Study On Pectin From Sunflower Head And The Methyl-esterification Of Pectin

Low-methoxyl pectin(LMP)has excellent gelling properties and wide application.Although some LMP exist in plants,it is usually manufactured from high-methoxyl pectin(HMP)by chemical treatment,so the production cost is high.Looking for natural sources of low-methoxyl pectin is necessary,and has important economic and social benefits.Sunflower(Helianthus annuus L.)is one of the major oil economy crops in our country.It is reported that the natural LMP is high in sunflower head,and mature sunflower head contains 15-25%of pectin.When the sunflower seeds harvest for oil extraction,the head of sunflower is mostly abandoned or used as heating fuel,which not only takes less advantage of netural resources,but also causes environmental pollution.So the development of pectin from sunflower head is not only enriching the types of commercial pectin and improving the quality of LMP,but also useful for making full use of sunflower head and preventing environmental pollution.Although sunflower head is an excellent natural source of LMP,there are no mature industrialized extraction methods and research on the physical and chemical properties and structure of it now.The reality severely restricts the practical application and structure-function relationship studies of the LMP from sunflower head.In view of the above reasons,we designed the research topic,and obtained the following results.1.The response surface methodology(RSM)technique was applied to optimize the extraction conditions to obtain a high yield of pectin with high uronic acid content form sunflower head.Analysis of variance showed that extraction temperature,extraction time and oxalic acid concentration were all significantly affect the yield and uronic acid content of sunflower head pectin(LAHP).The optimum extraction conditions of LAHP were as follows:extraction temperature 96.0oC,extraction time 1.6 h and oxalic acid concentration 0.2%.Under the optimal conditions,the yield of LAHP was 18.83±0.2%,and the uronic acid content was 85.43±2.9%.The physical and chemical properties of LAHP obtained under the optimal conditions were in agreement with the state quality standards of pectin.So the optimal extraction conditions could be used in the industrial production of sunflower head pectin.2.The rheological properties and gelling properties of sunflower head pectin were measured by rheometer and texture analyzer.The results showed that LAHP solution was a typical pseudoplastic fluid and has shear-thinning properties.The apparent viscosity decreased with the increase of shear rate and temperature,increased with the increase of LAHP concentration,and firstly decreased and then remained the same as the pH increasing.The viscosity of LAHP solution was also influenced by bivalent cation,firstly increased andthen decreased with the increase of Ca2+ concentration.When the pectin concentration reached 0.5%,LAHP could form gel,and the gelling properties increased firstly and then decreased with the increase of pectin concentration,Ca2+ concentration and pH.The addition of proper sucrose could improve the appearance of LAHP gel,but too much sucrose would result in pre-gel.The optimal gel conditions were determined as follows: LAHP concentration was 1%,Ca2+concentration was 40 mg/g,solution pH was 4.0 and sucrose content was 10%.3.Sunflower head pectin LAHP was fractionated into four fractions by ion-exchange chromatography.The main fractions LAHP-2 and LAHP-3 were typical HG pectin that had high GalA content(higher than 85%)and high molecular weights(103 and 226 kDa,respectively),and low degree of methylation(DM)and degree of acetylation(DA).One neutral fraction(E-N)and four RG-I fractions(E-A,E-B-I,E-B-II and E-C)were isolated from LAHP by Endo-PG hydrolysis and a combination of ion-exchange and gel permeation chromatography.E-A and E-B-II were mainly composed of HG domain and RG-I domain that had lower DM and molecular weight,and a certain DA.While E-B-I and E-C were mainly composed of RG-I domain and a small amount of oligomeric GalA,and their degrees of branching were very low.And the DM and DA of the two fractions were also very low.So the high content of HG domain,low DM and high molecular weight of sunflower head pectin may be the structure basis of its excellent gelling properties.4.A new method catalyzed by cation exchange resin was developed to methyl esterify pectin.Compared to the commonly used methods such as methyl iodide or HCl acidified methanol,the new one could produce high yields of products without destroying the structures of either HG-or RG-I-type pectins.And the method provides a convenient way to prepare pectins with any degree of methylation of pectin simply by controlling reaction conditions like the mass ratio of resin to pectin,along with the reaction time and temperature.Moreover,the used resin and methanol could be recycled to conserve resources,reduce costs,and prevent environmental pollution.So the novel method could be used for industrial production.The results will provide the theoretical basis and technical support for development and utillzation of low-methoxyl pectin from sunflower head and the depth studies of structure-function relationships of pectin.