Carotenoid pigments in plants

Plant pigments fall into three major groups: carotenoids chlorophylls and flavonoids. Plant carotenoids are responsible for the red, orange and yellow pigments found in fruits and roots such as tomatoes, red peppers, pumpkins and carrots.

Carotenoids pigments are hydrocarbon chains with 40 carbon atoms. They can be seen in the petals of many flowers and are the primary pigments responsible for the fall coloration of deciduous trees.

More than 450 carotenoids occur in nature. The carotenoids can be divided into two basic types:
*Carotene which contain no oxygen atoms
*Xanthophyll which does contain oxygen Heat affects the color of vegetables, most likely because it modifies the pigments’ chemical structure.

Vegetables containing β–carotenes should not be overheated, because this pigment not only contributes to color but can also be converted to vitamin A; therefore, its destruction would be doubly undesirably.
Carotenoid pigments in plants

What is quinone?

Quinone is a lipid-soluble hydrogen (i.e., proton plus electron) carrier that mediates electron transfer between respiratory chain components. By definition, a quinone is a cyclohexadienedione. Those with carbonyl groups ortho to each other are called o-quinones; those with carbonyl groups para to each other are called p-quinones.

Quinones can also be obtained by oxidation of 1,2-benzenediol or 1,4-benzenediol.

Perhaps the most important chemical property of quinones is that they are readily reduced to benzenediols. For example, p-quinone is readily reduced to hydroquinone by sodium dithionote in neutral or alkaline solution.

In structure, the coenzyme Q group closely resembles the members of the vitamin K group and the tocopherylquinones, which are derived from tocopherols (vitamin E), in that they all possess a quinone ring attached to a long hydrocarbon tail.

The quinone pigments, of which there are at least 1200 structures range in color from yellow to almost black, but most are yellow, orange or red. Although they are widely, albeit sporadically, distribute in higher plants, they contribute little to plant color.
What is quinone?

Vitamins as antioxidants in processed foods

Vitamins as antioxidants in processed foods
Oxidation, a series of chemical reactions yielding undesirable and products (off odors, colors, and flavors), may occur in many fruits and vegetables and foods high in fat and oil during exposure to air, light, heat, heavy metals, certain pigments or alkaline conditions. Enzymatic browning may occur in some fruits and vegetables, particularly apples, banana, peaches, pear, and potatoes, which contain phenolase enzymes. When these fruits and vegetables are cut or sliced and exposed to air, the phenolases catalyze oxidation of phenolics compounds to ortho-quinone compounds, which then polymerize, forming brown pigments.

Oxidation in lipids (autoxidation) and in fat and oil containing foods, on the other hand, occurs as a result of the susceptibility of fatty acids (building blocks of fats and oils) to oxidations and subsequent formation of reactive compounds referred to as “free radicals”.

The free radicals promote the development of a series of chemical reactions which lead to the production of off-flavors, colors, odors, and rancidity. While both saturated and unsaturated fatty acids are susceptible to oxidation, unsaturated fatty acids are significantly more susceptible than their saturated counterparts at room temperatures and at elevated temperatures.

Antioxidants, as defined by Food and Drug Administration are “substances used to preserve food by retarding deterioration, rancidity or discoloration due to oxidation.” Some oxidations have more than one function. For example, Ascorbic acids may function as a free-radical chain terminator, and oxygen scavenger, or a metal chelator. Under certain conditions, it may act as a promoter for oxidation.
Vitamins as antioxidants in processed foods