水分含量及添加剂对面团玻璃化转变温度的影响

本实验应用差示扫描量热仪(DSC),测量了不同水分含量的面团的玻璃化转变温度以及NaCl、卵磷脂、抗坏血酸、明胶、海藻糖、单干酯及黄原胶等常见食品添加剂对面团玻璃化转变温度的影响。结果表明:水分含量为40%的纯精粉面团的玻璃化转变温度为-27.75℃,水分含量在38%～45%的玻璃化转变温度有逐渐降低的趋势。NaCl、抗坏血酸、海藻糖分别以5%、1%、3%加入面团以后,面团玻璃化转变温度分别为-13.68、-12.73、-15.74℃。加入明胶、单干酯、黄原胶时,面团的玻璃化转变温度提高并不明显,而卵磷脂的加入却降低了面团的玻璃化转变温度。     

浅述玻璃化转变温度与食品成分的关系

食品体系的玻璃化转变温度会对食品的加工和贮藏过程及食品的品质产生重要影响。重视食品体系的玻璃化转变温度并分析其影响因素,可帮助人们更好的了解食品加工和贮藏特性,提高产品品质。该文就水分含量、碳水化合物、蛋白质、平均分子量及食品添加剂等因素与一定的食品体系的玻璃化转变温度的关系进行了综述。     

论玻璃化转变温度与食品成分的关系

食品体系的玻璃化转变温度,会对食品的加工和贮藏过程及食品的品质产生重要影响.重视食品体系的玻璃化转变温度并分析其影响因素,可帮助人们更好地了解食品加工和贮藏特性,提高产品品质.该文就水分含量、碳水化合物、蛋白质、平均分子量及食品添加剂等因素与一定的食品体系的玻璃化转变温度的关系进行了论述.     

面团的玻璃化储存

由于面团在冷冻储存过程中受到结晶与再结晶的影响,产生结构松弛和水份迁移,品质显著下降。实现面团的玻璃化储存是解决问题的最佳方案。通过加入合适添加剂,可提高面团玻璃化转变温度,实现一般冷冻储存温度（-18℃）下的面团玻璃化储存。分析了各种玻璃化转变温度测定方法和添加剂在提高面团玻璃化转变方面的应用。      

面团的玻璃化储存

由于面团在冷冻储存过程中受到结晶与再结晶的影响,产生结构松弛和水份迁移,品质显著下降。实现面团的玻璃化储存是解决问题的最佳方案。通过加入合适添加剂,可提高面团玻璃化转变温度,实现一般冷冻储存温度（-18℃）下的面团玻璃化储存。分析了各种玻璃化转变温度测定方法和添加剂在提高面团玻璃化转变方面的应用。     

乳化剂对冷冻面团水分状态和玻璃化转变温度的影响

乳化剂能通过改变面团中的水分状态来改变面团的玻璃化转变温度(Tg)和低温贮藏后的微观结构。利用低场核磁共振技术(LF-NMR)研究乳化剂对面团中水分状态的影响,并利用差示扫描量热法(DSC)和扫描电子显微镜(SEM)研究乳化剂对面团的Tg和低温贮存后面团微观结构的影响。结果表明：乳化剂能不同程度地降低面团中自由水含量,当加入0.15%双乙酰酒石酸单(双)甘油酯(DATEM)时,面团中自由水含量相对空白面团减少了5.78%;乳化剂也改变了面团的Tg,空白面团的Tg为－31.3℃,当加入0.50%的单甘酯时,面团的Tg为－17.3℃,提高了14℃,而山梨醇酐单硬脂酸酯(SP60)和卵磷脂在本实验的添加量范围内,未能将面团的Tg显著提高;乳化剂能不同程度的改善低温贮藏后面团的微观结构,尤其是加入0.50%单甘酯或0.15% DATEM后,面团实现玻璃化贮存,其微观结构得到了很好的保护。     

不同变性淀粉对冷冻面团热力学特性的影响

采用差示扫描量热法(DSC)研究4种不同种类变性淀粉对冷冻面团热力学特性(玻璃化转变温度、冰晶融化特性和可冻结水含量)的影响。结果表明,冷冻面团的玻璃化转变温度在-30℃左右,不同变性淀粉对冷冻面团玻璃化转变基本无明显影响;添加5%马铃薯羟丙基淀粉、木薯羟丙基淀粉和木薯醋酸酯淀粉可以显著降低冷冻面团冰晶融化范围,面团中形成的冰晶大小更加均匀;冷冻面团可冻结水含量随着马铃薯醋酸酯淀粉和马铃薯羟丙基淀粉添加量的增加呈降低趋势,添加10%木薯羟丙基淀粉时,面团可冻结水含量显著低于空白组,而木薯醋酸酯淀粉对面团可冻结水含量无显著影响。     

不同变性淀粉对冷冻面团热力学特性的影响

采用差示扫描量热法（DSC）研究4种不同种类变性淀粉对冷冻面团热力学特性（玻璃化转变温度、冰晶融化特性和可冻结水含量）的影响。结果表明,冷冻面团的玻璃化转变温度在-30℃左右,不同变性淀粉对冷冻面团玻璃化转变基本无明显影响;添加5%马铃薯羟丙基淀粉、木薯羟丙基淀粉和木薯醋酸酯淀粉可以显著降低冷冻面团冰晶融化范围,面团中形成的冰晶大小更加均匀;冷冻面团可冻结水含量随着马铃薯醋酸酯淀粉和马铃薯羟丙基淀粉添加量的增加呈降低趋势,添加10%木薯羟丙基淀粉时,面团可冻结水含量显著低于空白组,而木薯醋酸酯淀粉对面团可冻结水含量无显著影响。      

玻璃化技术在速冻面制品中的应用

速冻面制品的出现丰富了人们的生活,但许多速冻面制品的质量随贮存期延长而显著下降,出现萎缩开裂、表面发干、内部结构变差、失去原有风味等现象。针对速冻面制品在贮藏过程中出现的质量问题,该文提出了贮存速冻面制品的一种新方法——玻璃化保存技术,介绍了面制品玻璃化加工与保存的理论基础,分析了影响面制品玻璃化保存的因素,提出了升高面制品玻璃化转变温度的方法。     

食品添加剂对面团流变学特性影响的初步实验研究

面团的流变学特性会对面制品的质量产生重要影响,而食品添加剂的种类和添加量将显著改变面团的流变学特性。本研究利用质构仪考察了若干种食品添加剂对面团拉伸特性的影响。结果表明:面团中添加NaCl、单甘酯、明胶、抗坏血酸、面粉强筋剂、海藻糖等都对面团的拉伸性能有一定的影响,不同的添加剂影响各异。相对而言,1.5%～2%的NaCl、0.5%的单甘酯、0.4%的明胶、0.4%的面粉强筋剂等都对面团的抗拉伸性能和稳定性有明显改善。而总体上,抗坏血酸和海藻糖对面团拉伸性能的作用主要是增加其抗拉伸应力,但会使面团的拉伸时间显著缩短,本研究的结果为面制品生产中正确选择适当的食品添加剂及添加量提供了基础数据。     

小麦淀粉老化动力学及玻璃化转变温度

采用差示扫描量热法研究不同温度及储藏时间下小麦淀粉不同组分(小麦总淀粉、小麦A淀粉、小麦B淀粉)的老化动力学及最大冷冻浓缩状态下玻璃化转变温度(glass transition temperature of the maximally freezeconcentrated state,T_g’)。测定小麦淀粉各组分于-18、-5、4、22℃储藏3~21 d的老化度、T_g’及非冻结水含量。结果表明,不同淀粉组分在-18℃下储藏未发生老化,而在-5、4、22℃条件下储藏会发生老化,且4℃时的老化度最大,22℃时的老化度最小,-5℃时的老化度居两者之间;小麦B淀粉的T_g’比A淀粉的T_g’高。小麦淀粉不同组分老化动力学存在差异,小麦A淀粉的老化度较总淀粉及B淀粉大;非冻结水的含量对不同组分小麦淀粉T_g’有很大影响。     

深海养殖大黄鱼鱼肉玻璃态转化调控技术

为了提升深海养殖大黄鱼玻璃态保藏工艺,寻找适宜的大分子添加剂组合配方,并提高其玻璃态转变温度(T_g),通过添加不同浓度和不同种类的添加剂,以T_g为指标,使用Box-Benhnken试验设计和响应面分析法对添加剂进行优化组合。结果表明,最优组合设计:质量分数0.2%乳酸钠,4.0%海藻糖,4.0%麦芽糊精,0.3%柠檬酸钠。该组合条件下,样品T_g实际值可提升至-53.31℃。扫描电镜结果显示,添加组内部结构紧密、表面平整、无明显空洞,而空白组有较多的空洞,组织比较松散,说明大分子添加剂与样品内组织发生交联作用,可以有效地提升其T_g。     

Properties of Wheat Dough at Sub-Zero Temperatures and Freeze Tolerance of a Baker's Yeast (Saccharomyces cerevisiae)

ABSTRACT: This work studied the relationship between the freeze tolerance of a baker's yeast ( Saccharomyces cerevisiae ) and the physical properties of the frozen wheat dough. The behavior of wheat dough, of the gluten phase, and of the liquid phase at sub-zero temperatures was examined by differential scanning calorimetry (DSC) and cryomicroscopy. The effect on yeast viability of dough water content, freezing and storage temperatures, and prefermentation before freezing was studied. Yeast viability was mostly affected by the freezing and storage temperatures, with temperatures below the glass transition temperature (T_g) giving the highest survival ratios. At temperatures above T_g, viability after freezing treatment and during storage seemed to be governed by different mechanisms, encompassing osmotic and mobility factors. Those factors were also found to influence the freeze tolerance of growing yeast in the presence of ethanol.     

玻璃化转变对食品稳定性的影响

本文首先简要介绍玻璃化转变对黏度、扩散和反应速率的影响,而后从物理稳定性、化学稳定性和生物学稳定性三个方面详细论述了玻璃化转变对食品稳定性的影响。在玻璃化转变温度附近温度降低使黏度增大,但小分子物质的扩散系数不再进一步减小。食品可能因发生玻璃化转变而丧失稳定性,但玻璃化转变并不能成为衡量食品稳定性的唯一标准,发生玻璃化转变也不意味着食品稳定性立即丧失。根据玻璃化转变可以较好地预测食品的物理稳定性,而难以有效预测食品的化学和生物学稳定性。     

Determining the critical relative humidity at which the glassy to rubbery transition occurs in polydextrose using an automatic water vapor sorption instrument

Similar to an increase in temperature at constant moisture content, water vapor sorption by an amorphous glassy material at constant temperature causes the material to transition into the rubbery state. However, comparatively little research has investigated the measurement of the critical relative humidity (RHc) at which the glass transition occurs at constant temperature. Thus, the central objective of this study was to investigate the relationship between the glass transition temperature (Tg), determined using thermal methods, and the RHc obtained using an automatic water vapor sorption instrument. Dynamic dewpoint isotherms were obtained for amorphous polydextrose from 15 to 40 °C. RHc was determined using an optimized 2nd-derivative method; however, 2 simpler RHc determination methods were also tested as a secondary objective. No statistical difference was found between the 3 RHc methods. Differential scanning calorimetry (DSC) Tg values were determined using polydextrose equilibrated from 11.3% to 57.6% RH. Both standard DSC and modulated DSC (MDSC) methods were employed, since some of the polydextrose thermograms exhibited a physical aging peak. Thus, a tertiary objective was to compare Tg values obtained using 3 different methods (DSC first scan, DSC rescan, and MDSC), to determine which method(s) yielded the most accurate Tg values. In general, onset and midpoint DSC first scan and MDSC Tg values were similar, whereas onset and midpoint DSC rescan values were different. State diagrams of RHc and experimental temperature and Tg and %RH were compared. These state diagrams, though obtained via very different methods, showed relatively good agreement, confirming our hypothesis that water vapor sorption isotherms can be used to directly detect the glassy to rubbery transition. Practical Application: The food polymer science (FPS) approach, pioneered by Slade and Levine, is being successfully applied in the food industry for understanding, improving, and developing food processes and products. However, despite its extreme usefulness, the Tg, a key element of the FPS approach, remains a challenging parameter to routinely measure in amorphous food materials, especially complex materials. This research demonstrates that RHc values, obtained at constant temperature using an automatic water vapor sorption instrument, can be used to detect the glassy to rubbery transition and are similar to the Tg values obtained at constant %RH, especially considering the very different approaches of these 2 methods--a transition from surface adsorption to bulk absorption (water vapor sorption) versus a step change in the heat capacity (DSC thermal method).