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Analysis of antioxidant metabolites by solvent extraction from sclerotia of Inonotus obliquus (Chaga).

INTRODUCTION
The sclerotia of Inonotus obliquus (Chaga) are effective therapeutic agents to treat several human malignant tumours and other diseases without unacceptable toxic side-effects.


OBJECTIVE
To investigate solvent effects on metabolic profiles and antioxidant activities of extracts of Chaga.


METHODOLOGY
Chaga was extracted by petroleum ether, chloroform, ethyl acetate, acetone, ethanol and water. Solvent effects on metabolites in the extracts were assayed by NMR-based metabolomic analysis. Antioxidant activities were indicated as capacities for scavenging superoxide anion, DPPH and hydroxyl radicals.


RESULTS
Petroleum ether and chloroform extracts contained primarily lanostane-type triterpenoids (LT), whereas the extracts of ethyl acetate, acetone and ethanol were characterised by the predominant presence of hispidin analogues and LT, and water extracts by polysaccharides and phenolic compounds. The ethyl acetate, acetone, ethanol and water extracts revealed remarkable potential for scavenging the tested radicals, while those of petroleum ether and chloroform did not. Polyphenols are the major contributors for quenching the tested free radicals, while in LT only compounds 16, 17 and 22 participated in scavenging hydroxyl radicals.


CONCLUSION
Polyphenols in Chaga are the principles for quenching free radicals while polysaccharides and a few LT compounds contribute partially in scavenging DPPH and hydroxyl radicals, respectively. NMR-based metabolomic analysis is a useful method by which to correlate ¹H-NMR spectra of Chaga extracts with their antioxidant activities, and this allows the prediction of potentials for scavenging free radicals by ¹H-NMR spectroscopy.