Water status of cooked white salted noodles evaluated by MRI

Transverse relaxation time (T₂)-weighted images and T₂ maps of white salted noodles (WSN) were investigated by magnetic resonance imaging technique. T₂-weighted images and T₂ maps clearly showed the differences in water status between noodles. The migration of moisture from surface regions to central regions of boiled WSN at different migration rates were investigated during storage. The distribution of T₂ values changed differently depending on the cooking and storage times. The small differences in T₂ values between surface region and central region of noodles cooked for 5 and 15 min were attributed to the limited water absorption during short cooking time, which resulted in high firmness. The changes in starch granules morphology observed under scanning electron microscope and the increase of noodle firmness measured by texture analyzer were significantly affected by the water status in noodles. The water status can be controlled by the cooking time.     

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.     

Kinetics of the migration of lipids in composite chocolate measured by magnetic resonance imaging

Migration of hazelnut oil into chocolate was followed non-invasively by magnetic resonance imaging, using a spin echo pulse sequence to acquire images with a 5 ms echo time and a 2000 ms repetition time. A calibration curve was used to correlate the image intensity with the concentration of hazelnut oil. Two different degrees of chocolate temper, at three different storage temperatures (20, 23 and 28°C), were monitored over a period of 80 days. The effect of thermal treatment (24 h at 30°C followed by 24 h at 4°C) on the speed of migration of hazelnut oil was also studied. Qualitative analysis yielded the spatial resolution of the oil migration data, whereas quantitative analysis gave the oil diffusion constants.     

NMR relaxometry and differential scanning calorimetry during meat cooking

By combining simultaneous nuclear magnetic resonance (NMR) T₂ relaxometry and differential scanning calorimetry (DSC) on pork samples heated to nine temperature levels between 25 and 75 °C, the present study investigates the relationship between thermal denaturation of meat proteins and heat-induced changes in water characteristics. Principal component analysis (PCA) on the distributed ¹H NMR T₂ relaxation data revealed that the major changes in water characteristics during heating occur between 40 and 50 °C. This is probably initiated by denaturation of myosin heads, which however, could not be detected in the DSC thermograms obtained directly on the meat. In contrast, the DSC thermograms revealed endothermic transitions at 54, 65 and 77 °C, probably reflecting the denaturation of myosin (rods and light chain), sarcoplasmic proteins together with collagen and actin, respectively. Simultaneous modelling of DSC and NMR data by partial least squares regression (PLSR) revealed a correlation between denaturation of myosin rods and light chains at 53–58 °C and heat-induced changes in myofibrillar water (T₂ relaxation time 10–60 ms) as well as between actin denaturation at 80–82 °C and expulsion of water from the meat. Accordingly, the present study demonstrates a direct relationship between thermal denaturation of specific proteins/protein structures and heat-induced changes in water mobility during heating of pork.     

Physical changes of significance for early post mortem water distribution in porcine M. longissimus

The post mortem changes in water mobility and distribution were followed in porcine muscle (M. longissimus dorsi) samples using continuous low-field NMR relaxation measurements and simultaneous measurement of changes in muscle impedance as an indirect measure of membrane integrity as well as muscle contraction measurements using a rigormeter instrument. Distributed exponential fitting analysis of NMR T₂ relaxation data revealed the presence of three distinct water populations (T₂₀, T₂₁, T₂₂) within the muscle during its conversion to meat. Comparison of T₂ relaxation patterns and contraction data indicates that rigor development affects the attributes of the T₂₁ water population and thereby contributes to myofibrillar water characteristics post mortem, as the T₂₁ water population is believed to reflect inter/intra-myofibrillar water. The volume of the water population believed to reflect extra-cellular water (T₂₂) in the living muscle. Early post mortem T₂₂ decreased slightly within the first 2–3 h post mortem followed by an increase and a change in its characteristic time constant. This was ascribed to an initial muscle cell swelling followed by water being expelled from the cellular space into the extra-myofibrillar space. Comparison of changes in the T₂₂ water population and impedance characteristics within the muscle during its conversion to meat revealed close relationship between progresses in the two attributes. Obtained data strongly support that the post mortem reorganization of water is closely associated with membrane properties, which moreover was found to affect the final water-holding capacity of the meat. Finally, a model for early post mortem events leading to changes in the distribution of water within muscles is proposed.     

Oil migration in chocolate and almond product confectionery systems

Oil migration from high oil content almond confections into adjacent chocolate causes changes in product quality. The objective of this study was to quantify the oil migration from almond products to dark chocolate. Magnetic resonance imaging (MRI) was used to monitor spatial and temporal changes of liquid lipid content. A multislice spin echo pulse (MSSE) sequence was used to acquire images with a 7.8-ms echo time and a 1000-ms repetition time using a 1.03T Aspect AI MRI spectrometer. Samples were prepared as a 2-layer model system of chocolate and almond confection. Six different almond products and 1 type of dark chocolate were used. Samples were stored at 20, 25, and 30°C for a time frame of several months. Rate and extent of migration were quantified by a kinetic expression based on the linear dependence of oil uptake by chocolate and the square root of the time. Samples showed distinctly different rate and extent of oil migration, as evidenced by quantitative differences in the kinetic rate constants and equilibrium uptake for the different sample types. This work will be helpful to design formulations for almond and almond-based products in confections. PRACTICAL APPLICATION: This work will be helpful to design formulations for almond use in confections.     

Effect of cocoa butter structure on oil migration

Oil migration from a high oil content filling into adjacent chocolate causes changes in product quality. The objective of this study was to quantify the oil migration from a cream filling system into cocoa butter, which provided a model for the behavior of chocolate-enrobed confectionery products with a soft, creamy center. Magnetic resonance imaging (MRI) was used to monitor spatial and temporal changes of liquid lipid content. A multislice spin echo pulse sequence was used to acquire images with a 7.8 ms echo time and a 200 ms repetition time using a 1.03 T Aspect Imaging MRI spectrometer. Samples were prepared as a 2-layer model system of cocoa butter and model cream filling. Three methods were used to prepare the cocoa butter: static, seeded, and sheared. Samples were stored at 25 °C for a time frame of 56 d. The rate of oil migration was quantified by a kinetic expression based on the linear dependence of oil uptake by cocoa butter and the square root of the time. Samples showed distinctly different rates of oil migration, as evidenced by quantitative differences in the kinetic rate constant. Practical Application: This work will be helpful to elucidate the influence of crystallization process and structural properties such as crystal nanostructure and crystal habit on the migration of oil through a crystalline fat matrix.     

Modelling the effect of a temperature shift on the lag phase duration of Listeria monocytogenes

The aim of this work is to study and model the effect of a temperature shift on h₀, the product of the growth rate by the lag phase duration (μλ). Our work is based on the data of Whiting and Bagi [Int. J. Food Microbiol. 73 (2002) 291], who studied the influence of both the pre-incubation temperature (T_prior) and the growth temperature (T_growth) on λ values of Listeria monocytogenes. We introduce a new model to describe the evolution of the parameter h₀ as a function of T_prior and T_growth, and compare it to Whiting and Bagi's published polynomial model that describes the influence of T_prior and T_growth on λ independently of μ. For exponential as well as stationary phase cells, h₀ increases almost linearly with the magnitude of the temperature shift. A simple linear model of h₀ turns out to be more suitable to predict λ values than a polynomial model of λ.     

The significance of cooling rate on water dynamics in porcine muscle from heterozygote carriers and non-carriers of the halothane gene-a low-field NMR relaxation study

The post mortem changes in the chemical/physical state distribution of water were followed in pig muscle (M. longissimus dorsi) from heterozygote (n=12) and non-carriers (n=12) of the halothane gene exposed to two different cooling profiles using continuous low-field NMR relaxation measurements. T₂ relaxation data were analyzed using distributed exponential fitting analysis. Independent of genotype post mortem changes were observed in the two water populations characterizing water within the myofibrillar space (T₂₁) and the extra-myofibrillar space (T₂₂), respectively, as a function of chilling regime. The effect was most pronounced in samples from heterozygote carriers of the halothane gene. The obtained results strongly suggest that improved water-holding capacity of muscles upon fast chilling can be ascribed to a reduced accumulation of extra-myofibrillar water in the meat post mortem, and it is hypothesized that differences in the accumulation of extra-myofibrillar water post mortem can be ascribed largely to the time at which disruption of cell membrane integrity takes place.     

Oil Migration in Chocolate–Peanut Butter Paste Confectionery as a Function of Chocolate Formulation

ABSTRACT:  Migration of oil from high oil content filling to the chocolate coating can result in undesirable quality changes in filled chocolate confectionery products. The objective of this study was to monitor and model peanut oil migration in a 2-layer chocolate–peanut butter paste model confectionery. Spatial and temporal oil content changes were evaluated using magnetic resonance imaging. Five formulations of chocolate, which varied in chocolate particle size, milk fat content, and emulsifier level, were assessed at 2 temperatures, 20 and 30 °C. The spatial and temporal experimental data were modeled using a Fickian-based diffusion model, fitting for the diffusion coefficient, D , over a time frame of 17 d. Values of the diffusion coefficient ranged from 1.82 to 3.23 × 10⁻¹¹ m²/s for the chocolate formulations stored at 30 °C. No significant mass transfer took place in the 20 °C samples over the experimental time frame. This study describes the dynamic nature of the interface between the chocolate and peanut butter paste layers, quantifies the mass transfer from the peanut butter paste to the chocolate, and reinforces the importance of temperature control.     

Diamagnetic susceptibility changes in apple tissue after bruising

In nuclear magnetic resonance images of bruised apples, the bruised tissue regions appear brighter than intact tissue regions. The cause for the contrast was investigated. The spin-spin relaxation rates (1/T₂) of the bruised regions were found to be greater than those of firm tissue regions ruling out this mechanism as a cause for the contrast. By comparing spin-echo images (with echo delays of 14 ms and 50 ms) with gradient-recalled-echo images (with echo delay of 5.5 ms) it was concluded that the contrast may be attributed to the decrease in the diamagnetic susceptibility variations within the bruised regions as a result of the partial destruction of the cellular structure caused by bruising. Images of a bruised apple were acquired before bruising, immediately after bruising and approximately every 4 h thereafter, and showed that the contrast between bruised and non-bruised regions increased with time.     

Diffusion of thiocyanate and hypothiocyanite in whey protein films incorporating the lactoperoxidase system

The diffusion of the thiocyanate (SCN⁻) and hypothiocyanite (OSCN⁻) components of a lactoperoxidase system (LPOS) in whey protein isolate (WPI) films was investigated. Diffusion coefficients for these molecules were measured for the LPOS-incorporated WPI films prepared with different WPI:glycerol ratios (1:1, 3:1, and 5:1). WPI film disks were coated on the surfaces of smoked salmon samples, and the samples were stored at 4, 10 and 22 °C. The diffusion coefficients were determined by fitting a mathematical model to the amounts of SCN⁻ and OSCN⁻ released from the disks during a period of time. The diffusion coefficients for SCN⁻ (D₁) and OSCN⁻ (D₂) in the films were 0.19–5.2 × 10⁻¹² m² s⁻¹ and 0.13–6.5 × 10⁻¹³ m² s⁻¹, respectively. The D₁ and D₂ decreased as the WPI:glycerol ratio increased and the storage temperature decreased. The E_a values for diffusion in 1:1, 3:1, and 5:1 WPI:glycerol films were 13.3, 29.5, and 35.6 kJmol⁻¹, respectively, for SCN⁻ and 15.8, 30.1, and 39.9 kJmol⁻¹, respectively, for OSCN⁻.     

Thermal inactivation of the frozen thawed traditional meat starter culture, Pediococcus pentosaceus, in a meat model system

The equation, y_(t) = y₍₀₎e^kt, was fitted (R = 0.9281, 0.9220 and 0.9117, respectively) to thermal inactivation data (55, 60 and 65 °C) of the traditional meat starter culture Pediococcus pentosaceus (10⁷ cfu/ml) in a meat model system. The population reduction constant (‘k’) increased (about 2.5- and 3-fold) with an increase in the treatment temperature (from 55 to 60 °C and from 60 to 65 °C, respectively). The Q₁₀ (55–65 °C) for ‘k’ was 7.63. Thermal treatments of 19.1, 9.0 and 3.1 min (55, 60 and 65 °C, respectively) reduced the population of P. pentosaceus by 2.0 logs. The value of ‘k’ and the duration of the thermal treatment played an important role in the extent of the inactivation of the culture. The “zero inactivation” temperature (T₀) for P. pentosaceus was 49.9 °C. About 5 logs of the culture would be destroyed at 63 and 68 °C within about 15.5 and 6.5 min, respectively.     

Inactivation kinetics of Escherichia coli by pulsed electron beam

ABSTRACT:  A novel and compact low-energy (keV) high-power pulsed electron beam (e-beam) that utilizes a secondary emission electron gun (SEEG) was designed and constructed. Escherichia coli JM 109 at a concentration of 10⁶ CFU/mL was spread-plated on Luria-Bertani (LB) medium and subjected to the SEEG e-beam. The e-beam was administered as 1 or 5 pulses. The duration of a single pulse was constant at 5 μs, e-beam current density was constant at 25 mA/cm², and e-beam energy varied between 60 and 82.5 keV. Following treatment with the SEEG e-beam, survivors of the irradiated E. coli samples were enumerated by a standard 10-fold dilution and spread-plated. The survivor curves were plotted on logarithmic scale as a function of e-beam dose. The D ₁₀-values were calculated as a negative reciprocal of the slope of the survivor curves. The D ₁₀-values for E. coli inactivated with 1- and 5-pulse SEEG e-beam were 0.0026 and 0.0217 Gy, respectively. These D ₁₀-values were considerably lower than published D ₁₀-values for E. coli inactivated with conventional high-energy continuous e-beam, likely due to shorter exposure time ( t ), greater current density ( J ), and a pulse mode of the SEEG e-beam. The SEEG e-beam showed promising results for microbial inactivation in a nonthermal manner; however, due to low energy of the SEEG e-beam, current applications are limited to surface decontamination. The SEEG e-beam may be an efficient processing step for surface inactivation of food-borne pathogens on ready-to-eat products, including fresh and leafy vegetables.     

Oil Migration in 2-Component Confectionery Systems

ABSTRACT:  Oil migration from high oil content centers into chocolate coatings results in product quality changes. The objective of this study was to monitor and model peanut oil migration in 2-layer systems of increasing phase complexity. Three 2-layer systems were prepared: peanut oil/cocoa butter; peanut butter paste/cocoa butter; and peanut butter paste/chocolate. Magnetic resonance imaging was used to measure liquid oil signal as a function of position over a storage time of 193 days at 25 °C. The 3 types of samples exhibited appreciably different patterns of oil migration. The peanut oil/cocoa butter samples had mass transfer typical of oil being absorbed into a liquid/solid region. The peanut butter paste/cocoa butter magnetic resonance profiles were characterized by mass transfer with a partition coefficient greater than unity. The peanut butter paste/chocolate samples exhibited a time-dependent peanut oil concentration at the interface between the chocolate and peanut butter paste. The spatial and temporal experimental data of the peanut butter paste/chocolate samples were modeled using a Fickian diffusion model, fitting for the effective diffusivity. Values of the diffusivity for the 6 chocolate formulations ranged from 1.10 to 2.01 × 10⁻¹³ m²/s, with no statistically significant differences.     

Interaction between flaxseed gum and meat protein

Thermal properties, dynamic rheological properties, texture and microstructure of salt-soluble meat protein and flaxseed gum (SSMP-FG) mixtures were investigated. Two transitions, 57.0 °C (T_SSMP1) and 63.2 °C (T_SSMP2), were observed for SSMP without FG with differential scanning calorimetry (DSC). Addition of 2% FG to SSMP increased T_SSMP1 and T_SSMP2 by 1.9 °C and 5.9 °C, respectively. Two transitions, 53 °C (T_SSMP1′) and 75 °C (T_SSMP2′), were also observed for SSMP without FG with dynamic rheological measurement. Addition of 2% FG to SSMP increased T_SSMP1^′ and T_SSMP2^′ by 9 °C and 14 °C. These results indicated that addition of FG increased thermal stability of SSMP. Addition of FG also increased the storage modulus G′, gel strength, decreased syneresis, and changed the microstructure of SSMP gels with texture analyser and scanning electron microscope (SEM), respectively, suggesting that an interaction between FG and SSMP may have occurred. The results of addition of destabilizer to SSMP gels indicated that electrostatic forces seemed to be the main force involved in the formation and stability of protein–polysaccharide gel.     

A STUDY ON SURVIVAL OF Staphylococcus aureus IN DARK AND MILK CHOCOLATE

Dark and milk chocolate bars were inoculated with Staphylococcus aureus to establish an initial population of approximately 10², 10⁴ and 10⁶ cells per gram. Samples were stored at room temperature and examined for the survival of staphylococci at 2-day intervals for the first 6 days and every 8 days thereafter. When samples were inoculated with 10² cells per gram, absence of staphylococci was observed after 2-days in dark and 14 days of storage in milk chocolate. Bars with 10⁴ cells per gram were free of cells after 38 days in dark and 86 days of storage in milk chocolate. Dark chocolate bars with 106 cells per gram, were staphylococci free after 86 days of storage; whereas the milk chocolate bars with same level of inoculation were shown to be staphylococci free after 110 days of storage     

Enthalpy-Entropy compensation in food vapor adsorption

Enthalpy-entropy compensation was analysed for sorption isotherms of potatoes, macadamia nuts, apricots, figs, currants, prunes and raisins. Plots of (ΔH_dif)_T vs (ΔS_dif)_T for potatoes and macadamia nuts presented two isokinetic temperatures: T_B1 = 272.0 ± 57.7 K (− 1 °C) for potatoes, T_B1 = 265.0 ± 18.8 K (− 8 °C) for macadamia nuts and T_B2 = 382.5 ± 7.3 K (109.5 °C) for both products. The first isokinetic temperature (T_B1) appeared only at the upper portion of the temperature range tested (50, 60 and 70 °C for potatoes and 50 and 60 °C for macadamia nuts). The two isokinetic temperatures observed for potatoes and macadamia nuts suggested that during the initial stages at low a_w T_B1 is controlled by changes in the entropy of water, whereas the second isokinetic temperature (T_B2) is considered to be enthalpy-controlled. Dried fruits presented only one isokinetic curve T_B = 315.7 ± 3.5 K (42.7 °C), for raisins, currants and figs (75.2–82.3% d.b. sugars) and T_B = 317.7 ± 4.6 K (44.7 °C) for prunes and apricots (51.5–54.5% d.b. sugars), indicating an enthalpy-controlled adsorption process for the whole range of moisture contents covered.     

Flavor perception of a model cheese: relationships with oral and physico-chemical parameters

The present study aims to investigate the relationships between perception, flavor release and oral parameters during the eating of a model cheese. A modified time–intensity (T–I) methodology, consisting in monitoring several attributes at several times over the same mastication, was used to evaluate temporal perception. A visual calibration with grey surfaces was used to adjust raw T–I data and reduce inter-individual variations due to different scale uses. Inter-individual differences observed in aroma and taste compounds were related to the inter-individual differences observed in flavor release and in oral measurements (mastication and salivation parameters). In particular, the time to reach the maximal intensity (T_max) of salty, sour and moldy attributes was positively related to the time to reach the maximal concentration (T_max) of sodium, citric acid and heptan-2-one and to oral parameters. No further relationship was found between T–I, flavor release and oral parameters.     

Spatial mapping of solid and liquid lipid in confectionery products using a 1D centric SPRITE MRI technique

Oil migration is responsible for the poor keeping qualities of composite confectionery products. Quality defects arising from oil migration include softening of the coating, hardening of the filling, deterioration in sensory quality and a greater tendency toward fat bloom formation. For this reason, oil migration has been extensively studied, and yet a clear understanding of the oil migration mechanisms still remains a challenge.Traditional MRI techniques are unable to acquire images from the solid lipid in chocolate. In this paper we employ a newly developed one-dimensional, centric-scan MRI technique to acquire images from the short lived signal components from the solid lipid, as well as the longer timescale components of the liquid lipid in a chocolate sample. We present one-dimensional images of a dynamic hazelnut oil absorption experiment, and one-dimensional solid and liquid distribution maps in a 5 mm thick chocolate sample in which oil migration occurs.