Sapid Compounds

By now, quite a range of bitter-tasting compounds has been isolated and characterised in Maillard-type reactions. 

Tressl et al.219 characterised eight 2-(l-pyrrolidinyl)-2-cyclopentenones and 11 cyclopcnt(/ )azcpin-8( lf/)-oncs from proline-monosaccharide and proline-cyclic enolone systems. The compounds possessed bitter tastes, with the former exhibiting concomitant astringency. The bitter thresholds in water of Structure 33 and 34 were 50 and 10 ppm, respectively. 

The effectiveness of various precursors of these compounds was investigated quantitatively by Ottinger and Hofmann.283 Hexose-derived cyclotene was the common precursor for both 33 and 35, as well as 34 and 36. The formation of each compound is very much determined by the nature of the N-containing precursor. Thus, for example, pyrrolidine (e.g., formed by thermal decarboxylation of proline) plus cyclotene produced 33 and 35 only, whereas 1-pyrroline (derived from proline 

Bitter compounds are also formed in solutions of alanine with xylose and rham-nose.284 Twenty-six HPLC fractions were obtained, seven of which were shown to have high impact on taste dilution analysis. Structures 37-41 accounted for 57% of overall bitterness. The compounds have low threshold values introduction of methyl groups into the furyl rings increase the threshold value. On the contrary, substituting the furyl ring-0 by S (42) lowered the threshold value to almost 104 times lower than that of caffeine on a molar basis. 

7-(2-furylmethyl)-2-(2-furylmethylidene)-3,8-bis(hydroxyniethyl)-1 -oxo-2,3-dihydro-ltf-indolizinium-6-olate 

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The level of proteolysis in cheese varies from limited (e.g. Mozzarella) through moderate (e.g. Cheddar and Gouda) to very extensive (e.g. Blue cheeses). The products of proteolysis range from very large polypeptides, only a little smaller than the parent caseins, to amino acids which may, in turn, be catabolized to a very diverse range of sapid compounds, including amines, acids and sulphur compounds. 

Affecting the rheology and texture of cheese and hence the rate of release of sapid compounds from the cheese matrix... 

Since cheese texture has a major impact on flavor perception, these attributes should, ideally, be considered together. For example, it has been suggested (McGugan et al., 1979) that the main contribution of proteolysis to cheese flavor is due to its effect on cheese texture which affects the release of sapid compounds on mastication of the cheese. However, these two aspects of cheese quality are rarely part of the same investigation and cheese texture is even less well understood at the molecular level than cheese flavor. 

As discussed in Section IVE, cheese contains a great diversity of protein-ases and peptidases with different and complementary specificities. Although detailed kinetic studies are lacking, at least some of the peptides in cheese are transient and hence bitterness may be transient as bitter peptides are formed and hydrolyzed, or masked by other sapid compounds. It is very likely that all cheeses contain bitter peptides, which probably... 

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. 

The comparative taste dilution analysis revealed a high TD factor of 16 for sweetness in fraction III (Figure 1). As this fraction showed no sweetness in the absence of sucrose, this fraction was assumed to contain a reaction product enhancing the sweetness of the sucrose solution by a factor of eight. Because sweetness enhancing compounds were not yet reported in beef bouillon, the following identification experiments were focused on the sapid taste modifier present in GPC fraction III (Figure 1). 

Thus, a great diversity of potentially sapid and/or aromatic compounds have been identified in one or more cheese varieties—these include small... 

As discussed in Section VB, most ripened cheeses contain essentially the same sapid and aromatic compounds but at different concentrations and proportions. Therefore, it appears reasonable to presume that inter- and intravarietal comparison, especially of closely related varieties, might help to identify compounds most likely to contribute to characteristic cheese flavors. However, although both the water-soluble and volatile fractions of several cheese varieties have been analyzed, there are relatively few intervarietal comparisons, especially of the water-soluble fraction. In this section, the results of some such studies will be discussed. 

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