Synthetic Natural Aroma Compounds

In spite of the fact that a great number of food aroma compounds have been identified, economic factors have resulted in only a limited number of them being synthesized on a commercial scale. Synthesis starts with a natural compound available in large amounts at the right cost, or with a basic chemical. Several examples will be considered below. 

A most important aroma compound worldwide, vanillin, is obtained primarily by alkaline hydrolysis of lignin (sulfite waste of the wood pulp industry), which yields coniferyl alcohol. It is converted to vanillin by oxidative cleavage  

The aroma compound menthol is primarily synthesized from petrochemically obtained m-cresol. 

Thymol is obtained by alkylation and is then further hydrogenated into racemic menthol  

A more expensive processing step then follows, in which the racemic form is separated and l(-)-menthol is recovered. The d-optical isomer substantially decreases the quality of the aroma (cf. 5.3.2.4). 

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Ingredients used in the industry typically fall into three categories natural aroma material, synthetic compounds, and isolated aroma chemicals. 

Many natural products and natural aroma components contain 2-furanone units and considerable synthetic work has thereby been engendered.In the context of these natural products, the name buteno-lide is generally employed and compounds are therefore numbered as derivatives of 4-hydroxybutenoic acid and not as a furan, for example a tetronic acid is a 3-hydroxybut-2-enolide. Butenolides can be converted into furans by partial reduction of the lactone, then dehydration.""... 

Aroma chemicals are an important group of organic molecules used as ingredients in flavor and fragrance composition. Aroma chemicals consist of natural, nature-identical, and artificial molecules. Natural products are obtained directly from the plant or animal sources by physical procedures. Nature-identical compounds are produced synthetically, but are chemically identical to their natural counterparts. Artificial flavor substances are compounds that have not yet been identified in plant or animal products for human consumption. 

Nature-identical aroma substances are, with very few exceptions, the only synthetic compounds used in flavors besides natural products. The primary functions of the olfactory and taste receptors, as well as their evolutionary development, may explain why artificial flavor substances are far less important. The majority of compounds used in fragrances are those identified as components of natural products, e.g., constituents of essential oils or resins. The fragrance characteristics of artificial compounds nearly always mimic those of natural products. 

Vanilla essence comes in two forms the actual extract of the seedpods and the far cheaper synthetic essence, basically consisting of a solution of synthetic vanillin in ethanol. Natural vanilla is an extremely complicated mixture of several hundred different compounds, versus synthetic vanillin which is derived from phenol and is of high purity. Many commercial vanilla extracts are now actually blends of natural and synthetic vanillin. The occurrence of several non-vanillin aroma and flavour components in minor or trace amounts in beans is the reason for their organoleptic superiority over synthetic vanilla and blends. Natural vanilla has a delicate, rich and mellow aroma and aftertaste, while the synthetic material is quite heavy, grassy and less pleasant. 

The onset of the industrial production of essential oils can be dated back to the first half of the 19 century. After the importance of single aroma chemicals was recognised in the middle of the century, efforts were started to isolate such compounds from corresponding natural resources for the first time. This was soon followed by the synthesis of aroma chemicals. In this context, the most important pioneers of synthetic aroma chemicals have to be mentioned, such as methyl salicylate [1843], cinnamon aldehyde [1856], benzyl aldehyde [1863] and vanillin [1872], as they constitute the precursors of a rapidly growing number of synthetically produced (nature-identical) aroma chemicals in the ensuing years. 

While essential oils and natural extracts, which are obtained from natural resources by various processes, mainly constitute complex mixtures, aroma chemicals are uniform compounds, which can be both of natural or synthetic origin. A number of representatives of frequently used aroma chemicals show an enormous discrepancy between synthetic and natural material. Raspberry ketone shall be used as an example here for the year 1992, an estimated yearly worldwide consumption of 400 kg of natural material is countered by the 300-fold amount of synthetic material which found industrial usage [8]. 

Taste, aroma, texture, and visual appearance play very important parts in the appeal of all prepared foods. Food flavorings are compounded from natural and synthetic aromatic substances. The compounded flavors may or may not be found in nature. Reasons for using flavors in foods include (Giese, 1994a, 1994b) ... 

Natural fruit aromas are mixtures of certain organic compounds and esters. Synthetic aromas prepared in laboratories are simple mixtures of these same esters and organic compounds. They are used in perfumes, foods and drinks to give taste and pleasant smells. Ethyl acetate, for example, is a colorless liquid with an apple flavour it is known as apple ester and is used in perfumery as a fruit essence. Propyl acetate has the smell of pears, isopentyl acetate that of bananas and ethyl butyrate smells of pineapples. All are colorless liquids. Higher molar mass esters are odorless. 

In the following section, the odor perception, psychological effects, and biological activity of a variety of essential oils are discussed. It is well known that the odors of naturally derived and chemically synthesized samples of the same compound may be quite different and that it is very difficult to reproduce or imitate the aroma profiles of an essential oil or a constituent natural material. These differences between a natural and a synthetic sample are due primarily to the relative ratios of geometric, chemical and stereochemical isomers constituting what might commonly be referred to as a single compound or material. 

An essential requirement of ice cream products is that they taste appealing. The flavours used in ice cream manufacture are usually supplied as solutions of aroma and taste compounds. Some flavour molecules are fat soluble, whereas others are water soluble. This affects the perception of flavour in ice cream water-soluble flavours are present in the matrix and are released rapidly on consumption, whereas fat-soluble flavours are released more slowly. Flavours may be natural, i.e. extracted from sources such as plants, or synthetic. The latter can be nature identical (artificially produced but identical to the naturally occurring form) or artificial (artificially produced and not occurring in nature). They are used to impart flavour to products, to enhance inherent flavours and to ensure uniformity of flavour between batches. Fruit acids, such as citric or malic acid are added to fruit flavoured water ice products to give them extra bite , by making them sour. The three most important ice cream flavours are vanilla, chocolate and strawberry. 

Aroma chemicals, fragrance chemicals. Name for natural or synthetic organic compounds used, on account of the usually pleasant odors, in the manufacture of perfumes and perfumed products. The fIavor compounds are distinguished from aroma chemicals by their occurrence and use in foods The term odorant chemical applies generally to conmounds that can be detected using the sense of smell. The term fragrance chemicals is used, except for aroma chemicals, also for odor complexes, e.g., the absolutes and essential oils used in the perfume indust. For the physiology of the sense of smell, see Zif. . 

Natural and natural-identical F. c. are used in the commercial production of aromas. The latter are F. c. that have been identified as components of foods and then produced synthetically. For the biotechnical production of natural F. c., see Lit.. The world m et of aroma and flavor substances in 1994 amounted to 9.7 billion US, the most important individual compounds being (consumption in t per year) 2-phenylethanol and its esters (7000), musk aromas (62()0), linalool or its esters (6()00), ester of lower fatty acids (5800) and vanilla (see 3,4-dihydroxybenzaldehydes) (5500) . Using tools of molecular biology, scientists are beginning to figure out how the olfactory sense works and how flavor impression is formed. ... 

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