Abstract: The objective of this study was to isolate a microorganism capable of producing β-glucosidase to transform ginsenoside Rg3. A modified esculin agar medium was used to the strain from kefir fermented ginseng slurry and this strain produced black hydrolysis spots on the medium and was identified as Kluyveromyces marxianus by observing its colony morphology and sequence analysis of the 26S rDNA D1/D2 region. The fermentation conditions of ginseng for the transformation of ginsenoside Rg3 by Kluyveromyces marxianus were optimized using one-factor-at-a-time method and response surface methodology with a three-factor, three-level Box-Behnken design. A regression model was established with ginseng-to-water ratio (m/m), inoculum concentration and fermentation time as independent variables. The results indicated that the optimized fermentation parameters were as follows: ginseng-to-water 1:2.65, inoculum concentration 2.94%, and fermentation time 3 days. Under these conditions, the content of Rg3 was 3.31 mg/g and its transformation rate was 248%. In conclusion, the results of this study can provide theoretical data for industrial production of fermented ginseng.

Key words: ginseng, kefir grains, β-glucosidase, ginsenoside Rg3, response surface methodology