Characterization of natural low-methoxyl pectin from sunflower head extracted by sodium citrate and purified by ultrafiltration

Sunflower head pectin was extracted by 0.6% (w/v) sodium citrate under 85 degrees C, 3.5 h with a solid to liquid ratio of 1:40, giving the maximum uronic acid yield of 16.90% (w/w). The extract was purified by an ultrafiltration membrane with the molecular weight cut-off of 8000 Da and dried by spray-drying to obtain SFHP(A) powders with particle diameters of 2-5 mu m. In comparison to the SFHP(B) extracted by ammonium oxalate and isolated by alcohol, SFHP(A) had a close DM (22.56%) but a considerably lower DA. (3.42%). HPSEC-MALLS analysis suggested that SFHP(A) has undergd a deeper degradation resulting in smaller M-w and M-n. HPAEC-PAD showed that SFHP(A) contains more neutral sugars since the degraded RG fragments have been retained during ultrafiltration. Finally, pectin aggregation in aqueous was investigated by FEG-SEIVI, which reveals that pectin network structure is constructed by microfilaments via coiling, intertwining and crosslinking. (C) 2015 Elsevier Ltd. All rights reserved.