Flavour / flavouring compounds enhancement

The dipeptide camosine, /J-alanyl-i.-histidinc, is one of the most abundant N compounds present in the non-protein fraction of vertebrate skeletal muscles. It constitutes, for example, 50, 150, and 276 mg per 100 g of muscle tissue from chicken leg, bovine leg, and porcine shoulder, respectively. Chen and Ho138 examined its effects on volatile generation in a model system of ribose and cysteine (180 °C, 2 h, pH 5 and 8.5). These were complex the levels of thiophenes and some meaty compounds, such as 2-methyl-3-furanthiol, 2-furfurylthiol, and their associated dimers, were generally lowered, but those of important N compounds, such as pyrazines and thiazoles, which are known to elicit roasty and nutty flavours, were enhanced. 

Kokumi (different from umami) is another food attribute identified by the Japanese. It is sometimes translated as heartiness or mouthfulness and describes compounds in food that do not have their own flavour or have a distinct flavour, but enhance the flavours with which they are combined by triggering calcium receptors in the tongue. In foods system, there are three types of flavour sensations attributed to kokumi ... 

Some of the volatile substances which are produced during fermentation, like acrolein, diacetyl, 2-butanol, allyl alcohol, or acetic acid, are a result of enhanced microbiological activities and may cause an unpleasant flavour (off-flavour) at certain levels thus, elevated concentrations of such compounds are markers for spoilage of the raw material, negative microbiological influences during or after the fermentation process, or a poor distillation technique. 

MDGC, and comprehensive two-dimensional GC, or GCxGC), faster separation techniques (fast GG), fast methods for quality assessment or process control in the flavour area ( electronic noses and fingerprinting MS) and on-line time-resolved methods for analysis of volatile organic compounds (VOGs) such as proton-transfer reaction MS (PTR-MS) and resonance-enhanced multi-photon ionisation coupled with time-of-flight MS (REMPI-TOFMS). The scope of this contribution does not allow for lengthy discussions on all available techniques therefore, only a selection of developments will be described. 

Based on a series of examples from publications and patents, I would like to discuss, however, the hypothesis, that in order to achieve flavour enhancing, glutamatelike effect, a compound must have two negative charges. 

It has been suggested that the addition of potassium bitartrate/tartaric acid to wines could induce a competition of these compounds for the free water involved in solvation enhancing ethanol aggregation. Although Escalona et al. (2001) did not find any effect of the addition of these compounds to model wine systems flavoured with ethyl hexanoate, they found a decrease in the activity coefficient of octanal. They explained this by the possible reactivity of the carbonyl group of the aldehyde with hydroxyl radicals. 

The other commonly occurring amino acid with an acidic side-chain is glutamic acid. This compound is probably best known as its monosodium salt (monosodium glutamate or MSG). This salt is added to foods (especially oriental food) to enhance the flavour and impart a meat-like taste to the food. Interestingly, both the d enantiomer of glutamic acid and the naturally occurring l form are used as food additives. Use of the nonnatural d isomer may account for some of the adverse reactions experienced by consumers of MSG in food. 

The formation of typical cheese flavours during natural ripening processes are not fully understood yet. The majority of reactions last for an extended time period (months) and comprise oxidative, inter- and intramolecular, enzymatic or microbial (cf. blue cheese) reactions. Substrates are partially very reactive milk-based ingredients which are mainly transformed to volatile flavour intensive compounds like esters, methylketones, aldehydes, lactones and sulphur containing products. The effect of enzymes on the flavour enhancement is also not fully understood. By variation of lipase dosage, reaction time and reaction temperature the production of different flavour notes from milk and butterfat is possible. 

Taste compounds and flavour enhancers are raw materials used in process flavourings and can also be added to the final product. Current examples are sodium and potassium salts, organic acids, monosodium glutamate (MSG) and the 5 -nucleotides 5 -inosine monophosphate (IMP) and 5 -guanosin monophosphate (GMP). 

Sulphur compounds furfuryl mercaptane with its very strong roasted coffee, sulphurous burnt character. This unstable component varies its flavour profile with the concentration. Methanethiol has a strong rotten, disgusting sulphurous odour, but at low concentrations it enhances an interesting, freshly brewed character to the coffee flavour. 

The most important factor during the production process is the best possible retention of the distinguishing, specific odorous and flavouring components (esters, essential oils) or the enhancement of these compounds (fermentation products, cognac oil). In order to mature the taste, the storage of the finished product is the decisive factor. 

Bentz A.P. and Scarpellino R. Flavour-enhancing materials prepared by reacting ammonia with carbonyl compounds in aqueous medium. US Patent 3 676 156. 

About 80 lactones have been identified in tobacco smoke. These compounds, especially they-butyrolactones, andothers, have alkylating potential and some have been reported to be carcinogenic in laboratory animals [Lawley (6A12)]. [see also Appendix 2, pp. 387-394) in (1870)]. Quantitatively, about half the lactones in the smoke consist of y-butyrolactone [lARC (6A10)] (about 10 pg/cigarette) and its derivatives 5-valerolactone and some alkylated and unsaturated 5-valerolactones, as well as coumarin [see pp. 427-430 in Wynder and Hoffmann (4332)], 6-methylcoumarin, and 3,4-dihydrocoumarin have also been isolated [Schumacher et al. (3553)]. The occurrence of coumarin derivatives in smoke could be due to pyrolysis of polyphenols with a coumarin structure. .. or of plant extracts added to tobacco to enhance flavour [see pp. 427-430 in Wynder and Hoffmann (4332)]. Coumarin itself is carcinogenic to rats after oral administration [lARC (6A10)]. 

Microemulsions play a special role in the incorporation of food additives in finished products [150]. Aromas and some food dyes are typically oil-soluble compounds. It has been shown experimentally that microemulsions formed with Tween 20 are able to solubilise quite large quantities of flavours. Up to 3 moles of flavour could be solubilised per mole of Tween 20. Incorporation of vitamins in foods, e.g. vitamin E, and p-carotene turned out to be also effective. In this case, the solubilisation of vitamin E in nonionic micelles protects it from oxidation decomposition. Finally, the solubilisation of ascorbic acid in sardine oil microemulsion droplets prevents lipid oxidation. The effect is enhanced on adding tocopherol into the oil phase. 

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. 

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