| Sunflower heads are rich in pectin which is a good resource of natural low methyl esterification pectin. Extracting pectin from sunflower heads not only avoids environment pollution and resource waste caused by burning, but also enriches raw material source of natural pectin. It has important economic value and social benefits. In this paper, boiling water was used to extract and separate low molecular weight sunflower head pectin. Its classification, purification and structure analysis were also studied. The conclusions of this paper were as follows:1. Sunflower heads were extracted by boiling water and then we obtained sunflower head pectin AHP. AHP was a kind of cinnamon powder with a yield of 12.5%. The sugar content of and uronic acid content of AHP was 85.2% and 67.6%, respectively. Its molecular weight distribution was very wide indicating it’s a kind of polysaccharide mixture. Its monosaccharide composition was Gal A(59.7%), Ara(6.6%), Rha(14.9%), Gal(12.2%), Glc(4.5%) and Man(2.1%).2. Low molecular weight sunflower head pectin was prepared using ethanol precipitation. AHP sample was re-dissolved to be 10% aqueous solution. After precipitation with 60% ethanol overnight, a polysaccharide fraction named AHP-60% was obtained. The supernatant was continued to be precipitated with 80% ethanol. After dryness, another fraction was obtained, named AHP-80%. AHP-60% belonged to a polymer with a large molecular weight, while AHP-80% had a small molecular weight, which was low molecular weight sunflower head pectin. Our previous work had already been done to study the AHP-60% fraction. In this thesis, we will focus on the preparation and structure of AHP-80% fraction.3. The yield of low molecular weight sunflower pectin AHP-80% was 1.0% in relation to sunflower heads. After decolorization with activated carbon, low molecular weight sunflower head pectin AHP-80% became a white powder. The physical and chemical study of AHP-80% showed that sugar content and uronic acid content of AHP-80% was 87.5% and 48.1%, respectively. Monosaccharide composition of AHP-80% was Gal A(37.6%), Ara(21.0%), Rha(17.4%), Gal(13.8%), Glc(6.0%), Man(1.0%), Glc A(0.8%) and Xyl(2.4%). The degree of methyl esterification of AHP-80% was 25.9%, showing AHP-80% was a low methyl esterification pectin.4. The fractionation of low molecular weight sunflower head pectin AHP-80% was achieved by gel column chromatography. Two fractions named AHP-80%-1 and AHP-80%-2 were obtained. The results of gel column chromatography, high performance liquid chromatography(HPLC), fourier transform infrared spectroscopy(FT-IR) and 13 C nuclear magnetic resonance spectrometer(13C NMR) showed that the molecular weight of AHP-80%-1 was 4.0×104 Da and its molecular weight distribution was homogeneous. The degree of methyl esterification of AHP-80%-1 was about 10.6%. It was a low methyl esterification pectin. Its monosaccharide composition was Gal A(36.3%), Rha(40.4%), Gal(21.5%), Ara(1.3%) and Man(0.5%) which showed AHP-80%-1 was mainly composed of type I rhamnogalacturonan(RG-I) domain. The molecular weight of AHP-80%-2, lower than that of AHP-80%-1, was 3.5×103 Da and its molecular weight distribution was homogeneous. The degree of methyl esterification of AHP-80%-2 was about 31.2%,higher than that of AHP-80%-1. It was a low methyl esterification pectin. Its monosaccharide composition was Gal A(56.4%), Rha(12.3%), Gal(15.9%), Glc(10.2%), Man(5.0%) and Ara(0.2%) which showed AHP-80%-2 was mainly composed of homogalacturonan(HG) domain. |
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