Methyl ketone, blue cheese

The flavor of blue cheese is produced by a combination of free fatty acids and methyl ketones derived from fatty acids. The partial oxidation of fatty acids to methyl ketones occurs via the /3-oxidation pathway (Kinsella and Hwang 1976A). 

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. 

Both the spores and the mycelium seem capable of producing methyl ketones from fatty acids (12, 13). Furthermore, both short chain and long chain fatty acids are metabolized, thereby giving rise to an homologous series of methyl ketones, the main ones being 2-pentanone, 2-heptanone and 2-nonanone (14). A number of processes have been developed and patented for producing blue cheese flavor via the fermentation of milk fat (15, 16). Usually the... 

F enici I Hum sp. Mushroom, blue cheese, rosey 1- Qctene-3-ol, methyl ketones, 2- phenylethanol, thujopsene, nerolidol... 

In many cases, molds such as Penicillium and Trichoderma produce volatiles only in the spore producing stage. Methyl ketone and blue cheese aroma generation by certain Penicillium species is a good example. Another example is Penicillium decumbens which produces characteristic odor only on media which allow sporulation... 

The fungus Penicillium roqueforti is used in the production of blue-veined Roquefort, Stilton and Gorgonzola cheeses. It contributes to the flavour of these cheeses by degrading medium-chain fatty acids to methyl ketones with one less carbon atom. The fungus is also a microbial spoilage contaminant of dairy products and it is found on some mouldy grains. There are several sub-species of... 

Extensive lipolysis occurs in mould-ripened cheese, particularly blue varieties. In some cases, up to 25% of the total FFA may be liberated (see Gripon, 1987, 1993). However, the impact of FFA on the flavor of blue mould-ripened cheeses is less than in hard Italian varieties, possibly due to neutralization as the pH increases during ripening and to the dominant influence of methyl ketones on the flavor of blue cheese. 

The taste and aroma of Blue cheese are dominated by saturated n-methyl ketones, a homologous series in which odd-numbered carbon chains from Q to Ci5, as well as a number of even-numbered carbon chains (including C4 to Cio), is present (Patton, 1950). Concentrations of methyl ketones in Blue... 

Undoubtedly, the products of these primary biochemical events, i.e., fatty and other acids, peptides, and amino adds, contribute to cheese flavor, perhaps very significantly in many varieties and proteolysis certainly has a major influence on the various rheological properties of cheese, e.g., texture, meltability, and stretchability. However, the finer points of cheese flavor are almost certainly due to further modification of the products of the primary reactions. The most clear-cut example of this is the oxidation of fatty acids to methyl ketones in blue cheeses. Catabolism of amino acids leads to the production of numerous sapid compounds, including amines, carbonyls, acids, thiols, and alcohols. Many of these compounds may interact chemically with each other and the compounds of other reactions via the Maillard and Strecker reactions. At present, relatively little is known concerning the enzymology of amino acid catabolism in most cheeses and even less is known about the chemical reactions. It is very likely that research attention will focus on these secondary and tertiary reactions in the short-term future. 

Dartley, C. K., and Kinsella, J. E. (1971). Rate of formation of methyl ketones during Blue-mould cheese ripening. J. Agric. Food Chem. 19, IIX-IIA. 

Patton, S. (1950). The methyl ketones of Blue cheese and their relation to its flavor. J. Dairy Scl 33, 680-684. 

Traditionally fermented dairy products have been used as beverages, meal components, and ingredients for many new products [60], The formation of flavor in fermented dairy products is a result of reactions of milk components lactose, fat, and casein. Particularly, the enzymatic degradation of proteins leads to the formation of key-flavor components that contribute to the sensory perception of the products [55], Methyl ketones are responsible for the fruity, musty, and blue cheese flavors of cheese and other dairy products. Aromatic amino acids, branched-chain amino acids, and methionine are the most relevant substrates for cheese flavor development [55]. Volatile sulfur compounds derived from methionine, such as methanethiol, dimethylsulflde, and dimethyltrisul-fide, are regarded as essential components in many cheese varieties [61], Conversion of tryptophan or phenylalanine can also lead to benzaldehyde formation. This compound, which is found in various hard- and soft-type cheeses, contributes positively to the overall flavor [57,62]. The conversion of caseins is undoubtedly the most important biochemical pathway for flavor formation in several cheese types [62,63]. A good balance between proteolysis and peptidolysis prevents the formation of bitterness in cheese [64,65],... 

There is evidence that among the fatty acids only butyric and caproic acids 42), at sub-threshold concentrations, interact to contribute to the desirable butter flavor 367). A whole set of fatty acids provide a background flavor in the case of Cheddar cheese. Propionic acid is an essential flavor component in Swiss cheese 330). The characteristic flavor of blue cheese, however, is due to the presence of aliphatic methyl-ketones 161, 308). 

The alternate metabolic pathway yielding alcohols involves the reduction of the corresponding carbonyl (Figure 5.12). Lamparsky and Klimes [98] demonstrated this mechanism by finding the equivalent alcohols (as aldehydes) in Cheddar cheese. Secondary alcohols corresponding to the methyl ketones found in blue cheeses have also been reported. 

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