Fragrance Chemistry: Scents As Secondary Metabolites

Secondary metabolites are compounds that are not necessary for the survival of a cell or organism but play a role in its interaction with its environment. They are often involved in protecting plants against biotic or abiotic stresses.

Fragrances are volatile compounds that contribute to the scent of flowers, fruits, seeds, and other parts of plants. They are considered secondary metabolites and are often used in the perfume industry.

Secondary metabolites are derived from primary metabolites and can be highly inducible in response to stress. They are classified into different families, including terpenoids, polyketides, and phenylpropanoids.

Terpenoids, which include monoterpenes, sesquiterpenes, and diterpenes, are the most common secondary metabolites in plants. They are derived from acetyl-CoA or glycolytic intermediates and play a role in plant defense against insects and mammals.

The fragrance industry has been increasingly turning to biotechnology to produce sustainable and high-quality fragrance ingredients. Microbial-based approaches, such as heterologous expression of terpene synthase and mevalonate pathway into Escherichia coli, have shown promising results.

Plants can be genetically engineered by introducing foreign genes or modulating the expression of native genes to alter their fragrance profile. This can be done by up-regulating or down-regulating specific genes in the pathway.

Microbial biosynthesis of fragrances offers advantages such as industrial-scale production, higher yields, and easier product recovery. It also allows for the use of renewable and sustainable feedstocks.

Overall, the use of biotechnology and metabolic engineering to produce fragrances is a promising approach that can help address supply issues and meet the demand for sustainable and high-quality ingredients in the fragrance industry.

Fragrances are secondary metabolites that are not essential for the survival of the organism but play a role in its interaction with the environment

Secondary metabolites are compounds that are not necessary for the survival of a cell or organism. They are, however, involved in the interaction of the cell or organism with its environment. They are often involved in protecting plants against biotic or abiotic stresses.

Terpenes are important in the perfume industry, as natural products have been used for millennia as raw materials for perfumery. The perfume of a natural product is usually the result of a complex interaction of different constituents, so each and every one of the components contributes to the total olfactory perception.

Terpenes are also important in the pharmaceutical industry, as they can be used as drugs, flavours, fragrances, insecticides, and dyes.

Secondary metabolites are often involved in the protection of plants against biotic or abiotic stresses

Secondary metabolites are unique to plants and are involved in a variety of biological and physiological activities, including defence and adaptation to harsh situations. They are distinct from primary metabolites, which perform essential metabolic functions in plants, such as nutrition and reproduction. Secondary metabolites are often involved in protecting plants against biotic or abiotic stresses.

Plants have evolved diverse defence mechanisms to cope with stress conditions, and the accumulation of secondary metabolites is one of these responses. Secondary metabolites can be highly inducible in response to stresses, and they play a critical role in defending plants against a variety of biotic and abiotic threats. For example, certain secondary metabolites can regulate in-plant defence against biotic stress. Plant glucosinolates, for instance, are important in producing callose plugs in cell walls to restrict pathogen entry.

Secondary metabolites can also help protect plants from abiotic stress, such as environmental stresses. They can serve as antioxidants or messenger molecules, enhancing the plant's survival, durability, and productivity. Additionally, secondary metabolites can contribute to ecological connections between plant species.

The metabolites biosynthesised by medicinal and aromatic plants are of particular interest to the fragrance industry. Flowers, fruits, seeds, leaves, whole plants, woods, roots, and resins have been used as sources of aromatic materials for millennia. These natural fragrances result from the complex interaction of different constituents, each contributing to the total olfactory perception.

They can also be used as drugs, flavours, insecticides, and dyes, and thus have a great economic value

Secondary metabolites are used in a variety of ways, including as drugs, flavours, insecticides, and dyes. They have a great economic value due to their wide range of applications.

As drugs

Secondary metabolites have been used as drugs for millennia, and many important modern drugs are derived from them. They have been shown to have a wide range of biological activities, including antibacterial, anti-inflammatory, anticancer, antiviral, and hepatoprotective effects. They can also be used to enhance agricultural productivity and as preservatives.

As flavours

Secondary metabolites can be used to enhance the flavour of food and beverages. For example, they can be used to enhance the flavour of beer and spirits, and they are a major contributor to the flavour of fresh beer. They can also be used to flavour tea, wine, grains, roots, bark, and stem.

As insecticides

Secondary metabolites can be used to deter or repel insects

The perfume of a natural product is usually the result of a complex interaction of the different constituents, so each and every one of the components contributes to the total olfactory perception

The perfume of a natural product is usually the result of a complex interaction of its different constituents, with each component contributing to the total olfactory perception.

Fragrances are substances that are not necessary for a cell or organism to live, but they play a role in the interaction of the cell or organism with its environment. They are often involved in a plant's protection against biotic or abiotic stresses.

Fragrances are volatile chemicals with a molecular weight of less than 300 Da that humans perceive through the olfactory system. In humans, about 300 active olfactory receptor genes are devoted to detecting thousands of different fragrance molecules through a large family of olfactory receptors of a diverse protein sequence. The sense of smell plays an important role in the physiological effects of mood, stress, and working capacity.

The olfactory system contains a sensory organ (olfactory epithelium) and specific olfactory brain regions (olfactory bulb and higher olfactory cortex). The olfactory mucosa is the region located in the superior and posterior part of the nasal cavity, especially for the detection of fragrant molecules. It includes the olfactory epithelium and its underlying lamina propria. In general, the olfactory receptor cells contain cilia where molecular reception with the fragrance occurs and sensory transduction starts.

The fragrance components have some specific molecular properties in order to provide sensory properties. It has a sufficiently high vapor pressure, low polarity, some ability to dissolve in fat and surface activity. Fragrance materials vary from highly complex mixtures to single chemicals. The fragrance molecules are mainly limited to the molecular weight of 200 to 300 Da but within that range, there are essentially a vast number of fragrant components and their molecular structures are highly varied. The natural fragrance materials are mainly obtained from plants, resins, animal secretion and their metabolites.

The fragrance stimulation of olfactory receptor cells in the nose involves interaction of fragrance molecules with olfactory-receptor proteins. Buck and Axel found the family of transmembrane proteins believed to be the odor receptors and some of the genes that encode them. They found that the proteins contained the seven-helical transmembrane structure and contained sequence resemblance to other members of the G-protein-coupled receptor family.

The EEG is a good temporal measure of responses in the central nervous system and it provides information about the physiological state of the brain both in health and disease. The EEG power spectrum is classified into different frequency bands such as delta, theta, alpha, beta and gamma, and each band is correlated with different features of brain states. A quantitative EEG uses computer software to provide the topographic mapping of the brain activity in frontal, temporal, parietal and occipital brain regions. It is well known that decreases of alpha and beta activities and increases of delta and theta activities are associated with brain pathology and general cognitive decline.

In the last few decades, many scientific studies were conducted to investigate the effect of inhalation of aroma on human brain functions. The studies have suggested a significant role for olfactory stimulation in the alteration of cognition, mood, and social behavior.

Secondary metabolites can be classified based on composition, synthetic pathway, and chemical structures

Secondary metabolites can be classified based on their composition, synthetic pathway, and chemical structures.

Composition

Secondary metabolites can be classified based on their composition into three groups: terpenoids, polyketides, and phenylpropanoids. Alkaloids are another class of secondary metabolites that are nitrogenous organic molecules biosynthesised from amino acids.

Synthetic Pathway

The three main synthetic pathways of secondary metabolites are the shikimate pathway, the isoprenoid pathway, and the polyketide pathway.

Chemical Structures

Secondary metabolites can also be classified based on their chemical structures. Here are some examples of how they can be categorised:

• Terpenes: These can be further classified into hemiterpenes, monoterpenes, sesquiterpenes, diterpenes, sesterterpenes, triterpenes, and carotenoids, depending on the number of isoprene units they contain.
• Alkaloids: These can be classified into non-heterocyclic or atypical alkaloids and heterocyclic or typical alkaloids.
• Phenols: This diverse group includes coumarins, quinones, naphthoquinones, anthraquinones, and flavonoids.

Frequently asked questions