Analysis of the oxidative degradation of proanthocyanidins under basic conditions.
Proanthocyanidin isolates from grape (Vitis vinifera L. cv. Pinot noir) skin and seed underwent oxidative degradation 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 the presence of excess phloroglucinol (phloroglucinolysis) and by high-performance gel permeation chromatography. All isolates degraded under these conditions and followed second-order kinetics for over 1 half-life, consistent with an oxidation reaction. The conversion of proanthocyanidins to known subunits (conversion yield) when measured by phloroglucinolysis showed a dramatic decline over the course of the reaction. With the exception of (+)-catechin extension subunits, all individual subunits decreased in concentration during the oxidation process, also following second-order kinetics for 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-ol monomers. Flavan-3-ol monomers slowed the rate of seed procyanidin degradation. The mean degree of polymerization (mDP) determined by phloroglucinolysis indicated a large decrease in mDP as the reaction progressed; yet, by GPC, the size distribution of all proanthocyanidins changed little in comparison. The conversion yield could be an important parameter to follow when using phloroglucinolysis as a means for determining proanthocyanidin mDP, and when monitoring the oxidative degradation of proanthocyanidins.
Jorgensen
Emily M
EM
Department of Food Science and Technology, Oregon State University, Corvallis, Oregon 97331, USA.
Marin
Anna B
AB
Kennedy
James A
JA
D002851:Chromatography, High Pressure Liquid; D005638:Fruit / Q000737:chemistry; D006207:Half-Life; D007700:Kinetics; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D044945:Proanthocyanidins / Q000737:chemistry*; D012639:Seeds / Q000737:chemistry; D027843:Vitis / Q000737:chemistry*
D044945:Proanthocyanidins; D010100:Oxygen