Abstract
•Abundant information on bioactive compounds in A. racemosus roots.•Very little is available on bioactives in A. officinalis L roots.•Asparagus roots are an excellent source of natural bioactive compounds.
Optimisation of the antioxidant activity of asparagus root extract (ARE) and inosine from New Zealand and Chinese asparagus root cultivars was carried out using a response surface methodology (RSM) using Box-Behnken design (BBD). The determination of inosine was carried out using HPLC under optimal extraction conditions. The independent parameters variables combination (extraction temperature 51 °C, extraction time 73.02 min, ethanol 75.23% and solid: liquid ratio 1:50) produced maximum total flavonoids content (TFC) (9.2–17.1 mg RE/g dry root), total phenolic content (TPC) (14.7–35.2 mg GAE/g dry root) and total saponin content (TSC) (9.2–17.1 mg RE/g dry root). Extraction at temperature 50 °C for 78.5 min, using 70% ethanol at solid: liquid ratio of 1:40 for maximum 2,2-diphenyl-1-picrylhydracyl (DPPH) (38.9–78.1%), 2,2-azinobis(3-ethylbenzo-thiazoline-6-sulfonate) (ABTS) (36.6–61.2%), ferric reducing antioxidant power assay (FRAP) (0.54–1.69 μmol/g), β-carotene bleaching assay (51.2–76.0%) and superoxide anion radical (O2−) scavenging capacity (42.5–70.2%). For methanol, extraction conditions viz. extraction temperature at 51 °C for 75 min, using 75% methanol at solid: liquid ratio of 1:50 resulted in maximum TFC (12.0–13.4 mg RE/g dry root), TPC (25.1–26.2 mg GAE/g dry root) and TSC (5.9–6.4 mg SE/g dry root). Extraction temperature at 50 °C for 76.5 min using 80% methanol at solid: liquid ratio of 1:50 produced maximum%DPPHsc (55.8–69.9%), %ABTSsc (43.0–52.0%), FRAP (0.54–0.59 μmol/g dry root), %βsc (49.2%–71.2%) and%O2−sc (34.4–41.6%). The content of inosine from ARC ranged from 1.3 to 6.0 mg/g with ethanol and from 0.9 to 4.1 mg/g with methanol extraction.