Kinetics Of Color Changes Research Articles

Enhancement of heat transfer and product quality using jet reattachment nozzles in drying of food products

In this paper, the drying characteristics of Radial Jet Reattachment (RJR) and Slot Jet Reattachment (SJR) nozzles, with an exit angle of +45∘ for the RJR nozzle and +20∘ and +45∘ for the SJR nozzle, were experimentally investigated in drying potato chip samples and apple slices, respectively. Dry basis moisture content of the samples using these innovative nozzles were compared to those of traditional nozzles, based on three criteria: identical air mass flow rate, identical fluid flow power, and identical exerted peak surface pressure. To appraise the performance of each nozzle, the corresponding local heat transfer coefficients generated by innovative and traditional nozzles for all the tests were measured. Subsequently, the average heat transfer coefficients of reattachment nozzles were calculated and compared against those of traditional nozzles. Moreover, the kinetics of color changes and structure analysis of apple slices, due to the drying by SJ and SJR + 20∘ nozzles were studied. The experimental results revealed that the RJR + 45∘ and SJR + 20∘ nozzles yield significantly higher drying rates, as well as significant improvement in average heat transfer coefficients, compared to those of ILJ and SJ nozzles, respectively, on a stationary basis. Besides, impingement drying with SJR + 20∘ nozzle produced dried apple slices with less color deterioration and fewer nutritional losses compared to drying with the SJ nozzle. Therefore, jet reattachment nozzles can provide faster drying rates and keep the nutritional values at a desirable level.

Comparative analyses of three pretreatments on color of kiwifruits during hot air drying

Color is one of the most important quality attributes for agricultural products due to its great influence on consumers’ appetite. Effects of pretreatments, including blanching with hot water, osmosis with sucrose solution, and soaking with ascorbic acid solution on the color of kiwifruit slices were investigated during hot air drying, and three models (i.e. zero-order, first-order and Weibull models) were used to describe the color change kinetics of soaking samples. The results illustrated that color parameters (L*, a* and b*) of dried kiwifruit slices were improved significantly by immersing in sucrose solution or ascorbic acid solution before drying, whereas immersing in hot water for long time led to severe color deterioration. For un-pretreated samples, the Weibull model was the best to describe change kinetics of L* and a* values with R2 =0.974 and 0.996, respectively, while the zero-order model was best for the changes of ΔE value (R2 =0.996). For samples immersed in 1% ascorbic acid solution for 15 min, change kinetics of L* and ΔE values were best fitted to zero-order models with R2 =0.988 and 0.972, respectively. ΔE of dried samples without pretreatment was 12.55, but decreased by approximately 16.33% when samples soaked in 1% ascorbic acid solution for 15 min before drying. Keywords: color, computer vision system, kinetic model, ascorbic acid, sucrose DOI: 10.25165/j.ijabe.20201302.5489 Citation: Xu R Z, Zhou X, Wang S J. Comparative analyses of three pretreatments on color of kiwifruits during hot air drying. Int J Agric & Biol Eng, 2020; 13(2): 228–234.

Drying characteristics and kinetics of colour change and degradation of phytocomponents and antioxidant activity during convective drying of deseeded Terminalia chebula fruit

Terminalia chebula Retizus fruit contains phytochemicals like phenols including flavonoids which are responsible for hypocholesterolaemic, anti-inflammatory, anti-allergic, antimicrobial, antioxidative properties. In the present study the effect of drying temperatures (40–80 °C) on drying kinetics during convective drying of deseeded T. chebula fruit was investigated. The data from the drying experiments were fitted into seven different drying models and the best model was selected by comparing the coefficient of determination (R2) and root mean square error (RMSE). Degradation kinetics for vitamin C, antioxidant activity (DPPH radical scavenging activity), total phenol content (TPC) and total flavonoid content (TFC) was evaluated at 60, 70 and 80 °C. Change in colour at these temperatures were also observed. From the results it was found that an increase in the temperature increased the drying rate and the drying time was reduced, and the mathematical model for drying which best fitted the experimental data was ‘Approximation of diffusion’ model. The degradation of the phytochemicals and change in colour followed the first order kinetics. The rate at which vitamin C degraded was found to be higher than the other components for all temperatures. The rate of change in total colour difference (ΔE*) decreased with increasing temperature.

Effect of drying temperature on color and desorption characteristics of oyster mushroom

Oyster mushroom (Pleurotus ostreatus) slices were dried in a hot air dryer at three temperatures (45, 55 and 65 °C). The sorption isotherm of dried samples in the water activity (aw) range of 0.556-0.970 was also determined at three temperature levels. Moisture desorption isotherms were obtained from changes in water activities of oyster mushroom slices during drying, and the fitness of GAB, BET, Oswin, Henderson and Halsey isotherm equations to sorption data was calculated. The effect of temperature on color change kinetics of oyster mushroom slices was also investigated during drying. GAB model was the best equation for the prediction of the desorption moisture content of samples. Mathematical modeling of color change kinetics indicated that both zero and first order kinetic models were adequate to describe the browning index (BI) value; however, total color change (ΔE) followed zero-order kinetics. The values of the reaction rate constant, found after the drying at 45, 55 and 65 °C, of the ΔE value were respectively 0.058, 0.065 and 0.089.

A Bio-Electrochemical Calculation Model for Color Decline Kinetics of Bruised “Shine Muscat” Fruit During Storage

Physical damage of fruits and vegetables during distribution accelerate their decline in quality during storage. This study was aimed to analyze the quality degradation that takes injuries into consideration by using estimation models. Estimation models for bruised “Shine Muscat” grapes during storage were investigated based on bio-electrochemical theory. An electrical indicator, LTO, defined as the length from the origin of the coordinate at the top of the circular arc of the Cole−Cole plot, was demonstrated to effectively quantify the degree of a bruise with high accuracy (r2 > 99). The color-change kinetics constant increased as LTO decreased, and a strong correlation was confirmed between these two parameters (p < 0.01). These results demonstrate that the LTO parameter can be used to characterize physical damage incurred by the fruit, and it may be used as an injury parameter to calculate their color-change kinetics constant during storage after physical damage.

Kinetics of colour and texture changes of button mushrooms (Agaricus bisporus) coated with chitosan during storage at low temperature.

Kinetics of color and texture changes in coated button mushrooms were investigated as a function of coating agent's rate (1%, 2% and 3% w/v chitosan). The inner and outer surface colours of mushrooms in terms of CIELAB parameters L*, a*, b*, C*, ° h, ∆E, and Browning Index (BI), and their textural properties in terms of firmness were evaluated. The color values on both sides of the mushrooms except for L* values increased and their firmness decreased with the coating treatment. The color changes of the inner and outer surface of mushrooms and their texture changes followed zero-order reaction models with higher R2 (0.9987-0.9999) and lower RMSE (4.8448 x 10-5-1.6690) and χ2 values (3.9120 x 10-9-4.6425). The 2% chitosan solution was determined to be the most effective coating agent among the coating agents used to extend the post-harvest shelf life by optimally preserving the color parameters of the mushrooms together with their texture properties.

Comparative analyses of three pretreatments on color of kiwifruits during hot air drying

Color is one of the most important quality attributes for agricultural products due to its great influence on consumers’ appetite. Effects of pretreatments, including blanching with hot water, osmosis with sucrose solution, and soaking with ascorbic acid solution on the color of kiwifruit slices were investigated during hot air drying, and three models (i.e. zero-order, first-order and Weibull models) were used to describe the color change kinetics of soaking samples. The results illustrated that color parameters (L*, a* and b*) of dried kiwifruit slices were improved significantly by immersing in sucrose solution or ascorbic acid solution before drying, whereas immersing in hot water for long time led to severe color deterioration. For un-pretreated samples, the Weibull model was the best to describe change kinetics of L* and a* values with R2 =0.974 and 0.996, respectively, while the zero-order model was best for the changes of ΔE value (R2 =0.996). For samples immersed in 1% ascorbic acid solution for 15 min, change kinetics of L* and ΔE values were best fitted to zero-order models with R2 =0.988 and 0.972, respectively. ΔE of dried samples without pretreatment was 12.55, but decreased by approximately 16.33% when samples soaked in 1% ascorbic acid solution for 15 min before drying. Keywords: color, computer vision system, kinetic model, ascorbic acid, sucrose DOI: 10.25165/j.ijabe.20201302.5489 Citation: Xu R Z, Zhou X, Wang S J. Comparative analyses of three pretreatments on color of kiwifruits during hot air drying. Int J Agric & Biol Eng, 2020; 13(2): 228–234.

Kinetics of nutrient change and color retention during low‐temperature microwave‐assisted drying of bitter melon ( Momordica charantia L.)

The changes in nutrient (phenolics and vitamin C) and color of bitter melon slices, during microwave-assisted drying (MWAD) at different microwave power values (1.5, 3.0, and 4.5 W/g) and air temperatures (20, 25, and 30°C) are reported. Fits of the experimental data to a semi-empirical mathematical model were used to determine the half-lives of the nutrients. Color change during drying was similarly characterized using CIELAB color space parameters. The rates of nutrient degradation and color change increased with an increase in microwave power, and drying temperature, but the drying times decreased significantly. The total electrical energy consumed under various drying conditions was measured. Although a microwave power of 1.5 W/g and an air temperature of 25°C resulted in the highest levels of nutrient retention, the drying time and process energy consumption were relatively high. In comparison, the drying conditions of 4.5 W/g and 30°C provided an acceptable compromise. Practical applications Low-temperature MWAD is a promising alternative to conventional drying for food that contains temperature-sensitive nutrients. This article provides a methodology for analyzing the kinetics of nutrient and color change during a MWAD process. A 32 factorial design was used to derive predictive correlations for drying time, nutrient half-life, time constants characterizing color change, and electrical energy consumed during the drying process. The relative influences of microwave power and drying temperature could be readily discerned using these correlations. The reported study will help in developing and optimizing microwave drying processes for a variety of food products.

The kinetics of colour degradation, chlorophylls and xanthophylls loss in pistachio nuts during roasting process

Abstract Objectives Colour is amongst the parameter which is used for process control during roasting. Materials and Methods In this study, the effects of hot air roasting temperature (120, 130, 145, 160, and 170°C) and hot air velocity (0.6, 1.3, and 2 m/s) on colour change kinetics of pistachio nuts were investigated by employing image analysis and simultaneously chlorophylls and xanthophylls (lutein and β-carotenoid) concentration were determined by spectrophotometric measurement method. Results We found that roasting temperature and hot air velocity had significant effect on colour changes. There is a correlation between a- and b-value with chlorophylls and xanthophylls concentration, respectively. The roasting temperature was found to be the main factor affecting colour development. The variations in the pigments concentration and colour parameters of pistachio nuts were adequately simulated by quadratic and cubic polynomials. The changes in L-, b-values, and xanthophylls degradation were well-fitted to the first-order kinetic model while a-value and chlorophylls degradation followed the zero-order kinetic. The activation energy was determined at 113.9, 116.7, and 117.2 kJ/mol with R2 ≥ 99.9 and 191, 195, and 163.2 kJ/mol with R2 ≥ 99.5 and 73.7, 71.3, and 81.6 kJ/mol with R2 ≥ 99.9 for L-, b-, and a-value in hot air velocity of 0.6, 1.3, and 2 m/s, respectively. Conclusions Activation energy of chlorophylls and xanthophylls degradation were in the range of the activation energy for the yellowness (b-value) and redness (a-value) reactions.

Color prediction of mushroom slices during drying using Bayesian extreme learning machine

Color is an important appearance attribute of fruits and vegetables during drying processing, as it influences consumer’s preference and acceptability. Establishing color change kinetics model is an effective way for better understanding the quality changes and optimization of drying process. However, it is difficult to quickly and accurately predict color change kinetics during drying as it is highly nonlinear, complex, dynamic, and multivariable. To alleviate this problem, a new model based on extreme learning machine integrated Bayesian methods (BELM) has been developed for the prediction of color changes of mushroom slices during drying process. The effects of drying temperature (55, 60, 65, 70, and 75 °C) and air velocity (3, 6, 9, and 12 m/s) on color change kinetics of mushroom slices during hot air impingement drying were firstly explored and the experimental results indicated that both drying temperature and air velocity significantly affected the color attributes. Then, to validate the robustness and effectiveness of BELM, the basic extreme learning machine (ELM) and traditional back-propagation neural network (BPNN) models have also been employed to predict the color quality. In terms of prediction accuracy and execution time, BELM could achieve least similar or even better performance than ELM and BPNN. It overcame the overfitting problems of ELM. The test results of optimal BELM model by two new cases revealed that the lowest R2 and highest RMSE of BELM model were 0.9725 and 0.0563, respectively. The absolute values of relative errors between the actual and predicted values were lower than 8.5%.

Kinetic Modeling Of A Bi-Enzyme Time-Temperature Indicator (TTI) Based on Different Parameters for Monitoring Food Product Quality

Time-temperature indicator has been widely applied in the food industry. And, the theoretical study shows that if the time-temperature indicator is applied to monitor food, the activation energy of TTI temperature-dependent must be consistent with the activation energy of food quality loss. In this study, kinetics of absorbance and color changes in bi-enzyme were investigated as a function of storage temperature. Absorbance value was used to evaluate the enzyme reaction process under different temperature. Color change was evaluated in terms of the total color difference (DE). The results indicated that the time - temperature dependence of Absorbance and DE values followed a zero-order model. The Arrhenius equation adequately described the temperature dependence of the reaction rate constants for both absorbance and color parameters, respectively, from which the activation energies and rate constant at different temperature were obtained. There were significant linear correlations between absorbance, color and time parameter.

Storage stability and degradation kinetics of bioactive compounds in red palm oil microcapsules produced with solution-enhanced dispersion by supercritical carbon dioxide: A comparison with the spray-drying method

Solution-enhanced dispersion by supercritical carbon dioxide (SEDS) and spray drying (SD) were used to microencapsulate red palm oil (RPO) to prolong the functionality of carotenes and vitamin E. The protective effects provided by SEDS and SD were evaluated in terms of the oxidative stability (65 °C for 35 days), fatty acid compositions, color change and degradation kinetics of carotenes and vitamin E (25 °C, 45 °C, 65 °C, and 85 °C for up to 198 days). SEDS microcapsules (SEDS-M) were the most oxidatively stable (total oxidation (Totox): 26.5), followed by SD microcapsules (SD-M) (34.9) and RPO (56.7). Degradation of carotenes and vitamin E fitted well a first-order kinetic model (average absolute relative deviation = 2–16%). SEDS-M offered better protection to vitamin E (Ea = 36 kJ/mol), whereas SD-M provided better protection for α + β carotene (Ea = 29 kJ/mol). Overall, encapsulation protected RPO during storage, with SEDS-microencapsulated RPO performing better than SD-microencapsulated RPO.

Combination of ultrasound and ultraviolet‐C irradiation on kinetics of color, firmness, weight loss, and total phenolic content changes in tomatoes during storage

A kinetic study was conducted to account for the changes occurring in color, firmness, weight loss, and total phenolic content of tomatoes subjected to combined ultrasound technology (40 kHz, 13.78 W/L) and ultraviolet-C radiation (639.37 µw/cm2) treatment for 28 min. Combined treatment delayed ripening, increased firmness, weight loss, and induced total phenolic content retention of tomatoes compared to untreated samples. The change in color parameters of hue angle and chroma was described using the fractional conversion and zero-order models, respectively. Fractional conversion kinetic model was also found suitable for firmness degradation, while the zero-order and first-order models were appropriate for change in weight loss and total phenolic content retention prediction, respectively. Activation energy for measured parameters ranged from 121.29 to 199.70 kJ/mol at a temperature range of 33.76–37.12ºC, and showed highest sensitivity to treatment temperature in reduced ranking for firmness degradation, weight loss, total phenolic content retention, hue angle, and chroma. Practical applications The research provides a new method for postharvest handling of fruits and vegetables. The method utilizes ultrasound technology and ultraviolet-C radiation in combination and finds potential application in industries for shelf life extension during the storage, processing, and supply chain management of fruits and vegetables. However, the method may result in undesirable changes like weight loss, physical softening, or bioactive content degradation. Optimized parameters of the method are essential for loss minimizations and cost-effective practical applications. A thorough understanding of the influence of temperature of the system, treatment time, ultrasound acoustic energy density, and ultraviolet-C dosage on the quality properties of tomatoes and their change kinetics through fundamental approach modeling as presented in this research, is a step toward optimization of the technology.

Effect of solar drying methods on color kinetics and texture of dates

The present work investigates the effect of solar drying methods on the color and textural attributes of Khalas dates at three ripening stages (khalal, rutab and tamr) and evaluates color change kinetics using three kinetic models. Three solar drying methods, namely, open sun drying (OSD), forced convective drying (FCD) and greenhouse tunnel drying (GTD) were studied. The drying methods and ripening stages had significant effect on all color attributes. Khalal stage dates dried in FCD had the lowest color variations (L*: −12%, a*: +4%, b*: −46%, chroma: −38%, hue angle: −21% and total color change, ΔE:14.05) and thus, the highest color stability. At the end of drying, color of rutab and tamr stage dates changed red-brown in all the three drying methods due to the massive loss of b* (88–92%) and hue angle (63–73%), and altering hue angle from 23° (tamr fresh) to 9–12° (dried), respectively. The most appropriate model to describe the color change kinetics of dates at the three ripening stages was the fractional conversion model. The texture profile analysis revealed that FCD produced the softest dates for all the three ripening stages (hardness ranged 2.52–3.42 N). Overall, dates dried in FCD had the best color and textural properties as compared to the OSD and GTD dried dates in all ripening stages.

Thermal kinetics of enzyme inactivation, color changes, and allicin degradation of garlic under blanching treatments

AbstractBlanching is a feasible and effective method widely applied to prevent greening in garlic puree. However, this processing may cause the physical and chemical changes in garlic puree. Therefore, an investigation was carried out to systematically explore the effects of hot water blanching on enzyme inactivation (alliinase and γ‐glutamyl transpeptidase, GGT), discoloration, allicin degradation, and antioxidant capacity of garlic puree. The results showed that the inactivation of alliinase and GGT was strongly dependent on blanching temperature and time. Garlic puree turned into white when blanched at 80°C for 5 min or at 90°C for 4 min, with a* value of −3.24 ± 0.11, −2.80 ± 0.43, respectively. The inactivation kinetics of alliinase and GGT followed a first‐order reaction, as well as the kinetic of green discoloration. However, allicin content was dropped by 71, 80, and 85% after blanching for 5 min at 70, 80, and 90°C, respectively. A decline in the antioxidant capacity of garlic treated by blanching was also observed. The current findings indicated that blanching could contribute to inhabit garlic greening but had negative effects on the nutritional ingredients of garlic puree.Practical applicationsGarlic is prone to greening when processed into garlic puree, garlic juice and other products. The occurrence of greening seriously hindered the further processing of garlic. Blanching is an effective and feasible method to prevent greening in garlic puree. In this study, the effects of blanching on enzyme inactivation, color changes, allicin degradation and antioxidant capacity of garlic puree were studied. This study provides a theoretical basis for the deep processing of garlic.

Color change, ascorbic acid degradation kinetics, and rehydration behavior of kiwifruit as affected by different drying methods

AbstractIn this study, the drying kinetics, ascorbic acid degradation, and color change kinetics of kiwifruit during hot air drying (HAD), vacuum drying (VD), freeze drying (FD), and hot air–microwave‐assisted vacuum combination drying (HA–MVD) were investigated. The applicability of Weibull model for describing the rehydration kinetics of dried kiwifruits was also assessed. The ascorbic acid content of the kiwi fruit decreased by 77.52, 75.41, 39.86, and 29.64%, and the total phenolic content decreased by 26.62, 29.24, 19.16, and 1.99% after HAD, VD, HA–MVD, and FD, respectively. For all drying processes, the ascorbic acid degradation was best described by the Weibull model. Zero‐order, first‐order, and combined kinetic models were examined to fit data of color parameters (L*, a*, and b*). Scanning electron microscopy images of the dried products were also obtained. The results indicate that HA–MVD may be an alternative method for the drying of kiwifruit since it provides good quality product in shorter time.Practical applicationsKinetic modeling of changes in foods during drying is an important issue in relation to predicting quality changes and setting optimal processing conditions. In this study kinetic models describing the ascorbic acid degradation and also the color change of kiwifruit during four different drying methods were determined. Kiwifruit contains high amount ascorbic acid which is widely considered as a marker of nutritional quality for fruits and vegetables subjected to various drying treatments. That is why it is important to build kinetic models to estimate the degradation rate of ascorbic acid during various drying processes. When the ascorbic acid content, total phenolic content, color, and rehydration properties of the final dried products were compared, it was seen that the hot air–microwave‐assisted vacuum combination drying (HA–MVD) method yielded good quality dried product in quite shorter time as compared to other methods. The results of this study show that the HA–MVD method could be successfully applied for drying of kiwifruits.

Quality-Based Thermokinetic Optimization of Ready-to-Eat Whole Edible Crab (Cancer pagurus) Pasteurisation Treatments

Traditional processing practices used in the manufacture of ready-to-eat edible crab products include a double-heat treatment involving an initial cooking step followed by washing and packaging and finally, a second heat pasteurisation. The latter, pasteurisation step, results in the most severe impact on product quality. The main objective of this research was to optimise this pasteurisation step using quality index degradation kinetic approach. Preliminary work involved the characterisation of temperature rise in the crab cold-spot during pasteurisation. Equivalent treatments (F90°C10°C = 10 min) were defined in order to assess the impact of pasteurisation temperature on different crab quality indexes in both crab meat types, white and brown. Colour degradation of crab white meat was defined as the critical quality parameter to be monitored during thermal pasteurisation. The effect of time and temperature on the kinetics of white meat colour change (ΔE*) were characterised and fitted to an exponential equation. Following this, an industry focus group was used to define white meat colour change vs product quality and defined ‘good’ (ΔE* ≤ 7), ‘acceptable’ (7 < ΔE* < 9) and ‘unacceptable’ (ΔE* ≥ 9) quality. Finally, using the developed equations, optimal pasteurisation conditions were defined and validated. To produce ‘good’ quality crab, optimal temperatures ranged between 96 and 100 °C while temperatures between 104 and 108 °C produced ‘acceptable’ quality in crabs of 400 and 800 g, respectively. Overall, the results show that the equations obtained could be used in a decision support system (DSS) to define heat pasteurisation conditions to optimise the quality of ready-to-eat edible crab.

Impact of sprouting on the degradation kinetics of color and vitamin C of onion powder packaged in different packaging materials

The present investigation was engrossed to depict the feasibility of sprouting process as an efficient way to retain various quality attributes in sprouted onion powder packed in high-density polyethylene (HDPE) and aluminum-laminated polyethylene (ALP) under accelerated storage conditions (40°C ± 1°C temperature, 90% relative humidity). There was significant (p < 0.05) influence of both packaging material and storage period on the various analyzed parameters. The kinetics of color change (ΔE) and vitamin C degradation followed zero-order and first-order reaction, respectively, with the type of packaging material affecting the reaction rate constants. Sprouted onion powder was found to retain quality characteristics with lower moisture content, better flowability, less color, and vitamin C degradation in both HDPE and ALP throughout the storage period. The intensity of quality degradation suggested the application of sprouting as an efficient tool to enhance the storage stability of onion powder. Practical applications This research shows less degradation of color and vitamin C with maximum retention of quality index parameters in sprouted onion powder as compared to raw onion powder. The findings revealed that the process of sprouting can be used to enhance the storage life of onion products with improved quality parameters. The research is also valuable in terms of promoting exploitation of sprouted onions by preparing various products which can alleviate the problem of postharvest losses and environmental concerns arising as a result of sprouted onion disposal.

Kinetics of Color Change in Squash (&lt;em&gt;Cucurbita maxima&lt;/em&gt;) During Frying by Immersion at Atmospheric Pressure and Vacuum Pressure

The goal of this study was to determine the kinetics of the change of color in squash (Cucurbita maxima) during frying by immersion under conditions of atmospheric pressure and vacuum. Methodologically, the color of the rind of the external surface of the product conditioning in geometry of cylinders circulars, was evaluated in terms of the parameters CIELAB concerning L*, a* and b* post-process of frying under conditions of temperature of 150, 170 and 190°C, pressure of 40 and 80 kPa and during the time of processing time of 30 to 270 sec in intervals of 60 sec. The darkening of the surface of the product by effect of the process of frying in both procedures was evident in the decrease of the parameter L* as well as the parameters a* and b*, being more severe effect of darkening of the frying atmospheric higher temperature and experiencing changes of zero order for L*, zero for a* and first order for b*. The unit of the temperature and the speed of the reaction is explained by the Arrhenius equation. The activation energy obtained for the parameters of L*, a* and b* were 58.050, 13.709 and 53.545 kJ/mol and 32.082, 13.336 and 63.768 kJ/mol for the process of frying to the vacuum and frying in atmospheric conditions respectively.

Kinetic Analysis of the Color of Larch Sapwood and Heartwood during Heat Treatment

The kinetics of color changes in larch sapwood and heartwood during heat treatment were investigated in this study in order to determine if the process of color change that occurs in the surface of wood can be regulated. Wood samples were heated at 90, 110, 130, and 150 °C in an oven, vacuum, and in an oven subjected to saturated steam for 3, 6, 9, and 12 h each. The results of the color measurement showed that the values of L* (lightness) and ΔE* (total color difference) decreased and increased in both the sapwood and heartwood, respectively, with increasing temperature and treatment time. The three kinetic model approach, consisting of (i) the time-temperature superposition principle (TTSP); (ii) zero-order reaction model; and, (iii) first-order reaction model, was used to model the kinetics of color changes. The results indicated that the L* value of the sample (including heartwood and sapwood) was well fitted to the first-order reaction model (R2 = 0.9999). The Arrhenius activation energy was 14.2369 and 11.0984 kJ/mol for the sapwood and heartwood, respectively. The first-order reaction model also showed a better fit for the ΔE* values between sapwood and heartwood with higher R2 values than the other two methods. Therefore, the color changes of larch wood could successfully be analyzed using the first-order reaction model.