Water properties and salt uptake in Atlantic salmon fillets as affected by ante-mortem stress,rigor mortis,and brine salting: A low-field H NMR and H/Na MRI study

A low-field (LF) ¹H NMR T₂ relaxation and ²³Na/¹H MRI study was performed on Atlantic salmon to study the effect of ante-mortem handling stress and rigor mortis on muscle water properties and subsequent post-rigor salting. Compared to rested fish, exhausted fish exhibited a more rapid and stronger development of rigor mortis. This resulted in significant differences in post-rigor water-holding capacity and salt uptake. By LF NMR T₂ relaxation analysis significant differences in water distribution according to (1) ante-mortem handling, (2) fillet location, and (3) brine salting were detected. Furthermore, ²³Na MRI revealed differences between the two treatments in fillet salt distribution, where the salt penetration in exhausted fillets was more pronounced. By combining ¹H and ²³Na MR images, the salt diffusion and distribution seemed to be highly affected by the distribution of fat.     

Comparative NMR relaxometry of gels of amylomaltase-modified starch and gelatin

With the aim of generating gelatin-like starch gel functionality, starches extracted from normal potato, high amylose potato, maize, waxy maize, wheat and pea and oxidized potato starch were modified with amylomaltase (AM) (4-α-glucanotransferase; E.C. 2.4.1.25) from Thermus thermophilus. Gel characteristics after storage for 1 and 10 days at 20 °C of 12.0% gels were assessed by monitoring proton relaxation for the resulting 51 enzyme-modified starches and two gelatins using low-field ¹H nuclear magnetic resonance (LF NMR) relaxometry. Discrete and distributed exponential analysis of the Carr–Purcell–Meiboom–Gill (CPMG) LF NMR relaxation data revealed that the pastes and gels contained one water component and that the spin–spin relaxation time constants (T₂) and distributions differed with respect to starch type and enzyme modification. Typically, AM modification resulted in starches with decreased T₂ relaxation time and a more narrow T₂ distribution indicating a more homogeneous water population. In contrast, treatment with a branching enzyme (BE) (EC 2.4.1.18) combined with AM increased T₂ relaxation time and a broadened T₂ distribution. As evaluated by the principal component analysis (PCA), long chains of amylopectin generated hard gels and decreased T₂ relaxation time at both day 1 and day 10. Especially at day 10, T₂ relaxation time could be predicted from the amylopectin chain length (CL) distribution. Reconstructed amylopectin CL distribution required to emulate gelatin LF NMR data suggest the importance of combined fractions of long (DP 60–80) and short (DP 10–25) amylopectin chains.     

Water molecular dynamics during bread staling by Nuclear Magnetic Resonance

Bread staling is a complex phenomenon that originates from multiple physico-chemical events (amylopectin retrogradation, water loss and redistribution) that are not yet completely elucidated. Molecular properties of white bread loaves were characterized by multiple proton Nuclear Magnetic Resonance (NMR) techniques (proton FID, T₂ and T₁ relaxation time) over 14 days of storage. Changes at a molecular level (faster decay of proton FIDs and shifting of proton T₂ relaxation times distributions towards shorter times), indicating a proton mobility reduction of the bread matrix, were observed during storage. Multiple ¹H T₂ populations were observed and tentatively associated to water-gluten and water-starch domains. Proton T₁ of bread was for the first time measured at variable frequencies (Fast Field Cycling NMR) and found to be strongly dependent upon frequency and to decrease in bread during storage, especially at frequencies ≤ 0.2 MHz. An additional proton T₁ population, relaxing at 2 ms, was detected at 0.52 MHz only at early storage times and tentatively attributed to a water-gluten domain that lost mobility during storage.     

Proton NMR transverse relaxation measurements to study water dynamic states and age-related changes in Mozzarella di Bufala Campana cheese

Proton transverse magnetization decay curves of Mozzarella di Bufala Campana samples were measured and analysed for the presence in the sample of four components, namely “serum water”, “entrapped water”, “junction zone water” and “fat”, characterised by different transverse relaxation times, T₂. T₂ values were interpreted on the basis of the diffusive and chemical exchange model that allowed information to be obtained on the size of diffusive domains and dynamics of the water molecules. Furthermore, T₂ values were measured as a function of the aging time of Mozzarella samples, as produced by different cheese-makers. A decrease of “serum water” T₂ value with aging time was found and this may be used to monitor the evolution of Mozzarella samples up to seven days after manufacture.     

Distribution of Water in Fresh Cod

Low-field ¹H nuclear magnetic resonance (NMR) transverse relaxation was used to measure water mobility and distribution of water in fresh cod fillets. The NMR relaxations were analysed with the so-called SLICING method giving uni-exponential profiles from which the transverse relaxation time (T₂-values) and the relative sizes of the water populations were calculated. Two water populations with the T₂-values of 50 and 94 ms were obtained. The shortest relaxation time was primarily found near the head, and water with the longest relaxation time was primarily found near the tail. This variation can be explained by the smaller muscle cells and muscle fibers in the tail, which may influence the distributions of water into the different pools. The amount of one of the water populations was correlated to the overall water content with a correlation coefficient of −0.94.     

Determination of royal jelly acids in honey

In the present work we report on the compounds characteristic of larval food (royal jelly, RJ) of the honeybee (Apis mellifera L.) that were identified in 34 different samples of genuine honey and in 3 sugar-adulterated “herbal honeys” by using solid-phase extraction and gas chromatography–mass spectrometry (SPE/GC–MS). The unique feature of RJ is a set of C₈, C₁₀ and C₁₂ hydroxy fatty acids. In all, ten acids characteristic of this bee product were identified in different combinations in the analysed honey samples, namely: 7- and 8-hydroxyoctanoic, 3-hydroxydecanoic, 9-hydroxydecanoic, 9-hydroxy-2-decenoic, 10-hydroxydecanoic, 10-hydroxy-2-decenoic (10-HDA), 3,10-dihydroxydecanoic, 2-octene-1,8-dioic and 2-decene-1,10-dioic acids. The higher relative abundance of these compounds was determined in genuine honeydew and heather honeys, and in “herbal honeys” (23.8–40.8, 18.2–48.5, and 27.0–48.4 μg/g, respectively). Since RJ is known to have strong antibiotic efficacy, our results suggest that a part of the non-peroxide antibacterial activity of honey might be of bee origin.     

Use of low-field nuclear magnetic resonance to characterize water properties in frozen chicken breasts thawed under high pressure

The state of water in high-pressure-thawed and conventionally water bath-thawed chicken breasts was analyzed using low-field nuclear magnetic resonance. The influence of high-pressure thawing on water holding capacity, including thawing loss, cooking loss and expressible fluid, was evaluated. Thawing loss was significantly reduced (p < 0.05) compared to the conventional thawing method but neither cooking loss nor total expressible fluid changed significantly (p > 0.05). Higher thawing pressures lead to the T₂₁ relaxation time being increased from 39.9 to 55.9 ms, and P₂₁ increased from 89.5 to 94.9 %. Significant negative correlations (p < 0.01) were observed between the thawing loss and T₂₁, T₂₂, P₂₁. These results indicate that high thawing pressures can transform the water from the loosely bound water fraction (T₂₂) to a more tightly bound (T₂₁) water fraction with the increase in water relaxation time.     

Mobility and Stability Characterization of Model Food Systems Using NMR, DSC, and Conidia Germination Techniques

Mold conidia germination was used as a microbial probe of food stability in sucrose, starch, and sucrose/starch systems. A group of nuclear magnetic resonance (NMR) and differential scanning calorimeter (DSC) techniques were used to fully characterize the water and solid mobility and glass transition temperature (Tg) of the systems, respectively. Water content, a_w, and ²H NMR R₁ and R₂ relaxation rates did not predict mold germination time. We concluded that the self-diffusion coefficient, (translational mobility of water), the DSC Tg (overall system mobility), and to a more limited extent, the ²H NMR R*₂ relaxation rate and the ¹³C T_1p (solids mobility), could provide alternative measures to supplement a_w for predicting food stability and safety.     

Direct measurement of phase transitions in milk fat during cooling of cream—a low-field NMR approach

Low-field ¹H nuclear magnetic resonance (NMR) transverse relaxation (T₂) was measured during cooling (31–4 °C) of cream with low or high content of long-chain fatty acids (FA). Distributed analysis of the T₂ relaxation data revealed marked differences in the T₂ relaxation characteristics of the liquid fat population (10–100 ms), which was ascribed to differences in the size of the fat globules in the two types of cream. Principal component analysis (PCA) of the obtained T₂ relaxation decay data showed clear shifts in NMR relaxation behavior at 17 and 22 °C for cream with low or high content of long-chain FA, respectively. Differential scanning calorimetric measurements on the creams revealed that these shifts took place at the onset of crystallization of fat. Consequently, the present study demonstrated that low-field NMR can be used to measure phase transitions in cream.     

Water dynamics in white bread and starch gels as affected by water and gluten content

Three levels of water (180, 220 and 260 g/345 g flour) and three levels of gluten (giving 11.2, 13.0 and 14.2 g protein/100 g flour) were used to study the effects of water and gluten on water mobility in white bread using ¹H nuclear magnetic resonance (NMR) relaxometry. Changes in the transverse relaxation time (T₂) were related to water mobility. The three water levels resulted in three different moisture contents in the finished bread (0.55-0.77 g H₂O/g solids). Distributed exponential analysis showed two distinct regions of T₂ (30-600 μs and 1-60 ms), associated with multiple domains of water in the bread crumb. There was no significant difference in peak T₂ values with different gluten content, but significant differences were observed with different moisture content. The results suggested that the mobility of water associated with starch decreased dramatically because of gelatinization. To further investigate the effect of gluten on starch gelatinization, NMR measurements were made directly on model systems containing starch and various gluten amounts. The starch-gluten gels had higher T₂ values than pure starch gels, indicating less swelling of starch granules and absorption of water. This was attributed to less water available to starch in the presence of gluten.     

Origin Identification and Quantitative Analysis of Honeys by Nuclear Magnetic Resonance and Chemometric Techniques

The combination of ¹H NMR spectroscopy and multivariate statistical analysis has become a promising method for the discrimination of food origins. In this paper, this method has been successfully employed to analyze 70 Chinese honey samples from eight botanic origins, three geographical origins, and five production dates. Thirty-three components in honey samples were detected and identified from their ¹H NMR spectra, and 20 of them were accurately quantified by comparing their integral area with that of internal standards with relaxation time correction. Nontargeted principal component analysis (PCA) has been applied to distinguish the honeys from different botanical and geographical origins. The variations of components in the honeys, including saccharides and all kind of amino and organic carboxylic acids, confirmed their clustering according to their origins in PCA scores plots. Orthogonal partial least squares discriminant analysis (OPLS-DA) based on the NMR data for the different pairwise honey samples allows to identify the compositional variations contributed to geographical discrimination and storage time. Hence, NMR spectroscopy coupled with chemometric techniques offers an efficient tool for quality control of honey, and it could further serve to the classification, qualitative and quantitative control of other foods.     

Steaming time effects on the moisture migration and structural properties of Chinese Northern-style steamed bread

The aim of this study was to investigate the steaming time effects on proton transverse relaxation behavior with low field 1H nuclear magnetic resonance and structural properties of Chinese Northern-style steamed bread (CNSB). Three proton populations could be distinguished at the first 4 min: T_2b (0.1–1 ms) corresponded to rigid and exchangeable protons; T₂₂ (9–21 ms) was associated with the water protons in small and large meshes of the dough microstructure; T₂₃ (69–300 ms) was assigned to the water protons on the surface of samples. The starch gelatinization began and the water turned into the integral part of the biopolymer at 6 min, forming T₂₁ (1–3 ms) fraction. The gelatinization effect was strengthened up to 8 min and supplied a more mobile microenvironment, resulting in the increase of T₂₁, A₂₁ and M₂₁. However, the gelatinization process ended at 8 min, bringing about the stabilization of T₂₁, A₂₁ and M₂₁ until 25 min. T₂₂ fraction accounted for the largest proportion during all the steaming process. All variation trends on structural properties of CNSB and T₂ relaxation parameters including T_i, A_i (relative intensity of T_i), and M_i (population abundance of T_i) indicated that 6 and 8 min were the two transitions. The gluten matrix began to be disrupted at 6 min and was quite damaged up to 8 min by scanning electron microscopy. The peaks at 15°, 18°, 20°, and 23° in X-ray diffraction patterns appeared in the first 6 min but were lost up to 8, 10, and 25 min.     

Trace element levels in honeys from different regions of Turkey

A survey of 25 honey samples from different botanical origin, collected all over the Turkey was conducted to assess their trace element contents. The aim of this study was to determine the levels of cadmium (Cd), lead (Pb), iron (Fe), manganese (Mn), copper (Cu), nickel (Ni), chromium (Cr), zinc (Zn), aluminium (Al) and selenium (Se) in honey samples from different regions of Turkey. Trace element contents were determined by a flame and graphite furnace atomic absorption spectrometry technique after dry-ashing, microwave digestion and wet-digestion. The accuracy of the method was corrected by the standard reference material, NIST-SRM 1515 Apple leaves. The contents of trace elements in honey samples were in the range of 0.23–2.41 μg g⁻¹, 0.32–4.56 μg g⁻¹, 1.1–12.7 μg g⁻¹, 1.8–10.2 μg g⁻¹, 8.4–105.8 μg kg⁻¹, 2.6–29.9 μg kg⁻¹, 2.4–37.9 μg kg⁻¹, 0.9–17.9 μg kg⁻¹, 83–325 μg kg⁻¹ and 38–113 μg kg⁻¹ for Cu, Mn, Zn, Fe, Pb, Ni, Cr, Cd, Al and Se, respectively. Iron was the most abundant element while cadmium was the lowest element in the Turkish honeys surveyed. The results showed that trace element concentrations in the honeys from different regions were generally correlated with the degree of trace element contamination of the environment.     

Curing-induced water mobility and distribution within intra- and extra-myofibrillar spaces of three pork qualities

This study introduces the use of nuclear magnetic resonance (NMR) relaxometry in the elucidation of the curing‐induced water mobility and distribution within pork. Fresh meat samples of three different meat qualities [normal; pale, soft and exudative (PSE); dark, firm and dry (DFD)] were cured by using different curing conditions (0.9–9% NaCl and 6% NaCl + 10 mm Na₄P₂O₇). Distributed NMR T₂ relaxation data revealed the presence of three distinct water populations (T_2b, T₂₁, T₂₂), with the T₂₁ population being most influenced by the curing conditions, which was reflected by strong correlations between the salt‐induced swelling and the mean relaxation time of the T₂₁ population. Consequently, the T₂₁ population reflects the myofibrillar swelling, and is an excellent indicator of myofibrillar geometry upon curing. Both the NMR data and the salt‐induced swelling capacity were highly dependent on fresh meat quality. Independent of brine composition, the DFD meat had a significantly higher swelling capacity than the two other meat qualities. A higher response to NaCl concentration on the swelling capacity was observed for PSE and normal meat than for DFD meat, which suggests interactions between the pH of the meat and NaCl‐induced swelling.     

Initial evaluation of a field-friendly incubation procedure for the colorimetric assay of cassava linamarase

The Cooke colorimetric assay of cassava linamarase activity is temperature- and time-inflexible, making “real time” monitoring of linamarase activity in remote cassava-processing sites practically impossible. A modified incubation procedure is described, in which the 30 °C linamarase incubation step is terminated through acidification, yielding a stable cyanohydrin solution. Using partially purified linamarase as a “standard extract”, the solution – held for up to 21 days at ambient/refrigeration temperatures before colorimetry – showed reductions of up to 21% compared with the standard Cooke assay. In a separate trial, a strong linear relationship (r² > 0.95) was observed between recorded linamarase activity values and incubation temperature in the 25–40 °C range, indicating that incubation may take place in remote processing sites without a water bath, and resulting data may reliably be adjusted in keeping with the standard 30 °C incubation assay. The novel procedure thus appears to offer a satisfactory “field-friendly” means of assaying linamarase activity.     

Effect of microbial transglutaminase on NMR relaxometry and microstructure of pork myofibrillar protein gel

The effect of microbial transglutaminase (MTG) on nuclear magnetic resonance relaxation (NMR) behaviour, water holding capacity (WHC) and microstructure of pork myofibrillar protein (PMP) gel was studied. The enzymatic protein preparation had significantly lower values of spin–spin relaxation time (T ₂), higher WHC and more porous microstructure in comparison with the control system. T ₂ was reduced from 226 ms (peak value) of the PMP gel containing no MTG to 188 ms of the PMP gel containing 2 U/g protein. However, no further decrease was shown when the concentration of MTG increased. The reduction was attributed to reduced mobility of water protons in the system. Scanning electron micrographs (SEM) showed the mobility of water in the proteins gel network was related to gel microstructure.     

Storage-induced chemical changes in active components of honey de-regulate its antibacterial activity

To elucidate reasons for the observed variability in the antibacterial activity of honeys, we analysed a causal relationship between (a) honey floral sources and the activity and (b) the effect of honey storage on stability of compounds conferring this activity. Honeys from diverse floral sources were screened against Escherichia coli (ATCC 14948) and Bacillus subtilis (ATCC 6633) using the broth microdilution method. Among “active” honeys, 37% originated from buckwheat, 18% from clover and 12% from blueberry, indicating that these floral sources produced phytochemical(s) that inhibited bacterial growth. The stability of the putative phytochemical(s) was analysed in “active” honeys (MIC₉₀ 6.25% v/v) by measuring the activity every 3–6 months for a period of 1–3 years. A sharp decline in activity against both bacteria was observed in the first 3–6 months of storage. The decline coincided with major changes in chemical composition of honeys which included a significant change in colour (p < 0.0025), extremely significant change in concentration of UV-absorbing compounds (p < 0. 0001) and appearance of melanoidins. While these changes reduced E. coli sensitivity to honey, it rendered B. subtilis completely insensitive. Thus, the data indicates that the presence of phytochemical(s) conferring the antibacterial activity is sensitive to storage. The de-regulation of the antibacterial activity with the concomitant appearance of melanoidins suggests that the active phytochemical components might be sequestered into melanoidin aggregates, losing their function.     

Technological and functional properties of reduced-salt pork batter incorporated with soy protein isolate after pressure treatment

To investigate the effects of different pressures (0.1–400 MPa), the techno-functional properties, water distribution and mobility of reduced-salt pork batters (1% NaCl) supplemented with soy protein isolate (SPI, 2%) were examined. Compared with the batters treated at 0.1 MPa, those treated at 100–300 MPa showed significantly increased the cooking yield, hardness, springiness, cohesiveness, chewiness, and G′ values of gel and reduced the initial relaxation times of T_2b, T₂₁ and T₂₂, as observed from the results of low-field NMR. Among all samples, those treated at 200 and 300 MPa had the highest L^* value, cooking yield, hardness, springiness, cohesiveness, chewiness and G′ value of gel, with the largest peak ratio of P₂₁ and the smallest peak ratio of P₂₂. Overall, treatments at 200 and 300 MPa improved the gel properties and lowered the water mobility of reduced-salt pork batters supplemented with SPI.     

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.     

The impact of desmin on texture and water‐holding capacity of ice‐stored grass carp (Ctenopharyngodon idella) fillet

The objective of this work was to analyse the role of desmin in texture softening and water‐holding capacity (WHC) of ice‐stored grass carp fillet. Results indicated that shear force of the fillet decreased sharply within 3 days, while drip loss increased during the whole ice storage. Water mobility and distribution were measured by low‐field ¹H NMR T₂ relaxation that revealed a positive correlation (P < 0.01) between WHC and the mobility of the immobilised water (T₂₁ relaxation time). Meanwhile, negative correlation could be established between intact desmin and drip loss (P < 0.01). Intact desmin was extremely correlated with shear force (P < 0.01) and positively correlated with calpains activity (P < 0.05). This study demonstrated that the degradation of desmin was involved in the mobility of the myofibrillar water and softening of grass carp fillet during ice storage. Furthermore, calpains autolysis seemed to result in desmin degradation.