Abstract: Bletilla striata extracts were prepared by methanol circumfluence extraction.Five fractions of B.striata were achieved by extraction with different polar solvents including n-hexane,dichloromethane,ethyl acetate,n-butanol and water.The fractions were detected by the contents of total phenolics and total flavonoids,reducing power,scavenging DPPH and ABTS free radicals and α-amylase inhibitory activities.Gas chromatography-mass spectrometry (GC-MS) was used to identify the main constituents of the methanol crude extract.The results showed that there were significant differences in the contents of total phenolics and total flavonoids among different polarity fractions.Dichloromethane fraction exhibited the highest contents of total phenolics (311.27±0.96 mg/g) and total flavonoids (22.19±1.47 mg/g).All the fractions had strong antioxidant capacity such as reducing power,and DPPH,ABTS free radical scavenging abilities.There was a good linear dependence between the antioxidant capacity and the concentration.The fractions also exerted the inhibitory effects on α-amylase.The dichloromethane fraction presented the best α-amylase inhibitory effect with IC₅₀ value of 15.75 mg/mL.Total phenolics demonstrated positive correlations with antioxidant and α-amylase inhibitory activities,indicating that polyphenols were the bioactive components of B.striata.The methanol crude extract was analyzed by GC-MS,and fifteen compounds representing 93.13% of the total constituents were identified.Esters(53.01%),aromatic series(28.68%),and organic acids (8.97%) were the main components,among which,polyphenols were the major bioactive components,while esters,organic acids might be potential bioactive components.In conclusion, B.striata fractions contained high content of bioactive compounds,showed potent antioxidant and α-amylase inhibitory activities.This research was profitable for the study and use of the B.striata.

Key words: Bletilla striata, cas chromatography-mass spectrometry (GC-MS), bioactive components, antioxidant, α-amylase inhibitory activity