The inhibitory effects of apple polyphenols (APP) on the synthesis of water-insoluble glucans by glucosyltransferases (GTF) of streptococci of the mutans group and on the sucrose-dependent adherence of the bacterial cells were examined in vitro. APP markedly inhibited the activity of GTF purified from the cariogenic bacterial cells. However, APP showed no significant effect on the growth of the cariogenic bacteria. The strongest GTF inhibitors in APP were apple condensed tannins (ACT), a mixture of procyanidins. The 50% inhibitory doses of ACT against the GTF of S. sobrinus and that of S. mutans were 1.5 microgram/mL and 5 microgram/mL, respectively. The ACT efficacy largely depended upon the degree of polymerization. Interestingly, while the other polyphenols known to inhibit GTF such as tannic acid markedly inhibited salivary alpha-amylase activity, APP and ACT only scarcely inhibited that enzyme activity. This means that APP and ACT might selectively inhibit the bacterial GTF activity under oral conditions.

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Molecular size information for polymerized catechin larger than the decamer in unripe apple was obtained by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and by fast-atom bombardment mass spectrometry. Matrix-assisted laser desorption/ionization time of flight mass spectrometry provided evidence for the pentadecamer using trans-3-indoleacrylic acid as the matrix in the presence of silver ion. Even in the absence of silver ion, the dodecamer and undecamer were observed in the positive- and negative-ion modes, respectively. Fast-atom bombardment mass spectrometry also afforded evidence for the undecamer in both positive- and negative-ion modes.

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