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

• SFHP(A) is extracted by sodium citrate and purified by ultrafiltration.
• Structure features is compared to SFHP(B) extracted by ammonium oxalate and alcohol.
• SFHP(A) has a close DM (22.56%) to (B) but a significantly lower DAm (3.42%) than (B).
• SFHP(A) has smaller molecular weight but higher RG-I and RG-II content than (B).
• FEG-SEM suggests pectin network in aqueous is constructed by micro-scale filaments.

Sunflower head pectin was extracted by 0.6% (w/v) sodium citrate under 85 °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 μm. 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 DAm (3.42%). HPSEC-MALLS analysis suggested that SFHP(A) has undergo a deeper degradation resulting in smaller Mw and Mn. 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-SEM, which reveals that pectin network structure is constructed by microfilaments via coiling, intertwining and crosslinking.