Flavour reference compounds

As mentioned in the introduction to this section, there is the opportunity to recover aroma compounds from baking or roasting exhaust gases. The patent literature contains numerous references to the recovery of aroma compounds using this approach, most commonly from cocoa, coffee, or tea processing. Aroma compounds from the roaster exhaust gases are either condensed in cryogenic traps [29-32] or collected on absorbents (e.g. charcoal [33]) and then solvent-extracted to obtain a concentrated aroma extract. The concentrated extract may be used to aromatise a similar product (e.g. soluble coffee) or may be used to flavour other products (e.g. coffee-flavoured ice creams). 

Steam distillation is used when normal distillation is not an option, due to thermal sensitivities. By adding water or steam, the boiling points of compounds can be depressed, allowing them to evaporate at lower temperatures. After distillation the vapours are condensed and typically yield two phases water and organics. These can then be easily separated on the basis of their different densities. On a simple level, this can be seen every day in fresh black coffee, where small amounts of organic, water-immiscible oils float on the surface. Steam distillation is employed on an industrial scale in the manufacture of essential oils (e.g. lavender, eucalyptus and fruit oils) that are used in the food and flavour industries. In this area, the use of water is highly desirable as a natural solvent. Steam distillation is also used in petroleum refineries and petrochemical plants, where it is commonly referred to as steam stripping . 

Table 6.14 Authenticity and origin assignment of selected examples of flavouring compounds by deuterium-NMR. Further data on monoterpenes see [225, 227, 338, 351, 352] for MCNAIR see references [238, 239] and chapter 6.2.2.3.2., 0-pattern of vanillin [253]...

Likewise, chiral 5-lactones are known as characteristic flavouring compounds of fruits and dairy products /74y.Their stereodifferentiation was achieved with modified y-cyclodextrin by Konig et al. [84] and their chromatographic behaviour interpreted by coinjection with enantiopure references, as described by Palm et al. [36]. Using enantio-MDGC and the column combination OV 1701/octakis(3-O-butyryl-2,6-di-O-pentyl)-y-cyclodextrin the simultaneous stereodifferentiation of all aroma-relevant 4(5) alkylsubstituted y(5)-lactones has been reported recently [42, 85] (Fig. 6.30). 

The associated analytical instruments separate out some of the chemical compounds in a complex odour according to a physical property, for example, their solubility, mass, mass to charge ratio etc. Reference [1] provides an overview of these different analytical instruments. The disadvantages with these types of instruments for detecting odours are that they are relatively slow (minutes per reading), large, expensive and, more importantly, simply separate out the different constituents of a compound rather than provide a measure of their relative olfactory intensity. Indeed, the smell of a complex odour may well be dominated by a few key flavour compounds which occur below the detection threshold of even these analytical instruments - typically ng/ml. 

Essential oils are usually derived from the non-seed parts of the plants with chemical composition other than the triglyceride structure of natural fats and oils. They refer to the subtle, aromatic liquids extracted from the flowers, seeds, leaves, stems, bark and roots of herbs, bushes, shrubs and trees through distillation. Essential oils are concentrated liquids containing volatile aromatic compounds. They are used in perfumery, aromatherapy, cosmetics, incense, medicine, household cleaning products and for flavouring food and drink. Their use in aromatherapy and other health care areas is growing. 

Compound Structure Concentration (PPb) Reference Flavour threshold (ppb) [101, 109]... 

Besides nutrients, foods contain many substances that influence the food sensory impression and its organoleptic properties. These food constituents are known as sensoriaUy active compounds. They determine the sensory value (quality) of foods, inducing an olfactory sensation (perception), which is described as the aroma, odour and smell, gustative perception, which is the taste, visual perception, which is the colour, haptic (tactile) perception, which is the touch and feel, and auditorial perception, which is the sound. The olfactory sensation is derived from odour-active compounds and the gustative perception from taste-active compounds. Flavour is the sensory impression determined by the chemical senses of both taste and smell and is caused by flavour-active food components. Haptic sensation is the texture, which is affected mainly by high molecular weight compounds, such as proteins and polysaccharides, often referred to collectively as hydrocoUoids. Geometric aspects of texture that evoke both haptic and visual sensations symbolise the terms appearance and shape. 

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). 

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