Flavouring, synthetic

MSG, C8H8NNa04,H20. Flavouring agent extensively used as a food additive. Prepared from natural or synthetic L-glutamic acid. 

Figure 10.1 Analysis of racemic 2,5-dimethyl-4-hydroxy-3[2H]-furanone (1) obtained from a strawbeny tea, flavoured with the synthetic racemate of 1 (natural component), using an MDGC procedure (a) dichloromethane extract of the flavoured strawbeny tea, analysed on a Carbowax 20M pre-column (60 m, 0.32 mm i.d., 0.25 p.m film thickness earner gas H2, 1.95 bar 170 °C isothermal) (b) chirospecific analysis of (1) from the sti awbeny tea exti act, ti ansfened foi stereoanalysis by using a pemiethylated /3-cyclodextrin column (47 m X 0.23 mm i.d. canier gas H2, 1.70 bar 110 °C isothemial). Reprinted from Journal of High Resolution Chromatography, 13, A. Mosandl et al., Stereoisomeric flavor compounds. XLIV enantioselective analysis of some important flavor molecules , pp. 660-662, 1990, with permission from Wiley-VCH.

Yolk colour plays a role in consumer acceptance, but the preferred colour varies in different countries. Yolk colour has no relation to nutrient content, flavour or freshness, but is often enhanced in conventional production systems by addition of synthetic pigments to the animal feed. In organic production, synthetic yolk pigments are prohibited and this normally results in paler yolks, but may also lead to greater variability in yolk colour intensity. In many European countries paler yolk colour is perceived by consumers as being associated with less natural production systems, an issue that clearly needs to be addressed by improved consumer information. 

Flavours are complex substances that can conveniently be divided into three groups natural, nature identical and synthetic. 

These are materials that are synthetic but are the same compound as is present in a natural flavouring material. From time to time it emerges that one substance produces a given flavour. Most chemists know that benzaldehyde has a smell of almonds. Some chemists know that hydrogen cyanide smells of bitter almonds. If a natural flavouring can be represented by a single substance and that substance can be synthesised then the flavour is likely to be available as a nature identical flavour. Vanilla flavour is a good example. Vanilla flavour can be all natural and derived from vanilla pods or nature identical or artificial. The nature identical product would be based on vanillin, which is in vanilla pods and has a flavour of vanilla. An artificial vanilla flavour would be ethyl vanillin, which is not present in vanilla pods but has a flavour two and a... 

Practical flavours often contain a mixture of substances, some natural, some nature identical some synthetic. UK law classifies a flavour that contains any nature identical components as nature identical even though the rest of the flavour is natural. Similarly, the presence of any artificial components renders the flavour artificial. 

These are flavours that are produced synthetically but are not present in a natural flavouring material. The chemistry of flavours is a complex topic that has been the subject of many books, for example ref. 3. Synthetic flavours are made from a mix of flavouring substances that have been found to produce a given flavour note . Those who develop flavours are referred to as flavourists. Flavourists take the musical analogy of notes further by referring to the top notes and the bottom notes of a flavour. 

A typical synthetic flavour is a very complex mixture of substances. The mixture used will have been chosen to give the desired properties in the system of choice. Compounding flavours is a mixture of chemistry and sensory skills. Flavourists spend years learning how to produce flavours. 

Whether the flavour used is natural, nature identical, synthetic, or a mixture it has to be dosed into the product. Although some flavourings are very intense the volume added to the product has to be large enough for the equipment or the people to add it with sufficient accuracy. The flavour of course has to be uniformly distributed in the product. This normally means producing the flavour as a solution. Flavours are prepared for a particular use. As an example, citrus oil based flavours can be dissolved in various alcohols. 

The application of ever improving analytical methods will continue to reveal new flavouring compounds, be they natural, nature identical or synthetic. Not only are ever more sophisticated analytical techniques available but also improved methods of data analysis. The new science of chemometrics has developed to cope with the situation where chromatograms with hundreds of compounds are obtained. 

Since food additives are subjected to the most stringent toxicological testing procedures, only a few synthetic antioxidants have been used in foods for any length of time. Antioxidants are extensively tested for the absence of carcinogenity and other toxic effects in themselves, in their oxidised forms, and in their reaction products with food constituents, for their effectiveness at low concentrations, and for the absence of the ability to impart an unpleasant flavour to the food in which they are used. 

Partial least squares regression analysis (PLS) has been used to predict intensity of sweet odour in volatile phenols. This is a relatively new multivariate technique, which has been of particular use in the study of quantitative structure-activity relationships. In recent pharmacological and toxicological studies, PLS has been used to predict activity of molecular structures from a set of physico-chemical molecular descriptors. These techniques will aid understanding of natural flavours and the development of synthetic ones. 

But why are NP-rich plants more expensive than commodity or crops Simply because, in contrast to the easily substitutable staple foods, the plants that produce highly attractive NPs usually have a much more limited geographical distribution. Consequently, there is less competition in the market place and substitution remains very difficult in most cases (e.g., there is no satisfactory synthetic coffee, tea or chocolate). Some of the NPs used in scents and flavours have been substituted with synthetic chemicals but even then many consumers were prepared to pay a premium for plant-derived flavouring (e.g., natural vs. synthetic vanilla). 

Asa Griggs Chandler, another, more astute pharmacist who saw the potential in Coca-Cola as a soft drink rather than a tonic. In the next 15 years, he made a fortune from the Coca-Cola company and founded what was to become the world s best known multinational. The formula of Coca-Cola has chtmged over the years and the coca extract was removed in the early twentieth century and many decades later caffeine-free versions became available. Competitors produced their own versions of what became known as cola drinks, nearly always containing caffeine and a variety of natural and synthetic flavouring (Figure 2.7). 

Figure 4.1. The 2-D (left) and 3-D (right) structures of synthetic or naturally occurring vanillin, the chemical that gives vanilla extract its characteristic flavour and smell. Neither representation of the structure provides a guide to the fact that humans like its flavour or smell, or indeed that the human nose can specifically detect the molecule.

Obviously, these first perfumes were all natural, since the introduction of synthetic aroma chemicals happened only at the end of the nineteenth century. Along with the invention of certain aroma chemicals, the flavour and fragrance... 

In 1874, Holzminden chemists Ferdinand Tiemann and Wilhelm Haarmann first succeeded in synthesising vanillin from coniferin. Holzminden became the site where vanillin was first produced industrially. Haarmann Reimer was the world s first factory in which synthetic scents and flavourings were produced [5]. 

The US Regulations only distinguish between natural and artificial flavourings. The European category nature-identical is unknown in the legal definitions. If such substances are synthetically produced, they are classified as artificial flavouring substances in the USA. 

Most of the regulations on flavourings distinguish between natural derived flavouring components and substances produced synthetically. There are still some differences between the national rules regarding source materials and accepted techniques. 

To cater for the large demand for vanillin, besides different synthetic methods also biotechnological processes have been developed. Synthetic vanillin has a major drawback that products containing this compound cannot be labelled as containing a natural flavour. On the other hand, biotechnological products can be labelled as natural. 

The main renewable resource for L-carvone is spearmint oil (Mentha spicata), which contains up to 75% of this flavour chemical. There also exists a synthetic process for the manufacturing of L-carvone, which is based on (-t)-limonene, which is available as a by-product of the citrus juice industry as a major component of orange peel oil (Scheme 13.4). The synthesis was developed in the nineteenth century and starts with the reaction of (-t)-limonene and nitrosyl chloride, which ensures the asymmetry of the ring. Treatment with base of the nitrosyl chloride adduct results in elimination of hydrogen chloride and rearrangement of the nitrosyl function to an oxime. Acid treatment of the oxime finally results in l-carvone. 

Certainly, most of the data given in Table 17.2 are not qualified as indicators in authenticity assessment of food flavour, owing to their low and non-characteristic enantiomeric distributions, which could be simulated easily by calculated blending of the (S)-enantiomer (from biotechnological origin) with the synthetic racemate. 

Of course, during processing of fruit juices hydrolysis effects may occur, leading to decreased amounts of ethyl 2-methylbutanoate. However, its enantiomeric purity remains unchanged, whilst the corresponding 2-methylbutanoic acid is found as the (S)-enantiomer (99.5% or more) [33-37]. Consequently, the detection of racemic 2-methybutanoic acid (or the corresponding esters) definitely proves the addition of a synthetic (so called nature-identical) flavour compound. 

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