at different storage time, the dough with emulsifiers had a higher storage module and average molecular weight. The dough frozen for two months with emulsifiers had a higher G'in the entire range of frequency sweeping, and it's cross point of storage module and loss module increased from 14.67Hz to 32.04Hz compared with dough without emulsifiers. The dough with emulsifiers was possessed of a bigger proportion of G'under the frequency sweeping, and the cross point moved to high frequency. The dough's average molecular weight was upgraded by emulsifiers.
The experiment of bread baking showed that emulsifiers could increase the loaf volume, improve sense properties, make the bread more softer and slow down the firming rate of bread crumb. The loaf volume of fresh dough without emulsifiers, dough without emulsifiers frozen for two months and dough with emulsifiers frozen for two months were 4.65 cm3/g,3.78 cm3/g and 4.55 cm3/g, and the bread crumb with emulsifiers was much softer, more uniform. Within one week storage, the bread made from control, with 2% and 3% emulsifier's dough had 157.1g/d、114.3g/d,100.0g/d firming rate at 4℃,121.4g/d、74.3g/d,60.0g/d at 20℃.
引文
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[2]Hsu, K., Hoseney, R., Seib, S. Frozen dough. Factors affecting the stability of yeasted doughs. Cereal Chemistry.1979(56):419-424.
[3]Tipples, K.H. The relation of starch damage to the baking performance of flour. Baker's Digest.1969(43):28.
[4]Ribotta, P.D., Leon, A.E., Anon, M.C. Effects of yeast freezing in frozen dough. Cereal Chemistry.2003(80):454-458.
[5]Lorenz, K., Kulp, K.Frozen and refrigerated doughs and batter. American Association of Cereal Chemistry.1995,St. Paul, MN, pp.135-153.
[6]Stauffer, C.E. Frozen dough production. Advances in Baking Technology. Blackie.1993, UK, pp.88-106.
[7]Murakami,Y.K. Yokoigawa,H..K. Lipid composition of a freeze-tolerant yeast, Torulaspora delbureckii,and its freeze-sensitive mutant. Microbiotechnology.1995(44):167-171.
[8]Kumio Yokoigawa, Machiko Sato, Kenji Soda. Simple Improvement in Freeze-Tolerance of Bakers'Yeast with Poly-y-Glutamate. Journal of Bioscience and Bioengineering.2006(102): 215-219.
[9]Yanli M, George Wood,and Laura Thoma. Cryoprotection Mechanisms of Polyethylene Glycols on Lactate Dehydrogenase During Freeze-thawing. The AAPS Journal.2004:6(3) Article 22.
[10]Rasanen J,Blanshard J M V,Siitari Kauppi M,et al.Water distribution in frozen lean wheat Boughs.Cereal Chemistry.1997(74):806-813.
[11]Czuchajowska Z,Pomeeranz Y,Jeffers H C. Water activity and moisture content of dough and bread.Cereal Chemistry.1989(66):128-132.
[12]Rouille J,Le-Bail A,Corcoux P.Influence of formulation and mixing on breadmaking qualities of French frozen dough[J]. Journal of Food Engineering.2000 43(4):197-203.
[13]Le Bail A,Pasco M,Meric L,et al. Influence of freezing rate on yeast activity in frozen dough.The Proceedings of The 10th International Cereal and Bread Congress,Greece,1996.
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