应用Matlab 6.5软件对奶酪和面包样品的核磁共振成像进行T2分布重建的研究

本文论述了采用低场核磁共振成像技术（magnetic resonance imaging,MRI）中的spin3D成像序列,采用不同Tau值对奶酪和面包样品进行成像实验.应用Matlab软件编程对图像进行数据处理,并对T2分布进行重建,最后得到T2分布状态图像.为核磁共振技术在食品中的应用打下良好的基础.     

南酸枣糕烘干过程中水分的迁移和分布

利用核磁共振及其成像技术,探究南酸枣糕在烘干过程中水分含量、迁移和分布情况。通过分析南酸枣糕烘干过程中核磁共振的自由衰减弛豫时间、自旋-自旋弛豫时间和核磁共振成像图发现:南酸枣糕的水分含量与体系的质子密度高度线性相关,其相关系数达到0.990 6。因此,可以通过建立水分含量与核磁共振质子密度的标准曲线实现南酸枣糕水分含量的核磁共振定量测定;在烘干过程中,随着时间的延长,南酸枣糕中的束缚水的流动性(T21)呈降低的趋势,自由水的流动性(T22)呈先增加后降低的趋势,核磁共振成像图逐渐变暗;从成像图也可直观地看出,南酸枣糕内部弛豫信号比外部强,证实南酸枣糕干燥是一个不均匀的干燥过程。     

核磁共振技术在脐橙保藏和质量评估中的应用

采用低场核磁共振技术研究脐橙储藏过程中水分的状态、变化以及水分的迁移.利用Carr-Purcell-Mei-boom-Gill(CPMG)序列采集样品的核磁共振受激回波信号,采用多重指数衰减模型对收集的信号数据进行分析并计算组织中不同水分自旋-自旋弛豫时间.探讨脐橙在储藏过程中品质变化与核磁共振弛豫参数变化的相关性.发现在脐橙的后成熟期、稳定期和腐烂期,对应的自旋-自旋弛豫时间变化呈现一个上升-稳定-急速下降的过程,且在脐橙腐烂前出现了一个自旋-自旋驰豫时间急剧下降的过程.该方法可以作为脐橙质量评估的有效手段,对于脐橙的质量评估和保藏方法的评估等具有指导意义.     

利用核磁共振技术研究添加剂对面团持水性的影响

本实验利用核磁共振技术探讨变性玉米淀粉、馒头改良剂和蔗糖脂肪酸酯(SE)对馒头面团形成过程的影响,并将核磁共振仪测定结果与TA质构仪测定结果相比较,确定三种面团改良剂的最优复配比例.通过正交试验得出,变性玉米淀粉:面粉为4:46,馒头改良剂添加量为0.5%,蔗糖脂肪酸酯添加量为0.5%时,面团的自旋-自旋弛豫时间较低,质子信号幅度较大,面团黏聚性好、硬度小、黏度适中,此时面团中的水分自由度较低,面团面筋充分形成,面团持水性和面团质构都达到最佳的状态.     

磁共振成像之IR序列在猪肉质量评估中的应用初探

采用核磁共振成像技术（MRI，magnetic resonance imaging）中的反转恢复自旋回波（IR，inversion recovery spin echo）序列对猪肉进行二维成像，从信号成像的质量效果人手，在改变成像参数的情况下分析图像变化规律。探索IR序列成像信号强度和对比度之间有相关性，得到最佳的参数。这将为今后在猪肉的保藏与加工过程中质量的评估打下良好的基础。     

利用核磁共振技术研究添加齐对面团持水性的影响

本实验利用核磁共振技术探讨变性玉米淀粉、馒头改良剂和蔗糖脂肪酸酯（SE）对馒头面团形成过程的影响,并将核磁共振仪测定结果与TA质构仪测定结果相比较,确定三种面团改良剂的最优复配比例。通过正交试验得出,变性玉米淀粉：面粉为4：46,馒头改良剂添加量为0．5％,蔗糖脂肪酸酯添加量为0．5％时,面团的自旋．自旋弛豫时间较低,质子信号幅度较大,面团黏聚性好、硬度小、黏度适中,此时面团中的水分自由度较低,面团面筋充分形成,面团持水性和面团质构都达到最佳的状态。     

核磁共振技术研究冷冻处理对魔芋粉丝中水分的影响

利用核磁共振技术测定魔芋粉丝在不同处理温度过程中质子的自旋-自旋弛豫时间(T2)以及质子信号密度(A)。魔芋粉丝体系中水分流动性不同,T2和A不同。结果表明,在魔芋粉丝冷冻处理过程中,其“束缚水”和“自由水”迁移行为不同。当处理温度为－12℃,处理时间为3h时,复水后的魔芋粉丝持水性质最佳。     

现代成像技术在食品/农产品无损检测中的研究进展

现代成像技术是应用物理技术、电子技术、计算机技术和材料科学等多种技术相互渗透的产物,近些年来也开始应用于食品、农产品的品质检测。本文介绍了现代成像系统的基本构成,阐述了可见光成像技术、光谱成像技术、X射线线性扫描成像技术、CT成像技术、超声成像技术、核磁共振成像技术的特点,及其在食品、农产品检测中的研究应用情况。最后对现代成像新技术在食品、农产品检测中的发展趋势进行了展望。     

利用核磁共振及成像原理研究鸡蛋的煮熟过程

利用核磁共振技术研究在不同的煮熟时间下带壳鸡蛋的弛豫特性.采用IR、CPMG脉冲序列来测定不同煮熟时间下质子的自旋-晶格弛豫时间(T1)和自旋-自旋弛豫时间(T2).在蛋清和蛋黄不同的凝固和成形过程中,其表现出不同的弛豫时间.实验结果表明,蛋清先于蛋黄逐渐变性,弛豫时间T23对应的质子密度逐渐降低,最后达到稳定的状态,说明整个带壳鸡蛋的流动性下降.通过核磁共振成像能够直观地说明带壳鸡蛋在煮熟过程中内部结构的变化情况.     

磁共振成像之SE序列在猪肉质量评估中的应用——TR值对成像质量的影响

本文论述了采用核磁共振成像技术（Magnetic resonance imaging，MRI）中的自旋回波（Spinecho，SE）序列对猪肉进行二维成像，从信号成像的质量效果入手，在改变重复时间（Repeat time，TR）值的情况下分析图像变化规律。利用一系列图像信号值拟合得出了所测猪肉的纵向弛豫时间T1范围，并发现了在SE序列成像过程中图像信号与T1之间有相关性。由此可推知，准确计算T1值时应采集相应TR值段的图像信号。而图像中脂肪与瘦肉两部分的对比度在此范围之内也是差别最大，这将有利于今后对猪肉进行NMR成像的质量分析的开展，提供了一种研究食品物质性质的方法。     

The effects of soy on freezable bread dough: a magnetic resonance study

Hygroscopic soy ingredients were hypothesised to slow the rate of water migration in unleavened bread dough during frozen storage. Thawed soy (18% dry weight) and wheat dough samples were assessed using non-destructive nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) for up to 8 wks frozen storage time. MRI suggested a spatially homogeneous, net increase in proton mobility with frozen storage and, with solution state proton NMR, distinct "free" and "bound" states were discerned. T(2) relaxation times of the majority proton population suggested increased mobility with frozen storage time, and statistical difference from the fresh sample was seen later for the soy samples than the wheat samples. As seen by (13)C-solid state NMR, the crystallinity of the starch was not affected by either soy addition or frozen storage. In conclusion, addition of soy to bakery products led to slightly enhanced preservation of "fresh" characteristics of the dough during frozen storage.     

利用NMR研究赤藓糖醇对糙米面包贮藏期间保水性的影响

利用低场核磁共振（nuclear magnetic resonance,NMR）及成像技术,研究赤藓糖醇和蔗糖对糙米面包贮藏期间保水性的影响。通过检测面包1H NMR弛豫时间、峰面积、核磁共振成像（magnetic resonance imaging,MRI）以及水分活度,得出贮藏期间面包结合水（弛豫时间T21）相对稳定,不易流动水（弛豫时间T22）和自由水（弛豫时间T23）逐渐减少,与蔗糖面包相比,添加赤藓糖醇的面包具有高水分含量和低水分活度的特点,MRI同样体现出添加赤藓糖醇的面包具有良好的保水性。     

Effect of moisture content and water mobility on microwave expansion of imitation cheese

The effects of moisture content (60–45%), and refrigerated storage (1–9 days) on the functional properties, water mobility and microwave expansion of imitation cheese are investigated. Cheese hardness, elastic (G′) and viscous moduli (G″) increased with decreasing moisture content and decreased during storage. Flowability, loss tangent (tan δ) and water mobility decreased with decreasing moisture content and increased during storage. Microwave expansion of imitation cheese decreased with decreasing moisture content and increased with prolonging storage time prior to microwaving. The changes in texture, rheology and flowability of cheese with decreasing moisture content, changes in water mobility and storage time reflected the level of cheese plasticisation by water and had strong linear correlations with microwave expansion. This work provides evidence that moisture content influences microwave expansion of imitation cheese by providing the driving force for expansion and plasticising the cheese matrix.     

核磁共振研究膳食纤维面包制作过程的水分迁移行为

利用核磁共振测定三种不同配方面包在制作过程(和面、发酵、醒发和焙烤)中质子的自旋-自旋弛豫时间(T2),面团中流动性不同的水分,表现出不同的弛豫时间。实验表明,在面包制作过程中,其束缚相和自由相的迁移行为不同,此外140MPa处理的膳食纤维具有强持水性,添加至面包中可改善其储藏性。     

Improving the yield of Mozzarella cheese by phospholipase treatment of milk

Part-skim Mozzarella cheese was manufactured from milk hydrolyzed with fungal phospholipase A₁ prior to renneting. The phospholipase treatment reduced fat losses in whey and cooking water and increased cheese yield as a result of improved fat and moisture retention in the cheese curd. The amount of phospholipids in the whey was reduced because of improved retention of lysophospholipids in the cheese curd. Water binding in the fresh curds and young cheeses up to 3 wk of storage was investigated by a ¹H nuclear magnetic resonance spin-spin relaxation technique. In the fresh curds, 2 dominant water fractions were present, characterized by average spin-spin relaxation times (T₂) of 14 and 86 to 89 ms, respectively. These 2 fractions of low- and high-molecular-mobility water were similar in all cheeses and presumed to represent water associated with the casein matrix and water present in the pores. A few hours after manufacture, cheeses made with phospholipase showed decreased T₂ of the high-mobility fraction, indicating improved water-holding capacity. It is suggested that lysophospholipids released from the fat globule membranes act as surface-active agents in the cheese curd, helping emulsification of water and fat during processing and reducing syneresis. During 3 wk of storage after manufacture, the mobility of both water fractions increased in all cheeses, but was highest in the cheeses made with phospholipase. The increase in mobility during the first weeks of storage has earlier been ascribed to structural changes in the protein matrix, which in principle could be accelerated because of the higher moisture content. However, the microstructure of phospholipase-treated cheese was investigated by confocal laser scanning microscopy and found to be very similar to the control cheese during processing and up to 28 d of storage. In addition, flowability, stretchability, and browning were acceptable and similar in all the manufactured cheeses. Thus, phospholipase hydrolysis of cheese milk improved the cheese yield without changing the cheese microstructure, and resulted in cheese with functional properties that were identical to traditional Mozzarella cheese.     

Water molecular dynamics during bread staling by Nuclear Magnetic Resonance

Bread staling is a complex phenomenon that originates from multiple physico-chemical events (amylopectin retrogradation, water loss and redistribution) that are not yet completely elucidated. Molecular properties of white bread loaves were characterized by multiple proton Nuclear Magnetic Resonance (NMR) techniques (proton FID, T₂ and T₁ relaxation time) over 14 days of storage. Changes at a molecular level (faster decay of proton FIDs and shifting of proton T₂ relaxation times distributions towards shorter times), indicating a proton mobility reduction of the bread matrix, were observed during storage. Multiple ¹H T₂ populations were observed and tentatively associated to water-gluten and water-starch domains. Proton T₁ of bread was for the first time measured at variable frequencies (Fast Field Cycling NMR) and found to be strongly dependent upon frequency and to decrease in bread during storage, especially at frequencies ≤ 0.2 MHz. An additional proton T₁ population, relaxing at 2 ms, was detected at 0.52 MHz only at early storage times and tentatively attributed to a water-gluten domain that lost mobility during storage.     

Effect of protein:starch ratio on microwave expansion of imitation cheese-based product

Microwave expansion of imitation cheese is a novel way of producing a potentially health crispy snack food. This study aimed to investigate the effects of protein:starch (P:S) ratios of 37:0, 24:13, 20:17 or 16:21 and refrigerated storage (1–9 days) on the functional properties, water mobility and microwave expansion of imitation cheese. Cheese hardness and rheological dynamic moduli decreased while water mobility increased with decreasing P:S ratio and prolonged storage time. The volumetric expansion increased with increasing storage time pre-microwaving. After storing cheeses for 9 days, a cheese with P:S of 37:0 and protein:emulsifying salt ratio of 17.12 exhibited the highest expansion of ∼1050%, while cheese with P:S of 20:17 exhibited the highest volumetric expansion of ∼900% among cheeses containing starch. The expansion of cheese with P:S of 37:0 suggests strongly that it is mainly the hydrated protein matrix that stretches under pressure generated by steam during microwaving to form the expanded structure.     

Determining effects of freezing on pasta filata and non-pasta filata mozzarella cheeses by nuclear magnetic resonance imaging

The formation of ice during freezing of pasta filata and non-pasta filata Mozzarella cheeses, and the spatial redistribution of water T2 relaxation time and the changes of water self-diffusion coefficient (D) within the unfrozen and frozen-stored cheese samples were observed by nuclear magnetic resonance imaging. Images of water spin number density and water T2 relaxation time were obtained using spin-echo imaging pulse sequence. The water self-diffusion coefficient was measured by pulsed-field gradient spin-echo technique. The ice formation was accompanied by loss of signal intensity in the affected areas of the cheese sample. There was a significant change in T2 and D values of water following freezing-thawing, which can be used to characterize the effect of freezing on cheeses. The D values of the frozen-stored pasta filata Mozzarella cheese samples were higher than those for the unfrozen samples. Such a difference was not observed for the non-pasta filata Mozzarella cheese samples. The T2 distributions of frozen-stored pasta filata Mozzarella cheese samples were narrower, and those for the non-pasta filata Mozzarella cheese samples were broader T2. This may be attributed to the microstructure differences between the two cheeses.     

Nuclear magnetic resonance study of water mobility in pasta filata and non-pasta filata mozzarella

Changes in molecular mobility of water in pasta filata and non-pasta filata Mozzarella cheeses were investigated during the first 10 d of storage using nuclear magnetic resonance (NMR) relaxation techniques. Water in pasta filata Mozzarella was classified into two fractions by spin-spin relaxation times, T21 and T22, and corresponding proton intensities, A1 and A2, representing low and high molecular mobility, respectively. Increase in A1 (and decrease in A2) suggested that, there was a redistribution of water from more- to less-mobile fraction (from T22 to T21 fraction) during the first 10 d of storage. The NMR data did not indicate the two-state behavior of water molecules in non-pasta filata Mozzarella. However, the T2 values of non-pasta filata Mozzarella were comparable to the T21 values of pasta filata Mozzarella indicating that the molecular mobility of water in non-pasta filata Mozzarella is comparable to that of the less mobile water fraction in pasta filata Mozzarella. Generally, T2 and T1 values of pasta filata and non-pasta filata Mozzarella cheeses increased during the 10-d storage. This is believed to be due to structural changes in the protein matrix.