水分含量对西兰花玻璃化转变温度的影响

在低温贮藏和冻干加工中,玻璃化转变温度是一个非常重要的参数.用差示扫描量热仪测量得到不同含水量西兰花和调理西兰花的玻璃化转变温度Tg.研究发现水分质量分数较高时(≥35%),西兰花和调理西兰花发生的是部分玻璃化转变,不同含水量西兰花的部分玻璃化转变温度Tg′基本相同,水分对其影响较小.而水分质量分数较低时(＜35%),西兰花可以实现完全玻璃化转变,含水量对西兰花的完全玻璃化转变温度Tg影响很大,Tg随着含水量的减少而升高; 拟合得到Tg随水分变化的公式.     

DSC在食品玻璃化转变中的应用

介绍了DSC在含水食品体系、小分子糖类体系、非淀粉多糖体系及淀粉体系的玻璃化转变中的应用,为测定食品原料的玻璃化转变温度(Tg)提供了一种新的测量技术。     

NMR在食品玻璃化转变中的应用

介绍了NMR (NuclearMagneticReso nance,核磁共振 )在含水食品体系、小分子糖类体系、非淀粉多糖体系及淀粉体系的玻璃化转变中的应用 ,为测定食品原料的玻璃化转变温度 (Tg)提供了一种新的测量技术     

草莓玻璃化转变温度的DSC测量

在测量溶液的部分玻璃化转变温度时,往往无法直接测得溶液在最大冻结浓缩状态下的部分玻璃化转变温度(Tg’),而是测得部分结晶玻璃化转变温度(Tgf)。本文用差示扫描量热仪,采用不经过退火处理的连续扫描法、分步扫描法对草莓打浆液、榨汁草莓经抽滤的草莓汁液和浓缩掉三分之一水分的浓缩草莓汁进行了玻璃化转变温度的测量。研究发现,用同一种方法测得的三者的玻璃化转变温度相差不大。在-48℃以下退火,玻璃化转变温度随着退火温度的增大而增大,在-48℃以上退火,玻璃化转变温度随着退火温度的增大而减小,并有很好的线性关系,从Tgf确定Tg’的新方法是两侧Tgf的交点对应的温度为Tg’。得到草莓的Tg’为-52.8℃。     

分子量对淀粉玻璃化转变温度的影响

采用相对黏度法及TDA与DSC法测定了淀粉同系物的黏均分子量和玻璃化转变温度,得到分子量对淀粉同系物的玻璃化转变的影响关系:即随着分子量的增加玻璃化转变温度也增加,当分子量增加到一定程度以后玻璃化转变温度增加趋于平缓,并得到实验关联式。根据这种关系我们可在一定的范围内根据实际生产、加工及贮存的需要,用改变淀粉体系的分子量分布的方法来改变其玻璃化转变温度。     

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。     

淀粉糖浆对硬糖品质的影响

为获得透明度高、贮藏性能佳的优质的硬糖产品,研究了不同蔗糖—淀粉糖浆配比对于硬糖品质的影响。通过常压熬糖,按不同蔗糖-糖浆配比制备硬糖,利用差示量热扫描法(DSC)测定其玻璃化转变温度(Tg),并结合透光率、色度、贮藏稳定性等各项指标,确定蔗糖—淀粉糖浆(43DE)的最优质量比为6∶4。该条件下制得硬糖Tg为43.01℃,透明度好,白度高且贮藏稳定性最好。     

NMR在食品玻璃化转变中的应用

介绍了NMR（Nuclear Magnetic Resonance，核磁共振）在含水食品体系、小分子糖类体系、非淀粉多糖体系及淀粉体系的玻璃化转变中的应用，为测定食品原料的玻璃体转变温度（Tg）提供了一种新的测量技术。     

水分含量对番茄粉非酶褐变及玻璃化转变温度的影响

测定了番茄粉的吸湿等温曲线,同时,采用差示扫描量热仪测定了在不同水分活度下番茄粉的玻璃化转变温度.另外,对番茄粉的非酶褐变与贮藏温度T和玻璃化转变温度Tg的差值(T-Tg)之间的关系进行了探讨.研究表明当水分活度超过0.50以后,番茄粉吸湿能力明显增强.随着番茄粉水分含量的增加,番茄粉的玻璃化转变温度迅速下降,要使番茄粉的玻璃化转变温度高于20℃(室温),番茄粉的水分含量不能超过5%.当贮藏温度低于玻璃化转变温度时,番茄粉的非酶褐变速率非常慢;而当贮藏温度高于玻璃化转变温度时,随着T-Tg的增加,番茄粉的非酶褐变速率迅速增加.     

聚合物玻璃化转变理论在干燥食品加工储藏中的应用

阐述了高聚物玻璃化转变理论及食品的玻璃态和玻璃化转变，介绍了玻璃化转变温度的测量方法和影响因素。食品是含有多种高分子物质的混合体系，它的玻璃化转变温度（Tg）影响到干燥食品的加工工艺和贮藏的稳定性。     

Amorphous state and delayed ice formation in sucrose solutions

Phase transitions of amorphous sucrose and sucrose solutions (20–100% sucrose) were studied using differential scanning calorimetry, and related to viscosity and delayed ice formation. Glass transition temperature (Tg) was decreased by increasing water content. Ice formation and concurrent freeze concentration of the unfrozen solution increased apparent Tg. Tg could be predicted weight fractions and Tg values of components. Williams–Landel-Ferry (WLF) relation could be used to characterize temperature dependence of viscosity above Tg. Crystallization of water above Tg was time dependent, and annealing of solutions with less than 80% sucrose at –35°C led to a maximally freeze-concentrated state with onset of glass transition at –46°C, and onset of ice melting at -34°C. The state diagram established with experimental and predicted Tg values is useful for characterization of thermal phenomena and physical state at various water contents.     

Glass Transition and Food Technology: A Critical Appraisal

ABSTRACT: Most low water content or frozen food products are partly or fully amorphous. This review will discuss the extent to which it is possible to understand and predict their behavior during processing and storage, on the basis of glass transition temperature values (Tg) and phenomena related to glass transition. Two main conclusions are provisionally proposed. Firstly, glass transition cannot be considered as an absolute threshold for molecular mobility. Transport of water and other small molecules takes place even in the glassy state at a significant rate, resulting in effective exchange of water in multi-domains foods or sensitivity to oxidation of encapsulated materials. Texture properties (crispness) also appear to be greatly affected by sub-Tg relaxations and aging below Tg. Secondly, glass transition is only one among the various factors controlling the kinetics of evolution of products during storage and processing. For processes such as collapse, caking, crystallization, and operations like drying, extrusion, flaking, Tg data and WLF kinetics have good predictive value as regards the effects of temperature and water content. On the contrary, chemical/biochemical reactions are frequently observed at temperature below Tg, albeit at a reduced rate, and WLF kinetics may be obscured by other factors.     

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。     

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。     

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。     

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。     

Understanding and Modifying Water Uptake of Seed Coats Through Characterizing the Glass Transition

The glass transition temperature (Tg) of seed coat was studied in relation to water uptake behavior. Tg values of seed coats were determined using differential scanning calorimetry (DSC) for selected pea and bean varieties. Rapidly hydrating samples showed a sharp Tg near ambient temperature with a range spanning 4–10°C. Samples that demonstrated a lag and consequently slow hydration exhibited a broad Tg above ambient temperature with a range spanning 22–33°C. Slow hydrating samples were processed via cyclic heating and cooling above and below Tg, resulting in elimination of the lag phase and markedly improved hydration rates. This research showed that Tg can be related to water uptake behavior and can be used as a parameter to determine processing conditions for improving water uptake in seeds.     

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).     

花生壳/仁的吸附等温线与热力学特性

为了解花生壳与花生仁的含水率、水分活度(a_w)与温度的关系,提高花生的贮藏稳定性。研究花生壳与花生仁在10、20、30℃时的吸附等温线;探讨花生壳与花生仁的净等量吸附热(q_(st))、微分熵(S_d)、扩张压力、积分熵、积分焓、熵-焓互补、玻璃化转变温度(T_g)等热力学特性。结果表明,花生壳与花生仁的水分吸附呈Ⅲ型等温线。温度一定时,花生壳与花生仁的干基含水率随a_w增加而增加。描述花生壳与花生仁吸附特性的最适模型为GAB模型。花生壳与花生仁的q_(st)与S_d均随含水率增加而降低。扩张压力随a_w增加而升高,但随温度升高而降低。积分焓随含水率增加而降低,而积分熵随含水率增加而升高。花生壳的q_(st)和S_d均高于花生仁,而同一温度条件下花生仁的扩张压力高于花生壳。含水率相同时,花生仁积分焓低于花生壳,而花生仁的积分熵则高于花生壳。花生壳与花生仁水分吸附过程均为焓驱动、自发过程。花生壳与花生仁的T_g随含水率增加而降低,相同含水率时,花生壳的T_g值高于花生仁。根据状态图得到温度为10℃时,花生壳与花生仁的临界水分活度与临界含水率分别为0.80、0.175 4 g/g与0.68、0.095 5 g/g。研究结果可为花生干制工艺及其干制品贮藏稳定性提供理论依据。