Bioactive compound production by adventitious root culture of Oplopanax elatus in balloon-type airlift bioreactor systems and bioactivity property

Abstract

Oplopanax elatus Nakai is a high-value medicinal plant, but the availability of this resource is rare under natural conditions. To provide a novel source of O. elatus products, we used balloon-type airlift bioreactor systems to investigate a culture method. This method was developed to obtain adventitious roots (ARs), which contain a high yield of bioactive compounds. Antioxidant and anticancer properties were also investigated to evaluate the bioactivity of AR extracts. The bioreactor culture more efficiently promoted AR growth and bioactive compound accumulation (polysaccharides, phenolics, and flavonoids) than the agitated flask and solid cultures. During bioreactor culture, the maximum AR fresh (114.6 g L⁻¹) and dry (12.7 g L⁻¹) weights were found in the medium supplemented with 50 g L⁻¹ sucrose and 3 mg L⁻¹ IBA. The highest bioactive compound content was also found in the same medium; the productivities of polysaccharides, phenolics, and flavonoids reached 1913.9, 459.7, and 713.7 g L⁻¹, respectively. The polysaccharide, phenolic, and flavonoid content of ARs from the bioreactor culture were compared with those of roots from field-grown plants. The polysaccharide content reached the maximum levels in ARs (152.5 mg g⁻¹ DW) and in roots of 3-year-old plants (147.5 mg g⁻¹ DW), with no evident difference. The phenolic (32.1 mg g⁻¹ DW) and flavonoid (50.5 mg g⁻¹ DW) contents in ARs were higher than those in the roots of plants grown in the field for 2 and 3 years. The kinetic study showed that the highest AR biomass and bioactive compound productivity were found at 40 days. Therefore, 40 days of culture is appropriate for the mass production of bioactive compounds from O. elatus by AR culture in bioreactor systems. Polysaccharide, phenolic, and flavonoid contents were higher in bioreactor-cultured ARs than in the roots of 2-and 3-year-old field-grown plants. ARs exhibited an effective antioxidant activity; the rate of DPPH radical scavenging in the AR extract was higher than that in the root extracts of field-grown plants (2 and 3 years); IC₅₀ of AR extract was only 33.5 μg mL⁻¹. The AR extract also elicited anticancer effect on human cancer cell lines, particularly the gastric cancer cell line AGS. AGS cell proliferation was reduced by 50 % after 24 h of these cells were exposed to 78.3 μg mL⁻¹ AR extracts. Our results suggested that the bioreactor culture of O. elatus AR can be used to produce bioactive compounds (polysaccharides, phenolics, and flavonoids). ARs are also a potential resource to develop O. elatus products.