PROANTHOCYANIDIN OLIGOMER CONTENT IN DIFFERENT BARLEY VARIETIES

Background and objectives: Proanthocyanidins are mixtures of flavan-3-ol units linked mainly via B-type bonds, i.e., C4-C8 or C4-C6 linkages. Occasionally an additional C2-O7 or C2-O5 linkage may exist, leading to doubly bonded A-type. These phenolic compounds are widely present in plants and have been suggested to demonstrate antioxidant, antibacterial, antiviral, anticarcinogenic, anti-inflammatory, and vasodilatory activities. Surprisingly, quantitative information on the proanthocyanidin profiles in plant products is quite lacking, largely due to the absence of appropriate analytical methodology and commercially available standards for oligomers. The study reported here was undertaken to detect and characterise the procyanidins in different type of barley. Methods: Fourteen barley varieties, four waxy and ten no-waxy, were collected and characterised. Proanthocianidin compounds were extracted and their separation was perfomed by normal phase HPLC-FLD-MS. Results: Monomers, procyanidin and prodelphinidin dimers, trimers, tetramers, and procyanidin pentamers were identified by mass spectrometry and quantified by fluorimetric detection. The total content of proanthocyanidins in barley samples ranged between 29.3 to 65.3 mg/100g. In all samples, the principal components consisting of procyanidin and prodelphinidin trimers with structure (gallocatechin-catechincatechin), followed by the procyanidin dimer and representing on average 19, 17 and 16 % of the total content. With exception of some barleys, monomer content was low. Waxy barley varieties reported the higher content of phenolic compounds compared to no-waxy varieties. Conclusions: These results estabilished that the barley varieties analysed in this work contain proanthocyanidins from monomer to pentamers and how these oligomers are a mixture of procyanidins and prodelphinidins, consisting mainly of catechin units. Moreover the waxy varieties showed the higher content of proanthocyanidins