Extraction And Properties Of Sunflower Head Pectin And Its Application In Fried Potato Sticks

Rich in low-methoxyl pectin, sunflower head is the byproduct of sunflower seed oilindustry. However, this resource is presently exploited at a low level and knowledge ofsunflower head pectin （SFHP） is limited. In the present paper, focus is emphasized on theextraction, physical and chemical properties, solution and gelling properties of SFHP, and itsapplication in lowering oil absorption of fried potato sticks （FPS）.Initially the extraction of SFHP was studied. Based on single factor experiments,0.5%（w/v） ammonium oxalate and acidified ethanol were chosen, respectively, as extractant andprecipitating/washing agent, while pH3.5,45min as extracting time,80℃as extractingtemperature, and1:30（w/v） as solid-liquid ratio were selected by orthogonal experiments.Under optimal extracting conditions, the yield of SFHP （calculated as the obtained amount ofgalacturonic acid） reached20.50±0.25%, with degree of methoxylation being31.67±0.51%.Molar mass and rms radius were determined, with results showing that Mw and Mn were4.183×10⁵g/mol and2.650×10⁵g/mol, and Rw and Rn were49.9nm and49.0nm,respectively. The main monosaccharide unit constituting SFHP molecule was galacturonicacid （82.1%）, followed by rhamnose （9.1%） and galactose （6.3%）.Based on extraction experiments, capillary viscometer and rheometer were employed toconduct viscometric analysis on SFHP solutions. Results showed that SFHP moleculesexpended while pectin solution was diluted; NaCl and Na₂SO₄had the effect of inhibiting theexpansion of pectin molecules in thin solutions. As pectin concentration was increased from0.1%（w/w） to3.0%（w/w）, the increase of pectin solution viscosity accelerated andshear-thinning and thinning-upon-heating effect became more apparent. When pH wasincreased from2.0to7.0, the viscosity of pectin solution firstly dropped and then increased,with pH5.0being the turning point.Then effects of pH and concentration of pectin, calcium and sucrose on the strength,stability and heat-reversibility of SFHP-calcium gels were studied. Gel strength was thehighest42.5±5.1g and stability was higher than99%when pH was maintained at3.0. Theformation of macrogels required the concentration of pectin and calcium to respectively reach0.3%（w/w） and12mg/g pectin. Gel strength increased with the rise of pectin concentration.28mg/g pectin of calcium witnessed the highest gel strength; As calcium concentrationreached40mg/g pectin, no marked change of gel strength was observed, while gel stabilitywas lowered from above99%to94.8±0.5%。Sucrose had the effect of lowering gel strengthand increasing gel stability on SFHP-calcium gels, with its intensity positively related tosucrose concentration. pH and concentration of calcium and sucrose had no significant effecton gels’heat-reversibility.Properties and the forming process of SFHP-sodium-salt gels were studied. NaCl orNa₂SO₄（concentration higher than0.10mol/L） had the ability to induce the gelation of SFHPwithout the presence of calcium and gel became stronger as salt concentration increased.SFHP-NaCl gel was whitely opaque while SFHP-Na₂SO₄gel appeared transparent; Gelstrength of the former was more significantly affected by pH and sucrose than that of the latter; Salt concentration, pH and sucrose had no marked effect on both of the gelsheat-reversibility. Within the cooling range from75℃to10℃, gelation of SFHP-sodium-saltgels could be divided into four stages, with the second （approx.70℃-25℃） and third （approx.25℃-13℃） stage being key period for gelation and SFHP-NaCl gel and SFHP-Na₂SO₄gelbehaving differently in these two stages.Finally the application of SFHP in the reduction of oil absorption of FPS was studied.The oil content of FPS treated with0.1%（w/w） SFHP solution and0.10mol/L CaCl₂solution（SFHP-CaCl₂FPS） was37%lower than that of FPS without any coating treatment. Thisreduction rate was16%higher than that of1.0%（w/w） MC coating （MC FPS）. Colormeasurement showed that the color of SFHP-CaCl₂FPS was similar to the color of uncoatedFPS, whereas MC FPS was more yellowish and darker. Sensory evaluation experimentsindicated that with respect to consumer acceptability, SFHP-CaCl₂FPS was superior to MCFPS, but inferior to uncoated FPS.