Improvement of formaldehyde-scavenging ability of condensed tannins by ammonia treatment

Abstract Condensed tannins have formaldehyde gas-scavenging ability. Tannins consisting of phloroglucinol-type A-rings, such as prodelphinidin and procyanidin, had higher formaldehyde-scavenging ability than those consisting of resorcinol-type A-rings, such as prorobietinidin and profisetinidin. This ability was markedly improved by ammonia treatment. The increase in formaldehyde-scavenging ability was especially notable in the case of condensed tannins with a high ratio of pyrogallol-type B-rings, such as prorobietinidin and prodelphinidin. To clarify the factors affecting improvement of the formaldehyde-scavenging ability by ammonia treatment, the reaction behavior of condensed tannins during ammonia treatment was studied. Analyses using 13C-NMR and on-line methylation pyrolysis/gas chromatography/mass spectrometry revealed that on treatment of condensed tannins with ammonia, amino-substitution at C-4′ of the pyrogallol-type B-ring occurred to form a 4′-amino-3′,5′-dihydroxybenzene-type B-ring. It can be assumed that the introduction of a 4′-amino-3′,5′-dihydroxybenzene-type B-ring into the tannin molecule results in improved formaldehyde-scavenging ability.

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