Characterisation of moisture migration of shiitake mushroom (Lentinula edodes) during storage and its relationship to quality deterioration

Water is a critical factor influencing the quality of mushrooms. This paper investigated the moisture migration of shiitake mushroom during storage using low-field nuclear magnetic resonance (LF-NMR) and magnetic resonance imaging (MRI) and its relationship to quality deterioration. Three water components assigned as water in different cell compartments of cell wall, cytoplasm and vacuole were observed in shiitake mushroom matrix. As the prolonging of storage time, the right shift of immobilised water and left shift of free water led to the merge of these two peaks at the end of storage. The increase in peak area of water in cytoplasm and decrease in the peak area of water in vacuole indicated evident moisture migration from vacuole to cytoplasm. MRI images showed heterogeneous water distribution in shiitake mushroom, and the water migrated from centre to surface, then evaporated to the environment. Besides, the moisture migration might be related to the weight loss and textural softening of shiitake mushroom.     

Changes occurring in potatoes during cooking and reheating as affected by salting and cool or frozen storage – a LF-NMR study

Low field nuclear magnetic resonance (LF-NMR) was measured continuously during cooking of salted and unsalted potatoes to investigate the effect of salt on the cooking process. The cooked potatoes were subjected to cool storage (1, 2, 24 and 48 h) or frozen storage (1, 3, 5 or 14 days). Upon storage they were reheated in the LF-NMR instrument to investigate the effect of different storage regimes and salt on the state of water in potatoes during a continuous reheating process. In salted potatoes, a broader distribution of T₂ times leaning towards longer relaxation times were observed for extra-cellular/cytoplasmic water at low temperatures during cooking. This could indicate that the extra-cellular space is increased due to salting. In samples subjected to cool and frozen storage an additional free water component was found, which reflects that syneresis occurs as a result of retrogradation. In the frozen samples, the T_2,1 and T_2,2 water populations merge, illustrating an increased cell wall permeability or freeze damage of the cell walls. This is more evident in the unsalted samples showing that the cell walls are stabilized by salt during freezing. In conclusion, the results showed that LF-NMR could monitor the changes during starch gelatinization, starch retrogradation and melting of retrograded starch in salted and non-salted potatoes.     

Water mobility in acidified milk drinks studied by low-field 1H NMR

Low-field nuclear magnetic resonance (LF-NMR) transverse relaxation (T₂) was used to characterise acidified milk drinks (AMDs) with varying composition. Pectin was added to the AMDs at concentrations of 0.0%, 0.1%, 0.3% or 0.5% and the protein used was either skim milk powder (SMP) or SMP with added whey protein concentrate. Distributed exponential analysis of the T₂ relaxation revealed that the AMDs contained a single water component and that the T₂ relaxation times and distributions differed significantly with respect to pectin concentration and protein type. Temperature profiles (5–25–5 °C) showed that pectin concentrations of 0.3% or 0.5% prevented phase separations in the AMDs as a consequence of heating and cooling, whereas a new free water component emerged in the samples with pectin concentrations of 0.0% or 0.1% pectin. Overall, LF-NMR provides a powerful tool for elucidating industrially relevant texture problems such as whey separation.     

Effect of Power Ultrasound and Pulsed Vacuum Treatments on the Dehydration Kinetics,Distribution, and Status of Water in Osmotically Dehydrated Strawberry: a Combined NMR and DSC Study

The effect of power ultrasound and pulsed vacuum (PV) treatments on the dehydration kinetics and the status of water during osmotic dehydration of strawberries was investigated. Low-field nuclear magnetic resonance (LF-NMR) and magnetic resonance imaging (MRI) were used to determine the spatial distribution and status of water within the cellular and intercellular spaces. Differential scanning calorimetry (DSC) was used to determine the freezing point depression and the amount of frozen water. Osmotic treatment was performed by immersing the samples in 25 and 50 % (w/w) sucrose solutions at 40 °C for 3 h. Water loss and solid gain of strawberry samples were measured and the data were fitted by Peleg’s model. The Peleg’s model fitted the experimental water loss and solid gain kinetics data well (R ²?>?0.98). At a given sucrose concentration, the highest water loss and the highest decrease in firmness occurred while using ultrasound treatment, while the highest solid gain and the highest firmness values were achieved by pulsed vacuum treatment. LF-NMR signals were able to quantify the effect of water-osmotic solute exchange on the cell compartments (vacuole, cytoplasm plus intercellular space, and cell wall). The LF-NMR data showed that the relative space occupied by the vacuole decreased and the relative space occupied by the cytoplasm and intercellular space were increased due to these osmotic treatments. MRI results indicated that a bright “water strip” appeared in the periphery of all the osmotically dehydrated samples. DSC results showed that the decrease in water content and the increase in the osmotic solutes depressed the initial freezing point and the freezable water content in osmotically dehydrated strawberry.     

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.     

1H and 23Na MRI studies of Atlantic salmon (Salmo salar) and Atlantic cod (Gadus morhua) fillet pieces salted in different brine concentrations

BACKGROUND: Applicability of magnetic resonance imaging (MRI) to quantitative analysis of sodium in salted fish products is usually impaired by the partial ²³Na MRI ‘invisibility’ phenomena as well as high investment costs of the MRI equipment. RESULTS: Salmon and cod fillet pieces, unsalted and brine salted (50, 100, 150, 200 and 250 g kg^?1 NaCl) for 48 h, were studied using ¹H and ²³Na MRI. Based on MRI results, T₁ and T₂ relaxation times were calculated for ¹H and the T₂ time for ²³Na nuclei. In addition, water diffusion images for all fillet samples and reference brine solutions were obtained. Variation of the nuclear magnetic resonance relaxation times and water diffusion constants with brine concentration is discussed in terms of the muscle structural changes. Sodium MRI visibility factors for the MRI method used were determined for all fish samples. CONCLUSION: Observed changes in proton and sodium NMR relaxation times with the salt content reflect complex counteraction of several factors related to the muscle structural changes. Sodium MRI visibility factors appear to be dependent on a number of experimental factors in a complex matter, making quantitative sodium analysis by the MRI technique used non‐trivial. Copyright © 2007 Society of Chemical Industry     

The effect of salt and fibre direction on water dynamics,distribution and mobility in pork muscle: A low field NMR study

The effect of salt concentration and fibre orientation on water within the meat matrix was investigated by low-field nuclear magnetic resonance (LF-NMR), water-binding capacity (WBC), diffusion studies and histological analysis. Pork M. longissimus thoracis et lumborum samples were cured with 5.7, 15.3 or 26.3% w/w NaCl at a parallel or perpendicular fibre direction. NMR transverse (T₂) relaxation identified three water components (T_2b, T₂₁ and T₂₂) which all exhibited characteristics correlated to WBC. Results indicated that T_2b increases with increasing NaCl concentration. Increasing intra-myofibrillar water and decreasing extra-myofibrillar water resulted in the highest WBC. Water diffused more quickly into the extra-myofibrillar space in samples cured at a parallel fibre direction. This water remained loosely bound in samples cured with the saturated solution (26.3% w/w NaCl) leading to decreased WBC. This study provides further information on water binding within the meat matrix by applying the results of LF-NMR to traditional water-binding theories.     

低场核磁共振测定鲜猪肉中水分分布的制样方法

目的应用低场核磁共振技术(low field nuclear magnetic resonance,LF-NMR)测定不同鲜猪肉的制样方法(肉样大小、分切方向、是否包膜)的水分分布,以确定其较佳制样方法。方法以宰后24 h的猪背最长肌为对象,采用单因素实验,分别按不同大小、不同分切方向和包膜与否进行3组实验,对LF-NMR的弛豫时间T_2相关指标进行方差分析和多重比较。结果随着肉样质量的增加,T_(2b)先减小后增大(P0.05),A_(2b)、A21逐渐增加(P0.05);肉样分切方向不影响样品水分含量分布测定结果;而包膜使样品的T_(2b)减小、A_(2b)和P-(2b)增加(P0.05)。结论猪肉的制样样品大小为2.0 cm(长)×1.0 cm(宽)×1.0 cm(高),分切方向为沿肌肉方向,不包膜处理,这种制样方法对样品中水分分布情况的影响最小,能相对准确地反映实际样品中水分分布及含量。     

Magnetic resonance relaxation measurements to determine oil and water content in fried foods

The quality and marketability of many fried food products is a function of the internal distribution of oil and water. French fries, for example, are well received when they are both crisp and moist, but not when they are soggy. A rapid technique for the measurement of local oil and water content is therefore highly desirable to guide the development and processing of fried food materials.Time-domain nuclear magnetic resonance (TD-NMR) has proven to be a quick, reproducible, accurate, and non-invasive technique, which is particularly well suited to measurements of oil and moisture content. Nuclear spin–spin relaxation times (T₂) are an excellent probe of molecular mobility, which in turn can be directly correlated to moisture content.In this work, a precursor to spatially resolved measurements, we measure T₂ in a model fried food crust sample as a function of moisture level. We observe multi-exponential behavior, which we assign to specific liquid constituents. We find a direct correlation between the component weightings and the known oil and water contents.By systematically varying the moisture level of the sample, we explore the nature of water uptake in these materials. Absorption is modeled with a modified BET sorption isotherm.These results provide a basis upon which magnetic resonance imaging (MRI) techniques can be applied to investigate cooked starch food crusts.     

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.     

NaCl-induced changes in structure and water mobility in potato tissue as determined by CLSM and LF-NMR

This study for the first time reports the combined use of low-field nuclear magnetic resonance (LF-NMR) and confocal laser scanning microscopy (CLSM) in the study of the effects of salting on low and high dry matter (DM) potato tissue. The simultaneous use of CLSM and NMR resulted in important information in relation to the interpretation of the origin of the NMR water populations. Salting caused the raw potato cells to loose weight, which in the microscopic images was observed as loss of turgor pressure still further away from the edges of the samples with increased salting time. The total water loss after salting was lowest for high DM potatoes. The LF-NMR analyses revealed that this could be ascribed to a faster T₂ relaxation time of the cytoplasmatic and extracellular water and thus to water being more restricted in high DM potatoes. In addition, a tendency to a faster T₂ relaxation time was observed for both low and high DM potatoes with increasing salting time, which reveals a salt-induced restriction of the cytoplasmatic and extracellular water population. The paper illustrates the aptitude of NMR and CLSM to determine and elucidate structural changes and associated changes in water mobility in potato tissue.     

Rapid Food Particle Temperature Mapping During Ohmic Heating Using FLASH MRI

A fast low angle shoot (FLASH) pulse sequence in combination with a multi-inversion procedure was used to rapidly acquire spin-lattice relaxation data for food particles undergoing ohmic heating. The relaxation data acquired by magnetic resonance imaging (MRI) were analyzed using a two-component exponential model to extract both short and long spin-lattice relaxation time, T₁. The longer T₁ showed a better linear relationship with temperature than the shorter T₁ and, therefore, was used to produce more reliable temperature maps. The MRI temperature maps constructed for ohmically heated food particulates showed an entirely different heating pattern than would be found for similar but conventionally heated particulates and indicated that the temperature inside the particulate could be higher than near the surface of the particulate.     

Effect of Thermosonic Pretreatment and Microwave Vacuum Drying on the Water State and Glass Transition Temperature in <Emphasis Type="Italic">Agaricus bisporus</Emphasis> Slices

This study aimed to understand the micromechanism of thermosonic pretreatment and microwave vacuum drying on Agaricus bisporus. The water state and glass transition temperature (T _g ) of fresh and thermosonically treated Agaricus bisporus slices during microwave vacuum drying were studied using differential scanning calorimetry (DSC), low-field nuclear magnetic resonance (LF-NMR), and magnetic resonance imaging (MRI). Results showed that four population groups were contained in the initial distribution of transverse relaxation time (T ₂) data of fresh A. bisporus slices: T ₂₁ (0.38–7.05 ms), T ₂₂ (9.33–32.75 ms), T ₂₃₁ (37.65–265.61 ms), and T ₂₃₂ (305.39–811.13 ms). Thermosonic pretreatment significantly decreased the initial free water content of A. bisporus sample but was accompanied by a sharp increase in its immobilized water. “Semi-bound water transfer” appeared during microwave vacuum drying (MVD) at moisture contents (X _w ) of 0.70 and 0.60 g/g (wet basis (w.b.)) for untreated and thermosonically treated samples, respectively. MVD caused dramatic changes in the water state and enhanced the T _g by decreasing the content and mobility of immobilized water in A. bisporus tissues. The mobility of semi-bound water for thermosonically and MVD-treated samples was higher than for MVD-untreated samples, resulting in T _g values decreasing by approximately 2–11.5 °C, but the uniformity of water distribution in thermosonic-treated and MVD-treated samples was better at X _w  ≤ 0.52 g/g (w.b.).     

Study on the water state,mobility and textural property of Chinese noodles during boiling

The water mobility, state and textural properties of Chinese fresh noodles (CFNs) and Chinese dried noodles (CDNs) made from same wheat cultivar were measured during boiling using low-field nuclear magnetic resonance (LF-NMR), low-field nuclear magnetic Imaging (LF-NMI) and a textural analyser. ‘The oil immersion method’ was applied to gain the clear images from LF-NMI measurement. The distributions of the three water states (T₂₁, T₂₂ and T₂₃) in the noodles were distinguished. The results indicated that water mobility in noodles was closely related to the gelatinisation of noodle starch. Compared with CFNs, CDNs need a longer cooking time for water mobility and starch gelatinisation. The results of the cooked noodle profiles showed that the cooked CDNs (8 min) had an undesirable textural properties compared with the cooked CFNs (2 min). The longer cooking time of CDNs is responsible for its undesirable texture since the textural properties change during the longer cooking time.     

低场核磁结合电子鼻判定复合保鲜剂对冷藏虹鳟鱼片品质变化的影响

以质构、pH值、硫代巴比妥酸(TBA)值、挥发性盐基氮(TVB-N)值及菌落总数为评价指标,同时采用低场核磁共振(LF-NMR)及电子鼻技术对鱼片贮藏期间的水分和挥发性成分变化进行检测,研究复合保鲜剂(壳聚糖、茶多酚及柠檬汁)对虹鳟鱼片贮藏期间品质的影响。结果表明,复合保鲜剂组能较好地维持鱼片质构特性,同时可延缓鱼片TBA值、TVB-N值及菌落总数的增加。低场核磁测得两组鱼片贮藏期间T21幅值逐渐降低,在贮藏后期(12~14d),保鲜剂组鱼片自由水比例显著低于对照组(P0.05),且两组鱼片自由水比例与初期比较均增加。电子鼻PCA分析及LDA分析均可较好地区分贮藏期间鱼片的品质变化,LA分析发现引起鱼片新鲜度变化的主要成分为氮氧化合物、无机硫化物、芳香成分物质和乙醇等,而PCA分析结果表明对照组鱼片第6天开始发生腐败变质,保鲜剂组鱼片第10天开始趋于腐败。综上表明,低场核磁及电子鼻检测结果与理化指标结果具有一致性。     

Pulse NMR Study of Glass Transition in Maltodextrin

A pulse nuclear magnetic resonance (NMR) technique was used to study the glass transition in maltodextrins. The spin-lattice relaxation time (T₁ and spin-spin relaxation time (T₂) of different molecular weight maltodextrins at different moisture contents and temperatures were measured using the pulse NMR tech nique. T₁, and T₂ were plotted against temperatures. From the resultant curves, the state transitions were observed and the corresponding state transition temperatures were determined. The state transition temperatures were very close to the glass transition temperatures (T_gs) determined with differential scanning calorimetry, suggesting a strong relationship between glass transition and proton relaxation behavior. Results indicate pulse NMR-based instrumentation could be very effective for the study of glass transition in food polymers.     

黄原胶对大豆蛋白营养棒体系质地及微观结构的影响

通过质构仪、激光共聚焦显微镜、电子扫描显微镜和低场核磁共振技术等手段,研究了添加1%黄原胶对含有大豆蛋白的营养棒模型体系质构、微观结构、水分子及亲水小分子的迁移等的影响。结果表明:黄原胶的添加改变了体系微观网状结构,同时影响了体系内水及糖醇等小分子的分布,从而对大豆蛋白模型体系的质构有明显的软化效果,改善其质构和口感。     

Suitability of low-field nuclear magnetic resonance (LF-NMR) combining with back propagation artificial neural network (BP-ANN) to predict printability of polysaccharide hydrogels 3D printing

The water state of polysaccharide hydrogel is closely related to its rheological properties, which is the critical parameter determining the printability of 3D printing. Low-field nuclear magnetic resonance (LF-NMR) results showed that T₂₃ (free water) values of polysaccharide hydrogels gradually decreased with increasing concentration, while the viscosity values exhibited a opposite trend. As concentration increased, the printed objects gradually changed from the fluid, which cannot form a shape, to a stable shape and then to a hydrogel of low fluidity that cannot print normally. Hydrogels became hard to extrude smoothly at the piston pressure higher than 428716 Pa. Back propagation artificial neural network (BP-ANN) nonlinear models established by taking the fingerprint LF-NMR signal as input variables yielded good predicting ability of the piston pressure values (R²_adj = 0.982) and printing scores (R²_adj = 0.988). The BP-ANN model based on LF-NMR might be a promising approach to quickly predict the 3D printability of polysaccharide hydrogels.     

Non-destructive measurement of water and fat contents,water dynamics during drying and adulteration detection of intact small yellow croaker by low field NMR

Non-destructive and fast measurement and characterization of fish is highly desired during various processing treatment. In this study, water dynamics during drying process and adulteration with carrageen were detected using low field nuclear magnetic resonance (LF-NMR) technique in small yellow croaker. Prediction models of water and fat contents were established based on LF-NMR Carr–Purcell–Meiboom–Gill (CPMG) data combined with principal component regression (PCR) or partial least squares regression (PLSR). The R_cv ² of water and fat content by PLSR model was 0.9877 and 0.9054, and the root mean square error (RMSE) of cross-validation was 9.2360 and 3.3730%, respectively. Water dynamics during hot-air drying process showed that the amount of immobile water significantly decreased, and good correlation was found between the moisture ratio and peak area by Two-term model. In addition, the adulterated small yellow croaker with carrageen or distilled water could be clearly distinguished by principal component analysis (PCA) in a fast and non-destructive manner. All the results demonstrated that the LF-NMR may have great potential in fast and non-destructive analysis of small yellow croakers during various processing treatment.     

STRESS RELAXATION AND LOW FIELD PROTON MAGNETIC RESONANCE STUDIES OF CHEESE ANALOG*

Cheese analog samples were prepared using two different sources of fat milkfat and vegetable oil. The rheological properties of the samples, which ranged in moisture from 42.5 to 50%, were examined using compression and stress relaxation tests. The values of peak stress (s? at 50% strain) from the compression tests and the initial stress (s?_o), equilibrium stress (s?_e), and elastic constant (g₁) from the stress relaxation tests, were compared. All four values were higher for the samples containing milkfat as compared to the samples containing vegetable oil. For both analog formulations, moisture content was negatively correlated with values of s?_o (R² > 0.91), s?_o (R² > 0.80) and g₁ (R² > 0.94) at 40 mm/min crosshead speed. The CPMG‐T₂ relaxation curves of the samples were determined using a low field (5.35 MHz) proton magnetic resonance sensor. The T₂ relaxation data were fit to a two‐term exponential model having time constants T_2a and T_2b In the model, the coefficients α and β indicated, respectively, the contribution of T_2b and T_2b to the T₂ relaxation. The T_2a value was associated with the water in the analog cheese while the T_2b value was associated with the oil. The T_2a value was correlated (R² > 0.95) with the relative proportion of water in each sample. It increased as the moisture content increased. There were negative correlations between T_2a and s?_o, s?_e, and g₁ from the stress relaxation tests.