2.2. Constituents that are formed during normal plant metabolism and remain when the plant is harvested
The characteristic aromatic profiles of plants used as a source of flavouring materials depend on a complex mixtures of chemicals that were formed in the plant tissues during the normal growth cycle and remain there, more or less intact, after harvesting. Plants are able to achieve, through the action of sunlight, nutrients and water, many complicated synthesis, which depend on its variety, its environment during the growth, maturation and fruiting.
Not all the chemicals found in plant tissues contribute to a desirable aromatic profile; some are odourless and tasteless, others may even present a toxic hazard.
All plants and animals are structurally composed of cellular matter comprising proteins, carbohydrates, fats and water together with variable amounts of inorganic salts, amino-acids, free fatty acids, phosphorylated sugars, enzymes and a complex and variable range of intermediate and final products of metabolism peculiar to the organism.
Essences or essential oils are the volatile compounds obtained by hydrodistillation, steam distillation or expression of the start material, usually plants or parts of plants (roots, stems, leaves or flowers). They are of great importance for the flavour and the fragrance industries. These products are complex mixtures of organic chemicals, from which nature and relative proportions determine the plant species and are dependent on agricultural factors such as environment, climate, soil conditions, time of harvesting and post-harvesting handling like drying, before the distillation. The proportions of the constituents of an essential oil determine the plant chemeotype and remain within some studied limits and the quality of an oil may be expressed in terms of one or more specific components.