Monday, May 5, 2008
9-37

Generation, identification, and quantification of thermal degradation products from Silybum marianum and their athero-protective effects

E.C. Clausen, Jack Lay, Sunny Noel Wallace, Danielle Julie Carrier, and Jennifer Gidden. Chemical Engineering, University of Arkansas, 3202 Bell Engineering Center, Fayetteville, AR 72701

Pressurized hot water (or subcritical water) has received attention as a green extraction solvent, but little attention has been paid to the thermal degradation products formed during pressurized hot water extraction (PHWE).  This study investigates the generation, identification, and quantification of thermal degradation products formed during PHWE of Silybum marianum fruits.  To generate thermal degradation products from the S. marianum flavonolignans, each of the individual flavonolignans (silichristin, silidianin, silibinin and isosilibinin) were dissolved in methanol and exposed to pressurized hot water at 500 kPa and 413 K for 0.5 hr.  LC/MS/MS characterization of the extracts showed the presence of multiple degradation products.  PHWE of silibinin A and B resulted in the formation of two degradation compounds.  PHWE of silichristin (which occurs in three forms, A, B, and C) resulted in a complete loss of form A, and the formation of one degradation compound.  PHWE of isosilibin A and B created six degradation products.  The extracts, before and after subcritical water extraction, were evaluated for their athero-protective effects by the thiobarbituric acid-reacting substances (TBARS) assay.  The TBARS assay evaluates the ability of the flavonolignans to inhibit the copper-induced formation of oxidized low-density lipoproteins (oxLDL).  Comparable athero-protective effects were observed for both the pure flavonolignan preparations and the extracts, indicating that degradation products formed during extraction do not diminish the potency of the flavonolignans, and likely do not display pro-oxidant effects.  300 μM silibinin standard decreased oxLDL formation by 63.6%, and 300 μM silibinin PHW extract decreased oxLDL formation by 55.9%.

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