Fractionation of the antioxidant (poly)phenol-polysaccharide-protein complex extracted with ammonia from wild blackthorn (Prunus spinosa L.) fruits: structural features of the fractions obtained

Abstract

Underutilized wild blackthorn fruits are an important source of mainly phenolic compounds, which makes them suitable as potential functional foods supporting human health. The crude polysaccharide complex (Am), isolated from wild blackthorn berries by ammonia, was subjected to ion-exchange chromatography to yield seven fractions differing in the content of carbohydrates, proteins, phenolics and constitutional saccharides. The non-retained fraction, eluted with water, was rich in α-D-glucan, while the fraction eluted with 0.1 M salts had a high xylose content, indicating the presence of a partly acetylated β-D-xylan-type polysaccharides (4-O-methyl-glucuronoxylan, etc.). However, the highest yields were obtained by elution with 0.5 and 0.25 M NaCl and 1.0 M NaOH solutions, while other fractions were low. The two dominant fractions eluted with 0.25 and 0.5 M saline solutions were found to have a high content of GalA and rhamnose, indicating the presence of rhamnogalacturonan (RGI) and 1,4-α-D-homogalacturonan (HG) regions with a low acetyl content and low degree of methyl esterification. The third fraction in terms of yield, eluted with 1.0 M alkali, was a dark brown material with the highest content of phenolic compounds among all fractions. Its carbohydrate portion was rich in glucose, galactose, rhamnose, xylose and arabinose residues, indicating the presence of polysaccharide complex such as α and β-D-glucans, rhamnogalacturonan, arabinan/arabinogalactan and β-D-xylan types of polymers.