Effect of Quillaja saponaria saponins and Yucca schidigera plant extract on growth of Escherichia coli.

Escherichia coli K-12 was exposed to Quillaja saponaria saponins from various commercial firms (Sigma, Roth and Nor-feed) and to an extract of Yucca schidigera plant powder (DK Sarsaponin 30) at different concentrations (0.05-1.0% w/v). A concentration-dependent response was observed. Quillaja saponaria saponins from Sigma increased growth up to 0.1% (w/v) level, whereas Nor-feed and Roth saponins produced maximum growth at a much higher level (0.5 and 0.75%, w/v, respectively). These results suggest that quillaja saponins from various sources differ in their biological activity, although all three saponins had the same content of vanillin-sulphuric acid reactive moieties. The lyophilized water extract from the DK Sarsaponin powder showed maximum growth at 0.1% (w/v) level. The levels at which maximum growth was observed did not change on subjecting the quillaja or yucca saponins to heat treatment in an autoclave (121 degrees C for 30 min). All the saponins and the plant extract increased growth of Escherichia coli up to a certain concentration and thereafter decreased growth. In spite of the decreased growth at higher levels of saponins, it was higher compared to the control (without saponin) up to levels of 1% (w/v) for all saponins except Quillaja saponins from Sigma, for which the growth was lower at levels of 0.25% (w/v) and higher. Saponins have the potential to modulate microbial growth in natural and artificial fermenters.