The impact of high-temperature, short-time thermal treatment on texture and weight loss of green asparagus

 The kinetics of the degradation of texture and loss of weight of green asparagus heated to between 100 and 130 °C was studied. The texture of the asparagus was evaluated with two types of cells fitted to a universal texturometer: one cell measured resistance to cutting with a wire and the other was a Kramer cell. The two methods enabled distinction between the different thermal treatments, although the Kramer cell gave information about the behaviour of parts of the spear further away from the tip. The thermally induced degradation of the texture and loss of weight followed first-order kinetics. With respect to the texture, the parameters obtained with the wire cell 2.5, 5 and 7.5 cm from the tip were activation energy (E _a)=19, 20 and 23 kcal/mol, respectively, and those obtained with the Kramer cell were E _a=18.3, 20.9 and 24 kcal/mol, depending on the section of asparagus investigated. For loss of weight an E _a of 8.9 kcal/mol was obtained; thus, it is an important quality factor to be taken into account when optimizing the process of canning green asparagus. Received: 7 November 1996     

The impact of high-temperature, short-time thermal treatment on texture and weight loss of green asparagus

 The kinetics of the degradation of texture and loss of weight of green asparagus heated to between 100 and 130 °C was studied. The texture of the asparagus was evaluated with two types of cells fitted to a universal texturometer: one cell measured resistance to cutting with a wire and the other was a Kramer cell. The two methods enabled distinction between the different thermal treatments, although the Kramer cell gave information about the behaviour of parts of the spear further away from the tip. The thermally induced degradation of the texture and loss of weight followed first-order kinetics. With respect to the texture, the parameters obtained with the wire cell 2.5, 5 and 7.5 cm from the tip were activation energy (E _a)=19, 20 and 23 kcal/mol, respectively, and those obtained with the Kramer cell were E _a=18.3, 20.9 and 24 kcal/mol, depending on the section of asparagus investigated. For loss of weight an E _a of 8.9 kcal/mol was obtained; thus, it is an important quality factor to be taken into account when optimizing the process of canning green asparagus. Received: 7 November 1996     

The effects of fermentation on the thermostability of the yellow-orange pigments extracted from cactus pear (Opuntia ficus-indica)

 Cactus pear (Opuntia ficus-indica) juice with a total soluble solids content of 15.94 °Brix was fermented using the wine yeast Saccharomyces cerevisiae. A 94.54% conversion of fermentable sugar was achieved with an ethanol production of 55.3 ml/l. The pigment degradation was found to be 17% at the end of the time allowed for fermentation. However, the fermentation had actually ceased due to depletion of fermentable sugars after 12 h, a point at which only 9.4% pigment degradation was observed and there was no further total soluble solids degradation. The thermal stability of the yellow-orange pigment of the fermented juice was determined as a function of temperature at pH 5.0. The kinetic experiments were carried out at three different temperatures, 50, 70 and 90  °C. For a pseudo-first order thermal degradation rate the reaction rate constants were determined to be 0.0066, 0.0206 and 0.1244 min^–1 for temperatures of 50, 75 and 90  °C, respectively. The activation energy was calculated as 15.71 kcal mole^–1. The fermentation process did not affect the thermostability of the pigment extract. Received: 10 January 2000 / Revised version: 31 March 2000     

Engineering Properties of Edible Transglutaminase Cross-Linked Caseinate-Based Films

In this work, the effect of the weight ratio (Y _E/C) between transglutaminase (TGase) and sodium caseinate on the main engineering properties and microstructure of maltodextrin/caseinate/glycerol-based films, as well as cross-linking kinetics of the corresponding film-forming mixtures, was assessed. In the absence of TGase, the film forming solution did not jelly at all even after a 20-h gel cure experiment at 30 °C. As Y _E/C was increased from 0.5 to 8.3 mg/g, the gel point time exhibited quite a hyperbolic dependence on Y _E/C, whereas the pseudo-first order reversible kinetic constant rate of casein reticulation linearly increased with the enzyme concentration. Despite a certain data scattering, the initial and equilibrium complex shear moduli appeared to be practically constant and independent of Y _E/C. This finding was also extended to the mechanical and water barrier properties of the films under study. This was also indirectly confirmed by scanning electron microscopy, the film structure being quite compact, dense, and about free of air bubbles. In particular, their complex tensile modulus (E*) resulted to be not only independent of the cross-linking agent dosage but also interconvertible with the elastic modulus (E) determined in the quasi-static mode at an initial strain rate equal to the angular frequency. The water vapor permeability (WVP) for all the films examined was found to be extremely dependent on the water, desiccant, or Permatran-W standard methods used as well as on the difference in water activity (a _W) at the inside (a _Wi = 1.0 or 0) and outside (a _Woi = 0 or ∼0.5) of the test cup. By maintaining a _Wi = 0 and a _Woi = 0.5, the Permatran-W method yielded practically constant WVP values (30 ± 4 pg m⁻¹ s⁻¹ Pa⁻¹) whatever the enzyme/caseinate ratio used. Nevertheless, TGase appeared to decrease the water vapor permeability of not cross-linked maltodextrin–caseinate films.     

Influence of ultrasound on mass transport during cheese brining

 The effect of ultrasound on mass transfer during cheese brining has been investigated. The rate of water removal and NaCl gain increased when ultrasound was applied in comparison with brining performed under static or dynamic conditions, suggesting that ultrasound improves both external and internal mass transfer. A simple diffusional model was developed to simulate mass transport during acoustic brining. Model parameters were estimated using experimental data from acoustic brining experiments carried out on cheese cylinders of 1.7×10^–2m radius and 3×10^–2 m height at different temperatures (5, 15 and 20  °C). Effective water (D _W) and NaCl (D _S) diffusivities estimated using the proposed model ranged from 5.0×10^–10m²/s and 8.0×10^–10 m²/s at 5  °C to 1.3×10^–9m²/s and 1.2×10^–9 m²/s at 20  °C. Both D _W and D _S varied with temperature according to the Arrhenius equation. Through the proposed model, water losses and NaCl gains of the experiments used in the parameter identification were accurately simulated (average %var=98.2%) and also of two additional acoustic experiments carried out under different conditions of temperature (10  °C) and sample size and geometry [parallelepiped of (6×2.5×1.25)×10^–2 m] to those used in the parameter identification (average %var=98.4%). Received: 22 September 1998 / Revised version: 20 November 1998     

Response surfaces for solubility of crude soylecithin lipid in super critical carbon dioxide

 The solubility of soy lecithin lipids in supercritical CO₂ was measured at pressures of 120, 200 and 280 bar and at temperatures of 40, 50 and 60  °C. The effects of temperature and pressure on the solubility of total lipids were studied by response surface methodology. The response surface equation to predict the solubility of total lipids in the above range of pressure and temperature is: Y=–3.237+0.0431* P–7.3×10^–5 P ²–0.00011 P*T where Y is the total lipid solubility in g/kg CO₂, P is the pressure in bar and T is the temperature in   °C. The total lipids solubility increased with pressure at constant temperature, but decreased with increasing temperature. The total lipids consisted of a very small phospholipid content compared to neutral lipids and glycolipids at all the pressures and temperatures studied. Optimum search indicated a maximum solubility of total lipids of 1.829 g/kg CO₂ at 263 bar and 40  °C. Received: 1 April 1999     

Ascorbic acid degradation kinetics in mushrooms in a high-temperature short-time process controlled by a thermoresistometer

The degradation of ascorbic acid was studied in mushrooms heated at temperatures between 110 and 140°C, high-temperature short-time conditions, in a five-channel computer-controlled thermoresistometer. The kinetics parameters were calculated on the assumption that there are 2 degradation mechanisms, one aerobic (during the first few seconds of the process) and the other anaerobic. The 2 stages followed first-order reaction kinetics, with E_a=46.36 kJ/mol for aerobic degradation and E_a=49.57 kJ/mol for anaerobic degradation.     

Kinetics of Crude Peroxidase Inactivation and Color Changes of Thermally Treated Seedless Guava (Psidium guajava L.)

Thermal treatment of seedless guava (Psidium guajava L.) cubes was carried out in the temperature range of 80–95 °C. The kinetics of peroxidase inactivation and color changes due to thermal treatments were determined. Peroxidase inactivation followed a first-order kinetic model, where the activation energy was 96.39 ± 4 kJ mol⁻¹. Color was quantified in terms of L, a, and b values in the Hunter system. The color changes during processing were described by a first-order kinetic model, except total color difference which followed a zero-order kinetic model. The temperature dependence of the degradation followed the Arrhenius relation. The activation energies (E _a) for L, a, b, and total color difference (ΔE) were 122.68 ± 3, 88.47 ± 5, 104.86 ± 5, and 112.65 ± 5 kJ mol⁻¹, respectively. The results of this work are a good tool to further optimize seedless guava thermal treatment conditions.     

Modelling the Dynamic Inactivation of the Probiotic Bacterium <Emphasis Type="Italic">L. Paracasei</Emphasis> ssp. <Emphasis Type="Italic">Paracasei</Emphasis> During a Low-Temperature Drying Process Based on Stationary Data in Concentrated Systems

In order to better understand inactivation of cells during a drying process, the inactivation kinetics of concentrated Lactobacillus paracasei ssp. paracasei (F19) was measured under stationary conditions for different combinations of water activities and temperatures in a water activity range of a _w = 0.23–a _w = 0.75 and temperatures between 4°C and 50°C. It was shown that the inactivation kinetics of the probiotic bacterium L. paracasei at moderate temperatures could, for all conditions, be formally described by a first-order reaction with activation energies that are much lower than for thermal inactivation (E _a = 61 kJ/mol). With regard to the water activity, the reaction rate constants exhibit a maximum inactivation rate at intermediate water activity a _w = 0.52. As this behavior has direct implications for the stability of cells in a drying process, the stationary data were used to model the inactivation during test vacuum drying processes, where both temperature and water activity dynamically change. It is shown that—depending on the drying rate—dynamic effects have to be taken into account when modeling the survival during drying. Nevertheless, the model based on stationary inactivation data is capable to predict the characteristics of inactivation during a drying process. Therefore, it can serve as basis to optimize the drying process with regard to maximum survival of cells. However, a further refinement of the model with regard to the drying rate is necessary.     

Kinetics of thermal degradation of vitamin C in marula fruit (Sclerocarya birrea subsp. caffra) as compared to other selected tropical fruits

The kinetics of the thermal degradation of vitamin C of marula, mango and guava pulp at different heat treatments at temperature ranging from 80 to 150 °C were investigated. For temperatures lower than 125 °C, the ascorbic acid in marula pulp was about 15 fold more stable to heat than the ascorbic acid in mango and guava pulp. The results showed that a simple first order degradation model could not describe the vitamin C degradation as biphasic behaviour was observed. Therefore the model was transformed in a two-fraction model in which the vitamin C content is divided in relatively stable and instable fractions. Marula had a low k_d1,100°C of 7.2 × 10^?3 min^?1 compared to k_d1,100°C of 1.2 × 10^?1 min^?1 for guava and 1.3 × 10^?1 min^?1 for mango. Guava had the highest activation energy, E_a of 58 kJ/mol, followed by mango with 39 kJ/mol and then marula with 29 kJ/mol.     

Kinetic Parameter Estimation in Conduction Heating Foods Subjected to Dynamic Thermal Treatments

The purpose of this work was to develop a means for determining product and process specific thermal kinetic parameters of constituents in foods that do not heat uniformly. The concept of the method of Paired Equivalent Isothermal Exposures (PEIE) was developed for such products. The ability of the PEIE to define Arrhenius parameters from simulated retort experiments was demonstrated. The PEIE was applied to survival data from retort experiments of canned pea puree inoculated with Bacillus stearothermophilus spores (NCA 1518). Mean activation energy and reaction rate constant (at 121.1°C) of the spores in retort processed canned pea puree were E_a= 250 (± 15) kJ/mol and k_121.1°C= 0.26 (0.23 < k_121.1°C <0.30) min^?1, respectively.     

Degradation Kinetics of Colour and Total Carotenoids in Jackfruit (Artocarpus heterophyllus) Bulb Slices During Hot Air Drying

The kinetics of colour and carotenoids degradation in jackfruit bulb slices was evaluated during hot air drying at 50, 60 and 70 °C. Visual colour as well as total carotenoids (TC) content was found to be influenced by the drying process. Tri-stimulus colour parameters such as Hunter L and b values decreased and a value increased during drying. The combination of Hunter L × b value was found to represent the colour change adequately. Degradation of TC and visual colour in terms of Hunter L × b value followed first-order reaction kinetics; however, zero-order reaction kinetics was found adequate to describe changes in total colour difference (TCD) and non-enzymatic browning (NEB). Dependence of the rate constant followed the Arrhenius relationship. The process activation energies (E _a) for Hunter L × b value, TCD, NEB and TC were 29.96, 27.21, 27.48 and 55.61 kJ/mol, respectively. Higher E _a for TC content indicated greater temperature sensitivity as compared with other colour parameters. Relationship of TC content and Hunter L × b value was found to be more consistent through regression analysis with R ² ≥ 0.979.     

Determination of Rheological Behavior,Emulsion Stability,Color, and Sensory of Sesame Pastes (Tahin) Blended with Pine Honey

In this research, rheological properties of blends of pine honey (3%, 6%, and 9%) with sesame pastes (tahin) produced from hulled roasted sesame seeds, called simply tahin, and from unhulled roasted sesame seeds, so-called Bozkir tahin, were determined at temperatures ranging from 10°C to 60°C and at speeds ranging from 0.5 to 100 rpm. Tahin and Bozkir tahin blends with pine honey were found to exhibit non-Newtonian, pseudoplastic behavior at all temperatures. Apparent viscosities versus speed data were successfully fitted to the power law model. The flow behavior index, n, varied in the range of 0.4226–0.6228 for the tahin–pine honey blends, and in the range of 0.4661 to −0.7266 for the Bozkir tahin–pine honey blends. The consistency index, K, was in the range of 9.34–36.42 Pa·sⁿ for tahin–honey blends, and in the range of 9.92–37.53 Pa·sⁿ for Bozkir tahin–honey blends. The consistency index (K) increased with increasing honey levels in both tahin types. According to statistical analysis, the exponential model was a better model to describe the effect of the soluble solids on the viscosity of tahin samples represented by the pine honey percentage. The emulsion stability of both tahin types improved with the addition of pine honey. It was also correlated with activation energy (E _a), Arrhenius constant, some sensory properties such as spreadibility, firmness and overall acceptance, and color parameters such as the C and h. Temperature sensitivity of the consistency index was assessed by applying an Arrhenius type equation, and E _a value appeared in the range of 7.61–10.05 kJ/mol for tahin–honey blends and in the range of 9.02–10.50 kJ/mol for Bozkir tahin–honey blends.     

Optimization of stepwise blanching of frozen-thawed potato tissues (cv. Monalisa)

 Response surface methodology was used to compare the effect of temperature and time of the first step of blanching on compression, shear, tension and stress-relaxation parameters of frozen-thawed potato tissues. A central, composite rotatable design was used to study the effects of variation in levels of temperature (52.93–67.07  °C) and time (15.86–44.14 min) on rheological parameters. Blanching temperature was the most important factor affecting the mechanical properties tested. The models fitted for the apparent modulus of elasticity in compression, maximum tension force, and relaxed force in the first cycle (F _r1); all had R ²>0.85 (P≤0.01) and were used for doing predictions. Optimum conditions were with in the ranges of temperature (60–65  °C) and time (25–35 min) used for each factor. In the experimental verification of the models at 65  °C during 30 min, the lowest percentage residual between experimental and predicted values was obtained for F _r1 (0.644), which was therefore the most appropiate parameter for detecting the firming effect that the pectinesterase activity produced on frozen potato tissues as a consequence of stepwise blanching under these conditions. Received: 3 February 1999 / Revised version: 12 April 1999     

Thermal inactivation kinetics of peroxidase and lipoxygenase from fresh pinto beans (Phaseolus vulgaris)

 Thermal inactivation kinetics of crude peroxidase (POX) and lipoxygenase (LOX) in fresh pinto beans were studied over the temperature range of 55–90°C. The inactivation of both enzymes followed first-order kinetics. The biphasic inactivation curves for POX indicate the existence of several isoenzymes of varying heat stability. In the temperature range of 55–70°C, the activation energies (E _a) of POX were 46.5 kcal·mol^–1 for the heat-labile portion and 37.6 kcal·mol^–1 for the heat-stable portion. On the other hand, the LOX enzyme had an E _a value of 42.26 kcal·mol^–1 at 55–75°C and 49.1 kcal·mol^–1 at 55–90°C. Received: 28 July 1997 / Revised version: 16 October 1997     

Thermal inactivation kinetics of peroxidase and lipoxygenase from fresh pinto beans (Phaseolus vulgaris)

 Thermal inactivation kinetics of crude peroxidase (POX) and lipoxygenase (LOX) in fresh pinto beans were studied over the temperature range of 55–90°C. The inactivation of both enzymes followed first-order kinetics. The biphasic inactivation curves for POX indicate the existence of several isoenzymes of varying heat stability. In the temperature range of 55–70°C, the activation energies (E _a) of POX were 46.5 kcal·mol^–1 for the heat-labile portion and 37.6 kcal·mol^–1 for the heat-stable portion. On the other hand, the LOX enzyme had an E _a value of 42.26 kcal·mol^–1 at 55–75°C and 49.1 kcal·mol^–1 at 55–90°C. Received: 28 July 1997 / Revised version: 16 October 1997     

Viscometric Behavior of Reconstituted Tomato Concentrate

The rheological properties of tomato concentrates produced by hot and cold break have been extensively studied by many authors. Only a few studies, however, focus specifically with the rheology of reconstituted concentrates from tomato powders. In this study, the rheological properties of reconstituted tomato concentrate from lyophilized freeze-dried tomato juice were evaluated using rotational viscometer at temperatures 20 °C, 30 °C, 40 °C, 50 °C, and 60 °C and at concentrations of 9.7%, 12.9%, 20.5%, and 26.8% total soluble solids. Using power law model, both flow behavior index (n) and consistency coefficient (k) were determined. The calculated values of flow behavior index (n) were less than unity (0.03–0.28) at all temperatures and concentrations indicating the shear-thinning characteristic of the concentrate. The effect of temperature and concentration on the consistency coefficient (k) was studied. Positive correlation between k in the range of 1.57 and 38.33 Pa s ⁿ and inverse absolute temperature (1/T) has been shown by Arrhenius model. Additionally, linear correlation between consistency coefficient (k) and concentration (C) was determined. The activation energies were found in the range of 3.63 and 7.36 kJ/mol K depending on concentration. The results of this study might be useful to improve the design of processing operations dealing with tomato powder reconstitution.     

Mass Transfer Coefficients for the Drying of Pumpkin (Cucurbita moschata) and Dried Product Quality

The aim of this work was to determine the mass transfer properties of pumpkin (Cucurbita moschata) exposed to air drying. The drying temperatures tested ranged between 30°C and 70°C, and the kinetic behavior was studied in this temperature band. The samples were analyzed in terms of moisture content, acidity, proteins, lipids, and crude fiber, both in the fresh state and after drying. From the chemical analyses made, it was possible to conclude that drying induces some reductions in acidity, lipids, fibers, and proteins. As to the influence of the drying temperature on the process, it was observed that a temperature rise from 30°C to 70°C led to a 70% saving in drying time. The results obtained by fitting the experimental data to the kinetic models tested allowed concluding that the best model for the present case is Henderson–Pabis, and the worst is Vega–Lemus. Furthermore, in this work, it was possible to determine the values of the diffusion coefficient at an infinite temperature, D _e⁰, and activation energy for moisture diffusion, E _d, which were, respectively, 0.0039 m²/s and 32.26 kJ/mol. Similarly, the values of the Arrhenius constant and the activation energy for convective mass transfer, respectively, h _m⁰ and E _c, were also calculated, the first being 3.798 × 10⁸ m/s and the latter 86.25 kJ/mol. These results indicate that the activation energy for convective mass transfer is higher than that for mass diffusion.     

Thermal Degradation Kinetics of Chlorophyll in Pureed Coriander Leaves

Coriander leaves are widely used in cooking throughout the world. Thermal degradation kinetics of chlorophyll a, b, and total chlorophyll in coriander leaf puree was investigated at varying levels of pH (4.5–8.5) and processing temperature (80–145°C). Coriander puree at pH 4.5 was processed at 80° to 100°C, whereas that at pH 5.5 to 8.5 was processed at 105° to 145°C. Chlorophyll degradation followed first-order reaction kinetics. Good agreement was found between estimated and experimental chlorophyll retention in all cases (R ² > 0.80). Activation energies ranged from 6.57 to 96.00 kJ/mol. Reaction rate and activation energy data indicated that chlorophylls were more stable at alkaline pH. Transition state theory was applied to estimate the enthalpy, entropy, and Gibbs free energy of activation. Enthalpy of activation (ΔH ^#) ranged from 3.46 to 91.99 kJ/mol, whereas entropy of activation (ΔS^#) ranged from −0.265 to −0.047 kJ/(mol K). The overall free energy change was 107.55 kJ/mol. Results indicated that, the compensation effect did not exist for chlorophyll degradation in coriander puree during thermal processing.     

Kinetics Modeling of Mass Transfer Using Peleg’s Equation During Osmotic Dehydration of Seedless Guava (<Emphasis Type="Italic">Psidium guajava</Emphasis> L.): Effect of Process Parameters

Peleg’s equation was used to study the effect of process parameters on kinetics of mass transfer in terms of solids gain and water loss during osmotic dehydration using 30–50% (w/w) sucrose solution at 30, 40 and 50 °C. The experimental data were successfully fitted employing Peleg’s equation with the coefficient of determination (R ²) higher than 0.88, the root mean square error, and the mean relative percentage deviation modulus (E) of less than 0.003% and 6.40% for all treatments, respectively. In all cases, initial mass transfer rate parameter (K ₁) decreased significantly (p < 0.05) as the solution concentration and solution temperature increased suggesting a corresponding increase in the initial mass transfer rate. Initial mass transfer rate followed an Arrhenius relationship which showed that solids gain had the highest temperature sensitivity (E _a = 21.93–33.84 kJ mol⁻¹) during osmotic dehydration. Equilibrium mass transfer parameter (K ₂) decreased significantly (p < 0.05) as solution concentration increased demonstrating that the equilibrium solid and water contents increased with increase in solution concentration. The equilibrium solid and water contents were also estimated adequately using Peleg’s equation (R ² > 0.78). The results of this work allow estimating the kinetics of mass transfer during osmotic dehydration in order to obtain products with determined solid and water contents.