Flavour-Isolation Techniques

With this introduction, we will present an overview of some of the more commonly used methods for aroma isolation. The reader is encouraged to obtain a comprehensive review of the topic for more detail and is referred to [1-3]. 

Absorption (Polymer Trapping, Solid-Phase Microextraction, 

Absorption methods (sorptive extraction) have become the method of choice for many researchers. They offer advantages of being rapid, solventless, automated, and reasonably sensitive and broad in isolation properties. However, they provide an aroma isolate that reflects the biases resulting from compound volatility and affinity for the absorbent matrix. 

Traps loaded with SPE (disk in a SPME (coated needle Twister (1 cm 

A contemporary of the method just described is the use of an absorbent (e.g. C-18) bonded onto granular or disk-type supports (solid-phase extraction [5]). The granular material is used in cartridge form (typically less than 5 ml), while disk forms are placed in a funnel/holder such as shown in Fig. 18.1b. A liquid (e.g. water, milk, or juice) would be passed through the cartridge (or filter disk), the analytes absorbed in the stationary matrix, the absorbent washed with water, and then the analytes of interest eluted from the absorbent with an organic solvent. This method has found limited use in the isolation of volatiles from foods but continues to find significant application in the analytical field overall [6]. 

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G. A. Reineccius, Flavour-Isolation Techniques. In Flavours and Fragrances Chemistry, Bioprocessing and Sustainability ... 

The analyses of the flavour composition of yellow passion fruits were performed by four dilferent isolation techniques, namely vacuum headspace sampling (VHS), the dynamic headspace method, simultaneous distillation and extraction at atmospheric pressure, and simultaneous distillation and extraction under reduced pressure [62]. Significant differences were found not only in the chemical composition of the resultant extracts but also in their sensory properties. The most representative and typical extract was obtained by VHS. 

Engel, W., Bahr, W., Schieberle, P. (1999) Solvent assisted flavour evaporation—a new and versatile technique for the careful and direct isolation of aroma compounds from complex food matrices. Eur. Food Res. Technof 209 237-241. 

It is very common to combine methods in obtaining aroma isolates. The simultaneous distillation/extraction method previously described is an example. Another popular combination method initially involves the solvent extraction of volatiles from a food and then high-vacuum distillation of the solvent/aroma extract to provide a fat-free aroma isolate. This technique is broadly used today to provide high-quality aroma extracts for numerous purposes. The apparatus used in solvent removal has been improved upon to reduce analysis time and efficiency the modified method is termed solvent-assisted flavour extraction (SAFE) [16]. 

Table 2.10 shows that the isolation and purification of naturally occurring flavour chemicals and extracts from animal and plant raw materials is most important for the preparation of natural flavours. About 75% of the commercially used flavours come from such natural sources. Physico-chemical reactions of typical flavour precursors may also lead to natural flavouring substances when mild conditions ( kitchen technology ) are applied. In addition, natural flavour chemicals may be prepared by biotechnological processes. This chapter outlines the most important biotechnical manufacturing techniques. 

Besides that, fermentation can only be industrially attractive if the process provides highest yields and exhibits an efficient isolation and purification process (downstream processing) with only minimal product losses. Additionally, suitable substrates must be commercially available at low cost. Finally, the generation of flavours by fermentation in bioreactors will only be profitable if the desired product, be it a pure substance or a complex flavour extract, is not obtainable with comparable quality by inexpensive classical techniques. 

Methods for the study of grape flavour have often been employed in flavour analysis of other fruits and beverages. Techniques such as solvent extraction (Cacho et al. 1992) or headspace methods (Kallio 1991) may be used to isolate volatiles, and analysis usually involves gas-liquid chromatography (Cronin 1982), coupled with mass spectrometry (Merritt and Robertson 1982). Such methods have provided qualitative and some quantitative assessment of grape aroma composition, usually as part of research on wine flavour (Strauss et al. 1986 Rapp 1988 Eti vant 1991). 

A strong smelling compound that is used as essence of rum in food flavourings, was isolated and analysed using different spectroscopic techniques. The IR spectrum shows an intense absorption band at 1740 cm and the mass spectrum shows a base peak at m/z 57, due to a fragment cation. Use this information, together with the H NMR spectrum shown below, to propose a structure for this compound. 

Some calculations use very general arguments to derive bounds for as yet undiscovered heavy flavoured particles. For example, Anselmino et al., (1990a) isolate the effects of colour-hyperflne terms and use experimental information to make predictions about the masses of baryons containing at least one heavy quark. Typical results are the predictions 64 < ft — ftc < 107 MeV/c, and 23 < ftj — ftj, < 39 MeV/c. These imply that ft and ftj cannot decay strongly. By the same technique one finds also 23 < EJ — Efc < 39 MeV/c so EJ cannot decay strongly into Ej, but both decay strongly into Aj,. 

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