Optimization of extraction parameters of antioxidant activity of extracts from New Zealand and Chinese Asparagus officinalis L root cultivars

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.