Лако-красочные материалы — производство

CHARLES SELL

PERFUMES AND ODOURS IN NATURE
Introduction

Like the pharmaceutical industry, the fragrance industry uses nature as its guide and source of inspiration. All the perfumes and perfume ingredients that we produce in our factories are modelled to a greater or lesser extent on those found in nature. We observe nature, analyse it to find out how it does the job and then modify and adapt its methods to suit our needs.

Smell and taste are the oldest of our senses. They probably developed in very primitive organisms as a means of obtaining information about chemical changes in the organism’s environment. Diurnal birds and aquatic animals rely heavily on sound; man and a few primates rely on vision; but all other species use smell and taste, the chemical senses, as the dominant medium through which they obtain information about the world in which they live. Since smell is such an important source of information for us, it is not surprising that nature has developed a very sensitive and sophisticated system for the analysis of the chemicals which make up our environment. It is intriguing that we can detect not only the natural odours, whether they have been placed deliberately or are simply artefacts of degradation processes, but also chemicals to which we have not been exposed before. We have only a very limited understanding of how this wonderful sense works; to find the solution to this riddle is one of the great scientific challenges of the moment.

Animals use smell and taste to find food and to assess its quality. The smell of food has a powerful effect on animals, whether it is a lion

smelling out a herd of wildebeest or a shopper being drawn to the in­store bakery at the back of the supermarket. Watch your cat when you give it a bowl of food. It carefully sniffs the food before eating, to check that it is fresh and good. Our aversion to the smell of amines and mercaptans is, doubtless, related to their presence in food that has been spoiled by bacterial decomposition, a strong warning signal against sources of food poisoning. Some degradation reactions are responsible for the development of flavour in food. For example, autoxidation of fatty acids can lead to the formation of materials of characteristic aldehydic flavour. It is important to note that the tongue (i. e. the sense of taste) only detects sweet, salt, sour and bitter. The rest of taste is, in fact, smell. The volatile flavour ingredients are vaporized in the mouth and reach the nose through the airways behind the roof of the mouth.

Living organisms also use the chemical senses as a means of communication. If the communication is between different parts of the same organism, the messenger is referred to as a hormone. Chemicals used to carry signals from one organism to another are known as semiochemicals, which can be grouped into two main classes: phero­mones and allelochemicals. If the signal is between two members of the same species, the messenger is called a pheromone. Pheromones carry a variety of types of information. Not all species use pheromones, but in those that do, some may use only one or two pheromones whilst others, in particular the social insects such as bees, ants and termites, use an array of chemical signals to organize most aspects of their lives. Sex pheromones are amongst the most widespread. Male moths can detect females by smell at a range of many miles. Androstenol is the compound that produces ‘boar taint’ in pork. It is produced by boars and is released in a fine aerosol when the boar salivates and champs his jaws. When the sow detects the pheromone in the air, she immediately adopts what is known as ‘the mating stance’ in readiness for the boar. Ants and termites use trail pheromones to identify a path between the nest and a food source, which explains why ants often walk in single file over quite long distances. The social insects also use alarm, aggrega­tion, dispersal and social pheromones to warn of danger and to control group behaviour. Chemicals that carry messages between members of different species are known as allelochemicals. Within this group, kairomones benefit the receiver of the signal, allomones its sender and with synomones both the sender and receiver benefit. Thus, the scent of a flower is a synomone since the attracted insect finds nectar and the plant obtains a pollinator. Some plants produce compounds known as antifeedants, the taste of which insects find repulsive. These are allomones since the signal generator, the plant, receives the benefit of not being eaten.

Unlike pheromones, many odorous chemicals in nature are pro­duced for properties other than their odour. Many plants, when damaged, exude resinous materials as a defence mechanism. The shrub Commiphora abyssinica, for example, produces a resin that contains a number of antibacterial and antifungal compounds. The role of the resin is to seal the wound and prevent bacteria and fungi from entering and damaging the plant. The resin has a pleasant odour and so was put to use by man as a perfume ingredient. It is known as myrrh. As a result of its antimicrobial properties, myrrh was also used as an antiseptic and preservative material, for instance, in the embalm­ing of corpses. Frankincense has been used in religious rites for thousands of years, and so two of the three gifts brought to the Christ Child by the Magi were perfume ingredients. Knowledge of perfumery thus helps us to understand the symbolism involved; gold, frankincense and myrrh represent, respectively, king, priest and sacrifice.