Antioxidant activity of the different polar solvent extracts of Magnolia officinalis leaves and purification of main active compounds

The leaf of Magnolia officinalis is abundant in natural resources as a novel potential antioxidant and has great commercial value. In this study, the contents of total phenolics, total flavonoids, magnolol and honokiol in different solvent extracts (acetone, methanol and water) were measured. Meanwhile, the antioxidant activity of extracts from M. officinalis leaves were evaluated using 1,1-diphenyl-2-picrylhydrazyl free radical scavenging assay, 2,2-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt free radical scavenging assay, FRAP assays and beta-carotene/linoleic acid system. In addition, the correlation between the antioxidant activity and the contents of the active compounds was analyzed. Experimental results indicated that three extracts exhibited antioxidant effects in a concentration-dependent manner, and acetone extracts had the highest antioxidant activity, next methanol and water. There was an intimate relativity between the contents of magnolol and honokiol in different solvent extracts and the antioxidant capability of them. So the magnolol and honokiol of M. officinalis leaves as a representative of the active compounds were extracted and purified by using the macroporous resin column. The purity of depurated sample could reach 82.6 %, which indicates the M. officinalis leaves have the potential to substitute the production of magnolol and honokiol in M. officinalis. The results of this study can provide theoretical and technical references for the reasonable use of the M. officinalis leaves and alleviate the shortage of M. officinalis resources.