Orange, Garlic and Grass

What have these got to do with Chemistry?

A lot more than any one can imagine.

All these are natural products. Each one is associaed with thousands of chemical compounds. Some of these are beneficial and some can be toxic. But they all have some role in the metabolism of plants and animals. It is not the aim here to list all these and by themselves they do not constitute chemistry. Their synthesis, biosynthesis, their interaction with other molecules is what chemistry is. However some compounds and their applications are listed here.


The yellow part of the orange peel through cold pressing and or steam distillation forms a pleasant smelling(orange flavour) compound Limonene.

Limonene is useful for various applictions including as food flavouring agent. Recently a company based in Florida has applied for a patent in which they claim that it is useful in cancer therapy. It is also a component of cleaning solutions, manufacture of resins among others.

Citric acid is another component of the pulp along with some sugars. Citric acid is involved in a sequence of reactions called the Kreb cycle. Along with glycolysis and electron transport chain, Kreb cycle are part of hundreds of reactions which oxidise glucose to CO2 and H2O stepwise. The energy released is conserved in the form of ATP and other energy rich molecules to be utilised when needed.

The white part of the orange peel is mainly cellulose, the most abundant compound on this planet. Many animals are capable of hydrolysing cellulose and utilising the glucose out of it for their energy needs.


White blood cells from garlic eating people have been found to kill tumour cells much more than from non garlic eaters. Among hundreds of compounds the one that is responsible for its odor is Allicin, formed from the interaction of allin and the enzyme allinase when garlic is crushed. Allicin is useful for the plant itself because it repels herbivorous animals. It has cholesterol and blood pressure lowering properties. It also cures certain repiratory problems, is an antibiotic and enhances digestion.


There are scores of different varieties of grass each differing in its chemical compositon. Water and cellulose are the major components.Chlorophyll is responsible for the green color of grass and all plants. Its chief role is in photosynthesis wherein it harnesses the solar energy and produces glucose using CO2 and H2O. This ability only plants have. Most animals depend on the starch plants synthesise for their energy needs. Starch can be considered as polymer of glucose and is the food reserve carbohydrate in plants. Humans depend on starch and are incapabale of digesting cellulose.

Lemon grass (smells of lemons) is cultivated in some countries which include India, South Korea and some parts of South America. The oil is extracted through mainly steam distillation. It contains many compounds including citral. This compound has many applications, it is an insect repellent, and can be used in the synthesis of Vit-A.

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C.V. Raman
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