COMPARISON OF KEY ODORANTS GENERATED BY THERMAL-TREATMENT OF COMMERCIAL AND SELF-PREPARED YEAST EXTRACTS - INFLUENCE OF THE AMINO-ACID-COMPOSITION ON ODORANT FORMATION

Application of an aroma extract dilution analysis (AEDA) on a flavor c oncentrate isolated from a heat-processed (145 degrees C, 20 min) aque ous solution of a commercial yeast extract (CYE) revealed 2-furanmetha nethiol, 4-hydroxy-2,5-dimethyl-3(2H)-furanone, 8-methoxyphenol, and 3 - and 2-methylbutanoic acid as the key odorants among the 16 odor-acti ve compounds of the intensely roasty, sweet smelling solution. Compare d with CYE, in a thermally treated autolysate prepared under laborator y conditions from baker's yeast (SPYA) several odorants, e.g., methion al, 2-acetyl-2-thiazoline, 3-hydroxy-4,5-dimethyl-2(5H)-furanone (Soto lon), phenylacetic acid, and 2,3-diethyl-5-methylpyrazine, showed high er flavor dilution (FD) factors, whereas the reverse was found for 2-f uranmethanethiol (FMT). The amounts of its precursor amino acid cystei ne in the CYE and the SPYA were well correlated with the different odo r activities of the FMT in both solutions. Detailed model studies on t he formation pathways of FMT indicated the binary mixtures 2-furaldehy de/cysteine as well as mercapto-2-propanone/hydroxyacetaldehyde as imp ortant intermediates in FMT formation. Heat treatment of a water-solub le, low molecular weight fraction isolated from baker's yeast cells pr edominantly generated the roast odorant 2-acetyl-1-pyrroline (ACPY). U nder certain fermentation conditions, the amounts of its precursor orn ithine in the yeast were increased, leading to higher odor activities of ACPY after thermal treatment of the extract.