A natural low-methoxyl pectin (LAHP), was extracted with oxalic acid solution from dried heads of sunflower (Helianthus annuus L.). The single-factor experiments and response surface methodology (RSM) were used to optimize LAHP extraction conditions. The extraction yield of LAHP was 18.83 ± 0.21%, and the uronic acid content was 85.43 ± 2.9% obtained under the optimized conditions (temperature of 96 °C, time of 1.64 h, oxalic acid concentration of 0.21%). Experimentally obtained values were in agreement with those predicted by RSM model, indicating suitability of the employed model and the success of RSM in optimizing the extraction conditions. LAHP has been characterized by ash content, degree of esterification (DE), galacturonic acid (GalA) content, molecular weight and intrinsic viscosity meanwhile commercial low-methoxyl pectin (CLMP) as comparison. This study finds out a potential source of natural LMP which expands the application scope of sunflower heads. It is an efficient reuse of waste resources and provides a novel thought to explore the natural resources for food and pharmaceutical applications. Pectin is a kind of complex polysaccharides from plant primary cell walls, always consisting of methyl esterified D-galacturonic acid 1. Pectin has been widely used in food, pharmacy and cosmetics industries as thickeners, stabilizers, gelling agents 2 and ingredients of medicine for the treatment of gastroenterological diseases, diabetes, hypertension and cancer 3. Up to now, most of commercial pectins produced from citrus peel, apple pomace 4 , sugar beet pulp 5,6 , orange 7 , lemon 8 , banana 9 , peach 10 , durian rind 11 and soy hulls 12 were high-methoxyl pectin (HMP, degree of esterification [DE] > 50%) 13. DE is a primary factor in terms of gelling forming conditions and mechanical properties. HMP usually cannot meet people's demand on food flavor because of its free of good taste. The gel forming of HMP is governed by hydrogen bonding and hydrophobic interactions, which requires the sugar solution at concentration higher than 55% and pH lower than 3.5. Nevertheless low-methoxyl pectin (LMP) 14 not only improves taste but also form gel easily induced by the presence of divalent ion, such as Ca 2+. The 'egg box' model 15 has been widely accepted for calcium pectate gels, which describes the junction zones in LMP chains 16. LMP could be widely used in low calorie foods or sugar-free food, healthy care medicines and cosmetics industries 17. In this case, HMP is usually served to manufacture LMP by chemical or enzymatic treatment to hydrolysis of the methyl esters from galacturonic acid C-6 carboxyl groups. However, this kind of synthesized LMP is costly and has hazardous residuals brought in by chemical and enzymatic treatment.
