Measurement of total water and bound water contents in human stratum corneum by in vitro proton nuclear magnetic resonance spectroscopy

The reliability of in vitro proton nuclear magnetic resonance (NMR) spectroscopy to specifically measure the water content of rehydrated human stratum corneum samples was assessed by comparison with the previously validated thermal desorption-mass spectrometry technique. The interest of proton NMR is that it can determine, in the same sample, both the amount of total water by recording the spectra at ambient temperature, and that of bound water (non-freezing water) by recording the spectra below 0 degrees C. Provided that enough samples of stratum corneum are analysed to average out the observed and well-known sample-to-sample variation, proton NMR may be of value in the evaluation of hygroscopic properties of raw materials for moisturizer formulations.     

Characterization of water distribution in xanthan-curdlan hydrogel complex using magnetic resonance imaging, nuclear magnetic resonance relaxometry, rheology, and scanning electron microscopy

Abstract: Xanthan‐curdlan hydrogel complex (XCHC) has been shown capable of retaining moisture up to 5 freeze‐thaw cycles (FTCs); however, moisture distribution in the complex in relation to the hydrogel composition and structure remains uncharacterized. In the present study, magnetic resonance imaging (MRI), nuclear magnetic resonance (NMR) relaxometry, rheology, and scanning electron microscopy (SEM) were used to examine the effect of water distribution and interaction with 2.0% aqueous solutions of xanthan, curdlan, and XCHC consisting of equal amounts of both polysaccharides. A gel structure with an indication of syneresis was clearly seen in the MR image of curdlan alone, whereas the distribution of protons throughout xanthan and XCHC samples remained homogeneous and showed no detectable syneresis. The three‐dimensional network, indicated by frequency sweeps, of curdlan was responsible for curdlan's gel structure. The frequency sweep and slope of the storage modulus (G′) of XCHC was significantly closer to curdlan with higher elasticity and less dependency upon angular frequency than xanthan alone. The reduction in XCHC dynamic moduli (G′ and G″) compared to curdlan could be attributed to the formation of wavy layers instead of a fully cured three‐dimensional structure. Addition of xanthan to curdlan restricted XCHC spin–spin relaxation time (T₂) to intermediate and slower exchange regimes, namely approximately 110 and 342 ms, respectively, promoting the polymer's interaction with water while inhibiting interpolymer interactions found in curdlan. A 3rd proton pool with the slowest T₂ seen in curdlan was not found in XCHC, correlating to the absence of syneresis. Practical Application: The combination of texture measurements and discrete noninvasive techniques was found capable of providing insightful understanding of water distribution in a gel system. These techniques may be applied to other hydrogel complexes. The XCHC system investigated has the potential to enhance freeze‐thaw stability in frozen food products by minimizing syneresis due to undesirable temperature fluctuations during distribution and consumer application.     

基于低场核磁共振技术研究大米冻融过程中水分状态变化

目的 确定大米反演峰的含义和大米冻融过程中水分迁移变化规律。方法 以苏州地产粳米(苏香粳100)为研究对象, 采用低场核磁共振技术作为检测手段, 分析不同温度(?30、?18、0、4、10、15、20 ℃)对弛豫时间、峰总面积、峰面积比的影响, 进而研究分析冻融过程中温度变化对大米本身的水分状态变化的影响。结果 大米中结合水与自由水在冻融过程中会出现一定程度的转化; 降温过程中大米结合水含量先降低再升高后降低, 升温过程中大米结合水含量逐渐升高; 15 ℃时大米自由水含量最低。结论 15 ℃适合大米贮藏, 冷冻大米可以长期贮藏, 适宜解冻后蒸煮。     

Determination of fat and water content in vitro and in vivo by proton nuclear magnetic resonance

Proton NMR spectroscopy was performed on a series of pork samples containing varying proportions of fat and muscle and on a series of control and obese mice. Initial measurements were made using a 0.5 T (21 MHz) whole body imaging system and the results were expressed as the ratio of water and lipid hydrogen peak areas. With pork samples the NMR results correlated well with per cent water or lipid in the tissue (r = 0.99 for 20- and 50-g samples). For the mice the correlation between per cent water or lipid in the body and the NMR measurement was 0.92. Subsequent measurements were made using a 4.7 T (200 MHz) imaging/spectrometer from which separate integral values were obtained for the water and lipid hydrogen peaks. The separation of the water and lipid peaks was 3.5 ppm. For pork samples measured with the 4.7 T system the correlation between the peak area and the amount of water or lipid in the sample was 0.997 with the standard error of the estimate being ±0.72 g for water and ±1.00g for lipid. NMR imaging was used to determine the relative amount of fat and muscle in a cross-section of a control and an obese rat.