ELASTIC MODULUS of ORANGE JUICE ICE

The elastic modulus of orange juice ice as well as pure water ice was measured at temperatures between ? 10°C and ? 196°C by compression tests. the elastic modulus of pure water ice was almost constant in the whole range of the tested temperatures: 5.6 × 10⁹ N/m² at ? 196°C and 4.0 × 10⁹ N/m² at ? 10°C. In contrast, the elastic modulus of orange juice ice changed greatly with temperature: 11 × 10⁹ N/m² at ? 196°C and 0.2 × 10⁹ N/m² at ? 10°C. Orange juice ice was considered to consist of pure water ice particles which are dispersed in a matrix of concentrated amorphous solution (CAS). the elastic modulus of CAS was calculated using an equation for a disperse system.     

Effect of Particle Size,Temperature, and Total Soluble Solids on The Rheological Properties of Watermelon Juice: A Response Surface Approach

Central composite design was used to analyze the effect of particle size (0.075, 0.15, 0.25, 0.355, 0.425 mm), temperature (1.6, 5, 10, 15, 18.4°C) and total soluble solids (14.77, 25, 40, 50, 65.23°Brix) on the rheological properties of watermelon juice. Experimental values of consistency coefficient k, varied from 0.178–0.628 Pa sⁿ and flow behavior index n from 0.281 to 0.949. Regression equation was computed and used to predict the values of k and n. Results revealed that coefficient of determination (R²) and standard error for consistency coefficient k were 0.84 and 0.043 and for flow behavior index n were 0.42 and 0.102 respectively. Surface graphs showed that k value increased with increase in total soluble solids and particle size while decreased with temperature.     

Pasteurization of mixed mandarin and Hallabong tangor juice using pulsed electric field processing combined with heat

Effects of pulsed electric filed (PEF) processing combined with heating (H-PEF processing) on the inactivation of microorganisms and the physicochemical properties of mixed mandarin and Hallabong tangor (MH) juice were studied. Using a pilot-scale PEF system, MH juice, pre-heated at 55 °C, was PEF-treated at 19 kV/cm of electric field and 170 kJ/L of specific energy and the juice, pre-heated at 70 °C, was PEF-treated at 16 kV/cm and 100 kJ/L or 12 kV/cm and 150 kJ/L. H-PEF processing at 70 °C–16 kV/cm–100 kJ/L reduced the aerobe, yeast/mold, and coliform counts of MH juice by 3.9, 4.3, and 0.8 log CFU/mL, respectively, without affecting the ascorbic acid concentration and antioxidant capacity of juice. H-PEF processing changed juice color and browning degree (p < 0.05), but not total soluble solid content or pH. By controlling initial juice temperature and electric field strength, H-PEF processing can be an effective pasteurization method for mixed juice with minimal changes in quality.     

Characterisation of frozen orange juice by ultrasound and wavelet analysis

Ultrasound technology was used to analyse the freezing behaviour of orange juice. The ultrasonic properties of orange juice, specifically velocity and attenuation coefficient, were characterised as the temperature was decreased from 20 to ?50 °C. The results were compared with NMR free induction decay data and correlated with the amount of unfrozen water present in the frozen sample. The velocities of longitudinal waves (P‐wave) and shear waves (S‐wave) in frozen orange juice were measured, yielding values of around 4000 and 2000 m s^?1 respectively. They were related to the amount of unfrozen water in the frozen sample. The elastic moduli of the samples at different temperatures were obtained from the measured ultrasonic velocities. Significant changes in the attenuation of the ultrasonic waves propagated through the frozen sample were observed as a result of ice nucleation and growth. Information about the spectral behaviour of the ultrasound signal was obtained by means of wavelet analysis. The analysis provided a direct measure of the spectral content of the ultrasonic waves over time and showed the variation in the ultrasonic velocity dispersion with temperature. Significant velocity dispersions occurred for frequencies less than 1 MHz. Copyright © 2004 Society of Chemical Industry     

THERMOPHYSICAL PROPERTIES OF PINK GUAVA JUICE AT 9 AND 11°BRIX

The effect of temperature on the conservation of pseudoplastic characteristics and on the physical properties of pink guava juice (Psidium guajava L.) variety Beaumont: B‐30 with two different total soluble solids (9°Brix and 11°Brix) was investigated. It was found that the juice exhibits pseudoplastic behavior in the range of shear rate between 40 to 160 s^?1 and within pasteurization temperature of 60–90C. While the flow behavior index (n) and density (p) increased, consistency coefficient (K), thermal conductivity (k) and specific heat capacity (C_p) decreased with increasing temperature. The linear regression equations or models for flow behavior index, consistency coefficient, density, thermal conductivity and specific heat capacity were determined with correlation coefficients ranging from 0.75 to 1.00.     

Comparison of rheological properties of native and pregelatinized potato starches

Rheological properties of native potato starch (NPS) and pregelatinized potato starch (PPS) were investigated under steady and dynamic shear conditions at 20°C and 60°C. The consistency index, apparent viscosity, and yield stress values of PPS were much lower than those of NPS. The flow behavior of PPS is more temperaturedependent. Dynamic moduli (G′ and G″) and complex viscosity of PPS were much lower than those of NPS, while tan δ values of PPS were in the range of 2.30–3.50 (tan δ>1), indicating that PPS is more viscous than elastic. Rheological properties of NPS are strongly influenced by pregelatinization.     

Rheological Behavior of Frozen and Thawed Low-Moisture, Part-Skim Mozzarella Cheese

Stress relaxation and dynamic profiles of low-moisture, part-skim (LMPS) Mozzarella cheese cylinders refrigerated 14 days (control), frozen and thawed, and stored frozen and refrigerated up to 90 days were compared. Samples were frozen at ?30°C and stored at ?20°C. Thawing and refrigerated storage were at 5°C. Stress relaxation tests were conducted at 20°C and dynamic spectrometry at 20°C and 60°C. The frozen and thawed Mozzarella cheese tested at 20°C became harder and more elastic with storage time, while refrigerated stored samples became softer and more elasticoviscous with time. Upon melting, both go-day-frozen and go-day-refrigerated cheeses were less elastic and less viscous than 14-day-refrigerated samples.     

Influence of Temperature and Solid Concentration on the Physical Properties of Noni (Morinda citrifolia L.) Juice

The effect of temperature on the physical properties of fresh noni (Morinda citrifolia L.) juice with three different solid concentrations (5, 10, and 15°Brix) was investigated. The flow behaviour index (n) and thermal conductivity (k) were found to increase with the increase in temperature. On the other hand, the juice density (??) and consistency coefficient (K) were found to decrease with increasing temperature. The increase in solid concentration leads to increase juice density and consistency coefficient, but reduce flow behaviour index and thermal conductivity. The experimental data were then correlated with temperature and solid concentration using nonlinear regression equations or empirical models. It was found that the physical properties calculated using proposed equations agree well with the experimental data with coefficient of determinations (R ² ) ranged from 0.9897 to 0.9998.     

Possible nutritional and health‐related value promotion in orange juice preserved by high‐pressure treatment

Effects of high‐pressure treatment on the orange juice carotenoids (β‐carotene, α‐carotene, zeaxanthin, lutein and β‐cryptoxanthin) associated with nutritional (vitamin A) and health‐related (radical‐scavenging capacity) values were investigated. Various high‐pressure treatments (50–350 MPa) combined with different temperatures (30 and 60 °C) and times (2.5, 5 and 15 min) of treatment were assayed. The carotenoid content of the orange juice was analysed by HPLC‐UV, the vitamin A value was determined as retinol equivalents (RE) and the free radical‐scavenging capacity was evaluated using the DPPH (2,2‐diphenyl‐1,1‐picrylhydrazyl) radical model system. A storage study was carried out at refrigeration temperature (4 °C). High‐pressure treatments at 350 MPa produced significant increases of 20–43% in the carotenoid content of fresh orange juice (from 3.99 to 4.78–5.70 mg l^?1). A non‐uniform behaviour of high‐pressure treatments was detected. An increase in time (beyond 5 min) or temperature (above 30 °C) of treatment did not improve the amount of carotenoids extracted. Owing to better extraction of carotenoids, an increase in vitamin A value from 164 to 238 RE l^?1 (45%) was achieved with the 350 MPa/30 °C/5 min treatment. No correlation was found between the increase in carotenoid amount extracted and the free radical‐scavenging activity. © 2002 Society of Chemical Industry     

Rheological and differential scanning calorimetry studies on structural and textural changes in frozen Atlantic mackerel (Scomber scombrus)

The viscoelastic behaviour and thermal stability of Atlantic mackerel fillets stored at ?20 and ?30 °C for up to 2 years were investigated. An increase in elastic (G′) and viscous (G″) modulus values, reflecting protein aggregation, was observed in samples stored at ?20 °C compared with those stored at ?30 °C, as well as with storage time. The results indicate that toughening on frozen storage is not just limited to lean gadoid fish but also occurs in fatty fish, leading to texture deterioration. Differential scanning calorimetry of fillets stored at ?20 °C showed a shift to a lower transition temperature (T_m) and a decrease in enthalpy (ΔH) compared with control fillets stored at ?30 °C; this change was enhanced when fillets were stored for a longer period of time, confirming protein denaturation and the formation of aggregates reported previously by the authors (J Sci Food Agric 82: 579–586 (2002)). The contribution of lipid oxidation to protein aggregation was shown by storing minced mackerel with or without the antioxidant vitamin E at ?10 °C. The G′ and G″ values were higher in samples stored without vitamin E than in samples stored with vitamin E; thus antioxidants may be used to minimise protein aggregation in fatty fish. The role of lipid oxidation in promoting protein aggregation and deterioration in the texture of fatty fish has not been reported hitherto. Antioxidants such as vitamin E may be used not only to prevent lipid oxidation but also to minimise protein damage in order to prolong the shelf‐life of fatty fish. Copyright © 2004 Society of Chemical Industry     

A Comparison of Creep Phenomena in Food Protein Gels

Rheological properties of gels made by heating (90°C for 20 min) and subsequent cooling (5°C) dispersions of gelatin, soy protein isolate, and a mixture of whey protein and casein were determined by creep measurements at various temperatures. The elastic component of soy protein isolate gels became soft with increasing temperature but did not fully melt even at 90°C. Whey protein concentrate gels deformed continuously upon compression above 70°C, reflecting viscous flow. The gel obtained from a mixture of casein and whey protein concentrate following acidification with glucono-δ-lactone and heating revealed significant plastic deformation, indicating the network was formed by packing of small size particles.     

Thermal degradation kinetics of anthocyanins from Chinese red radish (Raphanus sativus L.) in various juice beverages

Thermal and storage stabilities of red radish anthocyanins (RRAs) in various juice beverages (apple, grape, peach, pear, pomegranate and lemon) were studied over temperature range 70–90 °C and 4–25 °C. RRAs degradation in all juice beverages followed first-order reaction kinetics. RRAs showed a much faster degradation rate during storage at room temperature (t _1/2 value ≤84.0 days) than did in refrigerated temperature (t _1/2 ≥value 130.9 days). The rate constant (k), E _a and Q ₁₀ values for RRAs in juice beverages varied from 1.33 to 0.33, 47.94 to 14.77 kJ mol^?1 and 1.16 to 1.89 at 70–90 °C. During heating, RRAs in peach and pomegranate showed higher stability than others at these temperatures. There was a positive correlation (R ² > 0.9128) between ascorbic acid content of juice beverages (8–36 mg/100 mg) and stability of RRAs at 70–90 °C. It was found that RRAs in apple and pear juice beverage were more stable than in other juice beverages.     

Chemical Composition and Temperature Influence on the Rheological Behaviour of Honeys

The purpose of this work was to examine the viscoelastic properties of Spanish honeys with various sugar contents [fructose (32–42 g/100 g honey), glucose (24–35 g/100 g honey), sucrose (0.0–3.4 g/100 g honey)]; concentrations (79–83 °Brix), and moisture levels (16–19 g/100 g honey) at different temperatures (5, 10, 15, 20, 25, 30, and 40°C). Honey showed Newtonian behaviour, presenting a highly viscous part (loss modulus was much greater than the elastic modulus). The loss modulus (G″) and viscosity increased with moisture content and a decrease with temperature. Exponential and power law models were applied to fit loss modulus and viscosity data. Polynomial models were proposed to describe the combined effect of temperature, fructose, glucose, sucrose content, other sugars, non-sugar substance, and moisture content.     

Volatile odour components and sensory quality of fresh and processed mandarin juices

Twelve volatile compounds were quantified by gas chromatography/mass spectrometry in juices from two Spanish mandarin varieties, Fortuna and Clemenules. Fresh Clemenules juice contained a higher amount of total volatile compounds (61.1 ± 1.1 mg L⁻¹) than fresh Fortuna juice (48.8 ± 2.5 mg L⁻¹), with D ‐limonene (97.1%), myrcene (1.7%), sabinene (0.5%), α‐pinene (0.3%) and linalool (0.3%) being the predominant compounds. Pasteurisation of the mandarin juices (20 s at 98 °C) caused a significant reduction (∼12%) in vitamin C concentration. On the other hand, vitamin C was stable during storage of the juices for 60 days in aseptic tanks at 2 °C. Volatile compounds, however, were more affected by storage in aseptic refrigerated tanks (2 °C) than by heat treatment. Pasteurisation caused a mean decrease in the total concentration of volatile compounds of about 18%, while, after a storage time of 60 days, 36% of total volatiles present in the juices after pasteurisation were lost from both Fortuna and Clemenules juices. Significant reductions in the concentrations of D ‐limonene, myrcene, sabinene, α‐pinene and linalool were found, while those of α‐terpineol and terpinen‐4‐ol increased. Copyright © 2006 Society of Chemical Industry     

RHEOLOGICAL BEHAVIOR AND PHYSICOCHEMICAL CHARACTERISTICS OF GOLDENBERRY (PHYSALIS PERUVIANA) JUICE AS AFFECTED BY ENZYMATIC TREATMENT

Goldenberry (Physalis peruviana) juice was prepared and enzymatically treated with two dosages (300 and 600 ppm) of Pectinex Ultra SP‐L, then, the juice was concentrated to 30 and 40°Brix. Rheological properties of juices were studied at a wide range of temperatures (5 to 100C) and shear rate range from 0.3 to 100/s using Brookfield Digital Viscometer. The Herschel–Bulkley, Casson and Bingham rheological models were applied to describe the rheological properties of different juices. These properties are key parameters required to solve food industry problems in numerous areas such as quality control, evaluation of consumer acceptance and texture. The results indicated that juice concentrates behave as non‐Newtonian fluids (pseudoplastic) and have a definite yield stress. The Bingham and Casson, plastic viscosity, yield stress, consistency index and flow index decreased with increasing enzyme dosage and temperature. The effect of temperature on the viscosity described by means of an Arrhenius‐type equation. The activation energy for viscous flow depends on the total soluble solids. Moreover, sensory evaluation for juices was carried out. In consideration of industrial utilization, detailed knowledge on the rheological and physicochemical characteristics of cape gooseberry juice is of major importance.     

Thermal and viscoelastic properties of starch gels from maize varieties

The aim of this work was to determine the thermal, functional and rheological properties of maize (Zea mays) starch isolated from seven varieties. Chemical analysis was undertaken in all starch samples. The gelatinization and retrogradation temperature at different storage times, as well as the enthalpy of the isolated starches, were determined using differential scanning calorimetry (DSC). Swelling and solubility were also measured in individual samples. Dynamic oscillatory tests (amplitude and frequency sweeps) were undertaken on starch samples with 10% (w/v) of total solids during a cycle of three stages (kinetics) of heating/cooling, using a strain‐controlled rheometer. The samples presented an amylose content which ranged from 22% to 29%, typical in normal starches, the lipid values were under 1%, while the protein contents were just over 1%. The calorimetric profile for the studied starches showed a peak temperature (gelatinization) over the temperature range from 72.5 to 75.7 °C and enthalpy values between 13.68 and 17.58 J g^?1. Four starches presented enthalpy values of the retrogradation transition that increased with the storage time, showing differences among the starches analysed. Maximum swelling and solubility were usually found at the second stage of the above‐mentioned cycle. The rheological profile showed that the gels formed during the first stage of the above‐mentioned kinetics presented the behaviour of weak viscoelastic gels with the storage or elastic modulus (G′) higher than the loss or viscous modulus (G″) over the applied strain and frequency ranges. All samples showed a more elastic character as the kinetics progressed. Starches isolated from diverse maize varieties showed differences in their characteristics studied, and might produce different functional properties in the products where they are used. Copyright © 2006 Society of Chemical Industry     

Isolation and Partial Characterization of Mexican Oxalis tuberosa Starch

The chemical, physicochemical and rheological characteristics of Oxalis tuberosa starch were investigated. Oxalis starch presented an apparent amylose content of 33%, similar to maize starch used as control, with a granule size between 25–50 μm with oval and elliptical shapes and A‐type X‐ray diffraction pattern. The gelatinization temperature of oxalis starch was 64.0°C, that was lower than the one determined in maize starch (73.0°C), with an enthalpy value of 12.2 J/g, which was similar to that of maize starch. Both oxalis and maize starch pastes behaved as weak viscoelastic systems with the elastic character (G′) predominating over the viscous character (G′′). An increase in the level of solids in the pastes increased the values of the moduli. The results suggest that heating the systems (gelatinization), causes a more pronounced enhancement in the structure of the maize starch pastes than in that of oxalis starch pastes. Overall, it was concluded that due to its physicochemical, functional and rheological properties, Oxalis starch could be suitable for testing its use in the cosmetic and in the food industry.     

Effects of temperature,shear rate and constituents on rheological properties of tahin (sesame paste)

In this paper, rheological properties of tahin are reported at temperatures from 20 to 70 °C and shear rates in the range 0.13–500 s^?1. Temporary hysteresis loops were observed in the first cycle of the flow curves. The steady shear behaviour of tahin was pseudoplastic and described by a power law model. The consistency coefficient exhibited strong temperature dependence for which the activation energy of flow was 21.6 kJ mol^?1. The flow behaviour index of tahin tended to increase whereas the consistency coefficient tended to decrease during storage at room temperature. Tahin oil exhibited Newtonian behaviour with a strong dependence of viscosity on temperature. The activation energy of flow for tahin oil was 35.7 kJ mol^?1. While reconstituted suspensions containing up to 20% solids exhibited Newtonian behaviour, those with more solids and the original tahin showed pseudoplastic behaviour. The Krieger–Dougherty model fitted the suspension viscosity data well. Below 20% solids level there was no effect of particle size on the viscosity of the reconstituted suspensions. It was shown that for the same amount of solids the viscosity of a ‘polydisperse’ suspension was lower than that of a ‘monodisperse’ suspension. Copyright © 2004 Society of Chemical Industry     

The Effect of Hybrid Carrageenan on the Thermo-rheological Properties of Gluten-Free Flour Doughs Using a Modified Kneading Protocol

Thermo-rheological behaviour of chestnut flour doughs supplemented with kappa/iota-hybrid carrageenan (HC) (up to 2.0%, flour basis (f.b.)) and sodium chloride (1.8%, f.b.) was determined at both target (C1) and final (C5) mixing peaks. For this purpose, small amplitude oscillatory shear (0.01 to 100 Hz), creep–recovery (loading of 50 Pa for 60 s, 30 °C), temperature sweeps (from 30 up to 180 °C) and heating/cooling cycles (between 30 and 60 °C) were conducted on a controlled stress rheometer. Previously, the thermal-mixing behaviour at proposed mixing temperature (50 °C) was conducted on Mixolab® apparatus. Results showed that the dough stability (from 2.2 to 5.8 min) in mixing stage and starch heat resistance to dough processing were significantly improved at proposed mixing temperature, even in the absence of HC. No statistical differences in rheological properties were observed for doughs evaluated in C1; however, those analysed in C5 were significantly modified in the presence of HC, mainly in terms of viscous behaviour (from 52.1 × 10⁶ to 39.1 × 10⁶ Pa s). Creep–recovery data sets, successfully fitted using Burgers model, revealed that the elasticity (J _r/J _max from 73.3 to 87.6%) of doughs analysed in C5 improved with HC addition. Thermal tests showed that the starch transitions were significantly promoted and stabilized with HC addition.     

Effects of waxy maize and potato starches on the stability and physicochemical properties of model sauces prepared with fresh beef meat

Stability and physicochemical properties of model sauces containing 2.5 wt% fresh beef meat (related to raw material), 30 wt% rapeseed oil and native waxy maize starch (WMS) or potato starch (PS) at concentrations ranged from 0.5 to 4.0 wt% were assessed. Sauces thickened with WMS showed a significantly (P < 0.05) higher stability than respective ones made with PS. All studied systems exhibited non‐Newtonian, pseudoplastic behaviour. The Ostwald–de Waele and Herschel–Bulkley models were used to describe the flow properties of model sauces. In comparison with control sample (prepared without starch), addition of this polysaccharide (WMS or PS) increased consistency index, yield stress and apparent viscosity and decreased flow behaviour index of model sauces. The Arrhenius equation was used to determine the effects of temperature (20–50 °C) on the apparent viscosity. The activation energy values were in ranges 7.66–10.59 kJ mol^?1 and 8.87–11.82 kJ mol^?1 in sauces prepared with WMS and PS, respectively. The instrumentally detected changes in consistency and whiteness of model sauces were found, which may be used as the good predictors of the perceived sensory consistency and whiteness.