Abstract: Objective: To investigate the optimization of the fermentation of mixed extracts from Rhodiola sachalinensis and Codonopsis lanceolata (RCME) by Lactobacillus pentosus and to determine the composition of bioactive compounds and antioxidative activity of fermented RCME. Methods: The pH, acidity and mycelial biomass were evaluated as a function of the ratio between Rhodiola sachalinensis and Codonopsis lanceolata, soluble solid content of RCME and fermentation time. Variations in the total protein, neutral sugar, acidic polysaccharide and total phenolics contents in RCME before and after fermentation were determined using colorimetric method, as well as variations in salidroside and tyrosol contents by HPLC. The antioxidant activity of fermented RCME was evaluated using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2’-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) diammonium salt (ABTS) radical scavenging assay. Results: The pH and total acidity were little changed from 24 to 72 h of fermentation when Rhodiola sachalinensis was fermented alone and the viable cell count significantly decreased (P < 0.01). A 3:2 mixture of Rhodiola sachalinensis and Codonopsis lanceolata showed the greatest pH decline and largest increase in acidity at 24 h of fermentation, which remained little changed from 48 h onward, but the viable cell count dropped. Soluble solid content was in the range of 1.0%–3.0%, and the conversion rate of salidroside to tyrosol was not changed significantly from 48 to 72 h. However, salidroside content significantly decreased at 24 h compared with that at 0 h (P < 0.01), whereas tyrosol, acidic polysaccharide, total phenolics and protein significantly increased (P < 0.05 or P < 0.01). DPPH and ABTS+· scavenging activity of fermentation product were significantly higher than those of RCME (P < 0.01). Conclusion: The optimum fermentation conditions of RCME were determined as follows: ratio between Rhodiola sachalinensis and Codonopsis lanceolata ratio, 3:2; soluble solid concentration of RCME 1.0%–3.0%, temperature 37 ℃, and time 24 h.

Key words: Rhodiola sachalinensis, Codonopsis lanceolata, Lactobacillus pentosus, fermentation, antioxidant activity