28 Nov Yolk color – an important egg quality attribute
There is no doubt that color plays a very important role in our perception of food. Bright, fresh, typical colors stimulate the appetite whereas, if the color of a food deviates from what we expect, then it is likely that we will reject it in favor of an alternative. Therefore, color is a key aspect of food quality that should not be underestimated.
It is well recognized that yolk color is important to consumers. yolk color is one of the main parameters by which the quality of eggs is judged. Recent surveys in a number of different European countries
(France, Germany, Italy, UK, Spain, Poland and Greece) have confirmed that yolk colour is one of the main parameters by which the quality of eggs is judged. Although consumer perception as to what constitutes a good, appetizing egg yolk color is generally linked to geographical location, culture and traditions, it is certainly true that consumers in most parts of the world prefer deeply hued yolks.
Measurement of yolk color
The Roche Yolk Color Fan (RYCF) is widely accepted throughout the food chain as the standard for measuring yolk color on a routine and reliable basis. By using the fan to define the desired yolk color and by formulating the hens’ feed accordingly, the target yolk color can be achieved
Producing the required color
As with all birds, yolk color is primarily determined in the laying hen by the content and profile of pigmenting carotenoids present in the feed. Thus, once a particular yolk color target has been defined, it is a relatively straightforward process to control, via feed specification/formulation, the carotenoid content in the feed required to achieve that target.
Carotenoids can be included in the diet by the use of particular raw materials, for example maize or grass meal, and/or the addition of specific feed additives. Thus, the nutritionist can determine, based on local raw material cost/availability and target yolk colour, the most cost-effective approach to be taken to produce eggs of the required colour to meet the quality criteria of the market chain. The development of yolk colour can be viewed as a two phase. process. The first phase (‘saturation’) is the setting of a good yellow base by the deposition of yellow carotenoids and the second phase (‘colour’) is the addition of a red carotenoid to tone the colour to the golden-yellow. There are three main yellow carotenoids (lutein, zeaxanthin and apo-ester) and three main red carotenoids (canthaxanthin, citranaxanthin and capsanthin/capsorubin) used for egg yolk pigmentation.
The primary criterion for yellow carotenoids is the provision of a strong yellow base which is important for the development of a good final colour. A poor base can result in problems such as ‘off’ colours (too reddish or even pink) and high colour variability. the most important characteristic of the yellow carotenoids during the saturation phase is their deposition efficiency which for apo-ester (~40- 50%) is approximately three times that of either lutein or zeaxanthin
(~10-20%). Thus, three times more lutein/zeaxanthin than apo-ester is required in the feed to provide the same degree of yellow pigmentation in the egg yolk as can be seen in the data outlined in Fig. 2
Importance of carotenoids
As the red carotenoids are primarily responsible for the development of the golden
colour from the yellow base in the yolk, then both the deposition efficiency and the colour properties of the individual carotenoids are important.
The deposition efficiency of canthaxanthin is substantially higher than those of either citranaxanthin or capsanthin/Capsorubin . Canthaxanthin is a reddish orange colour, whereas citranaxanthin and capsanthin/capsorubin both have deep red colours.
Thus, 1.5 times more citranaxanthin than canthaxanthin and 2.5 times more capsanthin/ capsorubin than canthaxanthin would be required in the feed to achieve the same degree of red pigmentation in the egg yolk as can be seen.