Nature-identical compounds, aroma

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. 

Phenylethanol has a rose-like odour and makes the chemically produced compound the most used fragrance chemical in perfume and cosmetics, with a world market of about 7,000 t year [107, 108]. 2-Phenylethanol is also found in many foods as a characteristic flavour compound rounding off the overall aroma, especially in foods obtained by fermentation, such as wine, beer, cheese, tea leaves, cocoa, coffee, bread, cider and soy sauce [109]. In food applications, natural 2-phenylethanol is preferred rather than its nature-identical counterpart from chemical synthesis and it has a market volume of 0.5-11 year . This product is sold at market prices of up to US 1,000 per kiklogram and is mainly produced by yeast-based bioprocesses since its isolation from natural sources, e.g. rose oil, would be too costly [109]. 

For example, vanillin can be obtained via at least five different ways (i) by isolation from the orchid (Vanilla planifolia), which is a very expensive method (ii) by tissue culture followed by extraction (iii) by microbial transformation of eugenol, the main compound of clove (iv) from lignine by synthesis, and (v) from guaiacol, a natural aroma compound, with comparable molecular structure. Only the vanillin obtained via the first three methods is natural. The other routes afford a nature-identical vanillin. 

Biosynthetic pathways of aroma material in food are naturally identical with those found in nature. On the other hand, Maillard reaction that takes place especially when food is thermally processed is a formation pathway of aroma-active compounds that are characteristic to cooking art. 

The headspace sampling technique developed in the present study to collect volatiles from cold stored Black Truffles performed adequately. Indeed, the aroma Isolate obtained was described as typical, and 11 minor compounds could be described for the first time as Black Truffle aroma constituents. Moreover, these results allowed the formulation of the first Nature-Identical Black Truffle aromatizer. 

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. 

Owing to their common enzymatic pathways, chiral aroma compounds from fruits and other natural sources should be characterized by origin specific enantiomeric ratios. Indeed, from freshly harvested strawberries y-decalactone and y-dodecalactone have been detected with high enantiomeric purity favouring the (4R)-configurated y-lactones y-Cjo(4R >98 % ee), y-C,2(4R >99 % ee) [28]. On the other hand, racemic y-decalactone in aroma relevant amounts has not yet been observed in fruits. Thus, the detection of racemic y-decalactone from fruit-containing food indicates the addition of nature-identical y-C 10-lactone. 

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. 

Production Even today many aroma chemicals are still isolated from essential oils, others are prepared semisynthetically from the components of the oils or from other suitable oiganic compounds. The proportion of natural and nature identical aroma chemicals used in the perfume industry is ca. 70%. The aroma chemicals not occurring in nature are often structural analogues of natural products that are difficult to synthesize, e.g., the sandalwood aroma chemicals prepared from campholene aldehyde or camphene and guaiacol as substitutes for the expensive sandalwood oil or santalols. 

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. ... 

This mass spectral database is dedicated to the application areas of the food and flavour industries, and was selected and quality controlled by the mass spectral experts at the Central Institute of Nutrition and Food Research in the Netherlands. The collection includes 1620 reference mass spectra and covers the whole range of volatile compounds in food. Apart from the large number of natural, nature-identical and artificial flavours and aromas, there are - among others - food additives and solvents, pesticides and veterinary pharmaceutical compounds, which are frequently found as residues. Derivatives of non-volatile compounds such as sugars or polyhydroxyphenols are also available. The database is now available in its second edition (Central Institute of Nutrition and Food Research, 2003, ISBN 978-0-471-64825-3). 

The ultimate goal of flavor research in the food industry is to identify and classify unique aroma chemicals that contribute to the characteristic odor and flavor of foods. Having this knowledge enables flavor duplication through nature-identical or biosynthetic pathways and can facilitate better quality control of raw materials by screening of the appropriate analytical target compounds. 

As we saw with the early measurements of Biot, natural sources of chiral material such as lemon oil are complex mixtures. We will see shortly that not only are there differences in the smell of many enantiomers there are also large differences in threshold sensitivity, that is, the concentration in which the substance can be detected by the nose. So you might have a 99.9% pure sample, but the dominant aroma may be from the 0.1% impurity. It wasn t until the midtwentieth century that chemists were able to prepare "pure" compounds of enantiomers and then verify the different smells. One of the first examples of such compounds are P-(—)-carvone and S-(—)-carvone, which were studied by three different research teams and published independently in 1971 [5-7]. The structures of these enantiomers are shown in Figure 4.3. It is important to remember that these two compounds have identical physical properties unless they are being analyzed or reacted with... 

The aroma substances that comprise flavors are found in nature as complex mixtures of volatile compounds. A vast majority of volatile chemicals that have been isolated from natural flavor extracts do not provide aroma contributions that are reminiscent of the flavor substance. For instance, n-hexanal is a component of natural apple flavor (1) however, when smelled in isolation, its odor is reminiscent of green, painty, rancid oil. Similarly, ethyl butyrate has a nondescript fruity aroma although it is found in strawberries, raspberries, and pears, it does not uniquely describe the aroma quality of any of these individual fruits. It has long been the goal of flavor chemists to elucidate the identity of pure aroma chemicals that have the distinct character impact of the natural fruit, vegetable, meat, cheese, or spice that they were derived from. Often, these are referred to as character impact compounds (2). 

---