Modification Of Apple Dietary Fiber By Screw Extrusion And Sulfation Coupling Method

Dietary fiber is polymeric carbohydrates and the derivatives in the form of monosaccharide(glucose, galactose, mannose and xylan, etc.) as the basic units, and large numbers of hydroxyl on its glycosylated residue may be methylated, esterified, etherified and other derivatization of reactions. The sulfation of polysaccharides could not only enhance the water solubility but also change the chain conformation, resulting in the alteration of their biological activities, such as anti-coagulant, anti-virus, antioxidant and antitumor activities. The modification of apple dietary fiber by screw extrusion and sulfation coupling method could obtain soluble dietary fiber which has a better biological activity, and also could expanded its application on health food and functional medicine.In this study, amino acid and concentrated sulfuric acid were used as the composite esterification agent in preparation of sulfated soluble dietary fiber by coupling screw extrusion technology. We studied the decoloration, purification and structure of the sulfated apple dietary fibers.And determined of the monosaccharide composition and molecular weight were determined by means of high performance liquid chromatographic and gel permeation chromatography(GPC). The FT-IR and 13 C NMR analysis indicated that the positions substitution was predominant in sulfated SDF. Comparison studied on morphology of SDF and sulfated SDF was used to atomic force microscope. We choose the different ways(the reducing power, oxygen radical absorbance capacity, ABTS radical scavenging activity assay) to evaluate the antioxidant capacity with the different degrees of substitution samples.(1) The preparation of sulfated apple dietary fibers by extrusion was studied in this work. The results indicated that the optimistic process were as follows: the ratio of amino acid and dietary fibers was 3:10, and the ratio of concentrated sulfuric acid and dietary fibers was 4:10, standing time was 2h, screw rotation speed was 650r/min.The substitution degree on sulfated apple dietary fibers were 0.79.The FT-IR revealed that sulfated groups had been successfully grafted on the polysaccharide chains of dietary fibers.(2) Macroporous resins was selected to decolor the sulfated SDF. The optimum parameters of D-101 resin were as: one volume solution of crude polysaccharide was loaded in column at the flow rate 2 m L/min, sample volume of 60 m L, sample concentration of 2mg/m L.ASDF-P2 and ASDF-P2 were obtain after purification of sulfated SDF by anion-exchange DEAE-52. They were homogenous with a molecular weight of 73313 Da and 51300 Da by GPC respectively.The polysaccharide content(93.6%) of ASDF-P2 were higher than that of ASDF-P3(72.7%). However, ASDF-P3 had the higher content of sulfuric radical(17.8%) than ASDF-P2(13.6%). ASDF-P2 was mainly composed of mannose, rhamnose, glucuronic acid, xylose, glucose and galactose, with a molar ratio of 0.88:0.82:2.52:2.31:2.98:2.5. ASDF-P3 was mainly composed of mannose, rhamnose, glucuronic acid, xylose, glucose and galactose, with a molar ratio of 1.82:0.79:1.41: 3.69:3.29:3.24.(3)The FT-IR showed the ASDF-P2 and ASDF-P3 was characteristic absorption peaks at 810 cm-1 and 1210 cm-1. NMR showed that the ASDF-P2 and ASDF-P3 was made up of four types of sugar residues, and 13 C NMR spectra had signal at 72.10 and 72.06, with verifed the presence of galactopyranose. ASDF-P2 was sulfate substituted at C-2 positions.C-2 signal moved towards the low field, and the peak intensity reduced obviously.The AFM images showed that ASDF-P2 sugar chain cluster was winding like flamboyancy.The diameter were 4.92-19.49 nm, the heightwere 1.887-3.01 nm and the length were 79.30-94.07 nm. But a single spiral or aspherical structure did not appear.(4) It was suggested that the antioxidant capacity of the sulfated SDF had been enhanced after the modification. Finally, the reducing power, oxygen radical absorbance capacity, ABTS radical scavenging activity assay has significant higher with high degrees of substitution in sulfated SDF. KEY WORDS: apple dietary fiber, extrusion, sulfation, structure analysis,...