Color Change Kinetics of Okra Undergoing Microwave Drying

In this present study, the effect of microwave output power and sample amount on color change kinetics of Turkey okra (Hibiscus esculenta L.) were investigated by using microwave drying technique. The color parameters for the color change of the materials were quantified by Hunter L (whiteness/darkness), a (redness/greenness), and b (yellowness/blueness) values. These values were also used for calculation of the total color change (ΔE), chroma, hue angle and browning index. The microwave drying process changed color parameters of L, a, and b, causing a color shift toward the darker region. The values of L and b decreased, whereas values of a and total color change (ΔE) increased during microwave drying. The mathematical modeling study of color change kinetics showed that L and b fit a first-order kinetic model, whereas a and total color change (ΔE) followed a zero-order kinetic model. However, chroma and browning index (BI) followed a first-order kinetic model, whereas hue angle followed a zero-order kinetic model. On the other hand, the data of the total color change (ΔE), chroma, hue angle, and browning index depending on the ratio of the microwave output power to sample amount were adequately fitted to a quadratic model. For calculation of the activation energy for color change kinetics parameters, the exponential expression based on Arrhenius equation was used.     

Color Change Kinetics of Microwave-Dried Basil

The aim of this study was to investigate the effect of microwave output power and sample amount on color change kinetics of basil (Ocimum basilicum L.) during microwave drying. The color parameters for the color change of the materials were quantified by Hunter L (whiteness/darkness), a (redness/greenness), and b (yellowness/blueness) system. These values were also used for calculation of the total color change (ΔE), chroma, hue angle, and browning index. The microwave-drying process changed color parameters of L, a, and b, causing a color shift toward the darker region. The mathematical modeling study of color change kinetics showed that a and b fitted to a first-order kinetic model, while L and total color change (ΔE) followed a zero-order kinetic model. However, chroma and browning index (BI) followed a first-order kinetic model, whereas hue angle followed a zero-order kinetic model. For calculation of the activation energy for colour change kinetic parameters, the exponential expression based on Arrhenius equation was used.     

Color Change Kinetics of Spinach Undergoing Microwave Drying

In this present study, the effect of microwave output power and sample amount on color change kinetics of Turkey spinach (Spinacia oleracea L.) were investigated by using microwave drying technique. The color parameters for the color change of the materials were quantified by the Hunter L (whiteness/darkness), a (redness/greenness), and b (yellowness/blueness) system. These values were also used for calculation of the total color change (ΔE), chroma, hue angle, and browning index. The microwave drying process changed color parameters of L, a, and b, causing a color shift toward the darker region. The values of L and b decreased, while values of a and total color change (ΔE) increased during microwave drying. The mathematical modeling study of color change kinetic showed that L and b fitted to a first-order kinetic model, while a and total color change (ΔE) followed by a zero-order kinetic model. However, chroma and browning index (BI) followed a first-order kinetic model, while hue angle followed a zero-order kinetic model. To illustrate the relationship of the L, a, b, total color change (ΔE), chroma, hue angle, and browning index depending on the ratio of the microwave output power to sample amount, the data adequately fitted to a quadratic (second order polynomial) model. For calculation of the activation energy for color change kinetic parameters, the exponential expression based on an Arrhenius equation was used.     

EFFECT OF CHITIN ON COLOR DURING OSMOTIC DEHYDRATION OF BANANA SLICES

ABSTRACT

Five conditions of the osmo-dehydration process of banana slices, which in our previous study underwent the most adequate color parameter changes. L, hue and chroma values were studied with the presence of chitin added to the syrup solutions at the concentration of 0.05, 0.1 and 0.5% w/w. After four hours of osmo-dehydration, color space results of L, a and b as well as polyphenol oxidase activity were measured. Color space results were used to calculate hue and chroma and total color difference changes. Chitin presence did not change the tendency of polyphenol activity decreased during osmotic drying as well as has not effect on chroma, hue and total color difference changes. Chitin presence had an effect on L value decrease in the inner and outer part of the slice, and these changes did not depend to osmotic dehydration conditions. It is highly recommended to use chitin during osmotic dehydration of some fruits that would undergo undesirable darkening.     

Accuracy of approximations for CIELAB chroma and hue difference computation

The transformation in CIELAB from differences in the L^*, a^*, b^* coordinates to those in lightness, chroma, and hue, ΔL^*, ΔC_ab^*, ΔH_ab^*, can be approximated by a rotation in 3-space. Expressions for the error in the approximation of chroma and hue differences are developed. Significant errors are introduced if either the hue angle or chroma difference between reference and sample colors are large. A computed example illustrates the use of the analysis. © 1997 John Wiley & Sons, Inc. Col Res Appl, 22, 61–64, 1997.     

Influence of Drying Conditions on the Hazelnut Quality. III. Browning

ABSTRACT

The influence of drying conditions on browning in hazelnut (Corylus avellana L.) has been studied by means of color measurement. Samples of unshelled and shelled hazelnuts were dried under six air temperatures (30. 40, 50, 60, 70 and 80°C). The drying experiments were done with forced air circulation, and two varieties of hazelnut were investigated, Negret and Pauetet. CiELab system was used to evaluate changes in total color (δE^?), lightness (L^?), chroma (C^?) and hue angle (H^?) on dried hazelnuts. Browning of hazelnut was observed to occur a1 all temperatures studied. The rate of pigment formation was determined from the δE' values with zero-order kinetic model, and temperature dependence was described by the Arrhenius equation with an activation energy (E_a) varying from 28 to 39 kJlmol. Negret variety showed the highest rate of browning.     

Colorimetric study of SCOTDIC colour specifier

In this study, SCOTDIC cotton standard colours (a physical exemplification of the Munsell system) were studied extensively. L*, a*, b* values were measured and plotted to check the uniformity of the Munsell (SCOTDIC) hue, value and chroma values in a CIELAB diagram. Although for some borderline hues the hue angles were quite different than expected (around 0° or 360°), the correlation between SCOTDIC hue and CIELAB hue angle was fairly good and the correlation between SCOTDIC value and CIELAB lightness was also quite high. However, the correlation between SCOTDIC chroma and CIELAB chroma was only moderate. In the CIELAB diagram, the constant SCOTDIC hue and constant chroma loci took the shape of approximately linear radial lines starting from the origin and approximately concentric circles with the origin as their centres, respectively. However, some deviations were observed for high chroma colours and yellow hues in the respective cases. The instrumentally predicted Munsell notations were compared with the actual SCOTDIC notations. Some deviations of the SCOTDIC system from the Munsell system were observed.     

A fallacy in the definition of ΔH*

When a color differs from the reference, it is desirable to ascribe the difference to differences in the perceptual attributes of hue, chroma, and/or lightness through psychometric correlates of these attributes. To this end, the CIE has recommended the quantity ΔH* as a psychometric correlate of hue as defined by ΔH* = [(ΔE*)² - (ΔL*)² - (ΔC*)²]^1/2, where the correlates correspond to either the 1976 CIELAB or CIELUV color spaces. Since ΔH* is defined as a “leftover,” this definition is valid only to the extent that ΔE* comprises exclusively ΔL*, ΔC*, and ΔH* and that ΔL*, ΔC*, and ΔH* are mutually independent compositionally, both psychophysically and psychometrically. It will be shown that as now defined ΔH* lacks psychometric independence of chroma and always leads to incorrect hue difference determination. Such a deficiency causes problems, especially in the halftone color printing industry, since it can suggest an incorrect adjustment for the hue of the inks. A revised definition herein of ΔH* provides a psychometric hue difference independent of chroma, valid for large and small psychometric color differences regardless of chroma. However, for small chromas, the seldom used metric ΔC might be a better color difference metric than ΔH* because complex appearance effects make the perceptual discrimination of lightness, chroma, and hue components more difficult than for high chromas.     

Investigation of the Effects of Microwave Treatment on the Optical Properties of Apple Slices During Drying

The objective of this work was to study the changes of optical properties of apple (Golden Delicious) slices during drying. The optical parameters compared on the basis of Hunter values (L, a, b) changes as well as total color difference (Δ E) and browning index (BI). The effect of coating materials including carboxymethylcellulose (CMC), starch, and pectin as well as microwave treatment on optical properties and microstructure of dried samples were investigated. To analyze the effects of these processes on microstructure, scanning electron microscopy (SEM) was employed. Results showed that optical properties as well as microstructure of apple were affected by coating material and drying condition. Coated samples by CMC had a lower L and higher BI, but different results in the presence of starch were obtained. Microwave treatment in the presence of appropriate coating materials could improve the optical properties of dried apple slices.     

Effect of microwave pretreatment on the color degradation kinetics in mustard greens (Brassica juncea)

In the present work, the impact of microwave pretreatment on the thermal degradation of color (chlorophylls) in mustard greens was studied. The drying experiments were conducted in the range of temperatures from 50 to 80°C. The degradation in the levels of chlorophylls has been quantified using Hunter color values (L*, a*, and b*) and calculating total color difference (ΔE). From the color results, the changes in color values (L*, a*, and b*) were observed as inappreciable, and changes in ΔE were found to be increased during drying. Analysis of kinetic data displayed a first-order reaction kinetics for chlorophyll degradation. Arrhenius equation was used to calculate the activation energies for rate constants, and it has been varied from 13.3 to 27.4?kJ/mol. Thermodynamic parameters, enthalpy of activation (ΔH^#), and entropy activation (ΔS^#) were found to be in the range of 1.40–2.63?J/mol and ?293 to ?305?J/mol?·?K, respectively. The data from the present work revealed that the microwave pretreatment of mustard greens remarkably influenced the retention of chlorophylls in the final dehydrated powder.     

The Influence of the Measuring/Viewing Angle on the Color of Injection-Molded Plastics

A multi-angle spectrophotometer was used to measure the CIELab coordinates L?, a? and b? in different angles relative to the incident light. The specimens used were acrylonitrile-butadiene-styrene injection-molded plaques in different colors and with different surface textures. Variations in the coordinates when changing the measuring angle depended on the color and the texture. In general, however, smooth (glossy) surfaces were measured to be darker and of higher chroma than textured surfaces and as the gloss of the surfaces decreased (due to texturing), the lightness of the surfaces increased and the absolute values of a? and b? decreased over the range of measuring angles (not too close to the specular reflection angle). A psychometric study involving a human test panel was used as a complement to the measurement. The agreement between the measurements and this study cannot be said to be satisfactory, unless the variation in the color coordinates was quite clear. Possible reasons are discussed.     

Effect of mincing degree on colour properties in pork meat

Although the colour of different meat products has been studied, particularly in the final product , these studies do not separate the influence of degree of mincing from other factors such as additives, spices, manufacturing process, etc. The effect of degree of mincing on colour (CIELAB colour space) in pork meat was studied. Three mincing processes were studied, two using a grinder with 10 and 20 mm diameter holes in the plate, and a third in which a cutter was used to obtain a finely minced product. As control, intact meat was used. Colour parameters [lightness (L*), redness (a*), yellowness (b*), chroma (C*), hue (H*), a*/b* ratio, and colour differences], pH, and water holding capacity were determined. Mincing, regardless of the type used, increased the values of L*, b*, and H*, but decreased the values of a* and a*/b* ratio. The L* values increased with mincing degree. The H* values and a*/b* ratio of plate minced meats (10 and 20 mm) differed from that which had been finely minced. The mincing process did not modify the saturation values of the batters. Only the fine mincing process modified (increased) the water holding capacity of the batters. © 2000 John Wiley & Sons, Inc. Col Res Appl, 25, 376–380, 2000     

Extending CIELAB: Vividness, , depth, , and clarity,

CIE L*, a*, b* is a rectangular coordinate system used extensively for numerical color communication and quality assurance. Often the a*, b* coordinates are rotated to cylindrical polar coordinates of (radial distance) and h_ab (angle measured counterclockwise from the a* axis), reasonably relating to chroma and hue. When each coordinate is considered independently, it is observed that colors in our daily experiences do not change in a similar independent fashion. Changes in concentration for mixtures of colorants result in changes in both chroma and lightness. Directly illuminated three‐dimensional colored objects change in both chroma and lightness between direct illumination and either shadow or highlight. Two new coordinates are defined for CIELAB: vividness, , and depth, . Each represents a Euclidean distance from a color defined by L* and to of 0 and either L* = 0 for vividness or L* = 100 for depth. Image‐based visualizations were made to demonstrate how changes in these variables led to color changes more representative of our daily experiences. For cases where a color and background had the same lightness, it was observed that colors became less distinct with a reduction in chroma. A third dimension was defined, clarity, , a Euclidean distance from a color defined by L*, a*, and b* to its background color, similarly defined. © 2013 Wiley Periodicals, Inc. Col Res Appl, 39, 322–330, 2014     

Proposal of an opponent‐colors system based on color‐appearance and color‐vision studies

A new theoretical color order system is proposed on the basis of various studies on color appearance and color vision. It has three orthogonal opponent‐colors axes and an improved chromatic strength of each hue. The system has color attributes whiteness w, blackness bk, grayness gr, chroma C, and hue H. A method is given for determining Munsell notations of any colors on any equi‐hue planes in the system. A method is also given for determining grayness regions and grayness values on hue‐chroma planes in the system. It is concluded that colors with the same color attributes [w, gr, bk, C] but with different hues in the theoretical space have approximately the same perceived lightness, the same degree of vividness (“azayakasa” in Japanese), and also the same color tone. The tone concept, for example used in the Practical Color Coordinate System (PCCS), is clarified perceptually. The proposed system is a basic and latent color‐order system to PCCS. In addition, the concept of veiling grayness by a pure color with any hue is introduced. Further, relationships are clarified between generalized chroma c(gen) and grayness. © 2004 Wiley Periodicals, Inc. Col Res Appl, 29, 135–150, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.10234     

The perception of static colored noise: Detection and masking described by CIE94

We present psychophysical data on the perception of static colored noise. In our experiments, we use the CIE94 color difference formula to quantify the noise strength and for describing our threshold data. In Experiment 1 we measure the visual detection thresholds for fixed pattern noise on a uniform background color. The noise was present in one of three perceptual color dimensions lightness (L*), chroma (C*), or hue (h). Results show that the average detection threshold for noise in L* is independent of hue angle and significantly lower than that for noise in C* or h. Thresholds for noise in C* and h depend on hue angle in an opponent fashion. The measured detection thresholds, expressed in terms of the components ΔL*/k_LS_L, ΔC*/k_CS_C, and ΔH*/k_HS_H that build up the CIE94 color difference formula are used to tune CIE94 to our experimental conditions by adjusting the parametric scaling factors k_L, k_C, and k_H. In Experiment 2, we measure thresholds for recognizing the orientation (left, right, up, down) of a test symbol that was incremental in L*, C*, or h, masked by supra‐threshold background noise levels in L*, C*, or h. On the basis of the CIE94 color difference formula we hypothesized (a) a constant ratio between recognition threshold and noise level when the test symbol and background noise are in the same perceptual dimension, and (b) a constant recognition threshold when in different dimensions. The first hypothesis was confirmed for each color dimension, the second however, was only confirmed for background noise in L*. The L*, C*, h recognition thresholds increase with increasing background noise in C* or h. On the basis of some 16,200 visual observations we conclude that the three perceptual dimensions L*, C*, and h require different scaling factors (hue dependent for C* and h) in the CIE94 color difference formula, to predict detection threshold data for color noise. In addition these dimensions are not independent for symbol recognition in color noise. © 2008 Wiley Periodicals, Inc. Col Res Appl, 33, 178–191, 2008     

Evaluation of performance of various color‐difference formulae using an experimental black dataset

The objective of this study was to develop a specific visual dataset comprising black‐appearing samples with low lightness (L* ranging from approximately 10.4 to 19.5), varying in hue and chroma, evaluating their visual differences against a reference sample, and testing the performance of major color difference formulas currently in use as well as OSA‐UCS‐based models and more recent CAM02 color difference formulas including CAM02‐SCD and CAM02‐UCS models. The dataset comprised 50 dyed black fabric samples of similar structure, and a standard (L*= 15.33, a* = 0.14, b* = ?0.82), with a distribution of small color differences, in ΔE^*_ab, from 0 to approximately 5. The visual color difference between each sample and the standard was assessed by 19 observers in three separate sittings with an interval of at least 24 hours between trials using an AATCC standard gray scale for color change, and a total of 2850 assessments were obtained. A third‐degree polynomial equation was used to convert gray scale ratings to visual differences. The Standard Residual Sum of Squares index (STRESS) and Pearson's correlation coefficient (r), were used to evaluate the performance of various color difference formulae based on visual results. According to the analysis of STRESS index and correlation coefficient results CAM02 color difference equations exhibited the best agreement against visual data with statistically significant improvement over other models tested. The CIEDE2000 (1:1:1) equation also showed good performance in this region of the color space. © 2013 Wiley Periodicals, Inc. Col Res Appl, 39, 589–598, 2014     

Color appearance of a large homogenous visual field

In this article, the color appearance of a large (85°) homogeneous self‐luminous visual stimulus was studied in a psychophysical experiment. Large stimuli were displayed on a plasma display panal (PDP) monitor. The large stimuli were viewed with a fixed viewing time (2 s). They were compared with 2° and 10° stimuli presented on a grey background on a CRT monitor. The so‐called “color size effect” was found to be significant. The color stimulus was perceived to be lighter when it was large compared with the 2° and 10° situation. But we did not find the general increase of chroma claimed in previous literature. We found only small hue changes. A model of the color appearance of large‐field stimuli is presented in terms of the CIELAB L*, a*, and b* values of the corresponding 2° and 10° stimuli. © 2007 Wiley Periodicals, Inc. Col Res Appl, 33, 45–54, 2008     

Impact of melt impregnation on the color of wood–plastic composites

The aesthetics of wood–plastic composites (WPCs) can affect the acceptance of the products by consumers. This study was aimed at providing a better understanding of how impregnation variables affect color changes, thereby allowing for the development of an optimal process for WPCs. The effects of impregnation parameters and impregnants on the WPC color were investigated in this study via a screening design. Sixteen runs of resolution IV design for seven factors at two levels were conducted. The seven factors were the ratio of maleated polyethylene in the formulations, the ratio of polyethylenes with different molecular weights, four process factors (vacuum, pressure, time, and temperature), and wood species (red maple and aspen). The studied color parameters included the lightness change, chroma change, hue angle change, saturation change, and total color change. All treatments darkened the wood and increased the chroma values and the saturation. Even though all treatments had an impact on the hue angle, the changes were very small. The wood species, impregnants, impregnation time, and temperature played significant roles in the color change and chroma coordinates. However, no parameter dominated the hue angle change and saturation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2149–2157, 2006     

A shade guide model based on the color distribution of natural teeth

The objectives were to determine the color distribution of natural teeth sorted by the parameters of Value, Chroma, and hue angle measured with a colorimeter, and to suggest a shade guide model. The color of maxillary and mandibular 12 anterior teeth was measured with a tristimulus colorimeter for 47 subjects (n = 564). The color of teeth was grouped initially by Value (CIE L*) by the interval of 3.3 units. After then, within each main group, the color of teeth was subgrouped by Chroma by the interval of 3.3 units. Chroma was calculated as C*_ab = (a*2 + b*2)^1/2. Since the hue angles were in the first or fourth quadrant, subgroups were further sorted by the first or fourth quadrant hue angles. Hue angle was calculated as h° = arctan (b*/a*). Mean color difference (ΔE*_ab) between the color of an individual tooth and the mean color of each main group was 2.5–3.3, which was lower than acceptable limit (ΔE*_ab < 3.3), and that in each subgroup was 0.9–3.1. The number of subgroups was 22, which was comparable to those of conventional shade guides. A shade guide model based on the color distribution of natural teeth sorted by Value in six main groups, three or four subgroups within each main group sorted by Chroma, and further sorted by hue angle (first or fourth quadrant values) was suggested. © 2007 Wiley Periodicals, Inc. Col Res Appl, 32, 278–283, 2007     

Color effect of light sources on peridot based on CIE1976 L*a*b* color system and round RGB diagram system

Previous research indicated that the peridot's color is dominated by the selective absorption of visible light caused by ferrous ion, the hue angle of which is in an inverse ratio of the concentration of Fe²⁺. This article focuses on the color effect of peridot under different standard light sources based on the CIE1976 L*a*b* color space system and round RGB diagram system and tries to find the best one for its grading and display. Based on the results of a series of experiments, including electron microprobe analysis, spectrophotometer, UV‐Vis spectrum, standard illumination box, and Munsell neutral color chips, it was suggested that the spectral power distribution and color temperature of a standard light source significantly influence the color of peridot in terms of lightness and chroma, particularly in the hue of peridot. As for color grading and displaying of peridot, standard light source A fails to fit in, and the color of peridot under a fluorescent light source has a higher chroma but a lower hue angle than that under daylight light source. The best choice for grading and displaying peridot is the standard light source D₆₅. It is better to distinguish the hue of peridot when it is calculated by the round RGB diagram system.