Improving fed-batch culture efficiency of Rhodiola sachalinensis cells and optimizing flash extraction process of polysaccharides from the cultured cells by BBD–RSM

Fed-batch culture of plant cells can enhance biomass and bioactive compound accumulation compared with batch culture, in which the initial culture medium is one of the controllable factors in the fed-batch culture system. Rhodiola sachalinensis is a valuable medicinal herb and its cell culture is an alternative approach to obtaining plant material. R. sachalinensis cells has been previously cultured in a fed-batch culture system and the initial culture medium has been found to critically affect production yield. Therefore, this study investigated the effect of nitrogen concentration, ammonia and nitrate ratio (NH4+/NO3-), and phosphorus and calcium concentrations in initial culture medium on cell biomass, as well as salidroside and polysaccharide accumulation to improve the fed-batch culture efficiency. Then, the cultured cells were extracted by flash extraction and the extraction conditions were optimized by Box-Behnken Design Response Surface Method (BBD–RSM). Finally, the antibacterial and antibiofilm effects of the extract were examined to further utilize R. sachalinensis cell cultures. The results showed that the fed-batch culture efficiency was obviously improved when the initial culture medium was modified as 30 mM of nitrogen with 5/25 of NH4+/NO3-, 0.94 mM of phosphorus, and 2.3 mM of calcium, at which 277.3 mg/L of salidroside and 4.5 g/L of polysaccharides were obtained In flash extraction, polysaccharide yield was as the response value to optimize extraction process by controlling extraction time, extraction temperature, and liquid–solid ratio in the BBD–RSM experiments. The optimal flash extraction conditions were 55.7 s of extraction time, 56.5 °C of extraction temperature, and 37.0 mL/g of liquid–solid ratio, which the polysaccharide yield reached 12.76% under the optimized conditions. In antibacterial experiment, the cell extract (RCE) inhibited the growth of Bacillus subtilis, Pseudomonas aeruginosa, and Salmonella choleraesuis; the biofilm of B. subtilis and S. choleraesuis was scavenged in the groups of 8 mg/mL and 16 mg/mL RCE. The findings provided a basis for further industrial production of cell cultures and a theoretical reference in using R. sachalinensis cells in the production of antibacterial-related products.