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.     

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。     

Study of Caking in Powdered Foods Using Nuclear Magnetic Resonance Spectroscopy

Twenty-three powdered foods and ingredients were subjected to 2 treatments: temperature scan from -20 to 110 °C within 2 hours, and storage at 37 °C and 55 °C for 60 d. During temperature scans, the spin-spin relaxation time T₂ values of individual samples were determined using a nuclear magnetic resonance (NMR) technique, resulting in a temperature-T₂ curve for each sample. Four typical temperature-T₂ curve patterns were identified and were found to be closely related to the physical changes in the samples, including agglomeration, water vaporization, and caking observed during temperature scans. Based on the temperature-T₂ curve patterns, the samples were classified into 4 groups each having distinguished caking behavior. In the storage tests, the samples were removed from the incubators every half an hour during first 2 d of storage period and every day afterwards. The storage test also suggests a strong relationship between molecular mobility and caking. Monitoring changes in T₂ as a function of temperature provides information useful for predicting whether and when caking would occur.     

Relationships between sensory perception and water distribution determined by low-field NMR T(2) relaxation in processed pork - impact of tumbling and RN(-) allele

The relationships between water distribution, measured with low-field NMR (LF-NMR) transverse (T₂) relaxometry and sensory properties in tumbled and non-tumbled cured-smoked loins from 30 female Hampshire crossbred pigs were investigated. Upon distributed analysis of the T₂ relaxation, three populations centred at about 2, 40 and 600–800 ms, respectively, were detected. Clear differences in the characteristics of the intermediate population (T₂₁) were observed between loins from carriers and non-carriers of the RN⁻ allele, which implies differences in water–protein interactions between the two genotypes. PLS regressions between NMR T₂ variables and sensory attributes revealed significant correlations between NMR T₂ variables and the sensory attributes juiciness, acidulous taste and meat taste, which mainly could be ascribed to the T₂₁ time constant. In addition, the number of unappealing pores assessed by the sensory panel was highly related to the relative T₂ populations, implying that the microstructure is directly reflected in the NMR T₂ populations. However, prediction of the processing yield from NMR T₂ variables was poor. The correlation improved when RN genotypes and tumbling conditions were included as predictors. Thus, other effects of tumbling treatments and RN genotypes unrelated to NMR T₂ relaxation were observed.