Aroma Compounds from Fatty Acid Metabolism

1 Aroma Compounds from Fatty Acid Metabolism 

The widest variety of flavor compounds formed from lipids arises via lipoxygenase activity. Many of the aliphatic esters, alcohols, acids, and carbonyls found 

Carbonyls Lactones Carbonyls Monoterpenes Carbonyls Carbonyls 

FIGURE 4.1 The formation of fruit aroma from major food cxrmponents. (From Tressl, R., M. Holzer, M. Apetz, Aroma Research, IT. Maarse, P.J. Groenen, Eds., Wageningen, Netherlands, 1975, p. 41. With permission.) 

Cystine/cysteine Serine Fatty acids Linoleic acid 

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Many aroma compounds in fruits and plant materials are derived from lipid metabolism. Fatty acid biosynthesis and degradation and their connections with glycolysis, gluconeogenesis, TCA cycle, glyoxylate cycle and terpene metabolism have been described by Lynen (2) and Stumpf ( ). During fatty acid biosynthesis in the cytoplasm acetyl-CoA is transformed into malonyl-CoA. The de novo synthesis of palmitic acid by palmitoyl-ACP synthetase involves the sequential addition of C2-units by a series of reactions which have been well characterized. Palmitoyl-ACP is transformed into stearoyl-ACP and oleoyl-CoA in chloroplasts and plastides. During B-oxi-dation in mitochondria and microsomes the fatty acids are bound to CoASH. The B-oxidation pathway shows a similar reaction sequence compared to that of de novo synthesis. B-Oxidation and de novo synthesis possess differences in activation, coenzymes, enzymes and the intermediates (SM+)-3-hydroxyacyl-S-CoA (B-oxidation) and (R)-(-)-3-hydroxyacyl-ACP (de novo synthesis). The key enzyme for de novo synthesis (acetyl-CoA carboxylase) is inhibited by palmitoyl-S-CoA and plays an important role in fatty acid metabolism. 

The aroma of butter made from sweet cream is affected primarily by free fatty acids (especially capric and lauric acids), S- and y-lactones, dimethylsulfide, (Z)-hept-4-enal and the degradation products of tryptophan (indole and skatole). The butter obtained from sour cream contains mainly metabolic products of microorganisms (so-called starter cultures). Especially important compounds are biacetyl, lactic and acetic acids. 

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