Extraction and physico-chemical characterization of pectins from sugar beet pulp

Sugar beet pulb (SBP) pectins were isolated from the proteolysis hydrolysates or extracted by HCl (pH 1.5, 85 degrees C for 1-6h and pH 1.5, 4h at 40-90 degrees C), ethylenediamine tetraacetate (EDTA, 0.2%, pH 3.3, 85 degrees C, 1, 4h), ammonium oxalate (AO, 0.2%, pH 3.3, 4h), and sodium hexametaphosphate (SHP, 0.2%, pH 3.3, 4h). An optimal HCl extraction (pH 1.5, 85 degrees C, 4h) yielded 16.94% pectin from the dewaxed and protein-free SEP. The HCl extracted pectin contained 84.61% galacturonic acid and low ash, 2.69%. The degree of methylation was over 60% in all the pectin samples, indicating that the sugar beet pectin is a high methoxy pectin. The degree of acetylation ranged between 10.80% and 14.78%, resulting in poor gelling capacity of the pectins. The pectins also contained 7.21% to 10.73% neutral sugars, which were mainly arabinose and galactose. The molecular-average weights ranged between around 60000 and 90000 Da. It was found that lignin in SEP cell walls is tightly associated with pectin. Besides the esterified ferulic acid, seven other phenolic monomers, principally vanillin and p-hydroxybenzoic acid, were initially identified in the alkaline nitrobenzene oxidation of bound lignin in the isolated pectin samples.