Group Title: Citrus Station mimeo report - Florida Citrus Experiment Station ; CES 66-1
Title: Subjective and objective method for determining color of orange juice
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Permanent Link: http://ufdc.ufl.edu/UF00072433/00001
 Material Information
Title: Subjective and objective method for determining color of orange juice
Series Title: Citrus Station mimeo report
Physical Description: 5 leaves : ; 28 cm.
Language: English
Creator: Edwards, G. J
Huggart, R. L
Wenzel, F. W
Citrus Experiment Station (Lake Alfred, Fla.)
Florida Citrus Commission
Publisher: Florida Citrus Experiment Station :
Florida Citrus Commission
Place of Publication: Lake Alfred FL
Publication Date: 1965
 Subjects
Subject: Orange juice -- Color -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Includes bibliographical references (leaf 5).
Statement of Responsibility: George J. Edwards, R.L. Huggart and F.W. Wenzel.
General Note: Caption title.
General Note: "400-10/12/65-GJE."
 Record Information
Bibliographic ID: UF00072433
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 76037633

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Citrus Experiment Station CES 66-1
and Florida Citrus Commission,
Lake Alfred, Florida 400-10/12/65-GJE


Subjective and Objective Method for Determining Color of Orange Juice
George J. Edwards, R. L. Huggart and F. W. Wenzel


What is color and what is the color of orange juice?

To the chemist color is dyes and pigments. To the physicist color is a
phenomena in the fields of optics and electromagnetic radiation. To the physi-
ologist and psychologist color denotes a sensation to the human observer.

Our interest will be a combination of the physicist, physiologist and
psychologist. Our purpose is to give a score to the color of orange juice we
see and to find instruments that will give each color a number so there will
not be a difference of opinion between observers.

There are several ways in use today that compare color or give a value for
color difference. Such methods are either subjective or objective, the former
being dependent upon a visual evaluation by an observer while the latter makes
use of various instruments.

Subjective methods. The Maerz and Paul dictionary of color ( 7) contains
examples of many colors. Plate 10 on page 43 of this book shows various colors
that could apply to orange juice.

The Macbeth-Munsell Disk Colorimeter -(5, 6) can be used so that overlapping
color wedges are spun and the resulting color compared to that of a sample of
juice. By varying the amount of white, gray, yellow, and orange, the color of
orange juice may be matched.

The use of the USDA comparator tubes to obtain a score for orange juice is
another example of a subjective method. The first set of such tubes, consisting
of colored plastic in capped glass tubes were used in Florida from December,
1955, to October, 1964. These tubes were numbered 1, 2, 3, and 4 corresponding
to color score points of 32, 34, 36, and 38. The colored plastic used was
similar to the color of orange juice. A Macbeth Examolight visual color compara-
tor is used as a light source, which is similar to average daylight. The above
set of color comparator tubes was replaced with another set of tubes made en-
tirely of colored plastic. This set and their use are included in the U.S.
Standards for Grades of Frozen Concentrated Orange Juice (8).

Objective methods. Kramer and Twigg (5) and MacKinney and Little (6) in
their books describe many instruments for measuring objectively the color or
color difference of substances, such as food products. Instruments described
include spectrophotometers, Gardner Color and Color Difference Meter, Hunterlab
Color and Color Difference Meter, Colormaster Differential Colorimeter, Color
Eye, Photovolt Reflection Meter and the Agtron.

Some brief comments will now be made relative to instruments, which have
been used at the Citrus Experiment Station to measure, objectively, color or
color differences of citrus juices.

A Bausch and Lomb Spectronic 505 recording spectrophotometer was loaned to
us for a short time by W. H. Curtin and Company, Jacksonville, Florida. This










instrument, equipped with a reflectance accessory set, recorded the reflectance
from a sample of juice over a wide range of wave lengths. Thus, a spectral curve
was obtained. The instrument records directly on a trichromatic coefficient
computing chart. These charts make it simpler for conversion to C.I.E. tri-
chromatic coefficients (5, 6) which are needed to determine the dominant wave
length, brightness, and purity of the light reflected from the juice. Data ob-
tained with this spectrophotometer is discussed later in this report.

The Hunter Color and Color Difference Meter (5, 6) is a photoelectric tri-
stimulus colorimeter. This instrument was purchased in 1953 from Gardner
Laboratories, Inc. It can measure small differences in color with its three
tristimulus filters, which approximate the standard observer of the international
commission of illumination. Most of the information (2, 3, 9) on the color of
citrus concentrates and juices, obtained at the Citrus Experiment Station, has
been by the use of this instrument. Three readings are obtained; the Rd, a, and
b values. The Rd value indicates the luminous reflectance for 450 or the bright-
ness (whiteness) of the juice sample. Readings of either 0 or 100 means that the
sample is black or white, respectively. Values for RU between 0 and 100 indicate
different shades of grayness. The a values are measures of redness (+) or
greeness (-). The b values are measures of yellowness (+) or blueness (-).

Development of a single reading instrument for measuring color differences
between samples of orange or grapefruit juices was undertaken by Hunter Associ-
ates Laboratory in 1963. The design of this Hunter Citrus Colorimeter and its
evaluation have been discussed in previous reports (1, 4). It compares the
color of orange juice against that of one of the U.S.D.A. color comparator tubes.

The Photovolt Reflection Meter measures reflectance and furnishes readings
in terms of the filter being used, which usually extends over a wide range of
wave lengths. Using such values C.I.E. characteristics can be calculated. Re-
flectance readings, using monochromatic light, also can be obtained with the
Bausch and Lomb Spectronic 20.

The Agtron is a direct reading reflectance instrument. The light source of
this instrument is unique in that it uses a mercury lamp and a neon gas dis-
charge tube. The sensor is fitted with three filters that are selected to see
the specific spectral lines of mercury and neon. This gives the instrument
monochromatic light. The blue filter is for the 436 mu mercury line, the green
filter for the 546 mp mercury line and the red filter for the 640 mu neon line.
Calibration of this instrument is done with various shades of gray plastic discs.
The shades range from white to black. Several months ago Mr. Smith, a representa-
tive of Magnuson Engineers, Inc., brought the Agtron to Lake Alfred for testing.
Personnel of the Florida Citrus Commission and the Citrus Experiment Station
cooperated with Mr. Smith. Results from the examination of orange juices indi-
cated some modification of the filters in this Agtron would be necessary. This
was to be done as soon as possible.

Preparation of samples. A set of reconstituted frozen concentrated orange
juices was prepared by thawing and mixing together different samples of commercial
frozen Florida orange concentrates. This was done so that the reconstituted
juices would have wide ranges of USDA color scores and Hunter Color Difference


- GJE


Florida Citrus Experiment Station
and Florida Citrus Commission,
Lake Alfred, Florida. 400-10/12/65









Meter Rd, a, and b values. Scores ranged from 32 to 37
plastic-in-glass color comparator tubes were used. The
20.9 to 27.1, the a values from -7.5 to -2.8, and the b
29.8 (Table 3).


score points when the
Rd values ranged from
values from 28.1 to


Results and Discussion


Spectral curves were obtained with the Bausch and Lomb Spectronic 505
recording spectrophotometer. Characteristics of the spectral curves for the
USDA color comparator tubes are presented in Table 1.


Table 1. Dominant wave length, purity, and brightness
of color of USDA color comparator tubes

Score1 DWL Purity Brightness

32 571 nmi 70 % 25.5 %
34 572 74 24.6 "
36 573 81 22.3 "
38 574 84 21.0 "

Using plastic-in-glass color comparator tubes.


Note that there is only 1 mu difference between any two of the scores.
purity increased and the brightness decreased with the color scores.


The


Color scores, spectral characteristics and Hunter Color Difference Meter
values for samples of reconstituted frozen concentrated orange juice are listed
in Table 2.


Table 2. Spectral characteristics, Hunter Color Difference Meter values,
and USDA color scores for reconstituted frozen concentrated orange juices

Sample Score DWL Purity Brightness Rd a b

C-8 32 578 my 72% 33.8% 27.1 -6.7 28.5
C-7 33 577 76% 31.3% 24.5 -6.9 28.3
C-22 34 578 74% 31.0% 26.0 -6.2 29.2
C-13 35 579 81% 26.5% 23.8 -5.4 29.3
C-16 36 576" 88% 25.1% 21.9 -3.0 29.7
C'J 37 580 82% 23.3% 20.3 -3.1 29.4
1
Using plastic-in-glass color comparator tubes.


The juices had higher dominant wave lengths indicating more redness, than those
of the plastic-in-glass comparator tubes, which ranged from 571 to 574 mn It
ranged in the juices from 576 to 581 nmi with 78% of the samples being in the
range of 578 to 580 rmu (Table 3). The dominant wave length did not necessarily
increase with the scores, as it did in the case of the tubes (Table 1). The
position of the slope of a spectral curve indicates the redness or yellowness
of a juice. As the dominant wave length increases or decreases, the juice-be-
comes redder or yellower, respectively.








Table 3. Color scores, Hunter Color Difference Meter
reconstituted frozen concentrated orange juices


values, and Spectral characteristics for


Color HCDM values3
1,2
Sample scores Rd a b


C-8
C-7
C-9
C-10
C-ll
C-22
C-3
C-4
C-12
C-13
C-14
C-19
C-20
C-21
C-23
C-2
C-15
C-16
C-18
C-17


27.1
25.4
26.2
25.5
25.0
26.0
22.8
24.2
23.6
23.8
22.8
22.4
23.6
23.8
23.7
20.9
21.8
21.9
21.4
21.7


-6.7
-6.9
-7.4
-7.5
-7.1
-6.2
-5.4
-5.8
-6.5
-5.4
-4.6
-4.8
-4.9
-4.3
-5.0
-3.8
-4.0
-3.0
-3.8
-2.8


DWL Purity Brightness Computed Reflectance
mil % %7 Slope4 slope5 530 mn


28.5 578


28.3
28.3
28.1
28.2
29.2
29.0
29.0
28.9
29.3
29.4
29.1
29.2
29.8
29.1
28.9
29.3
29.7
28.3
29.6


577
578
577
578
578
579
580
579
579
580
576
579
580
579
581
580
576
580
580


33.8
31.3
29.4
29.8
29.1
31.0
26.4
26.5
26.3
26.5
25.5
25.8
26.9
28.0
28.3
24.2
25.0
25.1
24.4
25.2


3.38
3.52
3.84
3.53
3.68
3.76
4.29
4.81
4.68
5.03
5.00
4.58
4.57
4.75
4.26
4.78
5.00
4.84
4.65
5.04


8.1
8.9
9.2
8.2
8.8
9.5
11.5
12.0
10.6
12.0
13.1
11.5
11.0
13.0
11.6
16.1
13.0
15.9
13.4
17.5


.292
.270
.256
.261
.252
.259
.208
.202
.215
.208
.195
.201
.215
.216
.223
.175
.187
.181
.177
.179


Color scores determined visually
OJ4, OJ5, and OJ6, corresponding
2
The color scores were determined
Citrus Experiment Station.


using plastic comparator tubes. These tubes designated as OJ3,
to 38, 36, 34, and 32 color score points, respectively.

by personnel of the Florida Citrus Commission and the Florida


Hunter Color Difference Meter values.
4 0 560 MrI
4Slope of spectral curves = 560 m
500 mi
5 560-480 mu
Computed slope of spectral curves =50-480
500-480 myi









The portion on the right hand side of the slope of a spectral curve shows
the lightness or darkness of the juice. The higher the curve is, the brighter
the juice and the lower its score. When purity and brightness were plotted
against score, only brightness showed a trend with the scores.

The slope of a spectral curve can be determined by dividing the percentage
reflectance at one wave length by that at another. Thus, the slopes for the
spectral curves of 20 samples of reconstituted frozen concentrated orange juice
(Table 3) were determined by dividing the reflectance at 560 mp by that at 500
mp. When these results are compared with the scores, it is apparent that some
of the slopes, such as samples 3, 13, 14, 17 and 23, are in the wrong score
group. To obtain a better trend between the scores and the slopes of the spect-
ral curves, the reflectance value of 480 mp was subtracted from the 560 mp and
500 mu before dividing to bring all spectral curves to the same base. These
results (Table 3) showed a much better trend with both the scores and slopes in-
creasing. When the reflectances at 530 mn were compared with the scores (Table
3), correlation between them was very good.

Having obtained the above information the reflectance of only four orange
juices was measured using two filter type instruments, the Photovolt Reflectance
Meter with a green 540 mu tristimulus filter and a Bausch and Lomb Spectronic 20
with reflectance accessory unit and set at 520 np. Results are reported in
Table 4.


Table 4. Photovolt and Spectronic-20 reflectance values
and USDA color scores for reconstituted frozen concentrated
orange juices

Sample Score PV/540 mp. S-20/520 mp.

C-10 33 21.5 70.0
C-23 35 20.5 65.0
C-18 36 19 60.0
C-17 37 19 60.5

Using plastic-in-glass color comparator tubes.


It appears that an instrument with a monochromatic source of illumination and a
suitable set of filters might be used to obtain numerical color scores for
citrus juices. However, additional data are needed.











Florida Citrus Experiment Station
and Florida Citrus Commission,
Lake Alfred, Florida. 400-10/12/65-GJE










Literature Cited


1. Hunter, Richard S. A Colorimeter for Grading Citrus Juices. Citrus
Station Mimeo Report CES 64-3 (1963).

2. Huggart, R. L. and F. W. Wenzel. Measurement and Control of Color of
Orange Concentrate. Proc. Florida State Hort. Soc. 67, 210 (1954).

3. Huggart, R. L. and F. W. Wenzel. Color Differences of Citrus Juices
and Concentrates Using the Hunter Color Difference Meter. Food Technology 9,
27 (1955).

4. Huggart, R. L., R. W. Barron, and F. W. Wenzel. Evaluation of Hunter
Citrus Colorimeter for Measuring the Color of Orange Juices. Citrus Station
Mimeo Report CES 65-2 (1964).

5. Kramer, Amihud and Bernard A. Twigg. Fundamentals of Quality Control
for the Food Industry. The Avi Publishing Company, Inc., Westport, Connecticut
(1962).

6. MacKinney, Gordon and Angela C. Little. Color of Foods. The Avi
Publishing Company, Inc., Westport, Connecticut (1962).

7. Maerz, A. and M. Rea Paul. A Dictionary of Color. McGraw-Hill Book
Company, Inc., New York, New York (1930).

8. United States Standards for Grades of Frozen Concentrated Orange Juice.
United States Department of Agriculture, Agricultural Marketing Service,
Washington, D. C. (Effective October 19, 1964).

9. Wenzel, F. W. and R. L. Huggart. Relation Between Hunter Color-
Difference Meter Values and Visual Color of Commercial Frozen Concentrated
Orange Juice. Proc. Florida State Hort. Soc. 75., 331 (1962).



















Florida Citrus Experiment Station
and Florida Citrus Commission,
Lake Alfred, Florida. 400-10/12/65-GJE




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