Formation of furan and methylfuran from ascorbic acid in model systems and food

Abstract

Previous model studies have suggested ascorbic acid as one of the major sources of furan, a possibly hazardous compound found in thermally processed foods (e.g. canned products, jars). The study showed that about 2 mmol mol⁻¹ furan was obtained when dry-heating ascorbic acid, while much lower amounts were formed upon pressure cooking, i.e. 58 µmol mol⁻¹ at pH 4 and 3.7 µmol mol⁻¹ at pH 7. Model reactions also generated 2-methylfuran (MF). However, the MF levels were generally very low with the exception of the binary mixture ascorbic acid/phenylalanine (1 mmol mol⁻¹). Studies with ¹³C-labelled ascorbic acid indicated that furan comprises an intact C₄ unit, mainly C-3 to C-6, generated by splitting off two C₁ units, i.e. CO₂ and formic acid. Possible intermediates are 2-deoxyaldoteroses, 2-furoic acid and 2-furaldehyde, which are known as ascorbic acid degradation products. The mechanism of furan formation from ascorbic acid was validated based on the labelling pattern of furan and the identification of ¹³CO₂ and H¹³COOH. Furan formation is significantly slowed down in binary mixtures, e.g. the presence of erythrose led to 80% less furan under roasting conditions. This is most likely due to competing reactions in complex systems, thus disfavouring furan formation. The mitigation effect is because furan, contrary to MF, is formed without recombination of ascorbic acid fragments. Therefore, furan levels are definitely much lower in foods than expected from trials with pure ascorbic acid. Consequently, conclusions should be drawn with much caution from model reactions, avoiding extrapolation from oversimplified model systems to food products.

Keywords:

• Furan
• methylfuran
• ascorbic acid
• model systems
• food
• labelled precursors
• mechanistic study
• SPME-GC/MS
• isotope dilution assay

Acknowledgements

The paper was presented at the COST 927-IMARS Workshop, 24–26 May 2006, Naples, Italy.