Not all carotenoids are the same when it comes to yolk and skin pigmentation. As markets have different preferences for yolk and/or skin colours, it is of utmost importance to understand the colouring effect of different carotenoids used in poultry feeds.
By Catherine Hamelin and Ulrich Altemueller , DSM Nutritional Products Europe
Carotenoids are natural compounds present in animals and plants; with yellow, orange and red typically associated with birds. It is well known that birds are not able to synthesise carotenoids, and thus these essential compounds must come from their diet. Carotenoids are mainly found in the egg yolk, the skin and fat, the liver, and the feathers. They are essential not only for pigmentation, but also for immunomodulation as antioxidants, evidenced by the high disappearance rate of carotenoids from the blood stream during immune stress periods, and reduced pigmentation throughout the body.
Carotenoids were first discovered in carrots, from which in 1831 a compound that was to be named ‘beta-carotene’ was isolated. Since then, we have identified in the carotenoids family more than 600 molecules. The differences in carotenoid profiles in the various tissues are determined by the processes of absorption and transportation, and by the metabolic capacity to modify dietary carotenoids.
Colour is one of the most important factors affecting consumer choices through sensory evaluation of foods. In most countries, golden yolks are preferred because good colour has been traditionally associated with high health. Also, eggs used in recipes can influence the colour of pasta, bakery products and sauces. In addition, although consumer preference for broiler skin colour varies according to culture and region, here also, good health is generally associated with golden skin colour.
The most important carotenoids in modern poultry production include lutein, zeaxanthin, and canthaxanthin. Less frequent ones include citranaxanthin (only in eggs), apo-carotene-ester, and the infrequently used capsanthin. Under commercial conditions, carotenoids are provided by the ingredients mentioned in Table 1
: yellow corn and derivates such as gluten and distillers grains; alfalfa and concentrate; nature-identical or nature-extracted carotenoids (flowers like marigold/tagetes or paprika). Yellow carotenoids mainly originate in vegetable sources. For example, lutein and zeaxanthin are found in corn and its derivatives. Lutein is the main carotenoid in alfalfa and tagetes. Paprika extracts provide red carotenoids, mainly capsanthin and capsorubin, but they also contain lutein and zeaxanthin. Apo–ester, canthaxanthin, and citranaxanthin are commercially available sources of nature-identical carotenoids. Today, due to its high pigmentation efficacy compared to citranaxanthin, canthaxanthin is the preferred red xanthophyll in poultry production.
Yolk colour can be determined basically by two methods. An objective method uses a mechanical equipment (for example, MiniScan XE HunterLab, Minolta colourimeter CR 300) that expresses colouration in the so-called HunterLab scale (L, lightness; a, redness; and b, yellowness). A simple but subjective method involves the DSM Yolk Colour Fan that expresses results in a 1 to 15 scale by means of comparison with calibrated cards. Both systems are well correlated but because the DSM Fan is more economical and readily available it has become the preferred method in most parts of the world. With regards to the products containing eggs, both methods are suitable, but for scores higher than 15, the DSM Fan is insufficient. For this purpose, a new and fast method based on spectrophotometry can determine carotenoid content expressed as beta-carotene equivalents (BCE): the iCheck Egg. This fast method is perfectly correlated with the equivalent standardised method carried out in laboratory.
Compared to yolks which have homogeneous colour, broiler skin is much more difficult to assess because carcass colour is more heterogeneous. Colour can be assessed by the DSM Broiler Fan, expressed in a 101-110 scale, or by a colourimeter, as above. The results can vary according to the protocol. Ideally, measurements must be carried out on the fatty part of the breast collected after chilling. Sex (female birds have darker skin colour) and genotype are also important factors of variability.
In a French survey, the yellow value was more useful to distinguish yellow broilers, whereas the red value was more variable and did not depend on chicken type. Again, as the DSM Fan allows for a better ranking and is more economical and readily available, it has become the preferred method for many abattoirs. Finally, in markets where the shank colour is of importance when the broilers are sold with the feet, the red colour is the most important, with canthaxanthin being the most efficient compound for shank pigmentation.
Synthetic products are standardised and more stable than extracted products. For example, in one study, apo-carotene-ester concentration in feed samples showed very little variation from expected values, whereas it was 30% below expectations for marigold extracts. Esterification and saponification usually helps to produce better stable tagetes and paprika products; the same as spray-drying protection, but there is a wide variation in the quality of the coating. For example, the stability of various red carotenoids products in premixes was checked after three months of storage and recovery varied considerably: 66% to 92% for canthaxanthin, 76% for citranaxanthin, and 39% for capsanthin from paprika. Carotenoids are very unstable on their isomeric forms; the trans-configuration is the most common, found in the yolk, but the cis-configuration (less efficient for pigmentation) can be produced when heat, light, or oxygen damage occurs. Good coating usually prevents such damage.
In table eggs, from hens raised under traditional commercial conditions, six carotenoids are present at the greatest concentration. These include lutein, zeaxanthin, canthaxanthin, citranaxanthin, apo-caroten-ester, and cryptoxanthin. In contrast, organic eggs usually contain only lutein, zeaxanthin, and cryptoxanthin, as regulations do not allow synthetic carotenoid in the feed. Apo-carotene-ester is the most deposited yellow carotenoid in egg yolk with a transfer efficiency from feed to egg of about 55% (as compared to only 17% for marigold carotenoids). On the other hand, canthaxanthin is the most efficiently deposited red carotenoid in egg yolk, with an average deposition rate of about 40%. Interestingly, in the last years, new canthaxanthin commercial products have appeared on the European market. In a relevant study, the deposition rate for three such new products was 30, 27 and 24%, as compared with a traditional cantha-xanthin product that showed a 35% deposition rate. It should be noted here that bioavailability of formulated products can be influenced by many factors, including matrix type and structure, formulation particle size, formation of non-absorbable complexes with matrix components, and degradability of carrier.
Colour deposition in the skin
In broilers, zeaxanthin influences the yellow value in all tissues, more noticeably in the abdominal fat, with lutein and zeaxanthin being deposited in skin and fat with a rate of 8-12% and 4-9%, respectively. In broilers, the deposition of the isomerised tagetes (enriched in zeaxanthin) is lower than the standard tagetes (mostly lutein), whereas contents of apo-carotene-ester increases in skin and abdominal fat with increasing supplementation of this carotenoid, reflecting a linear increase over the entire dose range (not common among other carotenoids).
It has been determined that 1 ppm of apo-carotene-ester is equivalent to about 2 ppm of lutein-zeaxanthin (from tagetes). Canthaxanthin is the dominating red carotenoid in pigmented broilers, whereas paprika receives little attention because of its low efficiency (requiring two to three times the amount of paprika xanthophylls compared to canthaxanthin).
There are two components of the pigmentation process. The first refers to the saturation phase and involves the deposition of yellow carotenoids to create the yellow base (about 7 on the DSM Yolk Fan). Then the addition of red carotenoids is called colour phase and changes the hue in a more orange colour. For table eggs, quantities of yellow and red carotenoids can be added depending on market requirements (Table 2
). Feed supplementation should be implemented for at least 10 days to ensure a constant colour. For processed eggs, the requirement for yellow base is higher. When specification is above 20 ppm BCE (above 15 on the DSM Fan), it is better recommended to formulate according to the BCE value. High concentrations of apo-carotene-ester in the feed are frequently necessary to fulfil the requirements such as pasta production.
Regarding pigmented broilers, the amount of required feed carotenoids is higher than for table eggs, because of lower deposition rates. The most common practice is based on a lutein-zeaxanthin and canthaxanthin mix, with apo-carotene-ester added to ensure colour homogeneity. Feed supplementation should be done for three weeks minimum with no withdrawal before slaughter.