Analysis of the Oxidative Degradation of Proanthocyanidins under Basic Conditions

详细信息    查看全文

• 作者：Emily M. Jorgensen ; Anna B. Marin ; and James A. Kennedy
• 刊名：Journal of Agricultural and Food Chemistry
• 出版年：2004
• 出版时间：April 21, 2004
• 年：2004
• 卷：52
• 期：8
• 页码：2292 - 2296
• 全文大小：57K
• 年卷期：v.52,no.8(April 21, 2004)
• ISSN：1520-5118

文摘

Proanthocyanidin isolates from grape (Vitis vinifera L. cv. Pinot noir) skin and seed underwent oxidativedegradation in solution (10 g/L) under basic conditions while exposed to atmospheric oxygen.Degradation was monitored by reversed-phase HPLC following acid-catalyzed cleavage in thepresence of excess phloroglucinol (phloroglucinolysis) and by high-performance gel permeationchromatography. All isolates degraded under these conditions and followed second-order kineticsfor over 1 half-life, consistent with an oxidation reaction. The conversion of proanthocyanidins toknown subunits (conversion yield) when measured by phloroglucinolysis showed a dramatic declineover the course of the reaction. With the exception of (+)-catechin extension subunits, all individualsubunits decreased in concentration during the oxidation process, also following second-order kineticsfor over 1 half-life. Skin proanthocyanidins degraded the fastest due to the presence of (-)-epigallocatechin extension subunits. Seed procyanidins were degraded with and without flavan-3-olmonomers. Flavan-3-ol monomers slowed the rate of seed procyanidin degradation. The mean degreeof polymerization (mDP) determined by phloroglucinolysis indicated a large decrease in mDP as thereaction progressed; yet, by GPC, the size distribution of all proanthocyanidins changed little incomparison. The conversion yield could be an important parameter to follow when using phloroglucinolysis as a means for determining proanthocyanidin mDP, and when monitoring the oxidativedegradation of proanthocyanidins.Keywords: Proanthocyanidins; condensed tannins; oxidation; composition; size distribution; Vitisvinifera; grape; seed; skin