碾减率对成品大米品质影响的研究

对粳糙米采用不同的碾减率加工后,所得成品大米进行品质的检测分析。结果表明:随碾减率的增加,大米蛋白质减少;碾减率在9%～13%时,蒸煮品质较好,最适碾减率应在13%;在最适碾减率的情况下,糊化温度低,糊化前后温度范围(TC-T0)小,大米玻璃态转变温度Tg高。     

分子动力学模拟水分对小分子糖玻璃态转变温度及扩散性质的影响

为了预测水分对蔗糖、海藻糖等小分子糖玻璃态温度和扩散系数的影响,在恒温恒压(NPT)系综和COMPASS力场条件下,利用分子动力学模拟方法,通过模拟小分子糖体系在180~460 K温度范围内的比体积,与对应的温度作图,获得不同水分含量下小分子糖的玻璃态转变温度;在298 K下,模拟得到在不同水分含量下糖体系中水分子的均方位移(MSD),分析了水分对小分子糖扩散性质的影响;同时研究了温度为298 K,水分含量为5.0%时,小分子糖体系中氧原子与水中氧原子之间的径向分布函数。研究结果表明:在相同水分含量下,海藻糖的玻璃态转变温度大于蔗糖,海藻糖与水分子形成氢键的能力要大于蔗糖;随着水分含量的增加,两种糖模型的Tg都呈现显著下降趋势,水分子更容易在糖模型中扩散,与糖分子发生相互作用的概率增大。     

合成纤维的玻璃化温度及熔融温度是指什么?

合成纤维是高聚物通过纺丝成形、牵伸、热处理定型等工序而制成。它具有结晶和无定形二种形态,同时高聚物的分子又是参差不齐的。合成纤维的玻璃化温度（Tg）是反映高聚物无定形部分的形态变化。当温度低于Tg时,高聚物链段被“冻结”犹如玻璃;当温度高于Tg时,高聚物链段运动,物质处于高弹态;继续加高温度,高聚物结晶部分大分子链运动,物质呈熔融态,其对应的温度称之谓熔融温度。     

分子动力学模拟水分对直链淀粉扩散性质和玻璃态转变温度的影响

为了预测水分对直链淀粉玻璃态温度、径向分布函数和扩散系数的影响,在COMPASS力场和等温等压(NPT)系综下,利用分子动力学模拟方法,模拟得到了不同水分含量直链淀粉在298 K下的径向分布函数和扩散系数;在200~460 K温度范围内,通过模拟获得不同温度下的比体积,与对应的温度作图,研究了水分对直链淀粉玻璃态转变行为的影响。结果表明,所构建的直链淀粉模型属于一种无定型结构,其径向分布函数的形状和峰位基本没有发生变化。随着水分含量的增加,水分子更容易在直链淀粉中扩散,与直链淀粉分子发生相互作用的概率增大。水分含量对直链淀粉玻璃态转变行为影响显著,水分含量越高,直链淀粉的玻璃态转变温度越低。     

盐对颗粒态抗性淀粉形成的影响

抗性淀粉是一种极其重要的功能性食品添加剂。颗粒态抗性淀粉具有不同于传统抗性淀粉的性质,对其研究具有重要意义。文中考察了盐(NaCl、KCl和CaCl2)对颗粒态抗性淀粉形成的影响,得出NaCl和KCl的最适添加量分别为20%和12%,而CaCl2的添加对抗性淀粉形成不利。     

杨梅玻璃态保藏技术的研究

以杨梅(东魁)果实为研究对象,测定其玻璃化转变温度(Tg),并将该温度应用于实际的冻结保藏中。研究发现,杨梅部分玻璃化转变温度(Tg')的起始点为－ 44℃,中点为－ 42℃,终止点为－ 39.2℃。与－ 18℃冻藏相比较,－ 40℃冻结保藏(模拟玻璃态保藏)的果实解冻后汁液流失率低,可溶性固形物(SSC)含量高,果汁pH 值和可滴定酸(TA)含量无显著差异;仪器分析和感官评定的结果均表明,－ 40℃冻结保藏更有利于保持杨梅果实的质地品质。     

提高鲶鱼食用肉粉溶解度的研究

以鲶鱼为原料,经过漂洗、脱腥、斩拌、打浆、均质、乳化、干燥等一系列加工而制成的食用鲶鱼肉粉。通过添加不同的添加剂来提高其溶解度,在单因素试验的基础上设计了三因素二次通用旋转中心组合试验对添加剂的组成进行优化,得到鲶鱼食用鱼乳粉最高溶解度的添加剂组合为:单甘酯、蔗糖酯和黄原胶三者添加量分别为0.317%、0.312%和0.114%,加工出的鲶鱼肉粉溶解度在33%以上。     

天然玻璃与玻璃的鉴别

目前,在我国珠宝市场上有很多仿天然玻璃的饰品,其中以绿色玻璃最为常见,也最具欺骗性.本文从外观特征观察、常规仪器及红外光谱检测等方面对天然玻璃样品与玻璃样品的鉴别特征进行了简要总结.文中的天然玻璃样品主要指玻璃陨石,不包括黑曜石.笔者对所研究的样品做了薄片鉴定,天然玻璃样品中含少量矿物微晶,其余部分为玻璃态,玻璃样品则全部由玻璃质组成.     

模块组合全显色结构提花织物设计与仿色优化比较

为提升提花织物对特殊色相图像的色彩仿真效果,提出一种基于组合全显色结构的模块化设计方法。以2组基本组织构成的组合全显色结构为基础模块,与2种不同辅助模块进行组合设计,以满足奇数组显色纬对组合全显色结构的多样化设计需求。以4幅绿色调印刷品图像为色彩仿真对象,采用2种模块组合全显色结构配合五组显色纬,进行色彩仿真提花织物样品的设计与织造。通过对印刷品与织物样品图像的测色数据的色差比较分析表明,2种五组显色纬提花织物在绿色区域的红绿值色差分别平均降低了44.22%、37.78%,而总色差则分别平均降低了16%、10.55%,使提花织物色彩仿真度得到显著改善。     

不同配方面包制品的核磁共振状态图的研究

利用“NMR状态图概念”研究面包老化的动力学,利用NMR状态图可以分别求出它们的Tg,它们的值在-17℃到-19℃之间。添加三种不同天然食品添加剂对面包的Tg没有太大的变化。实验研究了大豆蛋白粉、木薯预糊化淀粉和大豆纤维三种不同天然食品添加剂对NMR状态图中的影响效果。从NMR状态图可以得知:添加三种不同天然食品添加剂对它们的Tg、T2、KBT和KPT都有作用,其中添加大豆蛋白和木薯预糊化淀粉能明显减低面包状态图的T2、KBT和KPT,说明添加大豆蛋白和木薯预糊化淀粉能促进面包中水分的结合方式;而添加大豆纤维只减低面包状态图的KBT和KPT,反而增加了T2,水分活度较高不利于面包的保藏。     

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).     

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。     

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。     

水分含量对草莓玻璃化转变温度的影响

在冻干和低温保存中,玻璃化转变温度是一个非常重要的参数。本文用差示扫描量热仪测量得到不同湿基水分含量的草莓汁的玻璃化转变温度。实验发现水分含量较高时(>50%),草莓发生的是部分玻璃化转变,不同湿基水份含量草莓汁的Tg’基本相同,水分对其的影响较小。而水分含量较低时(<45%),草莓降温时往往出现完全玻璃化转变,不同湿基水分含量草莓的Tg有很大不同,完全玻璃化转变温度随着水分含量的减少而升高,拟合得到Tg随水分变化的公式。     

食品添加剂对面团玻璃化转变温度的影响

实现食品的玻璃化贮藏是提高食品质量的有效手段。本研究利用差示扫描量热仪探讨了适用于面团玻璃化转变温度测量的扫描程序、研究了水分含量及若干食品添加剂对面团玻璃化转变温度的影响规律。结果表明,多次扫描法是一种可行的面团玻璃化转变温度的测量方法;水分添加量对面团的玻璃化转变温度有明显影响。在本研究的范围内,面团的玻璃化转变温度随面团水分含量的增加而明显下降。食品添加剂对面团的玻璃化转变温度有显著影响。添加抗坏血酸、海藻糖及明胶时,均可不同程度的使面团的玻璃化转变温度有所升高,这对于在现有储存条件下(-18℃)实现面制品的玻璃化保存,提高速冻面制品的稳定性,改善速冻面制品的质量有重要的应用价值。     

Corn Syrup Solids and Their Saccharide Fractions Affect Crystallization of Amorphous Sucrose

The effects of corn syrup saccharides on the glass transition (Tg) and crystallization of freeze-dried sucrose were studied using differential scanning calorimetry. Corn syrup (CS) solids were fractionated into samples with differing ranges and types of glucose polymers. Tg of the sucrose/CS additive mixtures depended on number-average molecular weight, rather than weight-average molecular weight, of CS material. Additive levels of 10% and 20% (w/w) of CS solids and their fractions interfered with crystallization of amorphous sucrose, whereas levels 50% prevented crystallization. The mechanism by which CS saccharides interfered with crystallization of amorphous sucrose depended not only on Tg but was also influenced by specific interactions between molecules.     

快速测量食品玻璃化转变温度新方法的研究

食品的玻璃化转变是影响食品品质和稳定性的关键因素。准确测量食品的玻璃化转变温度对改进食品的加工和贮藏条件非常重要。核磁共振技术(NMR／MRI)在研究食品玻璃化转变过程和测最玻璃化转变温度方面，具有一定的优势。它作为一种先进的分析测量工具，在食品科学领域具有广阔的应用前景。     

Use of ramping and equilibrium water vapor sorption methods to determine the critical relative humidity at which the glassy to rubbery transition occurs in polydextrose

Recent research has demonstrated that the critical relative humidity (RHc) values, obtained using automatic water vapor sorption instruments, can be used to detect the glassy to rubbery transition. However, reported time dependency of these RHc values suggests that additional research be carried out using equilibrium water vapor sorption methods. Thus, the objectives of this study were to: (1) determine the RHc for amorphous polydextrose at various temperatures using both instrumental (Dynamic Vapor Sorption [DVS] ramping and equilibrium) and saturated salt slurry methods, and (2) compare the RHc values obtained via sorption methods to the glass transition temperature (Tg) values obtained via differential scanning calorimetry (DSC). When plotted as a "glass curve" on a state diagram, the RHc values (plotted as a function of temperature) were found to be similar to the Tg values (plotted as a function of relative humidity). Of the 3 sorption methods employed, at 25 °C, the saturated salt slurry exhibited the lowest RHc value (34.3%), followed by the DVS equilibrium method (41.7%), and the DVS ramping method (49.9%). The RHc DVS equilibrium method was closest to the calculated DSC Tg onset RHc value (41.6% at 25 °C). These water sorption methods show promise as practical tools for predicting the quality and stability attributes of amorphous materials by being able to routinely determine the location of the glassy to rubbery transition. Future research applying these sorption methods to more complex amorphous food systems is suggested. Practical Application: Despite its extreme usefulness, the Tg, a key element of the Food Polymer Science approach, remains a challenging parameter to routinely measure in amorphous food materials. Recent research has demonstrated that the RHc values can be used to detect the glassy to rubbery transition. However, reported time dependency of these RHc values suggests that additional research be carried out using equilibrium water vapor sorption methods. Therefore, in this research 2 instrumental (DVS ramping and equilibrium) methods and the traditional saturated salt slurry method were used to obtain RHc values, comparing them to DSC obtained Tg values. The water sorption methods show promise as practical tools for predicting the quality and stability attributes of amorphous materials by being able to routinely determine the location of the glassy to rubbery transition. Future research applying these sorption methods to more complex amorphous food systems is suggested.     

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。