Mohammed R. Koupai-Abyazani

The proanthocyanidin polymers in some species of Onobrychis

Abstract Proanthocyanidin (PA) polymers (condensed tannins) were isolated and purified from the leaves of 26 accessions and species of sainfoin (Onobrychis). Analysis of the degradation products by HPLC revealed that epicatechin, gallocatechin and epigallocatechin were present as both terminal and extension units in all the samples studied while catechin was a terminal unit only. Quantitative analysis showed that epigallocatechin was the dominant extension unit in all of these polymers (52–63% total units). A mean degree of polymerization (DP) of 6.5 (by HPLC) and 9 (by Gel Permeation Chromatography) was obtained. The PA polymers consist principally (73–85%) of delphinidin units and 78–87% of cis-isomer units in all the samples studied.

Identification of the constituent flavanoid units in sainfoin proanthocyanidins by reversed-phase high-performance liquid chromatography

Abstract A rapid and sensitive method for the separation and identification of flavan-3-ols and their phoroglucinol adducts using reversed-phase high-performance liquid chromatography is reported. The application of the method is demonstrated for the analysis of the degradation products of sainfoin leaf proanthocyanidins. The results showed that the extension and terminal units in this sample are catechin, epicatechin, gallocatechin and epigallocatechin.

Biosynthesis of flavan-3-ols by leaf extracts of Onobrychis viciifolia

Abstract A subcellular enzyme fraction (Mr>20 × 106) from immature sainfoin leaves catalysed the two-step NADPH-dependent reduction of ( + )-dihydromyricetin to ( + )-gallocatechin. No enzyme-mediated (−)-epigallocatechin was formed under the conditions employed, and only traces of 2R,3S-trans-3S,4S-cis-leucodelphinidin were observed. The two-step reductase activity mirrored proanthocyanidin content, rising to a maximum before leaflet unfolding, then declining during leaf expansion. When [14C]( + )-dihydromyricetin and [C4-3H]2R,3S-trans-3S,4S-cis-leucodelphinidin were supplied to the same fraction, preferential utilization of ( + )-dihydromyricetin was observed. Enzymic formation of proanthocyanidin dimers could not be detected using these preparations under a variety of conditions. However, a small portion of radioactivity was bound to the subcellular fraction after addition of labelled ( + )-catechin. In addition, in vivo incorporation of ( + )-dihydromyricetin into proanthocyanidins was observed.

Gas chromatographic–mass spectrometric characterization of flavanones in citrus and grape juices

A method for the characterization of flavanones in fruit juices, involving solvent extraction, hydrolysis to the corresponding aglycones, trimethylsilylation and combined gas chromatography-mass spectrometry, is reported. The application of the method is demonstrated for the analysis of orange, lemon, grapefruit and grape juices.

Origin and control of multi-peak formation in the analysis of trimethylsilyl derivatives of flavanone aglycones by capillary column gas chromatography

Abstract Trimethylsilyl derivatives of flavanone aglycones give double peaks in their gas chromatograms. The origin of these peaks, from an isomerization between the flavanones and their corresponding chalcones, has been examined using gas chromatography-mass spectrometry and UV spectrophotometry. The effects of derivatization temperature, time and capillary column injection technique on the rate of the interconversion have been defined.

The condensed tannins of Leptarrhena pyrolifolia

Abstract A proanthocyanidin (PA) polymer, a condensed tannin, was isolated, purified and characterized from the leaves of Leptarrhena pyrolifolia. The predominant extension units in the polymer were (−)-epicatechin and (+)-gallocatechin with traces of (−)-epigallocatechin. (+)-Catechin was the predominant terminal unit. The PA polymer contained both prodelphinidin and procyanidin units in the estimated ratio of ca 1. The cis:trans ratio and the number-average Mr of the polymer were determined and are discussed.