Polysaccharides from sunflower stalk pith: Chemical, structural and functional characterization

Polysaccharides from sunflower stalk pith (SSP) were extracted by hot water and sodium hexametaphosphate (SHMP). Chemical analyses suggested both fractions dominated in galacturonic acids with a small amount of neutral sugars, indicating their identity as pectins. The weight average molecular weight and intrinsic viscosity for water-extractable pectin (WEP) and SHMP-extractable pectin (SEP) were 57.2 kDa, 0.48 dL/g and 23.1 kDa, 0.50 dL/g, respectively. The degree of esterification (DE) was calculated to be 92% and 64%, respectively. Methylation analysis demonstrated that 1,4-GalpA residues dominated all the sugar linkages, while other linkage types including 1,2-Rhap, 1,2,4-Rhap, 1,4-Galp and 1,5-Araf were also present in WEP and SEP. NMR spectroscopy further revealed WEP and SEP mainly demonstrated homogalacturonan (HG) structure and a small fraction of rhamnogalacturonan-I (RG-I) structure. The microstructure and water- and oil-holding capacity (WHC and OHC) of SSP was also examined. SSP was a microporous powder. Both WHC and OHC increased with particle size of the SSP, reaching up to over 40 g liquid/g fibre at particle size of 30 mesh (0.595 mm). However, the oil-SSP mixtures showed oil loss after absorption on filter paper for 24 or 48 h. Oil loss increased with SSP particle size decrease. 30 mesh SSP reduced oil loss in peanut butter by 74% with 2.2% addition.