Effects of xylitol/sorbitol combinations on bacterial growth and metabolism in Streptococcus sobrinus OMZ 176

Combinations of the non-cariogenic sugar alcohols xylitol and sorbitol are widely used as sucrose substitutes in lozenges and chewing-gums. In S. sobrinus OMZ 176 xylitol inhibits the metabolism of sorbitol, and the xylitol-induced bacterial growth inhibition of S. sobrinus OMZ 176 has been shown to be enhanced by sorbitol. In combination with xylitol the sorbitol transport changes from a pts- to a non-pts transport, while the transport of xylitol is unaffected by the presence of sorbitol. It would be of interest to know how much xylitol has to be added to a sorbitol-containing medium to inhibit the metabolism of this sugar alcohol. In the present study no optimal inhibitory concentrations of xylitol/sorbitol combinations were found. Growth and acid production in S. sobrinus OMZ 176 are essentially the same for xylitol: sorbitol ratios in the range from 1:7 to 7:1. The presence of intracellular xylitol metabolites seems to be essential.