FACTORS INFLUENCING EGG YOLK AND ITS PIGMENTATION
ABSTRACT
The evaluation of food color is a psychological problem of appeal and of sensitivity to attractiveness or to irritation. In the case of egg yolk color there exists an “optimal-yellow,” which must be “appetizingly pretty,” as determined by the “corruptible human eye”. Consumer’s preference, thus, depends on visual impression, which is not always well correlated with chemical determinations of yolk pigment concentration. The pigment found in egg yolk is widely considered very important as it determines the acceptability of the product by the consumer who prefers yolk colours ranging from golden-yellow to orange i.e. midway to high on the Roche yolk colour scale. The yellow pigment is mainly explained by the presence of xanthophylls derived from carotenoids. A golden yolk can come from a healthy hen; hence the hen, the environment and the feed have to work in concord to deliver an attractively pigmented yolk.So, carotenoids have to be ingested in sufficient quantities, absorbed (via a healthy gut), should not be used as antioxidants or vitamin precursor.In nature, the male birds with the best coloration will attract the females. Similarly, the healthier hens will have more carotenoids for their eggs. Thus, good quality feed, proper management practices and more importantly, a healthy hen are very crucial in order to obtain a golden yolk.
Keywords: EggYolk; Pigment; Roche yolk colour scale; Xanthophylls; Carotenoids
INTRODUCTION
Making up only 33% of the egg’s whole weight, the yolk contains 75% of an egg’s calories. An unpredictable pack of proteins and fats, the yolk additionally houses the vast majority of the iron and Vitamin A found in the cell. Chickens that eat plants with a higher centralization of specific shades (called xanthophylls) produce egg yolks with a profound orange tone. These eggs are not more nutritious than eggs with a light yellow yolk; they simply contain more shading influencing parts from the feed of the hen. Chickens that are permitted to meander will in general discover and eat up plants with these shades (like horse feed), however chicken feed made of corn will frequently deliver a comparable impact. A few ranchers who are focused on selling eggs with profound shaded yolks will even take care of their chickens’ feed (marigold petals) to guarantee that the yolk tone is perfect.
YOLK COLOR AND EGG QUALITY
Yolk tone has no relationship to egg quality, flavor, nutritive worth, cooking attributes or shell thickness, as per The American Egg Board. The macronutrient organization of more obscure shaded and lighter-hued eggs is indistinguishable; anyway there might be some minor contrasts in micronutrient fixations like Vitamin A and lutein. Egg yolks range in shading from light yellow to profound orange. The shade of an egg’s yolk relies exclusively on the hen’s eating regimen. The hazier shade of a yolk flags the presence of carotenoids, which are common colors found in certain plants. The accessibility of carotenoid-rich plants for chickens’ utilization influences the “orangeness” that you find in their eggs yolks. Remember that chickens ought to be taken care of an omnivorous eating regimen with creepy crawly and creature proteins just as vegetable and grain-based fixings; however the presence of carotenoids in hens’ weight control plans is the primary determinant of shading.
THE SPECTRUM OF YOLK COLOR
Deep Orange
Since carotenoid-rich grain is more normal and accessible in “Field Raised” activities, eggs from these chickens are bound to be more profound orange in shading. Be that as it may, any chicken egg can turn out orange, not simply field raised ones. However long chicken feed contains the supplements that trigger orangeness, the yolk will turn out this more profound tone.
MID-ORANGE TO GOLDEN YELLOW
Hen consumes less calories weighty in green plants, yellow corn, hay and other plant material with xanthophylls shade (a yellow-orange tone) will create a hazier yellow-orange yolk, as indicated by Food and Nutrition Magazine. This is the most widely recognized shading yolk we find in eggs accessible at the market.
LIGHT YELLOW
Diets lower in xanthophylls, for example, taking care of regimens that comprise of generally wheat, white cornmeal or grain produce light yellow yolks.
GREEN
It’s just the result of sulfur and iron mixes in the egg responding with the outside of the yolk. In the event that you need to evade the greenish color, ensure you follow the fitting cook time and temperature. Explicitly for hard-bubbled eggs, quickly cool them in the wake of cooking by setting in a bowl of ice water to additional shield against greenness.
| EGG COLOR | CAUSES |
| Yellow, Dark | Alfalfa meal, marigold petals |
| Yellow, Medium | Yellow corn |
| Yellow, Pale | Coccidiosis (rare), Wheat (fed in place of corn) |
| Orange to Dark yellow | Green feed, Yellow corn |
| Reddish, Olive green, Dark green | Grass, Cottonseed meal, Silage |
| Green | Acorns, Shepherd’s purse |
PIGMENTATION OF EGG YOLK
The shade of egg yolks is created by oxycarotenoids, usually known as xanthophyll colors, gotten from the hen’s feed. These oxycarotenoids, which are lipid-like mixes, are created mostly by plants, miniature life forms and crustaceans.the shade of oxycarotenoids and egg yolk tone is impacted mostly by the yellow and red oxycarotenoids. Both characteristic what’s more, manufactured types of these oxycarotenoids shading egg yolks. The engineered structures incorporate 13-apo-8 I carotenal (BAC), 13-apo-8 carotenoic corrosive ethyl ester (BACE) canthaxanthin (CHX) and citranaxanthin (CTX) which are presently fabricated on a business scale and are accessible for use in poultry apportions. Some of the examples of oxycarotenoids are R-Carotene, Zeaxanthin, Lutein, Cryptoxanthin, Capsanthin, Astaxanthin, Canthaxanthin, Citranaxanthin, R-Apo-8′ –carotenal, Ethyl 0-apo-8 –carotenoate.
FACTORS INFLUENCING EGG YOLK COLOUR
- GENETICS:
Additive genetic variation in yolk colour between birds is apparently low. The heritability of yolk colour was found to be 0.15. It was reported that heritability of 0.05 with some evidence of non-additive genetic factors. The differences existed between White Rocks and Leghorn hens in their ability to absorb oxycarotenoids and deposit them in yolks. Red and Indian desi breeds with reciprocal crosses being intermediate. There was an indication of a sex linked effect, pullets with the desi W chromosome producing higher scores than pullets with the RIR W chromosome. No estimates of the genetic correlation between yolk colour and other production characters have been reported. A highly significant positive phenotypic correlation between yolk colour and rate of lay in several flocks of birds (r = 0.70, b = 0.05 units per cent rate of lay). The magnitude of this correlation is such that despite the increased feed intake associated with increased rate of lay, it must be concluded that the efficiency of carotenoid absorption or transport or/both also must have increased with increased rate of lay.
- B) HOUSING SYSTEMS:
The birds housed in cages as compared to those on deep-litter laid eggs with higher yolk colour (80vs 59 mg BCE/gyolk) when given a diet with 44 mg/kgof oxycarotenoids. Some strains of layers laid eggs with higher yolk colour when housed in cages than on litter. In both these experiments, the difference in yolk colour between eggs from cages and litter pens was equivalent to 2 units on the Roche colour fan. The reasons for this difference in the utilization and deposition of yolk pigment sin birds housed in cages and on litter are not known. In some instances it may be due to differences in feed intake and consequent differences in pigment intake. However, the effect of unknown factors in the litter inhibiting the absorption and deposition of yolk pigments cannot be discounted.
- C) LIPIDS AND ANTIOXIDANTS:
Oxycarotenoid pigments are soluble in lipids and their absorption from the intestine is likely to parallel the absorption of lipids. The lutein-fatty acid esters (lutein dipalmitate) were more efficient in pigmenting egg yolks than the crystalline form of lutein. This has been attributed to the higher solubility of lutein-fatty acid esters in lipids. The laying hen deacylates the pigment esters before depositing them in the developing ova. The inclusion of 4% tallow in layer diets has been found to improve yolk colour, when either paprika or lucerne pigment extract or synthetic oxycarotenoids were the sources of pigments in the diet., however, found
that the inclusion of 4%animal fat in maize-soybean meal diets containing 3% dehydrated lucerne meal had no significant effect on yolk colour. The yolk colour response to the addition of vegetable oils has been more variable than when animal fats were added. The vegetable oils (sunflower, rapeseed oil) increased yolk colour by 1 to 2 units on the Roche colour fan at low concentrations (1.5 mg/kg) of synthetic oxycarotenoids in the diet, but at higher concentrations (7.2 to 8.8 mg/kg canthaxanthin) vegetable oils had no effect on yolk colour. Similarly, slight increases in yolk colour were observed when 3.0% maize oil or 2-4% sunflower oil was included in diets containing 2.2 mg/kg of a mixture of synthetic oxycarotenoids. The inclusion of 4-5% of either olive, sunflower or safflower oil in diets containing lucerne meal, maize or lucerne pigment extract had no positive effect on yolk colour. Oxycarotenoids lose their pigmenting power when oxidized by agents such as peroxides and trace minerals. The presence of moisture in the feed and high temperatures accelerates the oxidation of oxycarotenoids. The inclusion of ethoxyquin at dietary levels ranging from 100-1200 mg/kgeither in stored feedstuffs or in diets has stabilized the oxycarotenoids and consequently increased the deposition of pigments in the egg yolk by as much as 54% and 24% during hot and cooler weather, respectively. The magnitude of the yolk colour response to antioxidants seems to be dependent on the stability of the oxycarotenoids in the diet. The addition of 3%sunflower oil to a diet containing 8% lucerne meal as the only source of carotenoids and with or without 125 mg/kg BHT reduced the pigment content of egg yolks by 13% and 26%, respectively. In diets with the stabilized oxycarotenoid, β-apo-8’-carotenoic acid ethyl ester, the corresponding reductions in yolk pigments were 4.5 and 9.4% respectively. Vitamin E is more potent than BHT in preventing the oxidative destruction of carotenoid pigments. The dietary level of 14.6 mg/kg vitamin E was more effective than 125 mg/kg BHT in improving egg yolk colour when hens were given diets either with or without 3% sunflower oil. They also found that vitamin E and BHT had a synergistic effect in improving egg yolk colour. Neither a normal level of 1 10 mg kg – 1nor a massive level of 2500 mg/kg of ethoxyquin in a diet containing 70% yellow maize, 2% lucerne meal, 11 mg/kg vitamin E and without added fat had any effect in improving egg yolk colour. It appears that antioxidants are effective in improving yolk colour only when unsaturated fats, which are likely to undergo oxidation, are included in the diet. The experimental evidence indicates that lipids, particularly the saturated lipids, aid the transfer of oxycarotenoids from the diet to the egg yolk. However lipids containing peroxides resulting from oxidative rancidity will reduce pigmentation of egg yolks due to either in vitro or in vivooxidation of oxycarotenoids.
- D) EXCESSIVE LEVELS OF VITAMIN A AND CALCIUM.
The excessive levels (>25,000 I.U./kg) of vitamin A may reduce pigmentation of egg yolks. Acommon feature in all these studies was that the diets were not supplemented with fats. The depression in yolk colour caused by high dietary levels (>26,455 I.U./kg) of vitamin A was prevented by the addition of 3%tallow to the diet. Using a layer diet based on meat and bone meal which contains 11-12% fat, found that vitamin A levels of. 25,000 I.U./kg or more did not depress yolk colour. It appears that tallow has not only the effect of enhancing the absorption of carotenoids but also plays a role in counteracting the inhibitory effects of excessive levels of vitamin A. High levels of calcium in the laying diet may also cause a reduction in egg yolk colour. Increasing the dietary level of calcium from 3.0 to 4.0% reduced egg yolk colour by almost one unit on the Roche colour fan.
- E) ANTIBIOTICS AND DRUGS:
There are conflicting reports in the literature regarding the influence of antibiotics on egg yolk colour have reported that an abnormally low yolk colour in eggs laid in autumn by White Leghorn hens housed on litter-floor pens was improved by treatment with either penicillin, chlortetracycline, zinc bacitracin or furazolidone. Yolk colour is increased by the administration of antibiotics. Neither bacitracin nor a mixture of penicillin, streptomycin and sulphaquinoxaline had a significant effect on egg yolk colour. An antibiotic mixture consisting of penicillin, chlortetracycline and formosulphathiazole had no effect on the yolk colour of eggs from hens housed in floor pens with either dry or wet litter. The continuous feeding of either furazolidone or oxytetracycline also had no significant effect on egg yolk colour. Several coccidiostats such as amprolium zoalene, sulphaquinoxaline, arsanilic acid and 3-nitro, 4-hydroxyphenyl arsonic acid had no effect on yolk colour. However, 3-nitro-10 improves egg yolk colour. Egg yolk colour is reduced by subclinical coccidiosis due to Eimeria mervulina. In such asituation, the administration of coccidiostats may have a beneficial effect on yolk colour.
- F) OTHER YOLK COLOUR INHIBITORS:
The presence of unknown factors in feedstuffs which inhibit the deposition of carotenoid pigments in chickens was first reported in the 1940’s. These factors were found in meat scraps, fishmeal, soybean meal and cod liver oil. It appears that as antioxidants were not included in feeds at that time, the products of oxidative rancidity may have been responsible for the inactivation of oxycarotenoids. Rice pollard contains some heat-labile factors which reduce egg yolk colour by 4-5% when 20% or more is included in layer diets. Triticale also contains an unknown factor which inhibits the transfer of oxycarotenoids from the diet to the egg yolks. The replacement of either maize or wheat in layer diets with triticale reduces pigmentation of egg yolks by 7-11 %. High levels (50%) of barley in diets without added fat have also been found to reduce egg yolk colour by 3 to 6% when compared with diets based on wheat. When maize was replaced by either wheat or barley in diets containing 3% added soybean oil, better yolk colours were obtained with barley. It appears that the factor(s) in triticale and barley which depress pigmentation of egg yolks are similar as added fat seems to at least partially overcome the inhibitory effect. 5%dried orange pomace meal in layer diets caused pale egg yolks. This was despite the presence of 7.5- l0% lucerne meal in the diet 5% dried citrus pulp meal in diets with 119 mg/kgBHT had no adverse effect on yolk colour. Perhaps the influence of any oxidizing agents in the citrus pulp meal was counteracted by BHT.
CONCLUSION
Color is one of the most important factors affecting consumer choices through sensory evaluation of food, including egg yolks. In most of the countries, golden yolks have been traditionally associated with good health, and despite regional differences on the preferred shade of red and yellow, intense, bright colors are recognized as a sign of a healthy yolk. Carotenoids are not only responsible for yolk color, but also required for the development of other physiological functions.One of the most important of them is a competent immune system, essential for laying hens. The birds which are healthy are able to deliver most of the feed-derived carotenoids to the egg yolk; therefore a bright yolk color can be considered an indicator of the good health and performance of the flock.
REFERENCES
Barbosa, V.C., Gaspar, A., Calixto, L. F. L., & Agostinho, T. S. P. (2011). Stability of the
pigmentation of egg yolks enriched with omega-3 and carophyll stored at room temperature and under refrigeration. Revista Brasileira de Zootecnia, 40(7), 1540-1544.
Karunajeewa, H., Hughes, R. J., McDonald, M. W., & Shenstone, F. S. (1984). A review of factors influencing pigmentation of egg yolks. Worlds Poult Sci J, 40(1), 52-65.
Nys, Y. (2000). Dietary carotenoids and egg yolk coloration. Archiv Für Geflugelkunde, 64, 45-54.
Chidambaranathan Arumugasami
Final year BVSc & AH
GUIDED BY
D R. V. RAMAKRISHNAN, ASSISTANT PROFESSOR
VETERINARY COLLEGE AND RESEARCH INSTITUTE – TIRUNELVELI
TANUVAS – CHENNAI
