NMR和MRI技术对面包和奶酪二元体系在贮藏过程中水分迁移的研究(英文)

采用低场核磁共振成像技术中的spin3D、CPMG等序列对面包和奶酪二元体系进行成像并测定自旋-自旋弛豫时间等参数,并对其在贮藏过程中水分迁移行为及规律进行了研究,为核磁共振技术在食品中的应用打下良好的基础。     

低场核磁共振法研究NaCl对肌原纤维蛋白凝胶水分分布和移动性的影响

为解决凝胶类肉制品含盐量过高的问题,探讨了NaCl浓度对猪肉肌原纤维蛋白热诱导凝胶水分分布和移动性的影响。分别用离心法、低场核磁共振（low-field nuclear magnetic resonance,LF-NMR）、扫描电镜研究不同NaCl浓度下的猪肉肌原纤维蛋白凝胶保水性、水分移动性及分布状态和凝胶微观结构,并用主成分分析探讨它们之间的相关性。结果表明：随着NaCl浓度的上升猪肉肌原纤维蛋白的保水性显著增加、加热后形成了多孔致密的结构。LF-NMR T2驰豫反演为4 个峰,其加权T2分别为0.62～3.89、4.62～35.28、59.06～153.22、1 198.75～1 518.17 ms;合并后分别对应水的3 种存在状态,即大分子结合水、不易流动水和自由流动水。加入NaCl使水的移动性下降,并且使不易流动水的峰面积显著增加（P＜0.05）,从而增加了保水性。主成分分析结果显示不同NaCl浓度凝胶样品在主成分评分图上表现出明显的聚类,低浓度的NaCl在第1主成分的右端,而高浓度在第1主成分的左端,从变量评分图上也可以看出不同指标NaCl浓度的变化情况。因此,不同NaCl浓度下凝胶保水性的改善和不易流动水的增加明显相关。     

Temperature Mapping in Carrot Using T1 Weighted Magnetic Resonance Imaging

A two dimensional Fourier transform spin echo imaging sequence was used to obtain MRI T₁ weighted images from whole cooked carrots at temperatures between 18.6°C and 83.0°C. Sensitivity of temperature measurements from the images ranged from ±0.4°C to ±4.2°C, depending on the temperature of interest and the amount of signal averaging. Dynamic images were obtained with a 24 set acquisition time. Such temperature images could aid in evaluation of models used for aseptic processing simulation studies. Faster imaging techniques could enable on line temperature maps for flowing particulates in aseptic systems.     

Monitoring changes in feta cheese during brining by magnetic resonance imaging and NMR relaxometry

Magnetic resonance imaging (MRI) and NMR relaxometry were used to monitor changes in feta cheese during 169 h of brining at 4.8%, 13.0% and 23.0% salt solutions. Image and relaxation data were acquired to study salt uptake and water loss due to dehydration of cheese during brining. Saturation recovery and Carr-Purcell-Meiboom-Gill (CPMG) sequences were used to determine the longitudinal relaxation (T₁) and the transverse relaxation (T₂) times, respectively. Signal intensities of T₂ weighted images decreased during 169 h of brining. An excellent linear correlation between the average signal intensity and the water content was obtained (R² = 0.984). The T₁ values of cheese brined at 4.8% were almost constant but T₁ values decreased for both 13.0% and 23.0% salt brined cheeses. Analysis of the CPMG decays gave relaxation spectra containing two components which decreased during brining. The short component T_2a was highly correlated with salt content (R² = 0.974). Results showed that NMR and MRI can be used to follow salt uptake and changes in water content in cheese during brining.     

核磁共振及成像技术在食品工业中的应用

核磁共振技术以快速、无损伤、无侵入检测等优点使其在食品中得到广泛的应用,本文综述了其在食品工业中五大方面的应用,分别为测量食品和生物体系中的含水量、研究食品中水分的分布和水分的流动性、研究果蔬的成熟度和损伤程度、研究食品中的油脂、研究食品的玻璃态转变温度。     

Temperature Mapping in a Model Food Gel using Magnetic Resonance Imaging

Two dimensional temperature maps of a model food gel (agar, mi-crocrystalline cellulose, and water, 1.95:6.55:200), were obtained by MRI during heating and cooling. The molecular pseudo self-diffusion coefficient of water was used as a temperature indicator. A two dimensional Fourier transform spin-echo imaging sequence was used for data acquisition. The self-diffusion coefficient at room temperature was 1.26 7times; 1O^?3 mm²/sec. Two dimensional self-diffusion images were obtained, and temperature images were calculated. The error in MRI measurements, due to noise and temperature variation, was less than 1°C with 1.5 mm² resolution. The average variation between MRI and thermocouple measurements was < 1.26°C. This new non-invasive technique can be used to study heat transfer and to measure thermal properties of foods.     

High Resolution Magnetic Resonance Imaging Evaluation of Cheese

ABSTRACT: The curd granules/joints structure of the Emmentaler was observed by NMR micro-imaging during the different stages of cheesemaking. During the ripening process, many carbon dioxyde microbubbles have been visualized inside the curd grains, as well as some volumes of fat outside the grains. At the end of the ripening stage, images reveal the final structure does not have a uniform lipid distribution of grains: the density is high at the boundaries and low at the center. Moisture and fat content profile of the rind has been obtained and rind-dependent water and/or fat accumulations are observed. Finally, the contrast difference between curd joints and grains of the studied samples confirms that a higher draining occurs for the joints than for the grains during cheesemaking.     

磁共振加权像技术研究食品的结构特性

磁共振成像技术（MRI）因为能够在无需破坏样品的条件下获得样品组织中水分和油脂分布的空间信息，而逐渐成为一种应用在质量检测、组织结构分析等方面的有力工具。利用食品样品内部结构组织的固有特性（T1和T2），根据研究的需要，改变脉冲序列中可控制的参数，获得对比度不同的图像。以甜瓜和蛋黄月饼为研究对象，利用CPMG序列测量二者的T2值，在自旋回波（SE）中得到二者的质子密度加权像和T2加权像（T2WI）；再采用反转恢复（IR）中得到二者的T1加权像（T1WI），并根据T1加权像做组织的T1mapping，分析T1值的范围。