MANIPULATING THE EGG YOLK COLOUR THROUGH SUPPLEMENTATION OF PIGMENTS IN WHEAT-BASED DIETS OF LAYING HENS
The colour of the yolk is due to substances called carotenoids. The nutritional value of the egg is not affected by the yolk colour. The intensity of yolk colour may be measured against standards such as the DSM Yolk Colour Fan. Most egg marketing authorities require deep-yellow to orange-yellow yolk colours in the range 9 to 12 on the DSM Yolk Colour Fan. Yolks of more intense colour may be required for specifi c markets.
The most important sources of carotenoids in poultry feed are maize (corn), maize gluten, alfalfa (lucerne) and grass meals; these sources contain the pigmenting carotenoids lutein and zeaxanthin, which, together with other oxygen-containing carotenoids, are known by the collective name of xanthophylls.
However, the carotenoid content in the ingredients of poultry feed is not constant; the pigmentation properties of the carotenoids can be weakened or lost in a variety of ways. These fluctuations in carotenoid content and availability concern both the poultry nutritionist and the feed producer. Because of such fluctuations, naturally-occurring carotenoids cannot be relied upon to provide the desired yolk colour or to provide a consistent colour. Therefore, nature-identical yellow and red carotenoids, such as apoester and canthaxanthin, are commonly added to feed in order to achieve the desired egg yolk colour. Consumed by the laying hen, these supplemental carotenoids are readily transferred to the blood and then deposited in the yolk to provide pigmentation.
Incidence
A wide variation in colour may normally be expected in the yolks from any flock. If a flock averages a yolk colour score of 10 on the DSM Yolk Colour Fan, two out of every three eggs laid by the flock will score between 9 and 11. Also, one egg in 20 will score less than 8, and one in 20 greater than 12.
The ideal yolk colour doesn’t exist, because it is heavily influenced by consumer preference.Asian consumers like an orange to red yolk, European consumers prefer golden yellow: as a producer you can tune your birds to the right yolk colour by adding natural raw materials to the layer feed such as yellow maize, Lucerne, dried vegetables or other plant materials. For example, grass meal will give a darker yolk colour and feeding most other grains will actually make the yolk lighter. A golden yolk is determined by 2 compontents: a yellow base colour and red to deepen it. Lutein and zeaxanthin are the carotenoids that provide yellow, canthaxanthin provides red. Additives can be added to the feed accordingly, but don’t always have the desired effect.
Pigments are amongst the most commonly used additives in poultry diets. Additives are substances which are intentionally added to foods and do not necessarily contain nutritional value.
The incorporation of additives in bird diets has varied purposes. Some of these are:
- Meeting food needs
- Improving food characteristics or those of the final product
- Ensuring animal welfare
- Improving production parameters
- Ensuring gut health through the incorporation of probiotics or coccidiostats for example
- Improving the color of the final product
- Reducing the negative impact of production on the environment
Additives must meet certain conditions in order for them to be used. Some of these conditions are:
1) They are not harmful to animals or people
2) They leave no residues in final consumption products
3) They do not contaminate the environment
4) They are used according to regulations and certain standards
Additives are used to ensure that nutrients in the diet are ingested, digested, protected from destruction, absorbed and transported into the cell. In turn, they can alter the metabolism of birds to promote growth and/or improve the final product.
Additives are considered to account for 0.5% of the diet and 5% of the total ration cost.
Some of the most commonly used additives are: pigments, antioxidants, flavorings, growth promoters, mycotoxin sequestrants, exogenous enzymes, etc.
Pigments
Pigments are used in birds for the improvement of the final product according to consumer preferences, without altering the normal metabolism of animals.
Birds are able to store pigments in: yolk, fat deposits, skin and in their legs. It has been proven that color is associated with palatability amongst consumers. Therefore, alterations in color can be associated with better taste, or may cause rejection.
7 problems with pigmentation and actions
- Pigment breakdown in feed:Store additives and premixes in airtight containers, in a cool place and never in sunlight. Do not store them too long.
- Insufficient carotenoids in the feed:The amount of carotenoids might be insufficient. That can certainly be the case if you are using natural sources, in which concentrations can vary. Added pigments are easier to manage.
- Insufficient pigment reserve:Flocks that start coming into lay can have insufficient pigment reserves. Begin feeding pigment 2 to 3 weeks before the flock starts laying.
- Oxidising substances or pigment antagonists in the feed:Some substances may negate the effect of pigments, e.g. barley and triticale in the feed. In such cases, you have to add higher concentrations of pigment in the feed. If oxidants are the culprit, add antioxidants.
- Poor feed mixing:Always make a premix of the pigments before finally mixing them into the feed. This method produces better mixing results.
- Poor storage conditions:Keep feed cool and dry. Storing feed in damp and/or warm conditions reduces the effectiveness of pigments.
- Rough feed handling or transport:Handle feed carefully to ensure the different components do not separate. Take special care to check this if you use augers in your feed system.
The color of the egg yolk
As in other foods, the egg color is one of the most important aspects for consumers, especially the color of the yolk. It is an important organoleptic aspect for the acceptance of this product that the consumer relates to its quality. Both the color of the yolk and its homogeneity (within the yolk and between different eggs) are important.
The color of the egg yolk is determined by the type and profile of carotenoids present in the feed and their intestinal absorption. Carotenoids are a fat-soluble group of yellow, red and orange pigments. They can be divided into two large groups: carotenes and xanthophylls.
More than 600 different types of carotenoids have been described. Xanthophylls are more important in egg coloration than carotenes.
Illustration 1. Egg yolks with different color shades.
- What does the color of the yolk depend on?
The color of the egg yolk depends on numerous factors that can be divided into primary factors, those that depend on the type and concentration of carotenoids, and secondary factors, those that depend on the animal.
Primary factors include digestibility, metabolism, transference to the egg and deposition percentage of carotenoids administered with the diet. Food disbalances, such as vitamin deficiencies, can also affect the color of the yolk. Some of these carotenoids are precursors of vitamin A, metabolizing to this vitamin when there are deficiencies and reducing the quantity that is deposited in the yolk.
The composition of the diet affects the absorption of these pigments, for example, diets rich in fats favor their absorption. The percentage of deposition also shows great variations between the different carotenoids, from 14% fir astaxanthin to 40% for canthaxanthin.
Secondary factors include age, lineage, health status, as well as animal management. Studies show that all those factors that affect digestive health such as mycotoxins, aflatoxins or ochratoxins have a noticeable impact on the absorption of pigments and diseases, such as coccidiosis or the Newcastle disease.
Maintaining the intestinal health of the animals, for example, by using intestinal conditioner pronutrients, is key for an adequate and maintained pigment absorption throughout the laying phase.
Intestinal conditioner pronutrients are active molecules of botanical origin that act at a metagenetic level on intestinal cells. They stimulate the synthesis of functional proteins and increase the renewal of enterocytes, thus favoring the intestinal physiological status and nutrient absorption, including pigments present in feed.
- How to get the desired coloration by the consumer
A key point that egg producers should keep in mind is that there is no coloring capable of meeting the needs of all markets. There is a wide variation in the colors demanded by different countries and regions, ranging from pale yellow, for example, in Switzerland or Canada, to an intense reddish yellow, as demanded, for example, in the Japanese market.
Such preferences are usually determined by geographical and cultural differences. A factor that also influences consumer preferences for one or another color is the availability of raw materials to feed of hens. For example, in Tanzania, sorghum is used in feed and, since it contains a lower proportion of carotenoids than maize, yolks of a lighter color are preferred.
In order to evaluate the color of the egg yolk, a wide variety of scales have developed in recent decades. However, the scale of La Roche, created by the La Roche Vitamins laboratory, is the most accepted one. This scale relates a given color of yolk to a numerical value on a scale of 1-15, from lowest to highest color intensity.
Illustration 2. La Roche scale for the determination of the color of the egg yolk.
The preferences between the different European countries can be classified following this scale. In Germany, the Netherlands, Spain and Belgium, consumers prefer more orange colors, with values between 13-14 on the scale of La Roche, while countries such as Ireland, Sweden or the north of England prefer paler colors, with values between 8-9. There are also countries looking for intermediate colors such as northern France, the South of England and Finland, who demand colors with values between 11-12 in the La Roche scale.
Certain raw materials present in poultry diets contain natural pigments, such as maize or lucerne, although they are not in a quantity enough to obtain the color demanded by most countries. This is why concentrated extracts from certain plants such as marigold and paprika are used. The use of pronutrients also contributes to the absorption of the pigments in these raw materials.
To get the desired yolk color in each country, it is necessary to add pigments to the diet of birds. As each country, and region has different preferences in terms of yolk color, the dose of pigments should be adjusted for each individual case.
- Types of pigments
These pigments can have a natural origin, such as concentrated extracts from certain plants such as marigold or paprika, or a synthetic one. The current trend is to standardize the doses of natural pigment needed for different yolk colors.
There are 6 main types of carotenoids, three that provide yellow color: zeaxanthin, lutein and apo-ester, and other three that provide red color: canthaxanthin, astaxanthin and capsanthin. Different combinations of these pigments allow to obtain different yolk colors, for example, the combination of 2- 4 mg/kg canthaxanthin and 10-20 mg/kg of zeaxanthin allows to obtain eggs with a yolk color between 12 and 15. We must keep in mind that, for values greater than 10 on the La Roche scale, it is necessary to add a red pigment.
Assessing the value of the egg
The quality characteristics of eggs are usually divided into external features, such as:
- egg weight
· egg shape
· shell structure
· shell crack resistance
· dynamic shell resistance
· shell color
and internal characteristics, including:
- albumen weight
· Haugh unit (a measure of egg protein quality)
· yolk height,
· yolk diameter,
· albumen pH,
· yolk pH
· yolk color
For consumers, yolk color is probably the most important criterion for egg quality. Higher color intensity often is taken as indicating the good health of the laying hen.
Depending on the region or on the culture, people prefer more yellow or more orange yolks. In countries with traditional corn feeding, e.g., Mexico, they often like a deep yellow. In Northern Europe, consumers prefer a lighter yellow; in Southern Europe, more gold-orange yolks (see table 1).
| Country | Yolk color fan value* |
| Belgium | 12-13 |
| Denmark | 9-10 |
| Finland | 9-10 |
| France | 11-12 |
| Germany | 11-14 |
| Greece | 11 |
| Italy | 12-13 |
| Netherlands | 7-9 |
| Austria | 12-14 |
| Portugal | 12-14 |
| Spain | 11-14 |
| Sweden | 9-10 |
| United Kingdom | 10-11 |
Table 1. Egg pigmentation preferences – variation across European countries
* Values range from 1 (very pale yellow) to 16 (intense orange)
Egg yolk color is achieved via feed
The typical color of the yolk depends on pigments that are ingested with the feed. Corn and alfalfa meal provide the yellow pigments lutein and zeaxanthin, belonging to the xanthophylls, a sub-group of carotenoids. The golden-orange color is provided by red pigments from chili or paprika (Grashorn, 2008). Egg yolks start changing color about 48 h after the application of xanthophylls.
To reach an optimal yolk coloration in egg production, diets should be supplemented with yellow and red xanthophylls. Yellow xanthophylls achieve a correct yellow base coloration. The main yellow pigments used in poultry feeding are apoester, a synthetic carotenoid, and saponified marigold extracts, a natural alternative containing lutein and zeaxanthin. For the redness, paprika or chili offer natural sources; canthaxanthin is a nature-identical red xanthophyll.
For a long time, synthetic colorants were the substances of choice in the poultry industry because they provide consistently predictable results and high product stability. However, consumers’ preferences concerning food have shifted; demand favors natural over synthetic food ingredients. Moreover, current EU regulations restrict these synthetic molecules’ inclusion level due to their potentially harmful effects on human health if applied in excessive doses.
| Carotenoid | Maximum inclusion level |
| Apoester (ethyl ester of β-apo-8’-carotenoic acid) | 5 ppm |
| Canthaxanthin (β,β-Carotene-4,4′-dione) | 8 ppm |
Table 2. Maximum concentration allowed in feed for poultry production
Fortunately, there is already a natural, highly efficient option to replace apoester.
Lutein: a natural colorant, antioxidant, and provider of health benefits
One of these natural compounds is lutein, a lipophilic pigment. It is extracted from marigold petals, which contain up to 8.5 mg/g wet weight. Lutein is always accompanied by its isomer zeaxanthin.
Lutein – the yolk colorant
The use of xanthophylls such as lutein and zeaxanthin enables producers to safely control the color of the egg yolk and the broiler skin. In poultry, the carotenoids are deposited in high quantities in the epidermis, the fatty tissue, and the egg yolk. According to Grashorn (2016), between 4.4-23 % of dietary lutein and 23 % of dietary zeaxanthin are deposited in the egg yolk.
Lutein – the antioxidant protects the egg lipids
Another critical characteristic of lutein is its antioxidant effect. Egg yolks contain a high fat content. Therefore, they are very susceptible to lipid oxidation. Lutein, acting as an antioxidant, can prevent or at least limit lipid oxidation during egg processing. Kljak et al. (2021) compared different sources of pigments (basil, calendula, dandelion, marigold, and an industrial product containing canthaxanthin) concerning their antioxidant capacity. In this trial, marigold improved the yolks’ oxidative stability by 75 % compared to the control, with canthaxanthin showing no antioxidant effect. Kljak et al. attributed this effect to the carotenoids in the marigold extract.
Lutein – a value-added ingredient
Lutein and its isomer are nutritionally valuable and, therefore, welcome ingredients of the eggs. Once more, due to their antioxidant effects, they play an essential role in preventing and reducing cataracts and age-related eye dysfunctionalities in humans and animals (Landrum & Bone, 2001; Wang et al., 2016).
However, the amounts of antioxidant pigments in a standard egg are not very high (approx. 400 µg/egg). Compared to the total amount of antioxidants ingested, their importance for humans is only limited (Grashorn, 2008). The situation is different for functional eggs, which are widely sold in certain English-speaking countries. These eggs are enriched with n-3 fatty acids and with antioxidants such as ß-carotene (ca. 150 IE/egg).
The importance of color in food
The food color has played a fundamental role in our diet since prehistory, allowing us to discern between those healthy and nutritious foods and those that are toxic or in poor conditions.
This importance of the food color has been etched in our genes so that, to this day, the food color remains one of the organoleptic factors with a greater importance to the consumer. We relate the presence or absence of a certain color with quality and freshness and associate each product with a specific color.
A practical example of the importance of color in food can be found in the cola soft drink. In 1993, the multinational Pepsi launched a new transparent cola in order to differentiate itself from other cola soft drinks on the market. However, this product was a complete failure because it was a transparent product and people associated the cola with a dark color, so the previously established relationship between the color and taste of the product was not fulfilled.
Color is one of the main factors with effect on the choice of a food product by the consumer and, as the saying goes, “you eat with your eyes first”. Therefore, since ancient times different food additives have been used to meet the demands of the consumers.
The importance of color also affects products of animal origin, having a special relevance in poultry, where both the color of the egg yolk and the color of the skin and the legs of the chicken are of great importance from a commercial point of view.
- Food colorings
The use of food colorings is not a recent practice, in fact, Egyptians used natural colorings for candies (1500 b. C.). There are references to saffron as a food additive in Homer’s Iliad and it is known that, in the Middle Ages, dyes were used in products such as wine.
These additives were generally used to improve the appearance of foods by masking their natural color. However, in the absence of any legislation, any type of compound, such as chalk as a dye for bread, could be used to enhance its whitish color. This led to the emergence of the first legislations on the use of such products, and King Edward I (1272 to 1307) was the first person who regulated the use of food colorings in bread in England.
During industrialization the first synthetic additives were developed, and along with them, the first official laws emerged. Perkin’s mauveine or Perkin´s purple was the first synthetic coloring developed by the chemist William Henry Perkin in 1856.
Currently, the laws determine in detail those compounds that can be used as food colorings, both in animal and human food. In the case of the European Union (EU), this information is in the European (EU) Regulation No 1333/2008, which describes the food colorings as those additives that provide color to a food or return its original color. In the case of the United States, the FDA is the agency that determines the compounds that are eligible in the CFR (Code of Federal Regulations) 21 70.3.
- Pigments in animal feed
In order to offer to the consumers products of animal origin with a certain color that suits their preferences, pigments are commonly added to feed.
These pigments are absorbed by the animal and deposited in the different organic tissues to acquire the desired color. The percentage of deposition will depend on the species and the type of pigment. For example, in the case of birds, xanthophylls are more absorbed than carotenes.
The pigments used in animal feed can be natural or synthetic compounds. They are mainly used in poultry to obtain a certain yolk color and to enhance the color of the skin and legs of these animals. They are also used in salmonid aquaculture to enhance the orange color of muscle tissue.
Pigment incorporation in bird diets seeks to achieve a degree of pigmentation that satisfies consumers:
– For egg yolks, a yellow to orange color is sought. Which is equivalent to: 10 – 13 on the Roche scale. These preferences vary according to location and region.
– An intense yellow is usually sought for the color of chicken skin.
Besides the importance of the achieved color, a uniform pigmentation is also sought. In this sense, it is important to highlight the fact that certain products such as coccidiostat nicarbazine can interfere with color uniformity.
A golden yolk can only come from a healthy hen
In order for a yolk to present an attractive golden color, carotenoids have to:
- Be ingested in sufficient quantities
- Absorbed (via a healthy gut)
- Not be used as antioxidants (low immunological challenges)
- Not be used as vitamin precursor (good vitamin status).
Therefore the hen, the environment and the feed have to work in concord to deliver an attractively pigmented yolk. In nature, the male birds with the best coloration will attract the females. This makes sense, because only the healthier individuals will be able to obtain appealing feathers. The same goes for the females: the healthier hens will have more carotenoids for their eggs. So, in order to have a golden yolk, you need a good-quality feed, the correct husbandry practices and – more importantly – a healthy hen.
DR RASHVIHARI SAW, POULTRY CONSULTANT, KOLKATA
