Before we select the right natural pigment source, we must understand the nature of these compounds and why they are produced in such abundance in some plants.
Synthetic pigments are the norm in the egg-producing industry, but consumer demand for eggs produced with natural pigments is increasing. This development is in line with other trends in the human nutrition industry, especially within developed urban populations. So, before we select the right plant pigment to use in layer feeds, we need to understand their actual role in nature.
The role of pigments within plants
Plants have the capacity to synthesize an amazing variety of pigments that, in turn, result in a spectacular range of colors. The obvious reason for this highly developed ability of plants is to attract pollinators (such as bees) to flowers and seed dispensers (such as birds and animals) to their nutritious fruits. But there is more to pigments than meets the eye. Pigments have additional significant roles in plants. First, pigments are substances that absorb light – that is, solar energy. The color of any given pigment is determined by the wavelength reflected by it. The green color that all plants have is due to the presence of chlorophyll, the pigment responsible for photosynthesis, a process that animals lack. Chlorophyll as a part of a complex biological machinery is the key pigment that absorbs light energy from the sun to be fixed as chemical energy in the form of glucose. The two other most important types of pigments found in plants are carotenoids and anthocyanins that mostly act to protect chlorophyll against excessive oxidation, hence they are potent antioxidants.
Chemical nature of plant pigments
Chlorophyll, the green pigment in plants, has a remarkably similar chemical structure to hemoglobin in animals but, instead of iron, it contains magnesium in its tetrapyrole ring. It is this pigment that absorbs light, mainly in the red and the blue range of the light spectrum. Layers consuming green feed ingredients (for example, alfalfa meal) also consume this green pigment and, of course, plenty of magnesium.
Carotenoids belong to the terpene group of plant secondary metabolites and are found in all photosynthetic organisms. Carotenoid colors range from yellow to orange and red. They play two very important roles in the photosynthetic process. They serve as accessory pigments to chlorophyll, meaning they also absorb light but in a broader range (green part of spectrum), thus increasing light harvesting efficiency, which is especially important under low light conditions. Their second role is photoprotective under high sunlight conditions. They help dissipate extra solar energy which otherwise would lead to photo-oxidation of chlorophyll and, as a result, to the destruction of the photosynthetic machinery. Synthetic carotenoids are the main egg yolk pigments used today, and there is a great volume of research available on the subject.
Flavonoids is a third category that contains several plant pigments including yellow flavonols as well anthocyanins, which give red, blue and even purple colors. Anthocyanins are water soluble, in contrast to carotenoids that are fat soluble and, interestingly enough, their color is influenced by pH. Many flowers and fruits owe their attracting intense colors to anthocyanins. Their value in coloring egg yolk remains unclear, but they deserve further investigation.