'ZAHDI' DATES SKIN AS A SOURCE OF PROANTHOCYANIDIN

The present work investigates the location and structure of date’s proanthocyanidin. Sugar free skin of ‘Zahdi’ date cultivar obtained through dewaxing by organic solvents (petroleum ether and diethyl ether) has been extracted by acetone and water; 50:50 and 70:30. The hygroscopic brownish lyophilized extract gave the typical cyanidin chloride red color (λ_{max MeOH/HCl}=535 nm, PC R_f value=0.49 in Forestal solvent) when treated with MeOH/HCl. Approximate molecular weight studies by ultracentrifuge disclosed a molecular weight ranging from 1558-4792 depending on the fractions of sephadex LH 20 columns. The spectroscopic data IR and ¹³C-NMR spectra indicated the occurrence of proanthocyanidine oligomer. To confirm these finding and to elucidate the monomers structures, the propose oligomers have been degraded through thiolysis with benzyl mercaptan in acidic medium. Thiolysis products have been identified by capillary GC/MS. Fragmentation pattern of the silylated thioether showed derivatives of (+)-epicathecin [(2R,3S,4S)-4-β-Benzyl thioepicatechin] as the main monomer. As terminal units of the oligomer appear (-)-catechin and (+)-epicathecin in 1 and 1.5 ratio respectively. These results have been confirmed through the 2D-PC with 2,6-Dibromobenzoquinone-4-chlorimid acetone 0.5% w/v of the thiolysis products, and the reduction of (+)-epicathecin thioether derivatives by Raney Nickel reagent. Accordingly, the ‘Zahdi’ date skin contains two types of procyanidin oligomer: Epicatechin (4β→8)-(epicatechin)_n-(4β→8)-epicatechin, and Epicatechin-(4β→8)-(epicatechin)_n-(4β→8)-catechin.