Texture changes in frozen cod mince measured by low-field nuclear magnetic resonance spectroscopy

Studies were carried out on changes in water proton relaxation, Instron parameters, dimethylamine (DMA) content and sensory texture scores during storage of cod mince at -10°C, -20°C and -70°C. The longest transverse proton relaxation time measured by pulsed low-resolution nuclear magnetic resonance (NMR) spectroscopy increased with temperature and duration of frozen storage. These variations in the NMR parameter paralleled changes observed with analytical methods commonly used for evaluating fish texture, ie Instron measurements, as well as dimethylamine and sensory analyses. It is concluded that the NMR method can be an alternative tool to study textural modifications of cod during frozen storage. © 1997 SCI.     

Freezing-induced proton dynamics in tofu evaluated by low-field nuclear magnetic resonance

The main purpose of the study was to understand and interpret the effects of freezing times on the proton dynamics and chrominance of tofu. Low-field nuclear magnetic resonance (LF-NMR) and magnetic resonance imaging (MRI) were used to monitor real-time changes in microstructure and water distribution at different freezing times. The T ₂ relaxation parameters included the relative intensity (A _2i) and the population of T _2i component (M _2i). Three proton populations focusing on approximately 0.93–4.72, 25–49, and 402–505 ms were identified as T _2b, T ₂₁, and T ₂₂, respectively. The generated ice crystals damaged the hydration layer of the soybean protein and T _2b increased over the 2 h. The side chains of the soybean protein then began to unite owing to the protein’s reduced affinity for water, making the protons of the hydrophilic groups exchangeable, and resulting in decreased mobility of the T _2b fraction. The appearance of exchangeable hydrophilic group protons caused an increase in A _2b from 2 to 6 h. The subsequent increases in A _2b and M _2b 6 h later were due to access to the unfrozen free water. The water molecules (T ₂₁ fraction) changed into ice crystals, reducing A ₂₁ and M ₂₁. The disappearance of the T ₂₂ fraction peak 6 h later was attributed to residual unfrozen water molecules, with the minor component turning into ice with a fast relaxation time. The MRI results showed that the outline of the sample was blurred at 2 h and could not be detected 6 h later. Significant correlations were further detected between T ₂ relaxation parameters and color parameters. LF-NMR has great potential as a reliable tool for the study of tofu.     

结合LF-NMR研究不同处理对酱牛肉保水性的影响

为了探究二次杀菌处理对肉制品中水分的影响,将真空包装的酱牛肉经过600MPa/20min的超高压处理(HP)和90℃/10min的加热处理(HT),未处理(UT)组作为对照,利用低场核磁共振技术(LF-NMR)测定了3组样品第0d和第7d时保水性及水分分布的变化情况。结果表明,高压、加热及贮藏过程均会导致产品重量的损失,增加可压出汁液的比例,HP及HT组处理损失分别为4.36%、6.53%。LF-NMR检测到了四个明显的水分群,代表肉中的结合水、不易流动水和自由水三种存在状态。其中,HP和HT会使肉中水分变得活跃,表现为弛豫时间延长,结合水比例降低、不易流动水和自由水增多,但HP较HT的影响小。核磁成像结果显示第0d时UT、HP、HT的图像依次变亮,表明酱牛肉中自由水的含量依次增多。因此,高压比热处理对酱牛肉保水性的影响要小。     

Optimization of nuclear magnetic resonance and gas chromatography-mass spectrometry-based fingerprinting methods to characterize goat milk powder

This study is the first to provide a comprehensive characterization of the liquid and volatile fractions of whole goat milk powder (GMP). Robust nuclear magnetic resonance (NMR)- and gas chromatography-mass spectrometry (GC-MS)-based chemical fingerprinting methods were optimized and implemented. The untargeted ¹H-NMR analysis resolved 44 metabolites in the liquid fractions of GMP. The NMR fingerprinting technique effectively identified metabolites coming from the aliphatic, sugar, and aromatic regions that can be important in defining the technological properties and quality of the GMP. The untargeted headspace gas chromatography-mass spectrometry fingerprinting was able to detect a total of 50 volatiles including alkanes, ketones, alcohols, aromatics, alkenes, aldehydes, esters, acid, and sulfur compounds. The GMP was dominated by volatiles in the alkane group, while only a few esters were detected. Goat milk is a premium product and vulnerable to fraudulent activities such as adulteration or counterfeit. Therefore, proper characterization and identification is a crucial first step to verify its authenticity and quality.     

Detection of pits in olives under motion by nuclear magnetic resonance

One-dimensional magnetic resonance projections of pickled olives were acquired while they were travelling on a conveyor belt which passed through a 2-tesla NMR magnet and a 150-mm imaging coil. The projections were used to distinguish between pitted and non-pitted olives. The effect of fruit position in the coil was tested and coil end effects were noticed when projections were generated under dynamic conditions. Sorting of 300 pitted and non-pitted olives at various belt speeds was tested. Classification errors (pitted olives classified as non-pitted and vice versa) were 4·3, 4·7, 2·3 and 4·0% at 0, 5, 15 and 25 cm s⁻¹ belt speeds, respectively. ©1997 SCI     

Effects of pressure processing on strawberry studied by nuclear magnetic resonance

Two different nuclear magnetic resonance techniques, namely magnetic resonance imaging and ¹H-HR-MAS NMR spectroscopy, have been employed to study the extent of the damage caused by relatively low pressures (100–200 MPa) in strawberry. MRI maps showed important changes in the relaxation behavior of water molecules in pressurized samples. These differences increased with the pressure level applied. ADC values clearly showed the destruction of biological barriers and the loss of cell compartments produced by pressure. This induced major water redistribution in the tissues and; therefore, substantial changes in the interactions between water molecules and their environment. Relaxation times in T₁ and T₂ maps clearly depicted these pressure induced modifications. Moreover, NMR spectroscopy showed significant differences in the main sugars content in control and pressurized samples. Sucrose hydrolysis seems to be enhanced by the pressure treatment.

Industrial relevance

The research data presented in this paper show a deep insight into the phenomena which take place during pressure processing in a soft plant tissue. The Nuclear Magnetic Resonance (NMR) techniques employed offered the opportunity of studying the whole product without any preparative manipulation which could mask the pressure effects. The results obtained should be useful to understand how and why pressure causes damage to vegetal tissues and, therefore, to design optimized high-pressure treatments which minimize this damage.     

Low resolution pulse nuclear magnetic resonance study of water equilibration in dried carrots

Samples taken during air drying of carrots were analysed after different equilibration times. Low resolution NMR measurements were made and the longitudinal ( T ₁) and the transverse ( T ₂) relaxation times calculated. Both T ₁ and T ₂ decreased with the equilibration time for water contents above 0.30 and 0.47 kg water kg^-1 dry matter, respectively. The decrease in relaxation time increased with the water content. For the same water contents, grated carrots gave lower T ₁ values and smaller T ₁ decreases with equilibration time than 3-mm cubes. Low resolution NMR is a technique which is well suited to the monitoring of the tempering phases of industrial drying cycles.     

Simultaneous application of transglutaminase and high pressure to improve functional properties of chicken meat gels

Low-fat protein gels obtained by pressure are softer than those processed by conventional heat treatment. In this study, microbial transglutaminase (MTGase) (0.3%) was added to chicken batters in order to investigate the combined effect of pressure and enzyme on the functional properties of gels. Batters of meat with egg proteins were treated at 500 MPa for 30 min at 40 °C and then heated at 75 °C for 5 min to inactivate the enzyme. Treated samples showed, under confocal microscopy, a more compact and homogeneous microstructure and exhibited a notable increase in hardness and chewiness as compared to controls that were pressurized but contained no MTGase. They were also harder, more chewy and springy but had a similar cohesiveness and cutting force to those obtained by heat alone.     

Characterizing dissolved and particulate phosphorus in water with 31P nuclear magnetic resonance spectroscopy

Management of aquatic ecosystems is hampered because current methodology limits characterization of phosphorus (P)forms. We developed a procedure to characterize dissolved (DP) and particulate (PP) P from river waters by solution 31P nuclear magnetic resonance (NMR) spectroscopy, using 4-L samples, and tested this procedure with a spiking trial. Most P was orthophosphate. Organic P forms included phosphonates, myo-inositol hexakisphosphate, and orthophosphate diesters. This research represents an important technical advance to characterize DP and PP in natural waters. It is simple, uses samples small enough for routine collection, and puts PP and DP into the same chemical environment for direct comparison. The technique is sensitive, detecting changes in spectra from P additions as small as 2% of total P, and identifying differences from two points along the flow path of a single river. However, lyophilizing samples in NaOH-ethylenediamine-tetraacetic acid (EDTA) may alter some P forms, which requires further investigation.     

高静压对鸡肉凝胶品质影响的试验研究

通过单因素试验,在压力100~400 MPa、保压时间15 min、室温条件下,考察高静压对低盐(食盐添加量1%)鸡肉凝胶色泽、pH值、持水性与质构品质的影响。研究结果表明:200 MPa以上的高静压可导致鸡肉凝胶亮度的显著下降、以及凝胶硬度、弹性和咀嚼性的显著增加;300 MPa以上的高静压可引起鸡肉凝胶pH值和黏结性的显著升高(P<0.05);100 MPa与300 MPa压力使鸡肉凝胶的蒸煮损失率CL低于对照组,而200 MPa压力导致CL升高(P<0.05);100~400 MPa的高静压对鸡肉凝胶的保水性无显著影响(P>0.05)。因此,300 MPa的高静压可形成高硬度、高弹性与高黏结性、低CL值的低盐鸡肉糜凝胶制品。     

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.     

Inhibition of lipid oxidation in refrigerated and frozen salted raw minced chicken breasts with electron beam irradiated almond skin powder

Antioxidant effects of electron beam irradiated almond skin powder (ASP) in raw minced chicken breasts (MCB) during refrigerated and frozen storage were studied. MCB samples were treated with BHT, non-irradiated ASP (0 kGy), irradiated ASP (10 kGy, 20 kGy and 30 kGy) and compared to MCB without antioxidants. Colour was determined on initial and final day of analysis while conjugated dienes (CD), peroxide values (POV), TBARS and hexanal content were evaluated periodically for 12 days of refrigerated storage and seven months of frozen storage. ASP addition lowered L* values compared to MCB without ASP or BHT. During refrigerated storage, MCB containing ASP had decreased formation of lipid oxidation products ranging from 0 to 66%, 7 to 24%, 0 to 37% and 4 to 71% reduction in POV, CD, TBARS and hexanal content, respectively, as compared to MCB without antioxidants over duration of study. A 15–65%, 3–25%, 14–50% and 28–82% reduction in POV, CD, TBARS and hexanal content, respectively, for frozen MCB was detected.     

核磁共振技术在食品检测方面的应用

综述国内外核磁共振技术在食品检测方面的技术研究。从核磁共振技术定义与分类,及其对食品成分、分子结构的分析以及水果品质无损检测等方面的应用进行阐述。从目前的应用现状来看,该技术在食品检测方面具有快速、准确以及不损坏原料的优点,但在实际的应用中也还存在一些问题,有待于进一步深入研究。     

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.     

核磁共振技术在食品研究中的应用

介绍了核磁共振(NuclearMagneticResonance)技术的基本原理及其在食品分析和研究中的应用。     

Aging-induced changes in microstructure and water distribution in fresh and cooked pork in relation to water-holding capacity and cooking loss - A combined confocal laser scanning microscopy (CLSM) and low-field nuclear magnetic resonance relaxation study

Confocal laser scanning microscopy (CLSM) and low-field nuclear magnetic resonance (LF-NMR) relaxometry were combined to characterize microstructural changes and water distribution in fresh and cooked pork during an aging period of 14 days. At day 1 (24 h postmortem) a few muscle fibres, which appear swollen, were observed in both fresh and cooked meat. An identical microstructure was still apparent after 14 days, however, the number of muscle fibres showing distinguished characteristics was found to increase throughout the aging period. Hence, it was apparent that during aging the individual fibres swell and disintegrate at different rates. Development in water-holding capacity (WHC) was followed during the aging period using gravimetric methods, and an increase in the WHC in the fresh meat was observed, which resembled the amount of extramyofibrillar water measured by NMR relaxometry (T₂₂ population). This was consistent with the CLSM images, as a substantial increase in the number of myofibrils that appeared swollen, capable of holding more water, was observed during aging. In the cooked meat the width of the T_21c population, reflecting the myofibrillar water in the cooked meat, was seen to decrease during the entire storage period, which corresponds to the development of a more homogeneous structure. In the CLSM data a continuous degradation during the storage period was observed, which could resemble a shift to a more homogeneous structure. Comparison of CLSM of transverse sections of fresh and cooked pork revealed a pronounced shrinkage of muscle fibres upon cooking. This resulted in large gaps between the cooked muscle fibres, which also was visible as shrinkage at the level of the individual myofibrils. This pattern was also reflected in the NMR relaxation data. The cooking-induced shrinkage of the myofibrils occurred concomitantly with a decrease in the amount of intermyofibrillar water within the individual fibre and an increase in the larger extramyofibrillar spaces between fibres, i.e. water is expelled from the myofibrillar matrix upon cooking. Accordingly, the present study demonstrated that the use of CLSM together with NMR relaxometry can provide further information on the relationship between structural characteristics of meat and resultant water distribution.     

Simultaneous determination of oil and water content in olive husk by pulsed low resolution nuclear magnetic resonance

A pulsed low-resolution NMR method for the oil and water determination in olive husk samples is reported. It is based on the determination of the solid to liquid ratio of the sample and on the detection of the spin-echo decay curve. This method is very fast and can be fully self-contained, as it does not require either to weigh and dry the sample or any correlation curve. It seems suitable for other oil containing samples, such as seeds. The way to simplify and speed up the procedure is also discussed.     

1H nuclear magnetic resonance relaxometric characterization of fat and water states in soft and hard cheese

The aim of this work was to study the spin spin (T2) relaxation components of one hard cheese and three soft cheeses to characterize fat and water states. NMR signals were measured at 6 degrees C with a 0.47 T NMR device. The transverse relaxation decay was fitted using the Marquardt method. The T2 relaxometric behaviour of the cheeses under consideration was characterized by four relaxation components. To understand the chemical composition of each NMR component, we studied anhydrous milk fat extracted from each cheese analysed. At 6 degrees C, the fat was 60% crystalline. In cheese, the solid fat was found mainly in the shorter relaxation component with a T2 of 17 micros. The intensity of the NMR relaxation with a T2 > 1 ms was explained by the amount of water, liquid fat and proteins, and the associated relaxation time varied as a function of the process used. The composition of each relaxation component was confirmed by the temperature effect and the influence of the fat content on the NMR cheese signal. NMR relaxometry was able to provide information on water behaviour (i.e. the quantity and level of interactions with proteins) and on the solid:liquid ratio of anhydrous milk fat in the cheese.     

Hydration properties and proton exchange in aqueous sugar solutions studied by time domain nuclear magnetic resonance

Proton NMR relaxation rates (R₁ and R₂) were measured in aqueous solutions of sucrose, d-glucose and d-fructose with increasing concentration. The measurements were carried out using Bruker PC 20 NMR Process Analyzer. Inversion recovery and CPMG pulse sequences are used for the measurement of relaxation rates. Results show that the values of relaxation rate increase as the concentration of the sugar is increased. The relaxation rate appears to be higher for sucrose solutions as compared to glucose or d-fructose solutions. These results were discussed on the basis of molecular association between sugar and water molecules through hydrogen bonding. The water self diffusion coefficient was measured in these sugar solutions by using pulse field gradient NMR method. As expected, the water self-diffusion coefficient was reduced with increased sugar concentrations. The results of translational mobility exhibited a higher mobility for fructose than glucose or sucrose in aqueous solutions.