Activity of tyrosol glucosyltransferase and improved salidroside production through biotransformation of tyrosol in Rhodiola sachalinensis cell cultures

The activity of tyrosol glucosyltransferase (TGase) of Rhodiola sachalinensis cells was found to be the highest at the exponential growth phase while the intracellular tyrosol accumulated in large amounts at the stationary growth phase. This non-synchronization of the TGase activity with the tyrosol accumulation was responsible for the low yield of salidroside obtained in cell suspension cultures. When 1 mmol l−1 exogenous tyrosol was added to the culture at day 8 and subsequently incubated for 24 h, nearly 95% of the added tyrosol was transformed to salidroside. The optimal concentration of exogenous tyrosol for the glucosylation reaction was 3 mmol l−1. Excess high concentration of tyrosol was toxic to cell growth and inhibited the biotransformation reaction. By repeated addition of 3 mmol l−1 tyrosol at 24 h intervals over 3 d, very high salidroside yield of 516 μmol g−1 (15.4% of dry weight) was obtained.