Color degradation kinetics of pineapple puree during thermal processing

Improvement of color, as a quality attribute of processed pineapple puree, has been made possible by the increase in knowledge of kinetic of color change. The kinetics of color degradation of pineapple puree were investigated during heat treatment at 70-110 °C in order to cover the temperature range that used in preheat and sterilization of commercial aseptic pineapple puree. Color changes associated with heat-treated puree were monitored using Hunter colorimeter (L, a, b, total color difference—ΔE) and Browning index (A₄₂₀). The changes in L and b values fitted well to the first-order kinetic model while ΔE, a value, and Browning index followed the zero-order kinetic. The dependence of the rate constant on temperature was represented by an Arrhenius equation. The results suggested that ΔE and lightness, based on activation energy, were the most sensitive measures of color change at temperature range 70-90 and 95-110 °C, respectively.     

Desorption isotherms and thermodynamic properties of sweet corn cultivars (Zea mays L.)

The desorption isotherms and thermodynamic properties of two cultivars of sweet corn were obtained during the drying process of these products. The isotherms were determined by a dynamic method for various temperature and humidity conditions. Equilibrium moisture content (X_eq) data were correlated by the Guggenheim–Anderson–de Boer model and an artificial neural network (ANN) model. These models were fitted to the experimental data. The X_eq for corn grain increased with an increase in the relative humidity at fixed temperature and decreased with an increase in temperature at a constant relative humidity. The experimental data were analysed by a thermodynamic approach to obtain the isosteric heat of desorption (ΔH), differential entropy (ΔS), activation energy (E_a) and Gibbs free energy (ΔG). The ΔH and ΔS increased with a decrease in moisture content, while ΔG decreased exponentially with an increase in X_eq. The Arrhenius equation was used to obtain E_a values, with Supersweet corn having higher E_a.     

Effects of brine concentration and temperature on color of vacuum pulse osmotically dehydrated sardine sheets

The effects of brine concentration (0.15-0.27 g NaCl/g) and temperature (30-38 °C) on the color parameters (L, a, b, ΔE) of vacuum pulse osmotically dehydrated sardine sheets were investigated. The results showed that osmotic dehydration has a significant effect on color of sardine sheets. Redness (a-value) and yellowness (b-value) decreased through dehydration time while lightness (L-value) and total color difference (ΔE) increased. The decreases in redness and yellowness were lesser with increasing temperature and brine concentration while increases in lightness and ΔE were higher. These changes would be predicted by simple models as a function of the temperature, brine concentration, and dehydration time.     

Migration of antimony from PET trays into food simulant and food: determination of Arrhenius parameters and comparison of predicted and measured migration data

Migration experiments with small sheets cut out from ovenable PET trays were performed in two-sided contact with 3% acetic acid as food simulant at various temperatures. The fraction of diffusible antimony (Sb) was estimated to be 62% in the PET sample under study. Apparent diffusion coefficients of Sb in PET trays were determined experimentally. Measurement of migration between 20 and 150°C yielded a linear Arrhenius plot over a wide temperature range from which the activation energy (E _a) of 188?±?36?kJ?mol^?1 and the pre-exponential factor (D ₀) of 3.6?×?10¹⁴?cm²?s^?1 were determined for diffusing Sb species. E _a was similar to previously reported values for PET bottles obtained with a different experimental approach. E _a and D ₀ were applied as model parameters in migration modelling software for predicting the Sb transfer in real food. Ready meals intended for preparation in a baking oven were heated in the PET trays under study and the actual Sb migration into the food phase was measured by isotope dilution ICP-MS. It was shown that the predictive modelling reproduces correctly experimental data.     

A Viscoelastic Model for Honeys Using the Time–Temperature Superposition Principle (TTSP)

The viscoelastic parameters storage modulus (G′) and loss modulus (G″) were measured at different temperatures (5 °C, 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, and 40 °C) using oscillatory thermal analysis in order to obtain a viscoelastic model for honey. The model (a 4th grade polynomial equation) ascertains the applicability of the time–temperature superposition principle (TTSP) to the dynamic viscoelastic properties. This model, with a regression coefficient higher than 0.99, is suitable for all honeys irrespective their botanical origin (monofloral, polyfloral, or honeydew). The activation energy (relaxation“ΔH _a” and retardation “ΔH _b”), and the relaxation modulus fit the model proposed. The relaxation modulus has a 4th grade polynomial equation evolution at all temperatures. The moisture content influences all the rheological parameters.     

Baking of muffins: Kinetics of crust color development and optimal baking time

Baking is a decisive stage in the production of bakery products, in general—muffins, in particular—for most of the quality attributes of the final products depend on it. The aim of this work is to model the kinetics of muffin crust color development during baking and to evaluate the feasibility of this kinetic model to predict the baking times. Surface color is represented by the Browning Index, and the effect of baking temperature (from 140 to 220 °C) and process convective characteristics (natural convection, forced convection, and steam-assisted forced convection) are analyzed. Minimal baking times are calculated from experimental core temperature measurements. The modeling of browning kinetics, which incorporates the optimal crust color determined by sensory analysis, allows the estimation of optimal baking times. For all the tested conditions t _op?>?t _min, assuring a product whose inner structure was already totally baked. Finally, minimal, half, and optimal baking times present an exponential dependence with the oven temperature. Besides, there are no significant differences between both forced convection modes.     

Glass Transition Studies of Baked Tortilla Chips Using Dynamic Mechanical Thermal Analysis

The objectives were to determine the glass transition temperature (T_g) of baked tortilla chips and find a statistical model that represents the change in T_gwith respect to baking conditions. The dynamic mechanical thermal analysis (DMTA) was used to determine the glass transition temperature of samples. TheT_g of samples was in the range of 59 to 76°C with respect to baking temperature and time. The results indicated that the glass transition temperature increased with increasing baking temperature and at longer baking times. TheT_g of samples with longer baking periods increased up to 1.2 times those at smaller baking periods. Statistical analysis showed a linear relationship for T_gvs. baking time and temperature. A statistical model was obtained using a linear regression to describe the change in T_gin terms of baking temperature and time (R²=0.74).     

Color and Texture Change Kinetics in Ripening Bananas

Kinetics of color and texture changes in ripening bananas were investigated as a function of storage temperature (10, 16, 22, 28 °C). Color was evaluated in terms of L, a and b values as well as the total color difference (ΔE) representing the residual deviations from the ripe stage. Puncture force (PF) was used to evaluate the texture properties of banana. The results indicated that the time dependence of L, ΔE and PF values followed a logistic model, while a and b values were well described by a simple zero-order and fraction conversion models, respectively. The Arrhenius equation adequately described the temperature dependence of the reaction rate constants for both color and texture parameters, from which the activation energies and rate constant at reference temperature 15 °C were obtained. There were significant linear correlations between color parameters (L, a, b, ΔE) and texture parameter (PF).     

Rheological behaviour of sago (Metroxylon sagu) starch paste

Rheological behaviour of gelatinized sago starch solution was studied over the shear rate range of 13.61–704 s⁻¹ at various concentration and temperature ranges. A power law equation was used to describe the rheological behaviour of the starch solution, while the effect of temperature was evaluated by the Arrhenius equation. The effect of starch concentration on apparent viscosity was studied using the exponential model describing the relationship between apparent viscosity and concentration. Consistency index (κ) increased with concentration and decreased with the increase of temperature. Flow behaviour indices (η) were within the range of 0.495–0.559 which indicated the pseudoplastic nature of gelatinized sago starch. The amount of starch and shear rate affect activation energy (ΔE). Depending on the shear rate and concentration, activation energy varied from 0.619 to 1.756 kcal mol⁻¹. A mathematical relationship correlating the various parameters (temperature, concentrations, shear rates) was tested for its significance and validity.     

Development and characterization of a prototype of a lactic acid–based time–temperature indicator for monitoring food product quality

Temperature is a crucial factor affecting the quality and safety of food products during both distribution and storage. The difficulty in controlling and monitoring the temperature history of food products makes it difficult to precisely predict shelf life. Time–temperature indicators (TTIs) provide a visual summary of a product’s accumulated chill-chain history, recording the effects of both time and temperature. Attempts have been made to develop a prototype of a time–temperature indicator based on the diffusion of lactic acid, which is temperature-dependent. Four lactic acid-based TTIs were made in different substrate concentrations. Color changes associated with the diffusion of lactic acid were monitored. In the vapor diffusion of lactic acid, an irreversible color change of a chemical chromatic indicator (from green to red) clearly and progressively occurred due to the pH reduction. The temperature dependence of these TTIs kinetics was characterized isothermally in the range of 4–45 °C, yielding activation energy (E_a) of, approximately, 50 kJ mol⁻¹. The mathematical models of each TTI were established according to the relationships between color changes and time and temperature. The differences between the E_a values of the TTIs and the E_a associated with food quality losses – including enzymatic loss, hydrolysis, lipid oxidation, nutrient loss and microbial growth – were less than 40 kJ mol⁻¹, and therefore these TTIs could be considered as good candidates to monitor food quality losses. Although these TTIs do not cover the whole range of food quality losses, they could be applied to show the time–temperature history of some foods, especially fruits and vegetables, and to indicate food quality associated with time–temperature exposure.     

Prediction of freezing time for food products using a neural network

An artificial neural network (ANN) was developed to predict the freezing time of food products of any shape. The Pham model was used to generate freezing time data and to train ANN based on Wardnets. The product thickness (a), width (b), length (c), convective heat transfer coefficient (h_c), thermal conductivity of frozen product (k), product density (ρ), specific heat of unfrozen product (C_pu), moisture content of the product (m), initial product temperature (Ti), and ambient temperature (T_∞) were taken as input variables of the ANN to predict freezing time. The effects of the number of hidden layer nodes, learning rate, momentum on prediction accuracy were analyzed. The performance of the ANN was checked using experimental data. Predicted freezing time using the ANN was proved a simple, convenient and accurate method. Selection of hidden nodes, learning rate and momentum were important to ANN predictions.     

Neriifolin S, a dimeric serine protease from Euphorbia neriifolia Linn.: Purification and biochemical characterisation

A dimeric serine protease Neriifolin S of molecular mass 94 kDa with milk clotting activity has been purified from the latex of Euphorbia neriifolia by anion exchange and size-exclusion chromatography. It hydrolyses peptidyl substrates l-Ala-pNA with highest affinity (K_m of 0.195 mM) and physiological efficiency (K_cat/K_m of 144.5 mM s). Enzyme belongs to the class of neutral proteases with pI value of 6.8, optimal proteolytic activity displayed at pH 9.5 and temperature 45 °C. Its proteolytic activity is strongly stimulated in the presence of Ca⁺² ions and exclusively inhibited by serine protease inhibitors. Enzyme is fairly stable toward chemical denaturants, pH and temperature. The apparent T_m, was found to be 65 °C. Thermal inactivation follow first order kinetics with activation energy (Ea), activation enthalpy (ΔH∗), free energy change (ΔG∗) and entropy (ΔS∗) of 27.54 kJ mol⁻¹, 24.89 kJ mol⁻¹, −82.34 kJ mol⁻¹ and 337.20 J mol⁻¹ K⁻¹.     

Kinetics of Quality Changes of Shrimp (<Emphasis Type="Italic">Litopenaeus setiferus</Emphasis>) During Pasteurization

Effect of cooking between 1 and 80 min at 60 to 100 °C on several quality attributes of whole peeled shrimp (Litopenaeus setiferus) (80–90 counts/kg) was studied using an isothermal heating method. Cook loss, area shrinkage, and hardness of shrimp increased with increasing heating time and temperature, following a fractional first-order kinetic model with activation energies (E _a ) of 71.0, 53.3, and 29.9 kJ/mol, respectively. Cook loss, area shrinkage, and hardness were positively correlated. The toughness of shrimp muscle increased in the initial period of heating, then decreased in the later period during the treatments. The overall color change (ΔE) increased with increasing treatment time and temperature, and followed a zero kinetic model with an E _a of 37.2 kJ/mol. The kinetic parameters obtained from this study can be applied toward understanding and predicting shrimp-quality changes during pasteurization treatments, and further provides insight into the pasteurization conditions required to achieve safe and high-quality shrimp products and potentially other crustacean shellfish and seafood products.     

Kinetic and Thermodynamic of Thermal Inactivation of the Peroxidase,Polyphenoloxidase and Inulinase Activities during Blanching of Yacon (Smallanthus sonchifolius) Juice

The present study evaluated the kinetics and thermodynamic parameters for the thermal inactivation of peroxidase (POD), polyphenoloxidase (PPO) and inulinase (INU) from yacon juice. The yacon juice was acidified with 1 % citric acid prior to blanching at different time-temperature combinations in the range of 0–10 min, and 80–100 °C. All enzymes showed a biphasic kinetic behavior. The velocity constants increased and D values decreased with temperature for both the labile and the heat resistant fractions. The activation energy of the heat-labile (E _aL ) and heat-resistant fractions (E _aR ) were 38.19, 16.05, 30.08 kJ/mol, and 30.65, 71.94, 41.86 kJ/mol for POD, PPO and INU, respectively. Thermodynamic studies indicated a non-spontaneous (ΔG?>?0) and endothermic (positive enthalpy values) process, and the enzyme aggregation step is the rate determining of the reaction (negative entropy values).     

Accelerated shelf-life testing for oxidative rancidity in foods—A review

Accelerated shelf-life test (ASLT) methods for processed foods are receiving greater attention. In this paper, current ASLT methodology for fatty foods is reviewed with particular emphasis on the testing of antioxidant effectiveness.In all the classical ASLT methods temperature is the dominant acceleration factor used. Its effect on the rate of lipid oxidation is best analysed in terms of the overall activation energy, E_A for li?id oxidation. It is an inherent assumption in these tests that the E_A is the same in both the absence and the presence of antioxidants. An analysis of the rate equations for the uninhibited versus the inhibited oxidation indicates, however, that the E_A may be considerably higher in the latter case. ASLT data collected at 60–65°C bear this out and show that such tests lead to sizeable, but predictable, underestimation of the shelf-life extension by antioxidants for room temperature. In comparison, data collected at 98–100°C are much less predictable. At this higher temperature E_A-variations are generally smaller and both under- and overestimation of shelf-life is found. In addition, the use of such high temperatures for complex foods is ruled out because of secondary reactions of other food components.Other acceleration parameters for shelf-life used are the oxygen pressure, reactant contact and the addition of catalysts. The effect of these factors, although much less important than that of temperature, is discussed.     

Colour Changes in Brandy Spirits Induced by Light-Emitting Diode Irradiation and Different Temperature Levels

One aged brandy was subjected to an artificial visible light source from light-emitting diodes (2?×?10³ lx) and under dark conditions. The temperature was also controlled at 25, 35, and 45 °C (±2 °C); the samples were monitored for colour changes; and selected chemical parameters were at 0, 10, 20, 30, and 40 days. Colorimetric indices, CIELab parameters and spectra were also determined with UV–Vis spectrometry. Visible light modified the colour of brandy and an important colour decrease was observed, showing maximum values (ΔE _ab*) at 25 °C, under the studied experimental conditions. On the contrary, at higher temperatures, significant colour degradation was not revealed. Non-colour parameters were not significantly affected by both irradiation and storage temperatures (p?>?0.05). Kinetic parameters including rate constant and activation energy were calculated. Based on Arrhenius model, activation energies of a*, browning index and h _ab* at darkness were 12.2, 55.1, and 21.6 kJ mol^?1 respectively.     

Biochemical and Structural Changes of Taro (Colocasia esculenta) Tubers During Simple Thermal Treatments (Low Temperature) or in Combination with Chemicals

The present study set out to study the structural and biochemical modification of taro (Colocasia esculenta) grown in Cameroon, through simple heating or in association with chemicals. Both techniques are known to inactivate the reactions of polyphenol oxidase. The textural analysis was performed on tubers heated in water, 0.5% NaCl and 1% NaCl solution at various times from 0 to 105?min. The result showed optimum pH and temperature for taro polyphenol oxidase (PPO) activity at pH?6.0 and t?=?40?°C with 10?mM catechol in 0.1?M phosphate buffer as substrate. K _m and V _max values were about 7.317?±?0.012?mM and 0.148?±?0.0003 OD_{430 nm}/minute. Seven inhibitors were tested in this study, and the most effective inhibitors were found to be NaCl, CaCl2 and KCl. Kinetic studies showed that the thermal inactivation of taro PPO followed first-order kinetics, with an activation energy of E _a?=?422.79?±?0.52?kJ/mol. The textural modification of taro tubers during heating follows the kinetic of the fractional model. It was noticed that the activation energy increased with the concentration of NaCl.     

Effect of amylose content on estimated kinetic parameters for a starch viscosity model

The apparent viscosity profile of starches during gelatinization varies with different amylose content. This study focused on the influence of amylose content on the kinetic parameters of a starch viscosity model for corn starches. The five parameters were: gelatinization rate constant (k_g), gelatinization activation energy (E_g), relative increase in apparent viscosity during gelatinization (A^α), relative decrease in apparent viscosity during shearing (B), and viscous activation energy (E_v). The parameters were estimated at different amylose content using both ordinary least squares nonlinear regression and the sequential method. The mixer viscometry approach was used to measure apparent viscosity. The first part of this paper presents parameter estimation results for waxy corn starch. The model was validated by using the parameters to predict viscosity for the same starch in a different measuring system, i.e., the RVA. The second part of this paper presents the estimated parameters for corn starch blends at different amylose content. The following parameters were significantly affected by amylose content: k_g and E_g both decreased with amylose content by an power-law relationship. Activation energy of gelatinization ranged from 121 to 1169 kJ/mol. The other parameters A^α, B, and E_v were not significantly influenced by amylose content. In summary, the gelatinization parameters k_g and E_g dramatically decreased as amylose increased from 3% to 35% (waxy corn starch blends).     

A NUMERICAL APPROACH WITH VARIABLE TEMPERATURE BOUNDARY CONDITIONS TO DETERMINE THE EFFECTIVE HEAT TRANSFER COEFFICIENT VALUES DURING BAKING OF COOKIES

The increasing trade of ready‐to‐eat foods such as cookies highlights an interest in quality defects during baking. Heat (h and thermal diffusivity) and mass (mass transfer and diffusion coefficients) transfer parameters are significant parameters affecting the quality changes. Therefore, it is important to determine these parameters for modeling and process optimization studies. Among these, the h is important, revealing the relationship between the heating medium and product surface. As baking involves a simultaneous heat and mass transfer involving moisture diffusion and heat conduction inside and convective heat and mass transfer outside, a lumped system method may not be an accurate choice to determine the h value. Changes in the product volume and contact heating from bottom of the product also bring extra challenges to the determination of h. Therefore, the objective of this study was to use realistic approaches including simultaneous heat and mass transfer to determine the changes in h. The h_effvalues for the bottom and top surface of the cookies were then determined, applying a numerical procedure where the surface temperature changes were the boundary conditions with evaporation on the surface. The h_band h_t values increased with baking temperature and varied with baking time. The results of this study showed that evaporative mass flux for the top surface, heat flux for the bottom surface and the product's volume changes were significant in the variation of h values.     

Freshness assessment of gilthead sea bream (Sparus aurata) by machine vision based on gill and eye color changes

The fish freshness was evaluated using machine vision technique through color changes of eyes and gills of farmed and wild gilthead sea bream (Sparus aurata), being employed lightness (L^*), redness (a^*), yellowness (b^*), chroma (c^*), and total color difference (ΔE) parameters during fish ice storage. A digital color imaging system, calibrated to provide accurate CIELAB color measurements, was employed to record the visual characteristics of eyes and gills. The region of interest was automatically selected using a computer program developed in MATLAB software. L^*, b^*, and ΔE of eyes increased with storage time, while c^* decreased. The a^* parameter of fish eyes did not show clear a trend with storage time. The L^*, b^*, and ΔE of fish gills increased with storage time, but a^* and c^* decreased. Regression analysis and artificial neural networks approaches were used to correlate the eyes and gills color parameters with the time of storage and a strong correlation was found between color parameters and storage day. Gills color changes were more precise than those found for eyes in order to evaluate the fish freshness. However, the gills cover should be removed for taking the images and thus, the method is destructive and time-consuming. Therefore, the color parameters of fish eyes can be used as a green, low cost and easy method for fast and on-line assessing of fish freshness in food industry.