Minolta Chroma Research Articles

EFFECTS OF WATER STRESS ON CATHARANTHUS ROSEUS

The leaves of many plant species exhibit a noticeable color change in response to water stress. A study was conducted to determine if physiological changes associated with imposed water stress could be correlated with quantifiable leaf color changes in Catharanthus roseus. The Minolta Chroma Meter CR-200 was used to measure leaf color changes during water stress in three cultivars of Catharanthus. In addition, soil and plant water content, osmotic pressure, net photosynthetic rate, transpiration rate, and stomatal conductance were determined. Two components of light, chroma and L value, showed a correlation to the water content of the plant tissue. As plant water content decreased, both chroma and L value decreased. Since a change in leaf color (or a component of color) is easily monitored, the Chroma Meter could ultimately be used to detect incipient water stress in greenhouse crops.

THE EFFECTS OF LEAF PIGMENTATION ON RESISTANCE TO WHITEFLY INFESTATIONS IN PELARGONIUM XDOMESTICUM

The greenhouse whitefly (Trialcurodes vaporarorium) poses an acute and common production problem for growers of Pelargonium xdomesticum, the regal pelargonium. The main objective of this research was to ascertain whether leaf pigmentation is a feasible tool for selecting whitefly-resistant regal cultivars. Previous researchers have demonstrated that greenhouse whiteflies (GHWF) prefer yellow reflected light over all other hues. Five cultivars of Pelargonium xdomesticum were chosen for this study (`Country Girl', `Grand Slam', `Olga', `Elsie Hickman', and `Virginia'). Measurements of L* a* b* chromaticity valuer were performed using a Minolta Chroma Meter. model CR-100. For each experi-ment, L* a* b* measurements were taken on two leaves per plant for six plants of each cultivar. Plants were then randomized in three separate blocks and a known number of GHWF was released into each block. The numbers of eggs laid were evaluated 48 hours later. Three experiments took place between October, 1991 and April, 1992. Determinations of regression between individual chromaticity values (eg. L* or a*) for each cultivar and numbers of eggs laid revealed no correlations between color and whitefly preference. 'Country Girl' and 'Virginia' exhibited significantly higher levels of susceptibility at all three times. 'Elsie Hickman' was consistently the most resistant cultivar. `Grand Slam' also demonstrated significant levels of resistance and did not differ statistically from `Elsie Hickman'.

Denture base resins: Comparison study of color stability

Several denture base resins have been recently introduced that provide easier or faster processing. Although these materials have adequate strength properties, the color stability is also of interest. This study evaluated the color stability of five denture base acrylic resins and one denture base repair resin. The samples were subjected to conditions of accelerated aging to test color stability. Five samples of each material were processed and aged for 100 and 300 hours. The color stability was quantitatively measured using the Minolta Chroma Meter II. Color measurements were made before weathering and at 100 and 300 hours the color difference ΔE was calculated for all samples. At 300 hours the color change of the materials was significantly different at p < 0.01. It was found that: (1) the color of Lucitone Hy-pro and Acron was least affected by conditions of accelerated aging; (2) Triad, Accelar 20, and Perm demonstrated noticeable color changes; and (3) Compak-20 had an appreciable color change and was the least color-stable of the materials tested.

Composite resin color change after vital tooth bleaching

Color change of composite resin was determined with the Minolta Chroma meter (CR-100) after four sessions of vital bleaching. Specimens of selected composite resin materials were subjected to vital bleaching (37% H 3PO 4/1 minute, then 30% H 20 2/infrared light/30 minutes.) Specimens were stored in water between bleaching. Control specimens were used to determine the effects of water storage alone. Initial L *a *b * color readings were made on 24-hour hydrated specimens. Final L *a *b * readings were made on 24-hour hydrated specimens. Calculations were made for the A E values for each specimen. Mean Δ E values and standard deviations were obtained for each material. Two-way ANOVA and Newman-Keuls analyses showed significant (α = 0.05) color change for most bleached materials. Additionally, some materials had Δ E values greater than 3. These were visibly lighter compared to their controls. Vital bleaching produced color change in most composites as measured with the Chroma meter. This technique may be used to lighten dark-colored or stained composite resin restorations.

RELATIONSHIP BETWEEN CHROMATICITY VALUES AND LYCOPENE CONCENTRATION IN TOMATO FRUITS

Lycopene is the predominant carotenoid pigment in tomatoes and primarily responsible for red color. Spectrophotometric procedures for lycopene evaluation although accurate are time consuming and destructive. The objective of this study was to relate chromaticity values (L*,a*,b*) measured using a Minolta Chroma Meter CR-200b portable tristimulus calorimeter with lycopene concentrations in the pericarp of 'Celebrity', 'Mountain Delight' and 'Early Pick' tomatoes. Fruit were selected to encompass varying maturities from green to red ripe and were obtained from a commercial source. Lycopene from individual skin disks or pericarp plugs corresponding to each location of color measurement was extracted in acetone and measured spectrophotometrically at 503 nm. The L* value (a measure of lightness) or a* value (a measure of redness) was determined to be well correlated with lycopene concentration in all 3 cultivars. The linear regression of the lycopene concentration on the ratio of (a*/b*) provided the best R for all cultivars (0.75).

A comparison of two different instruments for measuring venison CIELAB values and colour assessment by a trained panel

Abstract Venison colour was measured with a Minolta Chroma Meter CR200b portable filter colorimeter to give CIE (1976) L*a*b* (CIELAB) values the results were compared with those obtained with a Hunter LabScan 6000 scanning reflectance spectrocolorimeter and a sensory evaluation panel. The values obtained depended on the instrument used, but the variations from one instrument to another were systematic, enabling the filter colorimeter to be calibrated against the reflectance spectrocolorimeter. Panel scores could be accurately predicted by a linear combination of CIELAB values (R 2(adj) = 0.86).

Quantification of skin-colour changes induced by topical corticosteroid preparations using the Minolta Chroma Meter

The Minolta tri-stimulus colorimeter CR-200 was used to quantify the blanching effect of topical corticosteroids in a non-occluded vasoconstriction test. To investigate the influence of time on variations in colorimetric parameters, an initial series of measurements was performed on Day 1 on six predetermined sites on the ventral surface of the forearm of six healthy volunteers every 2 h over a 12-h period. The colorimetric values were shown to be site related but hourly variations occurred with similar profiles for all the sites. On Day 2, four topical corticosteroid creams, representative of their potency groups, as well as a base were applied in a randomized double-blind manner on five of the predetermined sites. Visual gradings and colorimetric measurements were carried out every 2 h over the following 12-h diurnal period and were continued on Day 3. The colorimetric parameters L* (luminance) and a* (colour hue ranging from green(-) to red(+] gave a rank order correlated to corticosteroid potency that showed superior discrimination compared to simple visual grading. In this study, L* was more discriminative parameter than a*. The Minolta Chroma Meter CR-200 appears to be a simple and accurate device for objectively measuring the blanching effects of topical corticosteroids.

A New Objective Measurement of Eggshell Color.: 1. A Test for Potential Usefulness of Two Color Measuring Devices

A new technique for obtaining objective measurements of eggshell color was explored using the Hunter Lab Colorimeter D25A-9 and the Minolta Chroma Meter CR-200. A total of 1,299 eggs from 161 hens in five lines were measured on these two color meters. Measurements for individual eggs were highly repeatable (P>.25); differences between hens were significant (P<.005); and yolk shade affected the measurement of shell color in white-tinted eggs but not in brown eggs. Measurements with the Minolta meter agreed with visual color classification regardless of egg size; however, when the Hunter meter was used, agreement between visual classification and the meter measurement was reached only when eggs of a uniform size were used. Compared with the Hunter meter, the Minolta meter has more standardized reading values, more descriptive color scales, and is portable.

EFFECT OF CURVATURE AND SURFACE AREA ON COLORIMETER READINGS—A MODEL STUDY

ABSTRACTThe effect of sample curvature and surface area on colorimeter color readings was determined using samples with different radii of curvature (23.5, 28.5, 36.0, and 48.5 mm) on one side and flat on other side. No curvature effect was observed with an instrument having a small aperture (8 mm, Minolta chroma meter). An effect of surface area and curvature was observed for total color difference (ΔE), lightness (L) and chroma (C) but not hue angle with an instrument having a larger aperture (91 mm, Gardner XL‐845). L and C increased with increasing surface area and radius of curvature while ΔE decreased with increasing surface area and radius of curvature. The data from this experimental work indicate that reducing the area ratio (ratio between curved and flat surface area of the text sample) to less than 1.023 by using a smaller aperture will eliminate significant effects of sample curvature on colorimeter color readings. Hue angle results were unaffected by the curvature and can be reported if the area ratio criterion cannot be met.

Colorimetric quantification of erythema-a comparison of two colorimeters (Lange Micro Color and Minolta Chroma Meter CR-200) with a clinical scoring scheme and laser-Doppler flowmetry

Erythema elicited by the local irritant sodium lauryl sulphate was studied in comparison with unexposed skin. Colour coordinates of the CIE system were recorded using two commercially available colorimeters. With both colorimeters a positive movement of the alpha-axis (toward red, P less than 0.001) and a negative movement on the L-axis (toward dark, P less than 0.01) were registered. Technical and in-vivo experimentation showed the two pieces of equipment to be accurate. However, a simple conversion factor cannot be established. Both pieces of equipment correlated positively with clinical scoring of erythema and with measurement of cutaneous blood flow by laser-Doppler flowmetry. In conclusion, the two colorimeters appeared comparable. Colorimetry by the CIE system, which takes into account the non-linear colour perception of the human eye, was found useful with potential value in both experimental and clinical dermatology. The techniques appeared suitable for routine testing.

Evaluation of a portable colour meter for assessment of the colour of milled rice

A portable chromatic reflectometer, the “Minolta Chroma Meter” model CR-110 was compared with the mains-operated “Hunterlab Color Difference Meter” model D25D2M for the assessment of milled rice colour. Correlation coefficients for the blue-yellowness and lightness indices respectively for the two instruments were greater than 0.95. It is concluded that the portable “Minolta Chroma meter” provides an objective means for monitoring changes in milled rice colour, suitable for use in grain handling and storage facilities.

Evaluation of a Conduction Heating Food Model for Ascorbic Acid Retention and Color Formation During Thermal Processing

Ascorbic acid retention and color formation studies were carried out using a conduction heating simulated food model in cylindrical containers subjected to heat processing in a steam retort. Operating conditions, at temperatures from 110 to 127°C, were selected to study the influence of various process times/lethalities on the ascorbic acid retention and induced Maillard-type color formation. Ascorbic acid was analysed by a HPLC technique while the formed color was evaluated using a Minolta Chroma Meter. The study indicated that a food model of wetted celite could be used for distribution of ascorbic acid and/or color forming compounds and their subsequent recovery from the medium, both before and after thermal processing. The study also indicated that kinetics of ascorbic acid retention/destruction and color formation were different depending on whether they were tested individually or in mixtures, and the experimental design provided data for the verification of a computer model for predicting nutrient retention under a range of experimental conditions.

A Comparison of CIE (1976) L*a*b* Values Obtained from Two Different Instruments on Several Food Commodities

ABSTRACTThe relationships between CIE (1976) L*a*b* color parameters from a Hunter LabScan II Sphere Spectrocolorimeter and two Minolta Chroma Meters were evaluated. Jams, yoghurts with jam, salami‐type dry sausages, raw cauliflowers, mashed and raw potatoes and various color standards were used as samples. The numerical values of the color parameters depended upon the instrument used. The relationships between the color parameters could be described by linear regressions which were specific for each type of food except for mashed potatoes and cauliflower. Best predictions of color parameters from one instrument to another were obtained with the most homogenious types of food.

Instrumental colour analysis of farmed and wild Atlantic salmon when raw, baked and smoked

Flesh colour of eight canthaxanthin-pigmented farmed and eight astaxanthin-pig-mented with Atlantic salmon ( Salmo salar L.) was measured by instrumental analysis. The colour of raw, baked and cold smoked flesh from cultured and wild salmon was compared using reflectance spectra transformed into CIE (1976) L ∗a ∗b ∗ values. In this system L ∗ represents lightness of salmon flesh colour, a ∗ redness and b ∗ yellowness. CIE (1976) L ∗a ∗b ∗ values obtained with a portable instrument (Minolta Chroma Meter) showed that intensity of redness ( a ∗ ) of raw, baked and smoked salmon increased with increasing carotenoid concentration of the raw flesh, while lightness ( L ∗ ) decreased. Intensity of yellowness ( b ∗ ) was not significantly influenced by carotenoid concentration. Baking and smoking caused a ∗ to decrease, while L ∗ increased. Values obtained by the portable instrument were in good accordance with corresponding values obtained with a HunterLab LabScan II sphere spectrocolorimeter. The reflectance ratio R 650 R 510 of raw, baked and smoked salmon flesh was significantly correlated to carotenoid concentration, but to a lesser extent than CIE (1976) a ∗ values. The present analyses did not reveal colour differences between farmed and wild salmon except for those caused by differences in carotenoid concentration.

The Use of the Minolta Reflectance Chroma Meter II™ for Pigmentation Evaluation of Broiler Shanks

Abstract Broilers were fed different levels and types of xanthophylls to produce a wide range of skin and shank pigmentation. Color values [dominant wavelength (DWL), excitation purity (EP), and luminosity (LUM)] were obtained from the resulting shanks (live, dead, chilled) and removed shank skins using a Minolta Chroma Meter II™ and compared to values obtained on the removed shank skins with a MacBeth MC-1010™ reflectance colorimeter. Color values obtained with the two instruments on the color chips of the Hoffmann-LaRoche Yolk Colour Fan® were also compared. Intact shank values (live or dead) obtained with the Chroma Meter II™ were significantly lower and not significantly correlated to values obtained with the MC-1010™ instrument on skins from the same shanks. Removing the shanks and chilling them tended to increase correlation coefficients and decrease differences between means. A direct comparison of data collected with the two instruments on shank skins reduced mean differences and increased correlation coefficients. However, DWL values of shanks from broilers fed high pigment levels that were heterogeneous in type were not correlated. The uniformity of color within a particular sample, compounded by differences in sampling area, appeared to be the cause of the low correlation, because correlations between values obtained with the two instruments on the color chips of the color tan were high.