Gentle Thermal Product Treatment

Raw or gently pasteurised milk (e.g. for 10 seconds at 73 °C) has a fine characteristic odour and sweet taste. Typical components present in low concentrations are dimethylsulfide, biacetyl, 2-methylbutan-l-ol, (Z)-hept-4-enal and ( )-non-2-enal. Milk pasteurised at higher temperatures and Ultra High Temperature (UHT) milk present the so-called cooked flavour, the appearance of which is the first measurable manifestation of the chemical changes that occur in heated milk. The substances responsible for the cooked off-flavour are sulfane and other sulfur compounds. Of particular importance are dimethylsulfide, dimethyldisulfide and dimethyltrisullide that are produced from proteins contained in the membranes of fat particles and from thiamine. Also relevant are alkane-2-ones (methylketones) generated by thermal decarboxylation of P-oxocarboxylic acids (mainly hexane-2-one, heptane-2-one and nonane-2-one), y-lactones and 5-lactones produced by dehydration of y- and 5-hydroxycarboxylic acids (mainly 8-decalactone and y- and 8-dodecalactones). Important carbonyl compounds include biacetyl, hexanal, 3-methylbutanal, (Z)-hept-4-enal and ( )-non-2-enal. In the more intensive thermal treatment of milk (sterilisation), products of the Maillard reaction play a role, such as maltol and isomaltol, 5-hydroxymethylfuran-2-carbaldehyde, 4-hydroxy-2,5-dimethyl-2 f-furan-3-one (furaneol) and 2,5-dimethylpyrazine. [Pg.608]

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