The present invention relates to a method of modulating a selected biological activity of a naturally occurring material having one or more biological activities in an extract of the naturally occurring material, the method comprising incubating the extract in a medium in the presence of an aerobically metabolizing microorganism, under suitable aerobic conditions, for a period of time sufficient to modulate the selected activity with respect to baseline activity of the unincubated extract. The invention also relates to the bioconverted material so prepared, and the use of same in cosmetic or pharmaceutical compositions.