Non-volatile flavour compounds

Non-volatile flavour compounds in the sense of this chapter are defined as molecules which cause one of the sensory impressions sweet, bitter, salty, sour or umami (Fig. 23.2). 

By market volume the most important flavour molecule is L-glutamic acid. In 2004, the worldwide annual MSG production was estimated to be amount 1,500,0001 [21]. The amino acid is extensively used as taste enhancer, frequently in conjunction with nucleotides, a flavour impression which is also referred to as umamf, a term derived from the Japanese meaning deliciousness or a savoury or palatable taste. MSG is manufactured by aerobic cultivation of Coryne-bacterium glutamicum on starch hydrolysates or molasses media in large-scale bioreactors (up to 500 m ). Production strains with modified metabolic flux profiles and highly permeable cell walls for an improved product secretion are 

Product Precursor Microorganism Process data Remarks References 

L-Glutamic acid Corynebacterium glutamicum 150gL- ,60 h, 1.500,000 t year Aerobic cultivation up to 500-m scale mutants with highly permeable cell walls [21,22] 

Citric acid - Aspergillus niger 200 g. 9-12 days, 1,000,000 t year h yield 95% Downstream processing by precipitation as calcium citrate [21,22, 25] 

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Fig. 23.2 Some non-volatile flavour compounds produced with microorganisms...

Olive oil possesses a unique place among vegetable oils largely due to the mode of extraction and to the presence of volatile and non-volatile flavouring compounds. The most important constituents of the aroma of olive oil are C6 aldehydes and alcohols formed in the fruit from polyunsaturated fatty acids. This takes place on crushing, the first step of processing. The plant tissue... 

In recent years, non-volatile taste compounds have been becoming more important in the area of modern flavour development. Therefore, the principal approach of the OAV has been adapted for the taste side in the form of the so-called taste-activity value. In order to facilitate the search for taste-active materials and for a better understanding of the taste dimension of foodstuffs, a new instrumental setup called LC-Taste has been developed [58]. 

Shiratsuchi, H., Shimoda, M., Minegishi, Y. and Osajima, Y. (1993) Isolation and Identification of volatile flavour compounds in nonfermented coarse cut sausage. Flavour as a quality factor of non-fermented sausage, journal of Agricultural and Food Chemistry 47, 647-652. 

The root of carrot Daucus carota) is eaten raw or cooked. The characteristic aroma and flavour of carrots are mainly due to volatile compounds, although non-volatile polyacetylenes and isocoumarins contribute significantly to the bitterness of carrots [1,2]. More than 90 volatile compounds have been identified from carrots (Table 7.9) [207-215]. The carrot volatiles consist mainly of terpenoids in terms of numbers and amounts and include monoterpenes, sesquiterpenes and irregular terpenes. Monoterpenes and sesquiterpenes account... 

Semivolatile and non-volatile compounds of wood change the colour of the distillate and contribute to an up-rounded flavour. The wooden barrels which are permeable allow air to pass in and cause ethanol to evaporate thus, the ethanol content decreases and the aroma gets more intense, complex, and concentrated. Also harsher aroma constituents are removed and the spirit changes to mellow. The period of maturation depends on the size of the casks used, the alcoholic strength, as well as the temperature and humidity in the warehouse which leads to a smoother flavour. For production of neutral highly rectified distilled spirits like vodka, grain spirit, or white rum, the quality of water is of utmost importance to the flavour. In vodka production different treatments of water like de-... 

A typical REMPl at 266 nm mass spectrum is shown Fig. 15.22, obtained by roasting 80 g of Arabica coffee at 225 °C. The laserpower density was adjusted to 10 -10 W/cm in order to avoid non-resonant ionisation processes. The spectrum contains predominantly molecular ions. Chemical assignment of the ion peaks was based on three distinct pieces of information the literature on coffee flavour compounds [204], the mass as observed in TOFMS and optical absorption properties. With this information, many volatiles observed in Fig. 15.22 were unambiguously identified. 

It is well-known that in plant tissues certain amounts of flavour compounds are bound as non-volatile sugar conjugates. Most of these glycosides are jS-glu-cosides, but there are other glycones like pentoses, hexoses, disaccharides and trisaccharides too [46]. Acylated glycosides and phosphate esters have also been reported [47, 48]. Information about the analysis of glycosides can be found in the work of Herderich et al. [49]. 

Citrus essential oils are widely used as a raw material of flavour in food and perfumery industries. They are also called "cold-pressed oils" and contain more than 200 compounds which can be grouped in three fractions the hydrocarbon terpenes (unsaturated compounds) that constitute the major amount (from 60 to 98% by weight) but have undesirable off-flavours characteristics the oxygenated compounds (flavour fraction) that are directly responsible for the characteristic citrus flavour and the non-volatile residues. 

Generally quality control for most flavourings requires quantitative details of the individual components or of the entire composition. In such cases gas chromatography (GC) should be chosen for volatile compounds and high performance liquid chromatography (HPLC) for non-volatile compounds. 

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