Figure 6 General conversions of the milk constituents during the ripening of cheese. Three main pathways can be distinguished. The pathway from casein is the most important one, leading to typical cheese flavors.
alternatively be converted to various flavor compounds such as diacetyl, acetoin, acetaldehyde, or acetic acid, some of which contribute to typical yogurt flavors.
Lipolysis results in the formation of free fatty acids, which can be precursors of flavor compounds such as methylketones, alcohols, and lactones. Lactic acid bacteria contribute relatively little to lipolysis, but additional cultures (e.g., molds in the case of surface-ripened cheeses) (96) often have high activities in fat conversion. Flavors derived from the conversion of fat are particularly important in soft cheeses like Camembert and Roquefort.
The conversion of caseins is undoubtedly the most important biochemical pathway for flavor formation in hard-type and semi-hard-type cheeses (97). Degradation of caseins by the activities of rennet enzymes, and the cell-envelope proteinase and peptidases from lactic acid bacteria, yields small peptides and free amino acids. A good balance between proteolysis and peptidolysis prevents the formation of bitterness in cheese (38,39). Although it is known that peptides can taste bitter and that amino acids can taste sweet, bitter, or broth-like (98), the direct contribution of peptides and amino acids to flavor is probably limited to a basic taste (93). For specific flavor development, further conversion of amino acids is required to various alcohols, aldehydes, acids, esters, and sulfur compounds. The current knowledge on these pathways is shown in Fig. 7.
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