The effect of pH on the formation of aroma compounds produced by heating a model system containing L-ascorbic acid with L-threonine/L-serine

The identification of aroma compounds, formed from the reactions of L-ascorbic acid with L-threonine/L-serine at five different pH values (5.00, 6.00, 7.00, 8.00, or 9.55) and 143 +/- 2 degrees C for 2 h, was performed using a SPME-GC-MS technique, and further use of LRI. The results showed 35 aroma compounds. The reaction between L-ascorbic acid and L-threonine/L-serine led mainly to the formation of pyrazines. Many of these were alkylpyrazines, such as 2-methylpyrazine, 2,5-dimethylpyrazine, 2-ethylpyrazine, 2-ethyl-6-methylpyrazine, 2-ethyl-5-methylpyrazine, 3-ethyl-2,5-dimethylpyrazine, 2,3-diethyl-5-methylpyrazine, and 3,5-diethyl-2-methylpyrazine; other compounds identified were furans and aldehydes. More volatiles were generated in L-ascorbic acid with L-threonine systems than in L-ascorbic acid with L-serine systems studies showed that furans such as furfural, 2-furanmethanol, benzofuran, 2,5-furandicar-boxaldehyde and 2-furfurylfuran were formed mainly at acidic pH. In contrast, higher pH values could promote the production of pyrazines. (C) 2009 Elsevier Ltd. All rights reserved.