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 °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. The studies showed that furans, such as furfural, 2-furanmethanol, benzofuran, 2,5-furandicarboxaldehyde and 2-furfurylfuran were formed mainly at acidic pH. In contrast, higher pH values could promote the production of pyrazines.