Why is that some foods in nature are strongly colored and others are colorless or mildly colored? Many food constituents present in different concentrations have specific roles to play during germination, growth, maturity and senescence. If it is so the multitudes of colors with different hues, represented by different chemicals contained in these foods, must have definite roles during the life cycle of the plants that produce them. Organoleptically, human beings like foods that have bright colors and this may be the reason for the development of the food color industry. From a plethora of manufactured dyes and tints available for edible use a few years ago, the number has dwindled to a handful because of the long term toxicity associated with the use of artificial colors. Shift from synthetic colors to natural colors is a logical corollary to the realization of the dangers of using artificial color adjuncts during food processing.
One of the strong reasons for nature to produce colored fruits and vegetables might be the compulsion of sustaining each species through spreading the progeny to far and wide. Just like the colored flowers attracting bees, insects and birds which carry the pollens and seeds through long distances for propagation, colored fruits and vegetables also may be attracting birds, squirrels and similar creatures as a food material and they serve as propagating agents for the plants. Still it is a mystery why each plant is endowed with characteristic genetic apparatus to produce same colored flowers or fruits or vegetables. It is understandable that plants contain chlorophyll which gives them the distinct green color of varying intensity, vested with the responsibility of fixing CO2 for bio-synthesis of starch in presence of solar light and generating the life-sustaining oxygen in this planet. Plants are responsible for producing a significant portion of the oxygen in the atmosphere while cleaning up the green house gas CO2 responsible for global warming.
Red colored fruits like tomatoes contain Lycopene which gives it the distinct hue during ripening and it is recognized that Lycopene offers protection for humans from diseases like prostate cancer, heart ailment and lung disorders. Purple crops like beets, egg plant, red cabbage and red pepper, containing anthocyanin group of chemicals are considered good for a healthy heart. Orange colored foods like carrots, winter squash, sweet potato and others contain alpha-carotene and beta-carotene good for the eyes. Blue colored crops like blueberries, plum, raisins etc are rich in anthocyanins, phenolics, isoflavones, flavinols, catechins, ellagic acid and minerals like magnesium and are considered excellent protective foods. Yellow and green crops such as spinach, collard, corn, avocado, etc get their color mainly from lutein and zeaxanthine which are known to improve eye health. Green cruciferous vegetables which include broccoli, brussel sprouts, cabbage, kole etc contain valuable sulforaphane and isothiocyanates blessed with the ability to inhibit the adverse action of oxyradicals, responsible for the generation of carcinogens in the body and development of cancer. There is a class of crops with neutral or light color such as garlic, onion, sprouts, celery, asparagus, etc which contain allicin and some antioxidants with powerful anti-tumor properties. There are many health experts who advocate regular consumption of the seven groups of colored fruits and vegetables to keep away all the diseases that afflict the modern society.
Interestingly widespread apprehension about the long term effect of using artificial colors in foods on health has led to the emergence of color concentrates extracted from fruits, vegetables, flowers and seeds. One of the earliest used natural colors is annatto dye, extracted from annatto seeds, a forest produce available in plenty in India. Progressive elimination of many coal tar dyes from the list of permitted edible colors compelled the industry to look for alternate natural sources considered much safer. To day a wide choice of natural colors is available from sources like beetroot, safflower, blue grapes, alfa grass, parsley, spinach, carrots, red chilli, caramel, carbon black. blackberry, blackcurrant, kokum fruit, turmeric, etc. Though some of them have the advantage of being nutraceuticals also, the poor tintorial power necessitates use of large dosages which some times adversely affect the organoleptic quality of the end product. Efforts are called for in enhancing their color intensity through molecular modification by application of synthetic organic chemistry and modern physical chemistry.