Steady shear flow behavior of gum extracted from Ocimum basilicum L. seed: Effect of concentration and temperature

Steady shear flow behavior of basil seed gum (BSG) was investigated between 0.5% and 2% (wt/wt) concentration and temperatures of 5-85 °C. BSG showed shear thinning behavior at all concentrations and temperatures. The Herschel-Bulkley model was employed to characterize flow behavior of BSG solutions at 0.1-1000 s⁻¹ shear rate. The pseudoplasticity of BSG increased markedly with concentration. Flow behavior of 1% BSG indicated a higher viscosity of this gum at low shear rates compared to xanthan, konjac and guar gum at similar concentration. The activation energy of BSG quantified using an Arrhenius equation increased from 4.9 × 10³ to 8.0 × 10³ J mol⁻¹ as concentration changed from 0.5% to 2% wt/wt. This indicated a heat-resistant nature of BSG. Increasing the apparent viscosity of BSG as temperature increase from 60 °C showed a sol-gel behavior of BSG based on dynamic oscillatory measurements. The static yield stress was obvious between shear rates 0.001-0.1 s⁻¹ (9.98 Pa for 1% BSG at 20 °C). The existence of the yield stress, high viscosity at low shear rates and pseudoplastic behavior of BSG make it a good stabilizer in some food formulations such as mayonnaise and salad dressing.     

Rheological properties of ultraviolet-irradiated and thermally pasteurized Yankee pineapple juice

The rheological behaviour of Yankee pineapple juice was examined for the effect of ultraviolet (UV) irradiation (53.42 mJ/cm²) and compared with untreated juice and a thermally pasteurized (80 °C for 10 min) juice. A rheological test was performed on all types of juice in the temperature range 5 °C to 25 °C using a concentric cylinder rheometer at a shear rate range of 10–290 s⁻¹. The comparative analysis found that the best flow curves were described by the Bingham model with an initial shear stress. The entangled pulps in the juices prevented free flow at zero shear rate. There was no significant variation between the plastic viscosities of the untreated and UV-irradiated juice at all temperatures. The activation energy (E_a) of the untreated, UV-irradiated and thermally pasteurized juice was 6.80, 8.19 and 8.50 kJ/mol respectively.     

Shear and extensional viscosities of hard wheat flour dough using a capillary rheometer

The rheological behaviour of hard wheat flour dough was investigated for a high shear rate range (10-10⁴ s⁻¹) using a capillary rheometer. The shear viscosity obtained from capillary measurements demonstrated a shear thinning behaviour of dough and described by a power law model with a power law index n = 0.38, a consistency coefficient K = 1387 Pa sⁿ, and a coefficient of determination R² = 0.997. The extensional viscosity obtained from capillary measurements for a high extensional rate range (0.16-154 s⁻¹) showed a tension thinning behaviour and described by a power law model with a power law index m = 0.38, a consistency coefficient K_E = 353,000 Pa s^m, and a coefficient of determination R² = 0.977. Torsional measurements using a parallel plates rheometer for a shear rate range (10⁻³-20 s⁻¹) demonstrated the time or strain dependence of wheat flour dough, no steady state shear viscosity of dough, and the shear viscosity increased with time or strain to a maximum value and then decreased, suggesting a breakdown or rupture of the dough structure.     

Aqueous extraction of anthocyanins from Hibiscus sabdariffa: Experimental kinetics and modeling

Solid-liquid extraction of anthocyanins from calyces of Hibiscus sabdariffa L. was studied to evaluate the influence of the operating parameters. Solid-to-solvent ratio and particle size had the main impact on anthocyanin extraction efficiency. Maximum yield of anthocyanins (88%) was obtained at 25 °C with the highest solid-to-solvent ratio (1/25). The decrease in the particle size of the calyces from 2 cm to 150 μm drastically reduced the extraction time. The increase of temperature reduced the extraction time by increasing the diffusion coefficient (3.9 × 10⁻¹¹-1.35 × 10⁻¹⁰ m² s⁻¹ between 25 and 90 °C) but did not modify the extraction yield. A simple extraction model that integrated anthocyanin thermo-degradation kinetic was proposed. A good agreement between the predicted results of the models and experimental data was demonstrated. From a solid-to-solvent ratio of 1/5, an extraction yield of 63% and an anthocyanin concentration of 0.3 g L⁻¹ could be obtained in less than 10 min.     

Effect of temperature on rheological characteristics of molasses: Modeling of apparent viscosity using Adaptive Neuro - Fuzzy Inference System (ANFIS)

In this study, the effect of temperature on the rheological characteristics of apricot and date molasses was studied separately. Rheological characteristics of both molasses were evaluated in the shear rate range of 0.1-100 s⁻¹ at different temperatures (10-40 °C). Power law model was used for the calculation of flow behavior index and consistency coefficients of molasses. Consistency coefficients of apricot and date molasses were in the range of 5.408-39.905 Pa sⁿ and 0.910-2.852 Pa sⁿ, respectively. Molasses samples showed a non-Newtonian flow behavior. The effect of temperature on apparent viscosity was described by Arrhenius equation and calculated activation energy at the shear rate of 54.2 s⁻¹ was 41.42 and 38.19 kJ/mol for apricot and date molasses, respectively. An efficient predictive model for apparent viscosity values of molasses was constructed using Adaptive Neuro - Fuzzy Inference System (ANFIS) and this model showed satisfactory prediction with high coefficient of determination (0.979-0.999) and low root mean squared error (0.12-0.46).     

Migration of α-tocopherol and resveratrol from poly(L-lactic acid)/starch blends films into ethanol

Poly(L-lactic acid) (PLLA)/starch blends with various concentrations of two natural antioxidants, α-tocopherol (α-TOC) and resveratrol, were fabricated by a melt blending and compression molding processes. The effects of the two antioxidants on the optical (color), thermal and mechanical properties of PLLA/starch blends with antioxidants were assessed. PLLA/starch blend films with α-TOC and resveratrol showed a yellowish color influenced by the combined effect of white starch and the brown color of the antioxidants. The glass transition and melting temperatures were significantly reduced with the addition of antioxidants while enhanced thermal stability was observed, which could be a benefit and important for processing and production. The enhanced mechanical properties could be attributed to not only a compatibilization effect based on the chemical linkage between PLLA and starch chains, but also restriction of the chain mobility by antioxidants. The release of resveratrol from PLLA and PLLA/starch blend films into ethanol followed Fickian behavior. The D values of α-TOC were in the range of 0.47–3.95 × 10⁻¹¹ cm² s⁻¹ for PLLA films and 0.70–6.83 × 10⁻¹¹ cm² s⁻¹ for PLLA/starch blend films at 13 °C, 5.67–13.0 × 10⁻¹¹ cm² s⁻¹ for PLLA films and 4.10–24.2 × 10⁻¹¹ cm² s⁻¹ for PLLA/starch blend films at 23 °C, and 89.0–118.0 × 10⁻¹¹ cm² s⁻¹ for PLLA films and 123–282 × 10⁻¹¹ cm² s⁻¹ for PLLA/starch blend films at 43 °C. The D values of resveratrol were in the range of 0.073–0.54 × 10⁻¹⁰ cm² s⁻¹ for PLLA films and 1.42–6.93 × 10⁻¹⁰ cm² s⁻¹ for PLLA/starch blend films at 13 °C, 0.90–3.44 × 10⁻¹⁰ cm² s⁻¹ for PLLA films and 4.16–22.3 × 10⁻¹⁰ cm² s⁻¹ for PLLA/starch blend films at 23 °C, and 24.8–74.1 × 10⁻¹⁰ cm² s⁻¹ for PLLA films and 40.1–309 × 10⁻¹⁰ cm² s⁻¹ for PLLA/starch blend films at 43 °C.     

Hydrodynamic, thermo-analytical and molecular structural investigations of enzyme interesterified oil and its thermo-oxidative stability by thermogravimetric analysis

This paper deals with the effect of lipase-catalyzed interesterification of oil on hydrodynamic, thermo-analytical, structural properties and its stability. Interesterification of rice bran oil (RBO) and refined, bleached, deodorized palm olein (RBDPO) blend in 1:1 ratio was carried out at 60 ± 1 °C under stirring for 6 h. Results showed that hydrodynamic property of oils decreased from 3.61 × 10⁻⁶ in RBDPO to 2.91 × 10⁻⁶ m² s⁻¹ in enzyme interesterified oil (EI) and heat transfer coefficient increased from 221.0 in RBDPO to 250.7 Wm⁻² °C⁻¹ in EI over 170-190 °C. Peak melting point of triacylglycerols shifted from 10.36 °C in RBDPO to −4.76 °C in EI. Trisaturated triacylglycerols decreased from 4% in RBDPO to 0.6% in EI. The first step of thermal decomposition started at 190, 212.7 and 238.9 °C for RBDPO, RBO and EI, respectively. Sensory evaluation of poori fried using these oils revealed no significant (p > 0.05) differences in sensory attributes of the fried product.     

Effect of temperature and air velocity on drying kinetics, antioxidant capacity, total phenolic content, colour, texture and microstructure of apple (var. Granny Smith) slices

The aim of this work was to study the effect of temperature and air velocity on the drying kinetics and quality attributes of apple (var. Granny Smith) slices during drying. Experiments were conducted at 40, 60 and 80 °C, as well as at air velocities of 0.5, 1.0 and 1.5 m s⁻¹. Effective moisture diffusivity increased with temperature and air velocity, reaching a value of 15.30 × 10⁻⁹ m² s⁻¹ at maximum temperature and air velocity under study. The rehydration ratio changed with varying both air velocity and temperature indicating tissue damage due to processing. The colour difference, ΔE, showed the best results at 80 °C. The DPPH-radical scavenging activity at 40 °C and 0.5 m s⁻¹ showed the highest antioxidant activity, closest to that of the fresh sample. Although ΔE decreased with temperature, antioxidant activity barely varied and even increased at high air velocities, revealing an antioxidant capacity of the browning products. The total phenolics decreased with temperature, but at high air velocity retardation of thermal degradation was observed. Firmness was also determined and explained using glass transition concept and microstructure analysis.     

Design of a forced-air-twin-chamber for investigating the effects of controlled levels of non-uniformity in heat treatment of tomatoes on product quality

A twin-chambered forced-air apparatus was built to simultaneously apply different environments to each hemisphere of tomato (Lycopersicon esculentum Merr.) fruit. This setup enabled one hemisphere of each fruit to be exposed to an air temperature–velocity combination of 39 °C/0.24 m s⁻¹; while the other hemisphere was simultaneously exposed to a combination of 36 °C/0.24 m s⁻¹, 37 °C/0.24 m s⁻¹, or 36 °C/0.12 m s⁻¹. Tomato fruits were divided into four lots: one left untreated; two lots were uniformly heat treated by maintaining the same environment in each chamber; and the remaining were subjected to twin chamber heat treatment. The fruits were then transferred to storage conditions at 14 °C, and allowed to ripen at 20 °C or subjected to chilling injury at 2 °C. The temperature difference between the two chambers significantly influenced the uniformity of color, whereas the firmness, titratable acidity and sugar to acid ratio were only marginally affected. Decreasing the temperature difference between the two chambers or increasing air velocity in heated chamber significantly improved the uniformity of quality.     

Diffusion of carbon dioxide through grain bulks

The diffusion coefficient of carbon dioxide (CO₂) through grain bulks was determined using a transient method with the following variables: (1) grain bulk (wheat, barley, and canola); (2) moisture content (m.c.) (dry, damp, and wet conditions); (3) temperature (5°C, 15°C, 25°C, and 40°C); (4) direction of gas flow (upwards, downwards, and horizontal); (5) porosity (two levels for each grain bulk); (6) grain kernel orientation (vertical and horizontal); (7) initial concentration in the gas chamber (20%, 40%, and 60%); and (8) dockage (0%, 4%, 8%, and 12%). The diffusion coefficients of CO₂ through wheat bulks ranged from 5.9×10⁻⁶ to 7.6×10⁻⁶ m² s⁻¹, through barley bulks from 5.1×10⁻⁶ to 8.4×10⁻⁶ m² s⁻¹, and through canola bulks from 3.7×10⁻⁶ to 5.3×10⁻⁶ m² s⁻¹ for the test conditions studied.Increasing the m.c. decreased diffusion coefficients. An increase in temperature generally increased the diffusion coefficient of CO₂. Diffusion in the downward direction resulted in higher diffusion coefficients. No significant difference in diffusion coefficients was observed between the upward and horizontal directions of flow. An increase in porosity resulted in higher diffusion coefficients. The upward diffusion coefficient of CO₂ was higher for vertical grain kernel orientation than for horizontal kernel orientation for wheat and barley but for canola, the difference between the two kernel orientations was not significant. There was no significant difference in diffusion coefficients for different initial gas concentrations. The diffusion coefficient increased linearly as the dockage was increased.The amount of CO₂ absorbed by barley and canola increased with an increase in m.c. in polynomial fashion. There was no significant difference in the sorption of CO₂ by barley and canola when the temperature of the grain was changed from 15°C to 40°C.     

Thermal properties and resistant starch content of green banana flour (Musa cavendishii) produced at different drying conditions

The objective of this research was to verify the effect of drying conditions on thermal properties and resistant starch content of green banana flour (Musa cavendishii). The green banana flour is a complex-carbohydrates source, mainly of resistant starch, and quantifying its gelatinization is important to understand how it affects food processing and the functional properties of the flour. The green banana flour was obtained by drying unripe peeled bananas (first stage of ripening) in a dryer tunnel at 52 °C, 55 °C and 58 °C and air velocity at 0.6 m s⁻¹, 1.0 m s⁻¹ and 1.4 m s⁻¹. The results obtained from differential scanning calorimetry (DSC) curves show a single endothermic transition and a flow of maximum heating at peak temperatures from (67.95 ± 0.31) °C to (68.63 ± 0.28) °C. ANOVA shows that only drying temperature influenced significantly (P < 0.05) the gelatinization peak temperature (Tp). Gelatinization enthalpy (ΔH) varied from 9.04 J g⁻¹ to 11.63 J g⁻¹ and no significant difference was observed for either temperature or air velocity. The resistant starch content of the flour produced varied from (40.9 ± 0.4) g/100 g to (58.5 ± 5.4) g/100 g, on dry basis (d. b.), and was influenced by the combination of drying conditions: flour produced at 55 °C/1.4 m s⁻¹ and 55 °C/1.0 m s⁻¹ presented higher content of resistant starch.     

Rheological behaviour of aqueous systems of tragacanth and guar gums with storage time

Rheological properties of aqueous systems of tragacanth and guar gums at nominal concentration of 10 g/L were evaluated as a function of storage time (up to 47 days) under steady (at shear rates ranging from 0.01 to 1000 s⁻¹) and dynamic (at strain of 5% and angular frequency from 0.1 to 100 rad s⁻¹) shear testing conditions, using a controlled stress rheometer, at 25 °C.     

Giant Amazonian fish pirarucu (Arapaima gigas): Its viscera as a source of thermostable trypsin

A trypsin was purified from pyloric caeca of pirarucu (Arapaima gigas). The effect of metal ions and protease inhibitors on its activity and its physicochemical and kinetic properties, as well its N-terminal sequence, were determined. A single band (28.0 kDa) was observed by SDS–PAGE. Optimum pH and temperature were 9.0 and 65 °C, respectively. The enzyme was stable after incubation for 30 min in a wide pH range (6.0–11.5) and at 55 °C. The kinetic parameters K_m, k_cat and k_cat/K_m were 0.47 ± 0.042 mM, 1.33 s⁻¹ and 2.82 s⁻¹ mM⁻¹, respectively, using BApNA as substrate. This activity was shown to be very sensitive to some metal ions, such as Fe²⁺, Hg²⁺, Zn²⁺, Al³⁺, Pb²⁺, and was highly inhibited by trypsin inhibitors. The trypsin N-terminal sequence IVGGYECPRNSVPYQ was found. The features of this alkaline peptidase suggest that it may have potential for industrial applications (e.g. food and detergent industries).     

Water absorption and starch gelatinization in whole rice grain during soaking

Hydration of rough rice grain in hot water as a function of time was studied at temperature range 25-90 °C. A simple model which considers simultaneous unsteady-state water diffusion and first-order irreversible water-starch reaction phenomenon, was used to evaluate the kinetics parameters from experimental curves. The values of the diffusion coefficients and reaction rate constants were between 1.40×10⁻¹¹ and 9.36×10⁻¹¹ m² s⁻¹ and 2.29×10⁻¹⁰ and 3.72×10⁻⁵ s⁻¹, respectively. Both parameters followed a Arrhenius-type equation with distinct activation energies below and above a break temperature of 60 °C. It was 25.4 and 289.3 kJ mol⁻¹ for the activation energies of diffusion and reaction, respectively, below 60 °C. Above this temperature the respective values of the activation energies of diffusion and reaction were 30.0 and 16.6 kJ mol⁻¹. This break temperature was in agreement with the gelatinization temperature determined experimentally.     

Time-independent and time-dependent rheological characterization of vegetable-based infant purees

Flow behavior of vegetable-based infant purees was analyzed at different temperatures (5–65 °C) giving particular attention to their time-dependent properties in a shear rate range (5–200 s⁻¹). Power law model parameters describing flow behavior of samples depended on kind of infant puree, its water content and measurement temperature. Arrhenius model was used to explain temperature effect on apparent viscosity at 50 s⁻¹. Infant purees exhibited thixotropic behavior for all temperatures tested. For the same temperature, differences in hysteresis loop magnitudes were observed among purees, being more noticeable at lower temperatures. Two models were used to describe the time-dependent behavior, namely Weltman model, and second-order structural kinetic model. For all infant purees, the initial shear stress and the extent of thixotropy increased and decreased significantly with increases in shear rate and temperature. The breakdown rate of puree associations also accelerated at higher shear rates, but no trend was observed with temperature.     

Shear rate and cooling modeling for the study of candelilla wax organogels’ rheological properties

The rheological properties evolution, during the organogelation by cooling of candelilla wax (CW) solution in safflower oil, was studied using computational fluid dynamics (CFD). A simulated storage modulus (G′) model agreed satisfactorily with experimental observations. The gelation of 3% CW solutions was done using static conditions during the whole process (90–5 °C), or by applying a shear rate (180, 300 and 600 s⁻¹) during cooling from 90 °C to 52 °C and then continuing the cooling under static conditions up to the final temperature (i.e. 5 °C). The proposed model predicts G′ evolution as a function of temperature, and considers the final torque (Γ_f) of the sheared stage as an inductor of molecular flow alignment. Predictions revealed that the final solid-like component (i.e. G′) increases as the shear rate increases up to a maximum for a shear rate of about 400 s⁻¹. Then, final G′ value diminishes gradually, probably due to the destruction of microstructures that generate the gelation. The model was validated by graphical methods and variance measures. The results demonstrate the potential of CFD to allow the development of a model linking process variables (i.e. cooling and shearing) and rheological properties. This model can be successfully applied for process control purposes and for the design of organogels with predefined properties.     

Energetical and rheological approaches of wheat flour dough mixing with a spiral mixer

Wheat flour dough was mixed in a spiral mixer for different operating conditions, at a speed ranging from 80 to 320 rpm, for a period of 7-15 min. The specific mechanical energy E_s delivered and the dough temperature T_d were continuously recorded and varied from 7 to 82 kJ/kg and T_d of 13.5 to 36 °C, respectively. E_s and T_d were strongly correlated because of viscous dissipation but variations of ingredients initial temperature allowed to uncouple them. The energy balance during mixing process was set through a simple model assuming constant heat transfer (h = 75 W/(m² °C)) which took into account thermal losses. Shear viscosity curves of the dough were determined by correlating volumic power to angular speed; by comparison to typical dough shear flow curve, a constant characteristic of the mixer geometry (K_s = 1.55) was determined like for models of mixer power consumption. The impact of mixing on small deformation rheological properties was assessed by DMA and the variations of the ratio, of maximum (75 °C) to minimum (50 °C) elastic modulus, was interpreted in relation with gluten network development.     

Factors affecting water uptake of rice grain during soaking

The soaking process of rice (raw, dehulled or bran and white) in plain water was investigated between 25°C and 65°C. The corresponding effective diffusion coefficients were evaluated by fitting experimental absorption curves to Fick's second law for diffusion out of sphere. Effective diffusion coefficients for raw, brown and white rice varied between 1.56×10⁻¹¹ and 7.20×10⁻¹¹ m² s⁻¹; 2.22×10⁻¹¹ and 8.82×10⁻¹¹ m² s⁻¹ and 20.5×10⁻¹¹ and 47.0×10⁻¹¹ m² s⁻¹, respectively, for the temperature range investigated. The amount of total solids leached increased with the increase of temperature and time; the highest corresponded to white rice. The rates of absorption of raw rice in aqueous solutions of ClH, CH₃COOH and PO₄H₃ at 25°C were quite similar and much lower than those in plain water at the same temperature. Raw rice soaked in NaOH aqueous solutions and Na₂CO₃ aqueous solutions gave, in terms of the diffusion coefficients, higher absorption rates than raw rice soaked in plain water. Absorption rates for raw rice soaked in NaOH concentrations were higher than those found in Na₂CO₃ concentrations. When raw rice was soaked in NaOH aqueous solution at 55°C the rate of absorption was coincident to that found during soaking of dehulled rice in plain water.