Effect of high-pressure versus conventional thawing on color, drip loss and texture of Atlantic salmon frozen by different methods

Atlantic salmon (Salmo salar) samples were frozen by conventional air freezing, plate freezing and liquid nitrogen (LN) freezing, and subjected to different thawing treatments: water immersion thawing (WIT) (4°C and 20°C) and high-pressure thawing (HPT) at 100, 150 and 200 MPa with water (containing 2 g oil/100 g) as pressure medium at 20°C. Temperature and phase change behavior of fish samples were monitored during freezing and thawing. The phase change point of frozen salmon was lowered to −14°C, −19°C and −25°C for the HPT processes at 100, 150 and 200 MPa, respectively. These phase change temperatures were lower than for pure ice at the same pressures possibly due to the presence of solutes in salmon. The HPT times were 22.6±1.4, 18.1±1.4 and 17.0±1.3 min at 100, 150 and 200 MPa, respectively, as compared with 26.6±2.1 and 94.3±3.4 min for the WIT process at 20°C and 4°C, respectively. Employing pressures above 150 MPa caused noticeable color changes in salmon during the HPT process and the product texture was significantly modified during HPT at 200 MPa. Different freezing rates prior to thawing resulted in differences in drip loss in salmon samples, but they did not induce specific color and texture changes. A significant (P<0.05) reduction of drip loss by the HPT process was observed only for the LN frozen samples in which mechanical cracking occurred and much of the drip appeared after WIT process. Drip loss formed during pressure thawing seems to be a complicated process, for which further studies are needed.     

Steady-shear flow of semidilute guar gum solutions with sucrose, glucose and sodium chloride at different temperatures

Steady-shear flow curves of aqueous solutions of guar gum at 0.22% at different temperatures (5-65 °C), guar gum (0.22%) with sugars (sucrose or glucose) at different sugar/water ratio (0.10, 0.20 and 0.40) at 5 °C, guar-sugar (at 0.40 sugar/water ratio) at different temperatures (5-65 °C) and guar gum and guar-sucrose (0.40 sucrose/water ratio) with NaCl (1%) at 5 °C, were determined using a controlled-stress rheometer over a wide range of shear rate (1-1000 s⁻¹). Apparent viscosity increased with decreasing temperature and increasing sugar content independent of sugar type. Synergic effect on apparent viscosity due to sugar addition was found and was correlated with sugar content. Salt addition decreased slightly the apparent viscosity and increased the shear-thinning behaviour of the guar gum solution. Steady-shear flow curves were satisfactorily described by the Cross model. Semi-empirical correlations of Cross model parameters with sugar content and temperature were obtained.     

Studies on “sugar-reactivity” of agars extracted from some Indian agarophytes

Sugar reactivity was observed within the sugar–agar complexes in presence of sucrose and glucose with agars of Indian agarophytes viz. Gelidiella acerosa, Gracilaria edulis, Gracilaria crassa and Gelidium pusillum. The sugar reactivity was more pronounced in presence of sucrose than glucose. Oxoid agar was used as the reference material. Control agar gel contained 1.12% agar (w/w) in water. Sucrose–agar and glucose–agar gels in water consisted of 50% (w/w) sucrose and 50% (w/w) glucose, respectively along with 1.12% (w/w) agars of the four seaweeds mentioned above. Addition of sucrose resulted in increase (ca. 25–45%) in gel strength; increase (2–3 °C) in gelling and melting temperatures was observed in the gels prepared with agars from all the agarophytes and Oxoid agar. On the other hand, addition of glucose resulted in increase (19–34%) in the gel strength and gelling and melting temperatures of the agar gels of Oxoid as well as of all other agars decrease (2–3 °C). Maximum sugar reactivity was observed with the 50% level of sucrose and glucose in agar gels. Rheological and thermogravimetric characteristics of these gel samples were studied. The latter showed two patterns e.g. control agar gel of Oxoid agar was thermally less stable than the four control agar samples studied; in sugar–agar gel samples it followed a reverse pattern. To our knowledge, this is the first report of “sugar reactivity” of agar of Indian agarophytes. Sugar reactivity of agar in presence of glucose is also reported for the first time. The results of this study will be useful in bioprospecting as well as in exploring new applications.     

Experimental study on the freezing characteristics of four kinds of vegetables

Mushroom, green cauliflower, navy bean and pea pod are four kinds of favored vegetables. Their freezing characteristics are studied in this paper. For fresh samples, the moisture contents of mushroom, navy bean, pea pod and green cauliflower were 88.7±4.9, 92.9±0.4, 87.7±1.0 and 89.7±0.9 g/100 g, respectively. After pre-treating, cooling curve method and differential scanning calorimetry (DSC) were employed to measure the end-points of freezing and glass transition temperatures. The initial freezing points varied from −0.1 to −2.7 °C. The end-points of freezing were all below −20.0 °C. The partial glass transition temperatures varied from −50.3 to −76.1 °C. With a cryomicroscope, the sizes of ice crystals in frozen vegetable saps were found to decrease from 26 to 3 μm when the freezing rates increased from 1.0 to 10.0 °C/min.     

Weight loss of frozen bread dough under isothermal and fluctuating temperature storage conditions

Evaporative weight loss from food leads to both loss of saleable weight and quality deterioration so it need to be minimized. The effect of isothermal and fluctuating conditions on frozen dough weight loss was measured and compared with kinetic, physical and artificial neural network (ANN) models. Frozen dough samples were regularly weighed during storage for up to 112 days in loose-fitting plastic bags. The storage temperatures were in the range of −8 to −25 °C with fluctuations of ±0.1 °C (isothermal), ±1, ±3 or ±5 °C about the mean. For each combination of temperature and fluctuation amplitude, the rate of dough weight loss was constant. The rate of weight loss at constant temperature was nearly proportional to water vapour pressure consistent with standard theories for evaporative weight loss from packaged foods but was also accurately fitted by Arrhenius kinetics. Weight loss increased with amplitude of temperature fluctuations. The increase could not be fully explained by either the physic model based on water vapour pressure differences or the kinetic model alone. An ANN model with six neurons in the input layer, six neurons in hidden layers and one neuron in the output layer, achieved a good fit between experimental and predicted data for all trials. However, the ANN model may not be accurate for product, packaging and storage systems different to that studied.     

Optimisation of the aqueous extraction conditions of phenols from meadowsweet (Filipendula ulmaria L.) for incorporation into beverages

Meadowsweet was extracted in water at a range of temperatures (60–100 °C), and the total phenols, tannins, quercetin, salicylic acid content and colour were analysed. The extraction of total phenols followed pseudo first-order kinetics, the rate constant (k) increased from 0.09 ± 0.02 min⁻¹ to 0.44 ± 0.09 min⁻¹, as the temperature increased from 60 to 100 °C. An increase in temperature from 60 to 100 °C increased the concentration of total phenols extracted from 39 ± 2 to 63 ± 3 mg g⁻¹ gallic acid equivalents, although it did not significantly affect the proportion of tannin and non-tannin fractions. The extraction of quercetin and salicyclic acid from meadowsweet also followed pseudo first-order kinetics, the rate constant of both compounds increasing with an increase in temperature up until 90 °C. Therefore, the aqueous extraction of meadowsweet at temperatures at or above 90 °C for 15 min yields extracts high in phenols, which may be added to beverages.     

The comparative effect of steaming and irradiation on the physicochemical and microbiological properties of dried red pepper (Capsicum annum L.)

The comparative effects of steaming and gamma irradiation on the physicochemical and microbiological properties of dried red pepper (Capsicum annum L.) were investigated during post-treatment storage at refrigerated (4 ± 2 °C) and room (20 ± 2 °C) (RT) temperatures for 6 months. Whole dried peppers were either steamed, hot air-dried and processed into powder form or powderised, packed in PE bags and gamma-irradiated at 10 kGy. The commercial steam treatment led to a 1- to 2-log reduction in the initial microbial load (10⁶ CFU/g) accompanied with changes in spice as indicated by low Hunter’s colour values and reduced sensory scores in RT-stored samples. However, irradiation resulted in a 5-log reduction with minimal effects on the physicochemical properties, except for the decreased content of capsanthin in the irradiated samples. The functional components of spices were not apparently affected by both treatments. The refrigerated storage following irradiation is recommendable for powdered red pepper to minimise physicochemical changes.     

Phenolic content and antioxidant activity of extracts from whole buckwheat (Fagopyrum esculentum Möench) with or without microwave irradiation

The purpose of this study was to extract phenolic compounds and antioxidant activity from buckwheat with water, 50% aqueous ethanol, or 100% ethanol using microwave irradiation or a water bath for 15 min at various temperatures (23–150 °C). Phenolic content of extracts increased with increasing temperature. In general, phenolic contents in microwave irradiated extracts were higher than those heated with a water bath. The highest phenolic content, 18.5 ± 0.2 mg/g buckwheat, was observed in the extract that was microwave irradiated in 50% aqueous ethanol at 150 °C. The highest antioxidant activities, 5.61 ± 0.04–5.73 ± 0.00 μmol Trolox equivalents/g buckwheat, were found in the 100% ethanol extracts obtained at 100 and 150 °C, independent of heat source. These results indicate that microwave irradiation can be used to obtain buckwheat extracts with higher phenolic content and similar antioxidant activity as extracts heated in a water bath.     

C NMR and electrospray ionization mass spectrometric study of sucrose aqueous solutions at high pH: NMR measurement of sucrose dissociation constant

The ¹³C NMR technique is used for the measurement of the first dissociation constant of sucrose (HL) in highly alkaline solutions. In 1.0 M NaCl/NaOH medium and for 25 °C, the concentration dissociation constant (pK₁) was 13.1 ± 0.3; and, for 60 °C, pK₁ = 12.30 ± 0.05. The β-d-fructofuranosyl ring was found to be responsible for dissociation. The NMR data reveal no clear evidence of the second dissociation step below pH 14, either at 25 °C or at 60 °C. In the solutions with 4–10 mol dm⁻³ NaOH content the ¹³C NMR technique indicated the chemical shift changes, treated as the second dissociation step of sucrose and a sodium complex formation. A very rough estimation, for variable ionic strength, gives the value: pK₂ ∼ 15.8 ± 0.8. The anionic species L⁻ and NaH₋₁L⁻ have been registered by electrospray ionization time-of-flight mass spectrometry (ESI-ToF MS) for 0.01 M sucrose solutions with initial pH 13.     

Fat oxidation in freeze-dried grouper during storage at different temperatures and moisture contents

The effects of moisture content levels and storage temperature on the lipid oxidation in freeze-dried grouper were studied. Three trends were observed in the changes of PV (peroxide value) depending on the moisture content and storage temperature. An exponential rise of PV was observed (p < 0.05) at lower temperatures (−20 °C and 5 °C for samples at moisture 5 g/100 g; and −20 °C for samples at moisture 20 g/100 g). At temperatures 25 °C for samples at moisture 5 g /100 g, and 5 and 25 °C for samples at 20 g moisture/100 g peaks of PV were observed (p < 0.05). At higher temperatures (40 °C for both moisture content levels) an exponential decay instead of increase were observed (p < 0.05). Moisture content levels had no significant effect (p > 0.05) on PV stored at temperature of −40 °C. The monolayer moisture for freeze-dried grouper was estimated as 6.2 g/100 g dry solids using BET-isotherm. Differential scanning calorimetry (DSC and modulated DSC) thermogram line showed two shifts (i.e. glass transition) and two endothermic peaks, one for melting of oil and another for decomposition. The validity of the water activity and glass transition concepts were evaluated. It is concluded that glass transition concept may be used to explain the process more adequately.     

Persistence and activity towards Sitophilus zeamais (Coleoptera: Curculionidae) of pirimiphos-methyl sprayed at different temperatures on maize

The air temperature in storage units in tropical areas frequently exceeds 50°C during the warmest periods of the day. Since protectant insecticides are sprayed on grains under these conditions, such high temperatures may interfere with the insecticidal activity. To assess this possibility we sprayed maize grains with pirimiphos-methyl 500 EC (0.8 ml c.p./l and 1.5 l/t) at different temperatures (25°C, 30°C, 35°C, 40°C, 45°C, and 50°C) and 55% r.h. The grains were then maintained at 27±1°C and 55±5% r.h. throughout the experiment which lasted 90 days. Residues of pirimiphos-methyl on the sprayed grains were analyzed every 30 days. Grain samples were assessed every 15 days after the insecticide spraying for their effect on the maize weevil, Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae). Insect mortality was evaluated after 24 and 48 h of exposure to the treated grain. The level of pirimiphos-methyl residue on maize grains decreased with an increase in storage period and air temperature during the insecticide spraying (varying from 11.0±0.1 to 1.1±0.1 ppm, corresponding to the residue levels at 25°C on the day of the spraying and after spraying at 50°C and 90 days of storage). The same trend was observed for mortality of the maize weevil, which dropped from 95.4±13.3% to 2.5±2.5% after 90 days storage after insecticide spraying at 50°C. These results indicate that temperature at spraying can affect insecticide persistence and activity during storage.     

Effect of salt and sucrose content on dielectric properties and microwave freeze drying behavior of re-structured potato slices

Potato puree was used to prepare re-structured potato slices. The effect of salt and sucrose content on microwave freeze drying (MFD) and the variation of the dielectric properties of the potato slices were studied. Results showed that the dielectric constant (ε′) and loss factor (ε″) of the potato purees decreased significantly after freezing. Both salt and sucrose addition increased ε′ and ε″ of the samples at low temperatures (−25 to −5 °C). The salt content had greater influence relative to sucrose content on dielectric properties of the samples. Sucrose addition shows insignificant influence on dielectric properties of the thawing samples; while for the salted samples, ε′ decreased gradually with increasing salt content and ε″ increased significantly with increasing salt content and temperature. MFD drying rate was significant higher after adding salt and sugar.     

Impact of intake water temperatures on reticular temperatures of lactating dairy cows

Automatic temperature recording may allow early detection of disease, estrus, heat stress, and the onset of calving. The phase IV Cattle Temperature Monitoring System (MaGiiX Inc., Post Falls, ID) utilizes a passive bolus equipped with a temperature sensor, a stationary panel reader to query the bolus, and software to collect, analyze, and display data. One potential limitation to collection of reticular temperatures is the effect of water temperature and consumption on recorded temperatures. Two replicated 3 × 3 Latin square experiments were conducted at the Purdue Dairy Research and Education Center to assess the impact of water intake on reticular temperatures using the Cattle Temperature Monitoring System. Nine high-producing, mid-lactation, second-parity cows with low somatic cell counts were selected. Before administering a water treatment, access to feed and water was restricted for at least 2 h. Baseline reticular temperatures were established from measurements before water intake. In experiment 1, treatments were 25.2 kg of hot water (34.3°C ± 1.0), warm water (18.2°C ± 0.4), or cold water (7.6°C ± 0.4). In experiment 2, treatments were 18.9 kg of body-temperature water (38.9°C ± 0.2), cold water (5.1°C ± 0.4), or control (no water). Following water intake, reticular temperatures were collected for 3 h. In experiment 1, an initial dramatic decrease in reticular temperature was observed followed by a gradual increase toward baseline. Least squares means for maximum drop in temperature were 8.5 ± 0.5, 6.9 ± 0.5, and 2.2 ± 0.5°C for cold, warm, and hot water treatments, respectively. Yet at 3 h, reticular temperatures did not return to the baseline. In experiment 2, control cows remained within the baseline confidence interval through the observation period, and cows receiving body temperature water experienced an initial decrease in temperature (0.4 ± 0.2°C) with a return to within the baseline confidence interval within 15 min. Cows receiving cold water did not return to within the baseline confidence interval after a large decrease of 9.2 ± 0.2°C during the 3-h observational period. Moreover, a regression analysis of continued ascent in temperatures predicted that temperatures would return to baseline within 3.5 h. These results demonstrate that, when cows consume large quantities of cold water, the effect of water intake is sizable and sustained. The value of reticular temperatures for daily monitoring in a production setting hinges largely on the implications of this impact.     

Osmotic dehydrofreezing of strawberries: Polyphenolic content, volatile profile and consumer acceptance

We evaluated dehydrofreezing in strawberries in terms of retention of healthy compounds (i.e. polyphenolics) and sensory qualities for direct consumption in substitution of fresh fruit. Different osmodehydration (OD at 30 °C and 5 °C), vacuum osmodehydration (VOD at 30 °C) and immersion chilling freezing (ICF) processes were applied in sucrose syrup. Samples were analyzed for dry matter, soluble solids, pH, titratable acidity, mass transfers, polyphenolic content by HPLC-DAD/MSD, volatile profile by SPME-GC/MSD and consumer acceptance. The results of sensory evaluation, in particular, confirmed the cryoprotective effects of osmotic processes of fruits with respect to untreated frozen control samples. The OD samples at 5 °C presented a water loss to solid gain ratio comparable to OD at 30 °C and VOD samples. Moreover, while osmo-dehydrofreezing at relatively high temperatures caused a slight depletion of phenolic compounds, the samples osmodehydrated at 5 °C showed higher polyphenolic retention. Data on aromatic compounds showed that some compounds increased (e.g. ethanol and acetaldehyde), while others did not appear to be affected by the pre-treatments.     

Kinetics of formation of acrylamide and Schiff base intermediates from asparagine and glucose

From the concentration of glucose and asparagine as reactants and of acrylamide as product each determined by LC–MS during reaction in an acetonitrile/water (68:32) model system at pH 7.6 (0.04 M phosphate buffer) and from the relative concentration of the Schiff base intermediate, the decarboxylated Schiff base intermediate, the Amadori product and aminopropionamide determined in the same reaction mixtures at 120 °C, 140 °C, 160 °C and 180 °C for up to 16 min, the energy of activation for formation of the Schiff base intermediate was found to have the value 50 ± 2 kJ mol⁻¹, while the apparent activation energy for formation of acrylamide was 64.4 ± 0.6 kJ mol⁻¹, for formation of the decarboxylated Schiff base intermediate 92 ± 2 kJ mol⁻¹, and for formation of the Amadori compound 59 ± 4 kJ mol⁻¹, respectively. At high temperature conditions, formation of the Schiff base is accordingly rate determining, while at lower temperatures, decarboxylation becomes rate determining. Aminopropionamide was only detected at reaction times at which acrylamide formation already is significant in favor of, a reaction path including direct formation of acrylamide from the decarboxylated Schiff base, rather than including dissociation of ammonia from aminopropionamide.     

Kinetic analysis of isothermal crystallization in hydrogenated palm kernel stearin with emulsifier mixtures

The kinetics of isothermal crystallization of hydrogenated palm kernel stearin (HPKS) with emulsifiers was evaluated by applying the Avrami equation. Effects of five commercial emulsifiers (lecithin, monoglyceride, polyglycerol polyricinoleate, Span 60, and Tween 60) on crystallization behaviors were tested at four different isothermal temperatures (15, 20, 25, and 30 °C). It is shown that, as temperature increases, induction time for HPKS samples generally increased especially from 25 to 30 °C. Meanwhile, different nucleation mechanisms were observed according to Avrami exponent (n) values. The addition of emulsifiers generally accelerated crystallization rate without changing the growth mechanism (plate-like growth) under 25 °C. However, when the temperature increased to 30 °C, n ranged from 1.0 to 5.1, which indicated different nucleation mechanisms induced by different emulsifiers. Avrami constant (k) (indicating the crystallization rate) decreased as the temperature increased except for samples with Span 60. At higher temperatures, values of t_1/2 were significantly higher which reflects the decrease in k at higher temperatures. Crystal microstructures at 30 °C were obtained by using polarized light microscope. Lecithin and Span 60 samples showed large and dense crystals compared with the control sample. Tween 60 sample showed very small crystals which aggregated in a line trend. However, small differences were observed in fractal dimension results except for Tween 60 sample.     

Effect of ultrasound on banana cv Pacovan drying kinetics

The aim of this work was to study and to model the drying kinetics of fresh and ultrasonic pretreated banana cv Pacovan using the diffusional model (Fick’s second law) and an empirical two parameters model (Page model). The pretreatment was carried out in an ultrasonic bath at 30 °C. The drying process was carried out in a fixed bed dryer at two different temperatures (50 and 70 °C) and 3.0 m/s air velocity. Page empirical model provided the best simulation of the drying curves. The diffusional model was used to describe the moisture transfer and the effective diffusivities of water were determined and were in the order of 10⁻⁹ m²/s. These diffusivities increased with increasing temperature and with the application of ultrasound, while the process time reduced, which can represent an economy of energy, since air drying is cost intensive.     

Investigation of the diffusion of dyes in agar gels

An experimental set-up and a measurement technique were developed so that diffusion in model foods (gels of agar) could be visualised and quantified. The diffusion of aqueous solutions of varying concentrations of two dyes (rhodamine 6G and methylene blue) in gels of agar was followed in situ at three temperatures (30, 50, 70 °C) until equilibrium was reached. The nature of the diffusion process (in terms of the amount of dye diffused into the gel) was studied using image analysis techniques. The diffusion coefficient, D, was estimated using Fick’s second law of diffusion and found to be ∼10⁻¹⁰ m² s⁻¹. The effect of the size of the diffusing molecule, as well as that of the processing temperature on diffusion was investigated and found to be significant.     

Development of fish gelatin edible films using extrusion and compression molding

Fish gelatin was plasticized with 20% and 25% glycerol (w/w of gelatin) and used to develop edible films by twin-screw extrusion at 110 and 120 °C followed by compression molding at 80 °C. Tensile and moisture barrier properties and glass transition temperature were then measured and compared with solution-cast films. The films extruded at 110 °C and with 25% glycerol had the highest percent elongation at break of 293 ± 27%. The water vapor permeability values of extruded films (the highest value being 2.9 ± 0.2 g mm h⁻¹ cm⁻² Pa⁻¹) were higher than those of solution-cast films while the glass transition temperatures (T_g) of the extruded films were generally lower than those of solution-cast films. Films with 25% glycerol that were extruded at 110 °C had the lowest T_g (2.10 ± 0.31 °C). This investigation showed that extrusion processing followed by compression molding is a feasible method to produce fish gelatin films for commercial applications in a wide range of food products.     

Effects of processing parameters on the convective heat transfer rate during ultrasound assisted low temperature immersion treatment of a stationary sphere

The effect of ultrasound irradiation, as a novel method, on the enhancement of convective heat transfer between a stationary copper sphere and cooling medium was experimentally studied at different Re and Pr numbers. The high thermal conductivity of copper allowed the application of lumped system analysis which led to more accurate results on convective heat transfer. The ultrasonic cooling system included a refrigerated circulator, a flow meter, an ultrasound generator (25 kHz) and an ultrasonic bath. The studied parameters were sphere diameter (0.01 or 0.02 m), flow rate (1.67 × 10⁻⁵, 2.5 × 10⁻⁵ m³ s⁻¹), fluid temperature (0, −5, −10, −15 and −20 °C) and ultrasound intensity (0, 190, 890 and 2800 W m⁻²), leading to Re range of 0.98–3.4 and Pr range of 68.3–188.9. The Nu number varied from 6.8 to 19 for non-irradiated samples. When ultrasound was irradiated (890 W m⁻²) the range of Nu number increased to 11–31. Enhancement factors from 30% to 119% were observed for the irradiated samples. The largest values of the enhancement factor were observed for low values of Re and Pr which demonstrated a better efficiency of ultrasound irradiation at higher viscosities and lower flow rates as a result of its mixing and cavitation effects. The results obtained in this study confirmed that ultrasound irradiation is able to enhance the convective heat transfer rate between the cooling medium and the submerged object. Irradiation effect was independent of sphere diameter and a linear relationship was detected between the ultrasound intensity and the Nu number. A correlation was suggested to predict the values of Nu at the presence or absence of ultrasound for different Re and Pr values with good agreement with the experimental data (R² = 0.90). The obtained data for copper can be generalized for food products with similar geometries and can be used for process design, as the convective heat transfer is mostly controlled by the cooling medium.