Characteristics of pectic polysaccharides from leek obtained through consecutive extraction with various reaction agents

Abstract

Five polysaccharide fractions of commensurable by yield, but different in composition were obtained through consecutive extraction with water, solutions of ammonium oxalate, sodium carbonate, hydrochloric acid and sodium hydroxide from the alcohol-insoluble residue (AIR) of leek. In the polyuronide part of these fractions besides galacturonic acid was found also glucuronic acid. In the neutral sugar fraction, the prevailing sugar was galactose, followed by rhamnose. The water-extractable pectic polysaccharide was highly homogenous (93.3% of it had molecular mass of 1.3×10 6 kDa) and protein content of 8% (the highest compared to the other extracted polysaccharides). Extraction with diluted hydrochloric acid yielded polysaccharide with the highest neutral sugar content of 71.1% and a low uronic acids content. The water- and chelate-extractable fractions had a lower L-rhamnose content (2.7% and 2.9%, respectively) and the other polysaccharide fractions from leek were characterized by a high L-rhamnose content (from 14 to 28%). The pectic polysaccharides obtained from leek have shown good immunostimulating properties. The highest immunostimulating activity has been shown by the water- and chelate-extractable polysaccharides, which are also characterized by a high polyuronic acid content and polysaccharides with molecular mass over 10 6 Da.