As the saying goes “you eat with your eyes first”, nothing closer to reality: the color of the food is one of the main factors affecting our choice. Within animal production, this organoleptic aspect acquires a great importance in the case of eggs, especially the egg yolk color.

There are great differences between the yolk color preferred in different countries and multiple natural and synthetic colorings have been developed to cover this range of colors.

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.

• 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.

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.

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.

Conclusion

The color of the egg yolk, as in other foods, plays a fundamental role in the consumer’s choice of the product. Therefore, it is essential to know the demands of each country and to add the necessary pigments to obtain such color.

It is also essential that animals maintain a good intestinal health, to ensure the proper absorption of such pigments, avoiding diseases such as coccidiosis or Newcastle disease, which directly affect the pigment absorption.

Because of that, it is advisable to include molecules capable of promoting an adequate intestinal physiology, such as intestinal conditioner pronutrients.