Fatty acids flavours

Other common environmental examples of quantitative GC are in the determination of pesticides in water, dioxin levels in soil and air pollutants. It is routinely used to examine levels of volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). It is also a very important technique in the food industry, where it is used extensively for assay of fatty acids, flavours, sterols and residues such as insecticides, herbicides, preservatives, solvents and veterinary drugs. 

The restricted shelf life of liquid milk continues to be a problem that is often more influenced by the type of milk being sold rather than the pasteurisation technique. The shelf life of processed milk is determined primarily by the quality of the raw milk from the dairy herd. Increasing cell counts in the milk and a higher concentration of free fatty acids, contribute to rancidity in both liquid milk and milk products. Janzen (1972) reported that the 0-14 day shelf life of pasteurised milk is influenced by the somatic cell concentration in the raw milk and found that after 14 days any observed changes in the flavour and stability of the milk were attributable to microbial activity during storage. 

Cameron N D, Enser M, Nute G R, Whittington F M, Penman J C, Fisken A C, Perry A M and Wood J D (2000), Genotype with nutrition interaction on fatty acid composition of intramuscular fat and the relationship with flavour of pig meat , Meat Sci, 55, 187-195. 

The modern distinction between vegetable and fruit has been applied and therefore those plants or plant parts that are usually consumed with the main course of a meal will be regarded as vegetables thus, cucumber, tomato and pumpkin that botanically are classified as fruits are included in this section. The flavour compounds found in vegetables are diverse and include fatty acid derivatives, terpenes, sulfur compounds as well as alkaloids. This diversity is partially responsible for the unique flavours found in different species of vegetables. 

The biosynthesis of fatty acids produced during alcoholic fermentation is initiated in the yeast cell by the formation of acetylcoenzyme A, which reacts with malonylcoenzyme A to form mainly saturated straight-chained fatty acids with an even number of four to 18 carbon atoms the appearance of relatively low levels of fatty acids with odd numbers of carbon atoms as well as unsaturated fatty acids depends on the fermentation conditions [6]. The volatile fatty acids contribute to the flavour of fermented beverages like wine or beer and their concentration usually lies between 100 and 250 mg 0.1 L p.e. In distilled spirits the concentration of free fatty acids is significantly lower owing to the esterification... 

The flavour of distillates from apple and pear is characterised by typical aroma compounds from these fruits formed by enzymatic degradation of fatty acids to C6-fragments like hexanol, trans-2-hexenol, as well as ethyl esters and acetates of hexanoic acid. In distillates of pears, especially of the variety Bartlett pear, the characteristic pear flavour is mainly dominated by the ethyl and methyl esters of frans-2-czs-4-decadienoic acid and trans-2-trans-A-decadienoic acid [27-29], The biogenesis of these monounsaturated, diunsaturated, and triunsaturated esters may be explained by -oxidation of unsaturated linoleic and linolenic acid in the fruits. The sesquiterpene compound a-farnesene, which is formed during postharvest ripening and storage of Bartlett pears [28], shows that quality and intensity of distilled pear spirits is mainly influenced by the quality and degree of ripeness of the fruits. 

Lipolysed milk fat was one of the first flavours produced with the help of enzymes. The original process was based on the controlled lipase-catalysed hydrolysis of cream [18]. For instance, Mucor miehei lipase possesses a high selectivity towards flavour-active short-chain fatty acids. Additionally, lipases that prefer long-chain fatty acids or lipases without particular preferences can be found. The free fatty acids produced can be isolated by steam distillation and further purified. Thus, it is possible to obtain pure short-chain fatty acids like butanoic, hexanoic, octanoic and decanoic acid. 

Kinetic resolution of branched-chain fatty acids has been reported recently by Franssen et al. [24]. With the help of immobilised Candida antarctica lipase B, racemic 4-methyloctanoic acid (responsible for sheep-like and goat-like flavours in sheep and goat milk and cheese, respectively) was esterified with ethanol. Only the R ester could be obtained, whereas (S)-4-methyloctanoic acid was not converted (Scheme 22.1). 

Saturated and unsaturated y-lactones and 5-lactones which are synthesised from the corresponding acyclic hydroxy fatty acids by intramolecular esterification are important flavour compounds found ubiquitously in fruits and also in milk and fermentation products in parts-per-million concentrations. The natural lac-... 

Because of its wide range of fatty acids, the flavour of milk fat is superior to that of other fats. In certain products and after certain processes, fatty acids serve as precursors of very flavourful compounds such as methyl ketones and lactones. Unfortunately, lipids also serve as precursors of compounds... 

Short-chain fatty acids have strong, characteristic flavours and aromas. When these acids are released by the action of lipases in milk or... 

Lipase Triglycerides + HzO -> fatty acids + partial glycerides + glycerol Off flavours in milk flavour development in Blue cheese... 

Lipolysis. Some lipolysis occurs in all cheeses the resulting fatty acids contribute to cheese flavour. In most varieties, lipolysis is rather limited (Table 10.5) and is caused mainly by the limited lipolytic activity of the starter and non-starter lactic acid bacteria, perhaps with a contribution from indigenous milk lipase, especially in cheese made from raw milk. 

Extensive lipolysis occurs in two families of cheese in which fatty acids and/or their degradation products are major contributors to flavour, i.e. certain Italian varieties (e.g. Romano and Provolone) and the Blue cheeses. Rennet paste, which contains pre-gastric esterase (PGE) rather than rennet extract, is used in the manufacture of these Italian cheeses. PGE is highly specific for the fatty acids on the sn-3 position of glycerol, which, in the case of milk lipids, are predominantly highly flavoured short-chain fatty acids (butanoic to decanoic). These acids are principally responsible for the characteristic piquant flavour of these Italian cheeses. 

Blue cheeses undergo very extensive lipolysis during ripening up to 25% of all fatty acids may be released. The principal lipase in Blue cheese is that produced by Penicillium roqueforti, with minor contributions from indigenous milk lipase and the lipases of starter and non-starter lactic acid bacteria. The free fatty acids contribute directly to the flavour of Blue cheeses but, more importantly, they undergo partial /J-oxidation to alkan-2-ones (methyl O... 

Woo, A.H. and Lindsay, R.C. (1984) Concentrations of major free fatty acids and flavour development in Italian cheese varieties. J. Dairy Sci., 67, 960-8. 

Kuzdzal-Savoie, S. 1980. Flavour impairment of milk and milk products due to lipolysis. VII. Determination of free fatty acids in milk and milk products. Int. Dairy Fed. Bull. 118, pp. 53-66. 

A very well known dairy product is Roquefort cheese, its flavour is generated by mould action. This so called Blue cheese flavour is attributed to methyl ketones and is formed by the degradation of fatty acids by Penicillium roquefortii. The production of these bioflavours has also been investigated by our group [12,13] and will not be further discussed here. 

The oil content of flaxseed ranges from 400 to 450g/kg and the byproduct of mechanical oil extraction - flaxseed (or linseed) meal - can be used in organic poultry feeding. There is also interest in feeding the ground whole oil-containing seed to poultry for two main reasons to produce meat with a fatty acid profile in the fat that confers health benefits to the consumer (Conners, 2000) and to impart an enhanced flavour to the meat. 

In summary, Foeniculum is stated to have three species, F. vulgare (fennel), F. azoricum Mill. (Florence fennel) and F. dulce (sweet fennel). Fennel is widely cultivated, both in its native habitat and elsewhere, for its edible, strongly flavoured leaves and seeds. The flavour is similar to, but milder than, that of anise and star anise. Anethole and fenchone are the major constituents of the solvent extract of seed phenols, free fatty acids, carbohydrates, proteins, vitamins and minerals have been reported in varying proportions. In the mature fruit, up to 95% of the essential oil is located in the fruit, greater amounts being found in the fully ripe fruit. Approximately 45 constituents have been determined from fennel seed oil, the main constituents being frans-anethole, fenchone, estragol (methyl chavicol), limonene, camphene, a-pinene and other monoterpenes, fenchyl alcohol and... 

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