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The ‘Roche Yolk Colour Fan‘—An Instrument for Measuring Yolk Colour
The 'Roche Yolk Colour Fan'—An Instrument for Measuring Yolk Colour J E A N P A U L VUILLETJMIER
F. Hojftnann-La Roche &* Co. Ltd., Basle, Switzerland (Received for publication August 15, 1968)
INTRODUCTION
I
N C R E A S I N G importance is being given to the colour of egg yolk when judging the quality of eggs. Besides the customary standards of measurement such as shape and weight, firmness of the shell, freshness, structure of egg white and yolk etc. the colour of yolk and its year round constancy are decisive criteria in the maintenance of standardized egg quality (Farnsworth and Nordskog, 1955; Braunlich, 1962, 1966; Bartlett and Podger, 1962; Snyder, 1962; Tagwerker, 1962; Scholtyssek, 1962, 1964; Scholtyssek and Bohm, 1962; Torges, 1964; Mehner et al., 1965; Brown, 1964; Schmidt, 1963). I n the last ten to fifteen years a number of papers appeared which are concerned especially with pigmentation of the yolk, e.g. b y Rescheleit (1953); Steinegger and Zanetti (1957, 1959); Steinegger et al. (1957); Rauch (1959, 1960, 1961); Scholtyssek et al. (1961, 1966); Smetana (1961); Brown (1964); Carlson et al. (1961); T r e a t (1963); Boguth and Czernicki (1962); Mainguy and Rouques (1965); Hartfiel and Schmitten (1965, 1966); Blommaert and Steenis (1963). T h e numerical definition of colours according to present concepts is not a simple, pictorial representation such as scalar variables, e.g. mass, time, volume. T h e measurement of colour, or in other words the determination of values characterizing a colour perception, translates the functions of h u m a n vision with the help of physical measuring instruments. T h e laws of additive colour mixing show t h a t any colour perception can be pro-
duced b y mixing three suitable spectral stimuli or primaries in the proper ratio. The h u m a n eye seems to judge the visible p a r t of the electromagnetic spectrum by only three different spectral sensitivity functions, which are experienced b y the observer as a single effect or colour perception. T h u s three numbers or quantities are required in order to clearly define any one colour perception. Colours m a y therefore be understood as local vectors in a colour space. Each point within this colour space characterizes a colour according to hue (wavelength of identical hue), saturation (proportion of spectral light in the mixture of spectral and white light) and luminosity (intensity of light perception connected with colour perception). These are the three properties which any observer with normal vision would attribute to "colour" as a sensual perception. In the following, the ''tristimulus values" of the standard C L E . system as defined'by the International Commission on Illumination ( C L E . ) (1931) as a conventional reference system for colour measurements, will be used ( D . I . N . 5033, sheets 1-8. See also Mackinney a n d Little, 1962). T h e three quantities which characterize a colour perception with a defined illuminant are symbolized by X , Y and Z (transformed, unreal primaries); from these, chromaticity coordinates x, y, z can be calculated as follows:
767
X %
Y
~ X + F +• Z
y
~ X + F + Z
Z 2
~ F+ F+Z
768
J . P . VUILLETJMIER
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FIG. 1. The chromaticity diagram of the C L E .
and therefore:
x + y + z = 1. If the derived values of x and y are plotted in a rectangular co-ordinate system, a very convenient representation according to hue and saturation results; the luminosity, not defined in the diagram is expressed by adding the tristimulus value of Y to the coordinates x and v. The
chromaticity diagram of the C L E . is shown in Fig. 1. T h e chromaticity co-ordinates x, y of the spectral colours form an unclosed continuous curve. T h e straight line connecting its end points is called "purple line". Each real colour has its colour locus within the surface defined by this curve. For reflectance measurements, the colour of the illuminating light is considered
769
ROCHE YOLK COLOUR FAN
achromatic. All degrees of saturation of a colour hue lie on the connecting line between the location of the illuminant and the corresponding point on the spectral curve (line of constant dominant wavelength). Several measuring principles can be applied for the practical evaluation of colours. At the present time, the spectral method is generally considered to be the most accurate, being less dependent on the characteristics of measuring instruments than other methods. The measuring process and evaluation are, however, tedious, because the colour perception to be defined is understood as a sum of spectral stimuli. The tristimulus values X, Y and Z can be represented by the following integrals:
operations: X=770 nm
X =
V
/3x(aWx)
X=380 n m
for standard illuminant JV X—770 nm
y=
Z
A(5v*x)
X=380 n m
for standard illuminant ,Y X=770 nm X=380 n m
for standard illuminant N
The expressions in brackets are tabulated for the C L E . standard illuminants. The values of fi at 80 or 40 different wavelengths are to be measured and the products and sums formed. The whole measuring process is actually an approxima1 r L 1 r L tion or estimation, and becomes less X = — I\xxd\, Y = — J \y*d\ accurate with a decreasing number of meak JK k JK suring points. Therefore, depending on which apparatus or measuring method is and used, the results obtained for the three 1 rL values will differ for one and the same Z = — I 4>\Z\d\ colour. It may be possible to obtain conk JK sistent results between different investiLimits of integration are the short-wave gators by fixing the type of instrument (K) and the long-wave (L) limits of the and the method of calculation; but this visible spectrum. \ d\ is the colour stim- procedure is rather difficult to put into ulus function in the wavelength range practice and is not suitable for serial exdX, i.e. an amount of light energy acting on amination of egg yolks. the eye, which depends on the radiation Besides objective measurement of the function Sx (spectral energy distribution) tristimulus values, there is another posand on the reflectance function fix (resibility of evaluating colours, i.e. by comflectance curve) of the surface colour parison with colour charts. According to (sample); therefore \ = s\-fi\. The terms DIN 5033, sheet 5, it is permissible to x, y and z are the distribution coefficients define colours by means of direct compariwhich relate the energetic value \ to the son with sample collections, provided that three equal energy distribution curves of each time an absolutely identical sample the C L E . standard observer. can be found. Such sample collections In practice, integration is replaced by have been developed e.g. by Ridgway summation of a number of readings, e.g. (1912), Munsell (1915), Ostwald (1917), with intervals of 5 nm or 10 nm (weighted Maerz and Paul (1930), Prase (Baumann, ordinate method). The measurement of 1927), and Hickethier (1952). However, colour is then reduced to the following
770
J . P . VUILLEUMIER
these charts are hardly suitable for measuring the yellow colour of egg yolk. These collections contain a relatively large number of colour samples in order to cover the whole range of real colours, and yet there remain within the relatively small range of yolk colour only a few samples, the gradation of which is in most cases unfavourable for measuring the yolk. The real purpose of measuring the colour of egg yolks however is not in fact to obtain an accurate colorimetric definition of egg yolk colour, but to make a selection according to quality. It seems feasible to replace the accurate reflectance measurement by a subjective assignment to classes with similar characteristics. With this method, all those colours are allotted to a class which in the observer's eye show only a slight deviation from a certain standard colour. The standard colour forms so to speak the centre of the class. If it were possible to choose standard colours in such a manner that each yolk colour could be attributed subjectively without any doubt to one, or in exceptional cases, to two adjoining classes, and if it could be demonstrated that these standard colours really show the usual range of yolk colours, then all the requirements of grading according to quality would be met. The colorimetric studies on egg yolk by Boguth and Czernicki (1962) have shown that it should certainly be possible to develop such a scale of standard colour samples. It was found, for example, that the yolk colours of eggs consumed in Germany, were all within a closely limited area of the C L E . chromaticity diagram. Mainguy and Rouques (1965) published similar findings on conditions prevailing on the French market. For the establishment of a colour scale it is sufficient to select as standard colours certain colour
samples situated within this zone, perhaps in such a way that the colours are perceived subjectively as being at equal intervals. Then the standard colour situated at one end of the zone, e.g. the one with the lowest saturation, is marked class No. 1, and the following standard colours numbered consecutively. The scale obtained in this way covers practically all eggs available on the market and can be used to define them clearly. Besides these eggs with yolk colours situated more or less within the zone defined by Boguth and Czernicki (1962) or Mainguy and Rouques (1965), there may be eggs which do not fit into this scale; the colour of these egg yolks is characterized by a strong greenish, or by a slight dirty red-orange tinge. These egg colours are usually the result of very particular feeding conditions, and most consumers refuse them. Yolk colours which cannot be classified with the scale described, must be designated "off" colours. Even before the studies by Boguth and Czernicki (1962), many attempts to develop such a scale were made. Probably the first suitable scale was described by Kupsch (1934). It consisted of ten grades, from white-yellow to orange-yellow corresponding to shades chosen from the Ostwald colour atlas. The colour samples were rectangular sheets fixed to each other in fan-like fashion and numbered on the back from 1 to 10. At about the same time, the 'yolk colour index' was produced in the United States by Heiman and Carver (1935). Coloured watch-glasses fixed to the edge of a circular black plate served as standard colours. The lacquer was applied on the concave side of the glasses, and they were fixed with the convex side pointing upward, to give the impression of whole yolks. The colour scale ranged from yellowish-white through yellow to red-
ROCHE YOLK COLOUR FAN
771
orange, and was numbered continuously and is referred to as "Roche Yolk Colour from 1 to 24. A small edition of this stan- Fan Edition 1965". dard was issued by the 'Federal DepartDESCRIPTION OF THE 15-GRADE ment of Agriculture' and was soon ex'ROCHE YOLK COLOUR FAN' hausted. /. Outer Shape. The shape of the original Another scale was made available in 12-grade colour fan was maintained for 1956 by F. Hoffmann-La Roche & Co. Ltd., Basle, and described by Steinegger the 15-grade 'Roche yolk colour fan'. The and collaborators. The scale consisted of colour layer is applied on flat cardboard 12 colour sheets, joined to form a fan sim- lamellae. Turner and Conquest (1939) ilar to the arrangement by Kupsch. This pointed out that colour layers of this type first 12-grade 'Roche Yolk Colour fan' cannot completely reproduce the colour was distributed only on a limited scale. impression of egg yolks. Ashton and The colour sheets were spray dyed press- Fletcher (1962) gave their standard board lamellae, 3X16 cm., the outer end colour holders a convex shape, as did also having a triangular recess. Egg yolks pig- Heimann and Carver (1935). There are, mented at different intensities served as however, very important reasons against guides for the blending of the lacquer pig- viewing the whole undisturbed egg yolk. ments, the match being checked merely by The undisturbed egg yolk is very glossy on visual comparison. Several editions of this the surface. This makes it difficult to meafan were produced up to the year 1962; the sure the colour objectively, and also to colour sheets of the different editions, evaluate subjectively with the help of however, showed deviations of varying colour scales. This difficulty can hardly be avoided by giving the reference standard degree. a special shape. Another point is that egg Finally, Ashton and Fletcher (1962) in yolks are slightly transparent; colour imCanada developed a yolk colour scale conpression is imparted via a certain depth of sisting of fifteen colour samples. The the layer. It would be very difficult techspray colouring method was used also by nically to reproduce these conditions on a these authors. The colour lacquer was apmodel, unless a method using standard plied to spherical light-metal caps with yolks for this purpose could be found. circular holes. Finally, egg yolk is formed in the developAll these colour scales are deficient in ing egg in concentric layers. About fourone or another. In some cases, this is due teen days are required to develop a comto technical difficulties, in others, the relationships demonstrated in the study of plete yolk. If during this period, there is a Boguth and Czernicki (1962) are not re- change in the ration, it is quite possible spected. Thus, it seemed appropriate to that the outer layers will have a colour develop a new colour scale which would different from the center. In this case it not have the deficiencies of the existing would lead to wrong conclusions to look only at the undisturbed egg yolk. If, howones. ever, the yolk is separated from the eggA first, small edition of the new colour white, then homogenised and poured into scale with 15 sheets was produced in 1962 a small petri-dish, the above-mentioned to 1963. This colour scale is referred to as difficulties do not apply, and the layer ob"Rouche Yolk Colour Fan Edition 1963". tained for observation of the colour can be A second larger edition appeared in 1965
772
J . P . VUILLEUMIER
regarded as infinitely thick. I t is now possible to select the best matching colour sheet; under these circumstances it is even possible at any time to check the validity of the visual choice objectively, as the colour locus of the homogenised yolk and of the colour sheet can be defined b y the same measuring method, e.g. t h a t described b y Boguth and Czernicki (1962). This is impossible with any other technique of visual comparison, because a series of auxiliary hypotheses would be required to relate it to the instrumental measurement. 2. Colour Holders. T h e choice of the colour holder depended on the colouring method used. Preliminary studies with transparent foil were unsuccessful, because the required high saturation could not be obtained. Only opaque materials which could be printed on both sides were found satisfactory. We decided on white Bristol cardboard. 3. Printing Method. Experience showed t h a t even small differences in the thickness of the colour layer altered the chromaticity coordinates x and y. This effect is particularly pronounced with colour samples of high saturation. T h e colour layer was, therefore, applied b y the screen printing technique. This method has a high covering capacity and yields a reproducible thickness of layer. Furthermore, it is suitable for serial production of colour sheets. However, the screen printing had to be performed with colour pastes of the thickest possible consistency to get into the range of high saturation. These pastes could only be handled by using coarser-meshed screens than the usual ones and by filling the screen before the actual printing. 4. Printing
Colours. Theoretically, carot-
enoids such as they occur in egg yolks, would be the ideal pigments for a colour fan. However, they had to be rejected because they are not light-fast. We used, therefore, very light-fast organic pigments of the type Hansa-yellow, permanent yellow, permanent orange and molybdate orange light-fast. T h e low degrees of saturation also contain titanium dioxide as a white component. A special alkyd resin resistant to yellowing was chosen as binding agent. 5. Tristimulus Values. Our first studies showed t h a t with each new edition of the colour fan, in spite of identical prescriptions for colour mixture, differences in the instrumentally determined chromaticity coordinates of individual colour sheets were liable to occur. Therefore, it was decided not to define the sheets of the colour fan by prescription of colour mixtures, b u t b y the chromaticity coordinates x and y. These chromaticity coordinates must be regarded as ideal values. Each edition of the colour fan m a y deviate very slightly, as shown in Fig. 2. But for the visual evaluation of yolk colour with the fan, these differences are of no consequence. At first it seemed obvious to refer exclusively to the study by Boguth and Czernicki (1962) when choosing these ideal coordinates. However, this did not prove practicable. On the one hand consideration had to be given to what could be realised with the pigments and printing methods chosen, on the other hand the customary yolk pigmentation in each different country bad to be considered. Particularly within the range of high saturation, a shift of the hues towards orange had to be extended somewhat further than planned by Boguth and Czernicki (1962). T h e procedure in detail was as follows:
773
ROCHE YOLK COLOUR FAN
7
5
8
f> 9
0,45
9
585 mu *%
11
2 1
u
X*o
* Coordinates selected for the Roche colour fan 0
Roche colour fon edition
1965
X Roche colour fan edition
1963
0,40
0,45
1 0,50
FIG. 2. Section of the chromaticity diagram.
First a series of pigment mixtures were produced, trying to keep prescriptions as simple as possible, so that the mixtures could be produced at any time. At the same time, eggs from different sources were supplied to the colourist. Some of the eggs came from the market, some were chosen because their yolks had particularly weak or strong colours due to special rations. Printings were made of the pilot mixtures obtained, and their chromaticity coordinates determined by reflectance measurement. All proofs which visually impressed as successful representations of yolk colours were also found to have the correct hue when measured objectively (chromaticity coordinates x and y). There were, however, considerable differences in luminosity in comparison with the egg yolks (value F). Attempts to decrease the luminosity by addition of black pigment
or by printing on grey or black cardboard were not successful. The brightness was indeed decreased by these measures, but at the same time the chromaticity coordinates * and y were altered. This shift always occurred toward lower saturation. Thus it became altogether impossible to produce sheets having both high saturation and the same luminosity as egg yolks. The sheets of lower saturation, though correct with regard to chromaticity, were of much poorer quality visually than the sheets with the above-mentioned difference in brightness. Some not clearly definable differences in the structure of the egg yolks and the colour sheets probably cause these discrepancies in the results of reflectance measurement. The choice of proofs were, therefore, made dependent on their suitability by visual evaluation; the objective measurement served merely as
774
J . P . VUILLEUMIER
TABLE 1.—Chromaticity coordinates x and y for the improved 'Roche yolk colour fan' Sheet No.
X
y
Sheet No.
X
y
1 2 3 4 5 6 7 8
0.393 0.407 0.421 0.435 0.449 0.462 0.473 0.483
0.417 0.428 0.438 0.446 0.452 0.456 0.458 0.458
9 10 11 12 13 14 15
0.493 0.502 0.509 0.515 0.521 0.526 0.530
0.457 0.454 0.448 0.439 0.429 0.418 0.407
the test for correct chromaticity. The coordinates x and y of the colour sheets obtained in this manner lie within the zone of the chromaticity diagram defined by Boguth and Czernicki (1962). The values x and y of these selected proofs are given in Table 1; as these numbers represent at the same time ideal values for the different editions of the improved 'Roche yolk colour fan', they were tabulated without the appertaining value of Y for luminosity. Fig. 2 shows the course of these colour points in a section of the chromaticity diagram. Table 2 contains the results of reflec-
tance measurements on proofs of the latest 1965 edition. The values of the 1963 edition are quoted for comparison; a graphic representation is included in Fig. 2. Agreement with the ideal values of Table 1 is excellent. The reflectance measurements were performed with two spectrophotometers 'Zeiss PMQ 11 with reflectance attachment RA 3' in position A (diffuse sample illumination; measurement of the vertically reflected light). One instrument was provided with a glass monochromator M4 G i l ; measurement was carried out between 380 and 770 nm from 5 to 5 nm (evaluation for standard illuminant C). The other instrument was fitted with a quartz monochromator M4 QII; measurement was carried out from 10 to 10 nm within the same range of wave lengths. With the usual smooth shape of the reflectance spectrum, the results of the measurements were identical with both instruments. 6. Method of Classifying Egg Yolks with the 'Roche Yolk Colour Fan'. For the practical use of the 'Roche yolk colour
TABLE 2.—Results of reflectance measurements of Z editions of the 'Roche yolk colour fan' Roche yolk colour fan, edition 1963
Roche yolk colour fan, edition 1965 Sheet No.
X
y
y
Sheet No.
X
y
Y
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
0.397 0.411 0.423 0.437 0.451 0.464 0.473 0.484 0.496 0.508 0.508 0.514 0.520 0.523 0.531
0.415 0.427 0.438 0.448 0.452 0.456 0.457 0.459 0.458 0.454 0.449 0.438 0.428 0.417 0.409
6.816 6.676 6.563 6.398 6.222 6.090 5.996 5.865 5.743 5.552 5.367 5.010 4.635 4.227 4.005
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
0.392 0.405 0.418 0.436 0.450 0.463 0.473 0.479 0.488 0.500 0.507 0.514 0.520 0.527 0.532
0.416 0.427 0.435 0.444 0.451 0.454 0.455 0.455 0.456 0.454 0.444 0.435 0.428 0.419 0.407
6.877 6.754 6.681 6.507 6.336 6.089 6.018 5.951 5.761 5.702 5.348 4.999 4.732 4.374 4.03
775
ROCHE YOLK COLOUR FAN
, 580 mji
X Roche egg yolk colour fan " "yolk colour index" \l2
X•
A
V
/ u • /u ' /
16 l'
1?
20
•
22
«
23
0,35-
0,35
0,40
FIG. 3. Colour prints of the standard glasses of the yolk colour index by Heiman and Carver, in comparison with the 15-grade 'Roche yolk colour fan'.
fan', the usual rules for comparing colours apply. Visual evaluation should be carried out against a neutral background (white, grey or black). Diffuse light is best, preferably daylight coming from a direction opposed to the sun. The yolks are separated from the eggwhite, and are evaluated either whole, or after stirring up, in small flat dishes. For accurate measurements, homogenisation of the yolk is to be preferred for the reasons mentioned before. The dishes should not be more than 3-4 cm. in diameter, so that the homogenised yolks are at least 10 mm. deep. The colour fan is opened, the leaves arranged in the correct sequence, and the yolk passed along the scale until the most suitable sheet is found. The scale is viewed from above and held in such a
manner that the surface does not appear glossy. The colour sheets should not be exposed to light for too long. When not in use, the fan is kept closed. If studies are carried out for comparison of pigmentation, it is recommended to have the evaluation done by the same observer; if this is not possible, the different observers should be tested for concordance in colour perception. COMPARISON OF THE 'ROCHE YOLK COLOUR FAN' WITH OTHER YOLK COLOUR SCALES
/. Standard Colour Values Shown on Diagrams. Fig. 3. shows the colour points of the standard glasses of the 'yolk colour index' by Heiman and Carver (1935), in
776
J . P . VUILLEUMIER
. 580 mu. X Roche egg yolk colour fan • Roche colour fan edition 1962
x
0,45-
X
.
• 4
X X
1— 0,35
5
X
*
:
X
y
x
6
> 585 mn
x x
.
X
7
3
0,40
1— 0,45
I 0,50
FIG. 4. Comparison of 12-grade 'Roche yolk colour fan' and 15-grade 'Roche yolk colour fan'.
comparison with the 15-grade 'Roche yolk colour fan'. The values for the 'yolk colour index' were determined by other investigators1 using the 10 selected ordinate method. The first four glasses of the 'yolk colour index' show very low colour saturation and are used only rarely, because they represent yolk colours resulting from carotenoid-free feeding. Glasses No. 5-12 are within the range of yolk colours, the following glasses, however, move too soon, i.e. with too low a saturation, into the orange region. The first, 12-grade 'Roche yolk colour fan' had the same deficiency, as demonstrated in Fig. 4. The break in the progression of the colour points at fan sheet No. 7 meant that only 1
Dr. John V. Spencer, Food Technology Section, Department of Animal Sciences, Washington State University, Pullman: private communication.
strongly pigmented or red-tinged yolks could be allotted to classes No. 7-12, the higher saturations of pure yellow accumulating in class No. 6. Fig. 5 represents a comparison between the Fletcher colour scale and the 15-grade 'Roche yolk colour fan'. The chromaticity coordinates of the Fletcher rings are quoted from the study by Ashton and Fletcher (1962). Both colour scales cover essentially the same zone of the standard colour chart; the Fletcher colour scale shows a rather irregular progression, which may be due to the technique of colour application by spraying. 2. Attempt to Correlate Different Yolk Colour Standards. Any attempt to select standards representing identical quality from the different volk colour scales, has
777
ROCHE YOLK COLOUR FAN
590 mil
X Roche egg yolk colour fan
10 •
* Fletcher colour rings
0,45'
11
X
;x
X 14
X
•
0,35 -
_L
0,35
_1_
_L
0,40
0,45
0,50
FIG. 5. Comparison between Fletcher colour scale and 15-grade 'Roche yolk colour fan'.
to be regarded as a rough approximation, because colour samples are assorted according to subjectively established similarity. As the colour glasses of the 'yolk colour index' and the Fletcher colour TABLE 3.—Assignment of class values with different scales by visual comparison Roche yolkcolour fan (15 grade) 1 2 3 4 3
6 7 8 9 10 11 12 13 14 IS
o+ S— S
Roche fan (12 grade) 1962 2 2 3 3 4
o+ o+ 0+
3
Fletcher colour rings 1 2 3 4 6 9
6 7 7
SS-
7J S -
8 9 9 10
SSSS-
(1) (5) (7) (8) (9)
10 12 (11) 13 14 14 IS
Clearly more reddish hue. Saturation insufficient. Saturation much lower.
yolk color index Heiraann-Carver 6 7 8 10 12 13 14 15 16 16 18 19 21 22 23
11
17 20 22
12 SSSS S S S - S S S S
rings were at our disposal at different moments and only for a limited period, the most similar standard colours were determined by direct visual comparison with the 'Roche yolk colour fan'. These results are given in Table 3. Somewhat different results are obtained if egg yolks are evaluated at the same time with different colour scales, instead of comparing colour scales direct. Such an experiment was carried out by Marusich et al. (1964). Two observers evaluated the same yolks with different scales; their evaluations were averaged. Table 4 shows the values obtained. The difference between the 'Roche yolk colour fan' and its predecessors becomes more apparent here. With the older colour scales, it was not possible, as with the new fan, to assign yolks to classes 8, 9 and 10, because the
778
J . P . VUILLEUMIER
TABLE 4.—Evaluation of egg yolks with different colour scales according to Marusich (1964) Roche fan 1962 12-grade
Yolk color index
4 5 6 7
9.0 10.8 12.1 14.3 15.7 17.5 18.9 20.8 21.7 22.7
n
8 9 10 11 12
Roche yolk Yolk colour fan color 15-grade index
Roche yolk Roche fan colour fan 1962 15-grade 12-grade
4 5 6 7
8.6 9.9 11.0 12.1
4 5 6 7
3.5 4.5 5.5 6.0
8 9 10 11 12 13 14 15
13.1 13.1 13.1 15.7 18.1 18.9 20.0 21.4
8 9 10 11 12 13 14 15
6.5 6.5 6.5 7.3 7.8 9.0 9.7 1 0.2
corresponding degrees of saturation of yellow were lacking. They were, therefore, assigned to class 6 or 7 of the 12-grade Roche fan 1962, or class 13 of the 'yolk colour index'. The assignment to higher classes of these scales required a marked shift of the yolk colour towards red. SUMMARY
The 'Roche Yolk Colour Fan' has been re-designed to match more closely the average egg yolk. Fifteen colour grades with chromaticity coordinates situated within the range of normal egg yolk colours have been selected and defined by hue and saturation in the C L E . system of colour measurement. A comparison is drawn between the 'Roche Yolk Colour Fan' and other yolk colour scales. ACKNOWLEDGEMENT
We are indebted to Professor W. Boguth, Giessen, for valuable suggestions, and for carrying out a series of reflectance measurements. The fan was produced jointly with Dr. Finckh & Co. Ltd., Schweizerhalle (Mr. G. Jegher), and Tagefa, Eptingerstrasse 4, Basle (Mr. H. R. Schaub). REFERENCES Ann Baker, C. M., 1960. The genetic basis of egg quality. Brit. Poultry Sci. 1: 3-16.
Ashton, E. H., and D. A. Fletcher, 1962. Development and use of color standards for egg yolks. Poultry Sci. 41: 1903-1909. Bartlett, B. E., and R. N. Podger, 1962. Some aspects of egg quality. J. Dept. Agric. Victoria, September. Bartlett, B. E., and M. R. Barlow, 1963. Consumers' choice prefer deep egg yolk colour. The Egg Producer, August 20, p. 12. Baumann, R., 1927. Neue Farbtonkarte, Syst. Prase, Aue in Sachsen. Blommaert, M., and G. Steenis, 1963. Prakttijkoproeven betreffende verbetering van de dooierkleur door toevoeging van o-carotenoid concentraten aan het voeder van leghennen. Vlaams Diergeneesk.Tijdschr. 32, (11): 306-317. Boguth, W., and B. Czernicki, 1962. Farbmetrische Untersuchungen an Eidottern nach Verfiitterung verschiedener Carotinoide. Zbl. Veterinarmed. 9, 779-786. Braunlich, K., 1962. Die Eidotterfarbe als Qualitatsfaktor. Gefliigelhof, 25 (26): 448, 449, 451. Brown, R. H., 1964. Yolk color important to consumer. Feedstuffs, 36: 55. Carlson, C. W., F. L. Shinnick, M. A. Sneller and A. W. Halverson, 1961. Producing dark colored egg yolks. South Dakota Farm Home Res. 12: 20-23. Commission Internationale de l'Eclairage, 1931. Proceedings, comptes rendus des seances. Proceedings Eighth Session, Cambridge, England, September 19-29. Czernicki, B., and H. Weiser, 1962. Zur Beeinflussung der Dotterfarbe durch einige reine Carotinoide sowie durch Paprika. Zbl. Veterinaermed. 9: 899-904. Farnsworth, G. M., Jr., and A. W. Nordskog, 1955. Breeding for egg quality. Poultry Sci. 34: 16-26. Hartfiel, W., and H. Schulze-Messing, 1963. Verfahren zur schnellen Bestimmung der Dotterfarbe bei Hiihnereiern. Arch. Gefliigelk. 27: 317324. Hartfiel, W., and F. Schmitten, 1965. Die Bestimmung der Eidotterfarbe. Arch. Gefliigelk. 29: 367-386. Hartfiel, W., and F. Schmitten, 1966. Untersuchungen iiber die vom Verbraucher bevorzugten Eidotterfarben. Arch. Gefliigelk. 30: 228-242. Heiman, V., and J. S. Carver, 1935. The yolk color index. U.S. Egg Poultry Mag. 41: 40-41. Hickethier,. A., 1952. Farbenordnung Hickethier, Publisher H. Osterwald, Hanover, Distributor "Der Polygraph," Frankfurt am. Main. Kupsch, W., 1934. Die Veranderung und Wertbestimmung der Eidotterfarbe. Arch..Gefliigelk. 8:97-115.
R O C H E Y O L K COLOUR F A N
MacAdam, D. L., 1953. Dependence of colour mixture functions on choice of primaries. J. Opt. Soc. Amer. 43: 533. Maerz, A., and M. R. Paul, 1930, 1950. Dictionary of Colour, McGraw-Hill Book Co., New York. Mainguy, P., and A. Rouques, 1965. Le jaune de l'oeuf. I. Etude generate de la colour du jaune d'oeuf. Bull. Soc. Sci. Hyg. Aliment. 53: 83-116; and II. La couleur des oeufs du marche francais' Bull. Soc. Sci. Hyg. Aliment. 53: 194-212. Marusich, W. L., G. Aeberman and T. Luciani, 1964. Unpublished work. Mehner, A., H.-G. Torges and H. Vogt, 1965. Der Einfluss erhbhter Vitamin A-Gaben auf die Eiqualitat. Arch.Gefliigelk. 29: 356-366. Munsell, A. H., 1915. Atlas of the Munsell Color System and Munsell Book of Color, Munsell Color Company Inc., Baltimore, Maryland. Munsell, A. H., 1946. A Color Notation, Tenth Ed. Munsell Color Company Inc., Baltimore, Maryland Normblatt DIN 5033, 1954. Farbmessung, Blatt 1-8 und Beiblatt. Distributor: Beuth, Berlin, April. Normblatt D I N 6164, 1955. DIN-Farbenkarte. Distributor: Beuth, Berlin, May. Ostwald, W., 1918. Der Farbenatlas. Unesma G.m. b.H. Publishing Company, Leipzig. Ostwald, W., 1919. Der Farbkorper und seine Anwendung zur Herstellung farbiger Harmonien. Unesma G.m.b.H. Publishing Company, Leipzig. Ostwald, W., 1945. Colour Table. Publisher: Pfenningsdorf, Berlin. Rauch, W., 1959, 1960, 1961. Ueber die Beeinflussung der Dotterfarbe durch carotinoidhaltiges Legehennenfutter. 1. Mitteilung: Arch.Gefliigelk. 23: 319-331. 2. Mitteilung: Arch.Gefliigelk. 24: 417-431. 3. Mitteilung: Arch.Gefliigelk. 25:494-502. Rescheleit, Ch., 1953. Beitrag zum Problem der Dotterfarbung. Dtsch.Wirtschaftsgeflugelzucht, 5: 13-15. Ridgway, R., 1912. Color Standards and Color Nomenclature. Published by the author, Washington, D.C. Schmidt, L., 1963. Ei und Ei-ist zweierlei. Deutsche Gefliigelwirlschaft, 15: 192. Scholtyssek, S., 1962. Stand der Qualitatsforschung bei Geflugelzuchtprodukten. Deutsche Gefliigelwirtschaft 14: 617-620 and 631. Scholtyssek, S., 1964. Der Einfluss der Fiitterung auf die Qualitat bei Eiern und Geflugelfleisch. Ziichtungskunde, 36: 449-458. Scholtyssek, S., and U. Bohm, 1962. Zur Bestimmung der Dotterfarbe des Hiihnereies. Kraftfutter, 45: 69-71.
779
Scholtyssek, S., R. Kirsammer, E. Hanser and B. Kurmann, 1965. Beitrag zur Frage der Dotterfarbung. Arch.Gefliigek. 29: 249-262. Scholtyssek, S., R. Kirsammer, E. Hanser and B. Kurmann, 1966. Die Eignung verschiedener objektiver Methoden zur Messung der Dotterfarbe. Arch. Geflugelk. 30: 177-191. Scholtyssek, S., G. Lorenz and H. Erfani, 1961. Die Beeinflussung der Eidotterfarbe durch synthetische Carotinoide. Arb.d.Landw.Hochsch.Hohenheim 1:77-91. Smetana, P., 1961. Feeding for egg yolk colour. Dept. Agric. of Western Australia, Bull. No. 2906, and J. Agr. Western Australia, 2: 3-6. Snyder, E. S., 1961. Eggs. The production, identification and retention of quality in eggs. Canada Dept. Agric. Publication 782. Splittgerber, H., 1961. Eiqualitat. Der Hiihnerbrief, Nr. 8. Steinegger, P., M. Menzi and R. Berger, 1956. Versuche zur Ermittlung der Einfliisse verschiedener Carotinoidzusatze zum Legehennenfutter auf die Dotterfarbe. Geflugelhof, 19: 215-220. Steinegger, P., K. Steriff and P. Zeller, 1957. Pigmentierung und Eidotterfarbung bei Geflugel nach Verfiitterung synthetischer Carotinoide. Mitt. Gebiete Lebensmitteluntersuch. Hyg. 48: 445-149. Steinegger, P., and G. Zanetti, 1957. Versuche zur Emittlung der Einfliisse verschiedener Carotinoidzusatze zum Legehennenfutter auf die Dotterfarbe. Arch. Geflugelk. 21: 236-245. Steinegger, P., and G. Zanetti, 1959. Versuche zur Ermittlung der Einfliisse verschiedener Carotinoidzusatze zum Legehennenfutter auf die Dotterfarbe. Arch. Geflugelk. 23: 166-173. Tagwerker, F. J., 1962. Yolk colour and its relation to quality. Paper presented at the First International Egg Marketing Conference, Sydney, August 20-22. Torges, H. G., 1963. Untersuchungen iiber den Erblichkeitsanteil der Eiqualitatsmerkmale Eiklarindex, Bruchfestigkeit der Eischale und Dotter farbe. Z. Tierzuchtung Ziichtungsbiol. 79(3): ; 197-216. Torges, H. G., 1964. Die Auswirkung einer iiber mehrere Generationen fortlaufenden Selektion von Leghornhennen auf Eiqualitatsmerkmale. Arch. Geflugelk. 28: 69-75. Treat, C , 1963. Egg yolk pigmentation. A discussion of the practical aspects of feeding for specific color. Feedstuffs 35(52): 18-22. Turner, A. W., and V. Conquest, 1939. A practical method of determining color in fresh and frozen egg yolks U.S. Egg Poultry Mag. 45: 668-670.
F. Hojftnann-La Roche &* Co. Ltd., Basle, Switzerland (Received for publication August 15, 1968)
INTRODUCTION
I
N C R E A S I N G importance is being given to the colour of egg yolk when judging the quality of eggs. Besides the customary standards of measurement such as shape and weight, firmness of the shell, freshness, structure of egg white and yolk etc. the colour of yolk and its year round constancy are decisive criteria in the maintenance of standardized egg quality (Farnsworth and Nordskog, 1955; Braunlich, 1962, 1966; Bartlett and Podger, 1962; Snyder, 1962; Tagwerker, 1962; Scholtyssek, 1962, 1964; Scholtyssek and Bohm, 1962; Torges, 1964; Mehner et al., 1965; Brown, 1964; Schmidt, 1963). I n the last ten to fifteen years a number of papers appeared which are concerned especially with pigmentation of the yolk, e.g. b y Rescheleit (1953); Steinegger and Zanetti (1957, 1959); Steinegger et al. (1957); Rauch (1959, 1960, 1961); Scholtyssek et al. (1961, 1966); Smetana (1961); Brown (1964); Carlson et al. (1961); T r e a t (1963); Boguth and Czernicki (1962); Mainguy and Rouques (1965); Hartfiel and Schmitten (1965, 1966); Blommaert and Steenis (1963). T h e numerical definition of colours according to present concepts is not a simple, pictorial representation such as scalar variables, e.g. mass, time, volume. T h e measurement of colour, or in other words the determination of values characterizing a colour perception, translates the functions of h u m a n vision with the help of physical measuring instruments. T h e laws of additive colour mixing show t h a t any colour perception can be pro-
duced b y mixing three suitable spectral stimuli or primaries in the proper ratio. The h u m a n eye seems to judge the visible p a r t of the electromagnetic spectrum by only three different spectral sensitivity functions, which are experienced b y the observer as a single effect or colour perception. T h u s three numbers or quantities are required in order to clearly define any one colour perception. Colours m a y therefore be understood as local vectors in a colour space. Each point within this colour space characterizes a colour according to hue (wavelength of identical hue), saturation (proportion of spectral light in the mixture of spectral and white light) and luminosity (intensity of light perception connected with colour perception). These are the three properties which any observer with normal vision would attribute to "colour" as a sensual perception. In the following, the ''tristimulus values" of the standard C L E . system as defined'by the International Commission on Illumination ( C L E . ) (1931) as a conventional reference system for colour measurements, will be used ( D . I . N . 5033, sheets 1-8. See also Mackinney a n d Little, 1962). T h e three quantities which characterize a colour perception with a defined illuminant are symbolized by X , Y and Z (transformed, unreal primaries); from these, chromaticity coordinates x, y, z can be calculated as follows:
767
X %
Y
~ X + F +• Z
y
~ X + F + Z
Z 2
~ F+ F+Z
768
J . P . VUILLETJMIER
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and therefore:
x + y + z = 1. If the derived values of x and y are plotted in a rectangular co-ordinate system, a very convenient representation according to hue and saturation results; the luminosity, not defined in the diagram is expressed by adding the tristimulus value of Y to the coordinates x and v. The
chromaticity diagram of the C L E . is shown in Fig. 1. T h e chromaticity co-ordinates x, y of the spectral colours form an unclosed continuous curve. T h e straight line connecting its end points is called "purple line". Each real colour has its colour locus within the surface defined by this curve. For reflectance measurements, the colour of the illuminating light is considered
769
ROCHE YOLK COLOUR FAN
achromatic. All degrees of saturation of a colour hue lie on the connecting line between the location of the illuminant and the corresponding point on the spectral curve (line of constant dominant wavelength). Several measuring principles can be applied for the practical evaluation of colours. At the present time, the spectral method is generally considered to be the most accurate, being less dependent on the characteristics of measuring instruments than other methods. The measuring process and evaluation are, however, tedious, because the colour perception to be defined is understood as a sum of spectral stimuli. The tristimulus values X, Y and Z can be represented by the following integrals:
operations: X=770 nm
X =
V
/3x(aWx)
X=380 n m
for standard illuminant JV X—770 nm
y=
Z
A(5v*x)
X=380 n m
for standard illuminant ,Y X=770 nm X=380 n m
for standard illuminant N
The expressions in brackets are tabulated for the C L E . standard illuminants. The values of fi at 80 or 40 different wavelengths are to be measured and the products and sums formed. The whole measuring process is actually an approxima1 r L 1 r L tion or estimation, and becomes less X = — I
770
J . P . VUILLEUMIER
these charts are hardly suitable for measuring the yellow colour of egg yolk. These collections contain a relatively large number of colour samples in order to cover the whole range of real colours, and yet there remain within the relatively small range of yolk colour only a few samples, the gradation of which is in most cases unfavourable for measuring the yolk. The real purpose of measuring the colour of egg yolks however is not in fact to obtain an accurate colorimetric definition of egg yolk colour, but to make a selection according to quality. It seems feasible to replace the accurate reflectance measurement by a subjective assignment to classes with similar characteristics. With this method, all those colours are allotted to a class which in the observer's eye show only a slight deviation from a certain standard colour. The standard colour forms so to speak the centre of the class. If it were possible to choose standard colours in such a manner that each yolk colour could be attributed subjectively without any doubt to one, or in exceptional cases, to two adjoining classes, and if it could be demonstrated that these standard colours really show the usual range of yolk colours, then all the requirements of grading according to quality would be met. The colorimetric studies on egg yolk by Boguth and Czernicki (1962) have shown that it should certainly be possible to develop such a scale of standard colour samples. It was found, for example, that the yolk colours of eggs consumed in Germany, were all within a closely limited area of the C L E . chromaticity diagram. Mainguy and Rouques (1965) published similar findings on conditions prevailing on the French market. For the establishment of a colour scale it is sufficient to select as standard colours certain colour
samples situated within this zone, perhaps in such a way that the colours are perceived subjectively as being at equal intervals. Then the standard colour situated at one end of the zone, e.g. the one with the lowest saturation, is marked class No. 1, and the following standard colours numbered consecutively. The scale obtained in this way covers practically all eggs available on the market and can be used to define them clearly. Besides these eggs with yolk colours situated more or less within the zone defined by Boguth and Czernicki (1962) or Mainguy and Rouques (1965), there may be eggs which do not fit into this scale; the colour of these egg yolks is characterized by a strong greenish, or by a slight dirty red-orange tinge. These egg colours are usually the result of very particular feeding conditions, and most consumers refuse them. Yolk colours which cannot be classified with the scale described, must be designated "off" colours. Even before the studies by Boguth and Czernicki (1962), many attempts to develop such a scale were made. Probably the first suitable scale was described by Kupsch (1934). It consisted of ten grades, from white-yellow to orange-yellow corresponding to shades chosen from the Ostwald colour atlas. The colour samples were rectangular sheets fixed to each other in fan-like fashion and numbered on the back from 1 to 10. At about the same time, the 'yolk colour index' was produced in the United States by Heiman and Carver (1935). Coloured watch-glasses fixed to the edge of a circular black plate served as standard colours. The lacquer was applied on the concave side of the glasses, and they were fixed with the convex side pointing upward, to give the impression of whole yolks. The colour scale ranged from yellowish-white through yellow to red-
ROCHE YOLK COLOUR FAN
771
orange, and was numbered continuously and is referred to as "Roche Yolk Colour from 1 to 24. A small edition of this stan- Fan Edition 1965". dard was issued by the 'Federal DepartDESCRIPTION OF THE 15-GRADE ment of Agriculture' and was soon ex'ROCHE YOLK COLOUR FAN' hausted. /. Outer Shape. The shape of the original Another scale was made available in 12-grade colour fan was maintained for 1956 by F. Hoffmann-La Roche & Co. Ltd., Basle, and described by Steinegger the 15-grade 'Roche yolk colour fan'. The and collaborators. The scale consisted of colour layer is applied on flat cardboard 12 colour sheets, joined to form a fan sim- lamellae. Turner and Conquest (1939) ilar to the arrangement by Kupsch. This pointed out that colour layers of this type first 12-grade 'Roche Yolk Colour fan' cannot completely reproduce the colour was distributed only on a limited scale. impression of egg yolks. Ashton and The colour sheets were spray dyed press- Fletcher (1962) gave their standard board lamellae, 3X16 cm., the outer end colour holders a convex shape, as did also having a triangular recess. Egg yolks pig- Heimann and Carver (1935). There are, mented at different intensities served as however, very important reasons against guides for the blending of the lacquer pig- viewing the whole undisturbed egg yolk. ments, the match being checked merely by The undisturbed egg yolk is very glossy on visual comparison. Several editions of this the surface. This makes it difficult to meafan were produced up to the year 1962; the sure the colour objectively, and also to colour sheets of the different editions, evaluate subjectively with the help of however, showed deviations of varying colour scales. This difficulty can hardly be avoided by giving the reference standard degree. a special shape. Another point is that egg Finally, Ashton and Fletcher (1962) in yolks are slightly transparent; colour imCanada developed a yolk colour scale conpression is imparted via a certain depth of sisting of fifteen colour samples. The the layer. It would be very difficult techspray colouring method was used also by nically to reproduce these conditions on a these authors. The colour lacquer was apmodel, unless a method using standard plied to spherical light-metal caps with yolks for this purpose could be found. circular holes. Finally, egg yolk is formed in the developAll these colour scales are deficient in ing egg in concentric layers. About fourone or another. In some cases, this is due teen days are required to develop a comto technical difficulties, in others, the relationships demonstrated in the study of plete yolk. If during this period, there is a Boguth and Czernicki (1962) are not re- change in the ration, it is quite possible spected. Thus, it seemed appropriate to that the outer layers will have a colour develop a new colour scale which would different from the center. In this case it not have the deficiencies of the existing would lead to wrong conclusions to look only at the undisturbed egg yolk. If, howones. ever, the yolk is separated from the eggA first, small edition of the new colour white, then homogenised and poured into scale with 15 sheets was produced in 1962 a small petri-dish, the above-mentioned to 1963. This colour scale is referred to as difficulties do not apply, and the layer ob"Rouche Yolk Colour Fan Edition 1963". tained for observation of the colour can be A second larger edition appeared in 1965
772
J . P . VUILLEUMIER
regarded as infinitely thick. I t is now possible to select the best matching colour sheet; under these circumstances it is even possible at any time to check the validity of the visual choice objectively, as the colour locus of the homogenised yolk and of the colour sheet can be defined b y the same measuring method, e.g. t h a t described b y Boguth and Czernicki (1962). This is impossible with any other technique of visual comparison, because a series of auxiliary hypotheses would be required to relate it to the instrumental measurement. 2. Colour Holders. T h e choice of the colour holder depended on the colouring method used. Preliminary studies with transparent foil were unsuccessful, because the required high saturation could not be obtained. Only opaque materials which could be printed on both sides were found satisfactory. We decided on white Bristol cardboard. 3. Printing Method. Experience showed t h a t even small differences in the thickness of the colour layer altered the chromaticity coordinates x and y. This effect is particularly pronounced with colour samples of high saturation. T h e colour layer was, therefore, applied b y the screen printing technique. This method has a high covering capacity and yields a reproducible thickness of layer. Furthermore, it is suitable for serial production of colour sheets. However, the screen printing had to be performed with colour pastes of the thickest possible consistency to get into the range of high saturation. These pastes could only be handled by using coarser-meshed screens than the usual ones and by filling the screen before the actual printing. 4. Printing
Colours. Theoretically, carot-
enoids such as they occur in egg yolks, would be the ideal pigments for a colour fan. However, they had to be rejected because they are not light-fast. We used, therefore, very light-fast organic pigments of the type Hansa-yellow, permanent yellow, permanent orange and molybdate orange light-fast. T h e low degrees of saturation also contain titanium dioxide as a white component. A special alkyd resin resistant to yellowing was chosen as binding agent. 5. Tristimulus Values. Our first studies showed t h a t with each new edition of the colour fan, in spite of identical prescriptions for colour mixture, differences in the instrumentally determined chromaticity coordinates of individual colour sheets were liable to occur. Therefore, it was decided not to define the sheets of the colour fan by prescription of colour mixtures, b u t b y the chromaticity coordinates x and y. These chromaticity coordinates must be regarded as ideal values. Each edition of the colour fan m a y deviate very slightly, as shown in Fig. 2. But for the visual evaluation of yolk colour with the fan, these differences are of no consequence. At first it seemed obvious to refer exclusively to the study by Boguth and Czernicki (1962) when choosing these ideal coordinates. However, this did not prove practicable. On the one hand consideration had to be given to what could be realised with the pigments and printing methods chosen, on the other hand the customary yolk pigmentation in each different country bad to be considered. Particularly within the range of high saturation, a shift of the hues towards orange had to be extended somewhat further than planned by Boguth and Czernicki (1962). T h e procedure in detail was as follows:
773
ROCHE YOLK COLOUR FAN
7
5
8
f> 9
0,45
9
585 mu *%
11
2 1
u
X*o
* Coordinates selected for the Roche colour fan 0
Roche colour fon edition
1965
X Roche colour fan edition
1963
0,40
0,45
1 0,50
FIG. 2. Section of the chromaticity diagram.
First a series of pigment mixtures were produced, trying to keep prescriptions as simple as possible, so that the mixtures could be produced at any time. At the same time, eggs from different sources were supplied to the colourist. Some of the eggs came from the market, some were chosen because their yolks had particularly weak or strong colours due to special rations. Printings were made of the pilot mixtures obtained, and their chromaticity coordinates determined by reflectance measurement. All proofs which visually impressed as successful representations of yolk colours were also found to have the correct hue when measured objectively (chromaticity coordinates x and y). There were, however, considerable differences in luminosity in comparison with the egg yolks (value F). Attempts to decrease the luminosity by addition of black pigment
or by printing on grey or black cardboard were not successful. The brightness was indeed decreased by these measures, but at the same time the chromaticity coordinates * and y were altered. This shift always occurred toward lower saturation. Thus it became altogether impossible to produce sheets having both high saturation and the same luminosity as egg yolks. The sheets of lower saturation, though correct with regard to chromaticity, were of much poorer quality visually than the sheets with the above-mentioned difference in brightness. Some not clearly definable differences in the structure of the egg yolks and the colour sheets probably cause these discrepancies in the results of reflectance measurement. The choice of proofs were, therefore, made dependent on their suitability by visual evaluation; the objective measurement served merely as
774
J . P . VUILLEUMIER
TABLE 1.—Chromaticity coordinates x and y for the improved 'Roche yolk colour fan' Sheet No.
X
y
Sheet No.
X
y
1 2 3 4 5 6 7 8
0.393 0.407 0.421 0.435 0.449 0.462 0.473 0.483
0.417 0.428 0.438 0.446 0.452 0.456 0.458 0.458
9 10 11 12 13 14 15
0.493 0.502 0.509 0.515 0.521 0.526 0.530
0.457 0.454 0.448 0.439 0.429 0.418 0.407
the test for correct chromaticity. The coordinates x and y of the colour sheets obtained in this manner lie within the zone of the chromaticity diagram defined by Boguth and Czernicki (1962). The values x and y of these selected proofs are given in Table 1; as these numbers represent at the same time ideal values for the different editions of the improved 'Roche yolk colour fan', they were tabulated without the appertaining value of Y for luminosity. Fig. 2 shows the course of these colour points in a section of the chromaticity diagram. Table 2 contains the results of reflec-
tance measurements on proofs of the latest 1965 edition. The values of the 1963 edition are quoted for comparison; a graphic representation is included in Fig. 2. Agreement with the ideal values of Table 1 is excellent. The reflectance measurements were performed with two spectrophotometers 'Zeiss PMQ 11 with reflectance attachment RA 3' in position A (diffuse sample illumination; measurement of the vertically reflected light). One instrument was provided with a glass monochromator M4 G i l ; measurement was carried out between 380 and 770 nm from 5 to 5 nm (evaluation for standard illuminant C). The other instrument was fitted with a quartz monochromator M4 QII; measurement was carried out from 10 to 10 nm within the same range of wave lengths. With the usual smooth shape of the reflectance spectrum, the results of the measurements were identical with both instruments. 6. Method of Classifying Egg Yolks with the 'Roche Yolk Colour Fan'. For the practical use of the 'Roche yolk colour
TABLE 2.—Results of reflectance measurements of Z editions of the 'Roche yolk colour fan' Roche yolk colour fan, edition 1963
Roche yolk colour fan, edition 1965 Sheet No.
X
y
y
Sheet No.
X
y
Y
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
0.397 0.411 0.423 0.437 0.451 0.464 0.473 0.484 0.496 0.508 0.508 0.514 0.520 0.523 0.531
0.415 0.427 0.438 0.448 0.452 0.456 0.457 0.459 0.458 0.454 0.449 0.438 0.428 0.417 0.409
6.816 6.676 6.563 6.398 6.222 6.090 5.996 5.865 5.743 5.552 5.367 5.010 4.635 4.227 4.005
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
0.392 0.405 0.418 0.436 0.450 0.463 0.473 0.479 0.488 0.500 0.507 0.514 0.520 0.527 0.532
0.416 0.427 0.435 0.444 0.451 0.454 0.455 0.455 0.456 0.454 0.444 0.435 0.428 0.419 0.407
6.877 6.754 6.681 6.507 6.336 6.089 6.018 5.951 5.761 5.702 5.348 4.999 4.732 4.374 4.03
775
ROCHE YOLK COLOUR FAN
, 580 mji
X Roche egg yolk colour fan " "yolk colour index" \l2
X•
A
V
/ u • /u ' /
16 l'
1?
20
•
22
«
23
0,35-
0,35
0,40
FIG. 3. Colour prints of the standard glasses of the yolk colour index by Heiman and Carver, in comparison with the 15-grade 'Roche yolk colour fan'.
fan', the usual rules for comparing colours apply. Visual evaluation should be carried out against a neutral background (white, grey or black). Diffuse light is best, preferably daylight coming from a direction opposed to the sun. The yolks are separated from the eggwhite, and are evaluated either whole, or after stirring up, in small flat dishes. For accurate measurements, homogenisation of the yolk is to be preferred for the reasons mentioned before. The dishes should not be more than 3-4 cm. in diameter, so that the homogenised yolks are at least 10 mm. deep. The colour fan is opened, the leaves arranged in the correct sequence, and the yolk passed along the scale until the most suitable sheet is found. The scale is viewed from above and held in such a
manner that the surface does not appear glossy. The colour sheets should not be exposed to light for too long. When not in use, the fan is kept closed. If studies are carried out for comparison of pigmentation, it is recommended to have the evaluation done by the same observer; if this is not possible, the different observers should be tested for concordance in colour perception. COMPARISON OF THE 'ROCHE YOLK COLOUR FAN' WITH OTHER YOLK COLOUR SCALES
/. Standard Colour Values Shown on Diagrams. Fig. 3. shows the colour points of the standard glasses of the 'yolk colour index' by Heiman and Carver (1935), in
776
J . P . VUILLEUMIER
. 580 mu. X Roche egg yolk colour fan • Roche colour fan edition 1962
x
0,45-
X
.
• 4
X X
1— 0,35
5
X
*
:
X
y
x
6
> 585 mn
x x
.
X
7
3
0,40
1— 0,45
I 0,50
FIG. 4. Comparison of 12-grade 'Roche yolk colour fan' and 15-grade 'Roche yolk colour fan'.
comparison with the 15-grade 'Roche yolk colour fan'. The values for the 'yolk colour index' were determined by other investigators1 using the 10 selected ordinate method. The first four glasses of the 'yolk colour index' show very low colour saturation and are used only rarely, because they represent yolk colours resulting from carotenoid-free feeding. Glasses No. 5-12 are within the range of yolk colours, the following glasses, however, move too soon, i.e. with too low a saturation, into the orange region. The first, 12-grade 'Roche yolk colour fan' had the same deficiency, as demonstrated in Fig. 4. The break in the progression of the colour points at fan sheet No. 7 meant that only 1
Dr. John V. Spencer, Food Technology Section, Department of Animal Sciences, Washington State University, Pullman: private communication.
strongly pigmented or red-tinged yolks could be allotted to classes No. 7-12, the higher saturations of pure yellow accumulating in class No. 6. Fig. 5 represents a comparison between the Fletcher colour scale and the 15-grade 'Roche yolk colour fan'. The chromaticity coordinates of the Fletcher rings are quoted from the study by Ashton and Fletcher (1962). Both colour scales cover essentially the same zone of the standard colour chart; the Fletcher colour scale shows a rather irregular progression, which may be due to the technique of colour application by spraying. 2. Attempt to Correlate Different Yolk Colour Standards. Any attempt to select standards representing identical quality from the different volk colour scales, has
777
ROCHE YOLK COLOUR FAN
590 mil
X Roche egg yolk colour fan
10 •
* Fletcher colour rings
0,45'
11
X
;x
X 14
X
•
0,35 -
_L
0,35
_1_
_L
0,40
0,45
0,50
FIG. 5. Comparison between Fletcher colour scale and 15-grade 'Roche yolk colour fan'.
to be regarded as a rough approximation, because colour samples are assorted according to subjectively established similarity. As the colour glasses of the 'yolk colour index' and the Fletcher colour TABLE 3.—Assignment of class values with different scales by visual comparison Roche yolkcolour fan (15 grade) 1 2 3 4 3
6 7 8 9 10 11 12 13 14 IS
o+ S— S
Roche fan (12 grade) 1962 2 2 3 3 4
o+ o+ 0+
3
Fletcher colour rings 1 2 3 4 6 9
6 7 7
SS-
7J S -
8 9 9 10
SSSS-
(1) (5) (7) (8) (9)
10 12 (11) 13 14 14 IS
Clearly more reddish hue. Saturation insufficient. Saturation much lower.
yolk color index Heiraann-Carver 6 7 8 10 12 13 14 15 16 16 18 19 21 22 23
11
17 20 22
12 SSSS S S S - S S S S
rings were at our disposal at different moments and only for a limited period, the most similar standard colours were determined by direct visual comparison with the 'Roche yolk colour fan'. These results are given in Table 3. Somewhat different results are obtained if egg yolks are evaluated at the same time with different colour scales, instead of comparing colour scales direct. Such an experiment was carried out by Marusich et al. (1964). Two observers evaluated the same yolks with different scales; their evaluations were averaged. Table 4 shows the values obtained. The difference between the 'Roche yolk colour fan' and its predecessors becomes more apparent here. With the older colour scales, it was not possible, as with the new fan, to assign yolks to classes 8, 9 and 10, because the
778
J . P . VUILLEUMIER
TABLE 4.—Evaluation of egg yolks with different colour scales according to Marusich (1964) Roche fan 1962 12-grade
Yolk color index
4 5 6 7
9.0 10.8 12.1 14.3 15.7 17.5 18.9 20.8 21.7 22.7
n
8 9 10 11 12
Roche yolk Yolk colour fan color 15-grade index
Roche yolk Roche fan colour fan 1962 15-grade 12-grade
4 5 6 7
8.6 9.9 11.0 12.1
4 5 6 7
3.5 4.5 5.5 6.0
8 9 10 11 12 13 14 15
13.1 13.1 13.1 15.7 18.1 18.9 20.0 21.4
8 9 10 11 12 13 14 15
6.5 6.5 6.5 7.3 7.8 9.0 9.7 1 0.2
corresponding degrees of saturation of yellow were lacking. They were, therefore, assigned to class 6 or 7 of the 12-grade Roche fan 1962, or class 13 of the 'yolk colour index'. The assignment to higher classes of these scales required a marked shift of the yolk colour towards red. SUMMARY
The 'Roche Yolk Colour Fan' has been re-designed to match more closely the average egg yolk. Fifteen colour grades with chromaticity coordinates situated within the range of normal egg yolk colours have been selected and defined by hue and saturation in the C L E . system of colour measurement. A comparison is drawn between the 'Roche Yolk Colour Fan' and other yolk colour scales. ACKNOWLEDGEMENT
We are indebted to Professor W. Boguth, Giessen, for valuable suggestions, and for carrying out a series of reflectance measurements. The fan was produced jointly with Dr. Finckh & Co. Ltd., Schweizerhalle (Mr. G. Jegher), and Tagefa, Eptingerstrasse 4, Basle (Mr. H. R. Schaub). REFERENCES Ann Baker, C. M., 1960. The genetic basis of egg quality. Brit. Poultry Sci. 1: 3-16.
Ashton, E. H., and D. A. Fletcher, 1962. Development and use of color standards for egg yolks. Poultry Sci. 41: 1903-1909. Bartlett, B. E., and R. N. Podger, 1962. Some aspects of egg quality. J. Dept. Agric. Victoria, September. Bartlett, B. E., and M. R. Barlow, 1963. Consumers' choice prefer deep egg yolk colour. The Egg Producer, August 20, p. 12. Baumann, R., 1927. Neue Farbtonkarte, Syst. Prase, Aue in Sachsen. Blommaert, M., and G. Steenis, 1963. Prakttijkoproeven betreffende verbetering van de dooierkleur door toevoeging van o-carotenoid concentraten aan het voeder van leghennen. Vlaams Diergeneesk.Tijdschr. 32, (11): 306-317. Boguth, W., and B. Czernicki, 1962. Farbmetrische Untersuchungen an Eidottern nach Verfiitterung verschiedener Carotinoide. Zbl. Veterinarmed. 9, 779-786. Braunlich, K., 1962. Die Eidotterfarbe als Qualitatsfaktor. Gefliigelhof, 25 (26): 448, 449, 451. Brown, R. H., 1964. Yolk color important to consumer. Feedstuffs, 36: 55. Carlson, C. W., F. L. Shinnick, M. A. Sneller and A. W. Halverson, 1961. Producing dark colored egg yolks. South Dakota Farm Home Res. 12: 20-23. Commission Internationale de l'Eclairage, 1931. Proceedings, comptes rendus des seances. Proceedings Eighth Session, Cambridge, England, September 19-29. Czernicki, B., and H. Weiser, 1962. Zur Beeinflussung der Dotterfarbe durch einige reine Carotinoide sowie durch Paprika. Zbl. Veterinaermed. 9: 899-904. Farnsworth, G. M., Jr., and A. W. Nordskog, 1955. Breeding for egg quality. Poultry Sci. 34: 16-26. Hartfiel, W., and H. Schulze-Messing, 1963. Verfahren zur schnellen Bestimmung der Dotterfarbe bei Hiihnereiern. Arch. Gefliigelk. 27: 317324. Hartfiel, W., and F. Schmitten, 1965. Die Bestimmung der Eidotterfarbe. Arch. Gefliigelk. 29: 367-386. Hartfiel, W., and F. Schmitten, 1966. Untersuchungen iiber die vom Verbraucher bevorzugten Eidotterfarben. Arch. Gefliigelk. 30: 228-242. Heiman, V., and J. S. Carver, 1935. The yolk color index. U.S. Egg Poultry Mag. 41: 40-41. Hickethier,. A., 1952. Farbenordnung Hickethier, Publisher H. Osterwald, Hanover, Distributor "Der Polygraph," Frankfurt am. Main. Kupsch, W., 1934. Die Veranderung und Wertbestimmung der Eidotterfarbe. Arch..Gefliigelk. 8:97-115.
R O C H E Y O L K COLOUR F A N
MacAdam, D. L., 1953. Dependence of colour mixture functions on choice of primaries. J. Opt. Soc. Amer. 43: 533. Maerz, A., and M. R. Paul, 1930, 1950. Dictionary of Colour, McGraw-Hill Book Co., New York. Mainguy, P., and A. Rouques, 1965. Le jaune de l'oeuf. I. Etude generate de la colour du jaune d'oeuf. Bull. Soc. Sci. Hyg. Aliment. 53: 83-116; and II. La couleur des oeufs du marche francais' Bull. Soc. Sci. Hyg. Aliment. 53: 194-212. Marusich, W. L., G. Aeberman and T. Luciani, 1964. Unpublished work. Mehner, A., H.-G. Torges and H. Vogt, 1965. Der Einfluss erhbhter Vitamin A-Gaben auf die Eiqualitat. Arch.Gefliigelk. 29: 356-366. Munsell, A. H., 1915. Atlas of the Munsell Color System and Munsell Book of Color, Munsell Color Company Inc., Baltimore, Maryland. Munsell, A. H., 1946. A Color Notation, Tenth Ed. Munsell Color Company Inc., Baltimore, Maryland Normblatt DIN 5033, 1954. Farbmessung, Blatt 1-8 und Beiblatt. Distributor: Beuth, Berlin, April. Normblatt D I N 6164, 1955. DIN-Farbenkarte. Distributor: Beuth, Berlin, May. Ostwald, W., 1918. Der Farbenatlas. Unesma G.m. b.H. Publishing Company, Leipzig. Ostwald, W., 1919. Der Farbkorper und seine Anwendung zur Herstellung farbiger Harmonien. Unesma G.m.b.H. Publishing Company, Leipzig. Ostwald, W., 1945. Colour Table. Publisher: Pfenningsdorf, Berlin. Rauch, W., 1959, 1960, 1961. Ueber die Beeinflussung der Dotterfarbe durch carotinoidhaltiges Legehennenfutter. 1. Mitteilung: Arch.Gefliigelk. 23: 319-331. 2. Mitteilung: Arch.Gefliigelk. 24: 417-431. 3. Mitteilung: Arch.Gefliigelk. 25:494-502. Rescheleit, Ch., 1953. Beitrag zum Problem der Dotterfarbung. Dtsch.Wirtschaftsgeflugelzucht, 5: 13-15. Ridgway, R., 1912. Color Standards and Color Nomenclature. Published by the author, Washington, D.C. Schmidt, L., 1963. Ei und Ei-ist zweierlei. Deutsche Gefliigelwirlschaft, 15: 192. Scholtyssek, S., 1962. Stand der Qualitatsforschung bei Geflugelzuchtprodukten. Deutsche Gefliigelwirtschaft 14: 617-620 and 631. Scholtyssek, S., 1964. Der Einfluss der Fiitterung auf die Qualitat bei Eiern und Geflugelfleisch. Ziichtungskunde, 36: 449-458. Scholtyssek, S., and U. Bohm, 1962. Zur Bestimmung der Dotterfarbe des Hiihnereies. Kraftfutter, 45: 69-71.
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Scholtyssek, S., R. Kirsammer, E. Hanser and B. Kurmann, 1965. Beitrag zur Frage der Dotterfarbung. Arch.Gefliigek. 29: 249-262. Scholtyssek, S., R. Kirsammer, E. Hanser and B. Kurmann, 1966. Die Eignung verschiedener objektiver Methoden zur Messung der Dotterfarbe. Arch. Geflugelk. 30: 177-191. Scholtyssek, S., G. Lorenz and H. Erfani, 1961. Die Beeinflussung der Eidotterfarbe durch synthetische Carotinoide. Arb.d.Landw.Hochsch.Hohenheim 1:77-91. Smetana, P., 1961. Feeding for egg yolk colour. Dept. Agric. of Western Australia, Bull. No. 2906, and J. Agr. Western Australia, 2: 3-6. Snyder, E. S., 1961. Eggs. The production, identification and retention of quality in eggs. Canada Dept. Agric. Publication 782. Splittgerber, H., 1961. Eiqualitat. Der Hiihnerbrief, Nr. 8. Steinegger, P., M. Menzi and R. Berger, 1956. Versuche zur Ermittlung der Einfliisse verschiedener Carotinoidzusatze zum Legehennenfutter auf die Dotterfarbe. Geflugelhof, 19: 215-220. Steinegger, P., K. Steriff and P. Zeller, 1957. Pigmentierung und Eidotterfarbung bei Geflugel nach Verfiitterung synthetischer Carotinoide. Mitt. Gebiete Lebensmitteluntersuch. Hyg. 48: 445-149. Steinegger, P., and G. Zanetti, 1957. Versuche zur Emittlung der Einfliisse verschiedener Carotinoidzusatze zum Legehennenfutter auf die Dotterfarbe. Arch. Geflugelk. 21: 236-245. Steinegger, P., and G. Zanetti, 1959. Versuche zur Ermittlung der Einfliisse verschiedener Carotinoidzusatze zum Legehennenfutter auf die Dotterfarbe. Arch. Geflugelk. 23: 166-173. Tagwerker, F. J., 1962. Yolk colour and its relation to quality. Paper presented at the First International Egg Marketing Conference, Sydney, August 20-22. Torges, H. G., 1963. Untersuchungen iiber den Erblichkeitsanteil der Eiqualitatsmerkmale Eiklarindex, Bruchfestigkeit der Eischale und Dotter farbe. Z. Tierzuchtung Ziichtungsbiol. 79(3): ; 197-216. Torges, H. G., 1964. Die Auswirkung einer iiber mehrere Generationen fortlaufenden Selektion von Leghornhennen auf Eiqualitatsmerkmale. Arch. Geflugelk. 28: 69-75. Treat, C , 1963. Egg yolk pigmentation. A discussion of the practical aspects of feeding for specific color. Feedstuffs 35(52): 18-22. Turner, A. W., and V. Conquest, 1939. A practical method of determining color in fresh and frozen egg yolks U.S. Egg Poultry Mag. 45: 668-670.