NMR State Diagram Concept

ABSTRACT:  This article introduces a new concept, the NMR (nuclear magnetic resonance) state diagram, in the context of food shelf-life stability as affected by the molecular mobility of the food matrix. Our literature review shows that some shelf-life–related changes cannot be explained or predicted by the current a _w and glass transition temperature concepts. This article presents the theoretical principles and some experimental evidence of the NMR state diagram concept that could be complementary to the a _w and glass transition concepts. An NMR state diagram is a curve of NMR relaxation time versus temperature. Some of the curve features were found to correlate highly to the physiochemical states and changes of food polymers, for example, caking, stickiness, and firming. The potential applications of this concept in quality and safety of food products, especially dry and intermediate moist foods, may include ingredients screening, prediction of physiochemical changes, chemical degradation, and microbiological activity. The goal concept of this article is to provoke more in-depth studies to analyze the relationships among NMR relaxation, molecular mobility, and stability of foods.     

Plasticizing and Antiplasticizing Effects of Water and Polyols on a Meat-Starch Extruded Matri

ABSTRACT: The effects of plasticizers on the mechanical properties and glass transitions of a meat-starch extruded system were studied. Mixtures of meat and potato granules (1.48:1) and up to 4% glycerol and propylene glycol, respectively, were extruded and equilibrated at different relative humidities. Storage moduli and glass transitions were determined by mechanical spectroscopy. Water was the major plasticizer of the system, decreasing its mechanical properties and glass transition temperatures. At low-moisture content, the addition of water determined an increase in mechanical properties, interpreted as antiplasticization. Glycerol and propylene glycol had a softening effect on the matrix at a_w> 0.67. Propylene glycol also determined a significant decrease of the starch phase Tg.     

Glass Transition State Diagram of a Baked Cracker and Its Relationship to Gluten

The polymer science approach can be applied to the understanding of physical changes in foods such as loss of texture upon moisture gain. The glass transition temperature (T_g) of a commercial cracker was measured by Dynamic Mechanical Thermal Analysis (DMTA) as a function of water content. The final state diagram showed that the cracker was plasticized by water with a glass transition temperature that decreased as water content increased. When compared with published glass transition data on cereal ingredients, gluten may be the main component responsible for the mechanical changes and loss of crispness of such products when moisture content is increased.     

Phase and State Transitions in Granular Starches Studied by Dynamic Differential Scanning Calorimetry

Phase and state transitions of granular starches heated in water are studied by dynamic differential scanning calorimetry (DDSC). The DDSC results of various granular starches show a stepwise heat capacity (C_p) change in the storage C_p curve, which starts at the beginning of melting or immediately preceding gelatinization and ends before the melting reaches its peak temperature. Annealing reduces the magnitude of this stepwise change in storage C_p. After the amorphous phase is selectively removed by acid, the stepwise storage C_p is greatly reduced. The stepwise storage C_p increase is not observed when recrystallized linear short chains from enzyme‐debranched waxy maize starch are heated in water. The results show that the stepwise change in C_p observed on the granular starch is a unique property associated with the phase transition of granular structure and reflects a glass transition of the rigid amorphous regions in starch granules. The glass transition of the mobile amorphous phase in granular starch is believed to extend over a broad range of temperatures before gelatinization. A small glass transition below 0°C is directly detected by DDSC and is attributed to part of the mobile amorphous fraction in granular starch.     

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。     

食品中核磁共振状态图的应用(英文)

食品中质量感官指标和货架期与它的理化特性有关,水是食品原料中重要组成部分,它的含量与食品的理化特性有关,并在其中扮演着重要角色。“玻璃态转化” 的概念是在研究食品原料和产品理化特性的聚合物理论时提出的。食品玻璃态转化状态图通常用来描述水含量与食品理化特性的关系。状态图能有效地反映在不同温度和水分含量下的物质的理化特性。本文提出一个新的观念-“核磁共振状态图” 概念,核磁共振状态图是指核磁共振弛豫时间(通常指自旋-自旋弛豫时间或T2)和温度之间的曲线图,它放映食品的核磁共振弛豫现象与食品的理化特性关系。我们在研究时发现这条曲线图与物质的许多理化特性有着良好的相关性。利用核磁共振状态图可以在以下方面得到应用:(1)通过分析产品的成分,确定产品变化的规律;(2)预测产品的理化性质的变化(质地、粘性、结块、水分和油脂的迁移等)的趋势,营养成分降解和微生物代谢与食品中水分活度之间的关系;(3)结合核磁共振成像技术能很好地帮助理解水分(特别游离水分)对食品的质量与安全的影响。本文描述了核磁共振的基本原理、核磁共振弛豫现象的特征与食品特性的关系,并为研究食品体系提供新的研究方法和途径。     

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。     

State Diagram of Freeze-dried Garlic Powder by Differential Scanning Calorimetry and Cooling Curve Methods

ABSTRACT: The state diagram of freeze-dried garlic powder was developed using freezing curve, glass transition line, and maximal-freeze-concentration condition. Freezing points of garlic powder were measured by differential scanning calorimetry (DSC) and the cooling curve method, whereas glass transitions were measured by DSC. The freezing curve and glass transition line were modeled using the Clausius-Clapeyron equation, adjusted with unfreezable water, and the Gordon-Taylor model, respectively. Maximal-freeze-concentrated condition was found as X '_s (characteristic water content) = 0.82 [ X '_g (characteristic solids content) = 0.18] with the characteristic temperature of glass formation being T '_m (characteristic glass transition) =−38.6°C and T '_m (characteristic end point of freezing) =−26.0°C. Other characteristic glass transitions T "_g and T ‴_g equal to −29.3°C and −48.6°C, respectively.     

Influence of Cooling Rate on Glass Transition Temperature of Sucrose Solutions and Rice Starch Gel

ABSTRACT: The study's objectives were to determine the influence of cooling rate through the primary zone of freezing on T_g in sucrose solutions and rice starch gels. The influence of cooling rate, water content, and annealing on T_g were evaluated. Results indicated that the observed T_g values for sucrose solutions were lower after rapid cooling (70% solids: rapid cooling −66.7°C; slow cooling −64.6 °C; 30% solids: rapid cooling −34.6 °C; slow cooling −33.3 °C). The T_g values of annealed samples are higher than the T_g of both rapidly and slowly cooled samples (70%: −44.2 °C; 30%: −32.7 °C). The T_g of the rice starch gel was −9.0 °C after rapid cooling and −7.5 °C after slow cooling.     

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。     

State diagram of salmon (Salmo salar) gelatin films

BACKGROUND: A state diagram presents different physical states of a biomaterial as a function of solid content and temperature. Despite their technological interest, little information is available on protein systems such as gelatin/water mixtures. The objective of this work was to develop state diagrams of salmon gelatin (SG) and bovine gelatin (BG) in order to determine maximal freeze concentration parameters (T′_g, T′_m and X_s′) and to relate possible differences to their biochemical characteristics. RESULTS: Biochemical characterisation of SG showed lower molecular weight and iminoacid concentration compared with BG. Likewise, the glass transition temperature (T_g) was lower for SG at X_s > 0.8, which was associated with its lower molecular weight. Unexpectedly, the depression of freezing temperature (T_f) was greater for SG at X_s > 0.1, which was associated with its higher ash content. Isothermal annealing produced effective values of T′_g ≈ ? 52 °C, T′_m ≈ ? 46 °C and X′_s ≈ 0.6 for both gelatins. Interestingly, the enthalpy change associated with T′_m (ΔH) was significantly higher for SG than for BG after annealing, indicating a higher proportion of ice present at about ? 50 °C. CONCLUSION: Maximal freeze concentration parameters were similar between the two gelatins, though differences in biochemical properties were evident. The results show that there are likely different ways of interaction of SG and BG with water. Copyright © 2011 Society of Chemical Industry     

Plasticizing—Antiplasticizing Effects of Water on Physical Properties of Tapioca Starch Films in the Glassy State

The effects of moisture sorption on physical properties of native and cross-linked starch films in the glassy state were studied. Water played a dual role as a plasticizer or an antiplasticizer, depending on the physical property measured. Plasticizing effects were clearly evident in the case of the calorimetric glass transition temperature ( T _g), tensile modulus, linear expansion, and water vapor permeability. In contrast, antiplasticization by water resulted in maxima in tensile strength, strain-at-break, and toughness of films that were observed at an intermediate moisture content ranging from 4% to 8% (RVP 0.1 to 0.4). The seemingly contradictory effects of water on mechanical properties associated with lower and higher deformation of starch films were reconciled by assigning different roles to water operating primarily via opposite entropic/free volume effects. Relationships, if any, between DSC thermal events and mechanical antiplasticization were not apparent.     

制取硼酸的相图工艺过程解析

以青海大柴旦盐湖富硼镁卤水及固态硼酸盐沉积为原料,以H3BO3-MgCl2-H2O体系、H3BO3-MgCl2-CaCl2-H2O体系0℃和25℃的相图为依据,分别制订了制取硼酸的不同的工艺过程解析方案,单次循环硼的理论收率分别为65.74%、99.41%.     

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。     

赤藓糖醇对南美白对虾肉玻璃化转变温度与状态图的影响

南美白对虾肉（PV）冻藏期间极易出现蛋白质变性,为提高虾肉贮藏稳定性,研究了PV与按虾肉质量添加5%赤藓糖醇的虾肉（PV-E）的吸附等温线;测定了PV与PV-E的玻璃化转变温度（Tg）和冻结点温度（TF）。采用Gordon-Taylor方程与Chen’s方程拟合数据,探讨添加赤藓糖醇对虾肉状态图的影响。结果表明,PV与PV-E水分吸附均为III型等温线,GAB模型为描述虾肉水分吸附特性的最适模型。PV与PV-E的Tg随着湿基含水率升高而降低;相同含水率时,PV-E的Tg高于PV。PV与PV-E的TF随着固形物含量的增加而降低。PV与PV-E最大冷冻浓缩溶液时的玻璃化转变温度T’g分别为-77.09℃和-62.23℃,与之对应的溶质含量分别为0.672 g/g和0.686 g/g。赤藓糖醇可作为一种新型抗冻剂,用于提高虾肉冻藏期间的贮藏稳定性。      

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。     

制取硫酸钾镁肥的相图分析及计算

以相图理论为依据，对青海某硫酸盐亚型盐湖日晒后的硫酸盐混盐和钾盐混盐加入适量芒硝，在15℃条件制取高品质的软钾镁矾即硫酸钾镁肥进行了相图分析和理论计算，给出了制取硫酸钾镁肥理想的配料比和加水量。     

制取硫酸钾镁肥的相图分析及计算

以相图理论为依据,对青海某硫酸盐亚型盐湖日晒后的硫酸盐混盐和钾盐混盐加入适量芒硝,在15℃条件制取高品质的软钾镁矾即硫酸钾镁肥进行了相图分析和理论计算,给出了制取硫酸钾镁肥理想的配料比和加水量.     

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。