| Increasing attention has been given to dietary fibre as the seventh of nutrients. A variety of natural raw materials from different sources have been used to preparation of dietary fibre. Dried apple pomace, a fruit industry by-product, is considered as a potential source of raw materials, which has not been fully utilized. This objective of the present study was to prepare dietary fibres with good properties by enzymatic and chemical method, and to characterize the dietary fibre physicochemically, and to study the influence of processing to its structure, functional properties.The content of apple pomace included 5.97% protein, 5.27% starch, 12.5% fat, 72.13% total dietary fiber (TDF), 13.06% soluble dietary fiber (SDF), 57.51% insoluble dietary fiber (IDF), 3.27% moisture and 2.17% ash.The process of extracting dietary fibre using enzymatic and chemical methods precipitation from apple pomace was studied. The optimal conditions of enzymatic precipition were gained by orthogonal test were as follows: the cellulose addition 8%, temperature 50℃, hydrolyzing time 3h, pH 4.8, solid to liquid ratio of 1:20, the yield of ESDF was 15.93%, 63.4% EIDF was recovered as the same time. In the process of chemical hydrolysis, the apple pomace was treated by hydrochloric solution at first, the parameters of acid hydrolysis was pH 1, extraction time of 70 min, extraction temperature of 90℃, the solid to liquid ratio of 1:20. The ACSDF yield was up to 23.4% under this condition. Then,the residue was hydrolysed by the alkaline solution under the optimal conditions for the NaOH concentration 0.8%, temperature 70℃, reaction time of 90min, the solid to liquid ratio of 1:8, 13.5% ALSDF was recovered as well as 7.43% IDFA, 51.8% IDFB. And it was observed that freeze-dried products have a better performance than the vacuum drying of products in the study. GPC data indicates that the relative molecular mass distribution of ESDF, ACSDF, ALSDF concentrates in the region of 12780 ~ 159300, 23310 ~ 815000,259600 ~ 554500.The water-holding capacites of dietary fibre extracted from apple pomace by chemical method is superior to the capacites of products by enzymatic method, as well as swelling capacities. Although the difference of the cation exchange capacity of products between two methods was less, the portion extracted by alkaline solution has a relatively high cation exchange capacity. Enzymatic-hydrolysis products on the adsorption of bile acids is much higher than that of chemical method. The adsorption of ESDF, ACSDF, ALSDF, EIDF,IDFA and IDFB were 50.29 mg/g, 35.43 mg/g, 48 mg/g, 55.43 mg/g, 25.71 mg/g, 35.42 mg/g, respectively. The adsorption of bile acids of dietary fibre was weakened by the role of chemicals. The solubility of ESDF, ACSDF and ALSDF is very low at room temperature, respectively, 16.2%, 12.7%, 42.9%. The solubility can increase with temperature, and ALSDF represent a good dissolved state at high temperature. Every kinds of SDF has a lower viscosity in the pH 2.0 than that in pH 7.0. The viscosity of 5% SDF solution is higher than that of 2.5% and 1.2%. Non-Newtonian fluid characteristics is observed in the test of gastrointestinal motility simulation at a low-speed movement. The contribution by ALSDF to change the viscosity of the solution system is the biggest, and the results can be verified by molecular weight.Cellulose degradation of the dietary fibre occurred in non-stereotypical areas, and the role of chemical reagents is higher than that of enzymatic processing. In the aspect of ultrastructure. Insoluble dietary fiber by chemical method have more cavity and porosity than that by enzymic method. According to these findings, such structure is conducive to holding more water. Soluble dietary fibres had the same ultrastructure and repersented a flake.IR specstrums showed the characteristic absorption peak of polysaccharides of all products by two methods, EIDF within theα-pyranose containing, EIDF containingβ-pyranose, although the high yield of alkaline method, but alkaline treatment resulted in intramolecular hydrogen bonds and hydrogen bonding changes, In addition,it had an impac to the carbonyl. Monosaccharide composition analysis of the products shows that the main ingredient of both of soluble and insoluble portions was cellulose. Meanwhile, the results also show that there was no chemical method and complete enzymatic hydrolysis, chemical method can be enriched to more hemicellulose components.The monosaccharide composition of ESDF was mainly composed of glucose, arabinose and galactose in the molar ratio of 1.6:1.9:1; the major composition of ACSDF was glucose; ALSDF was rich in monosaccharide compositions of glucose and small amounts of arabinose, xylose and galactose in a molar ratio 2.2:1.1:1:1; EIDF was mainly composed of glucose and small amounts of rhamnose and galactose in the molar ratio of 5.9:1.6:1; IDFA was consisted of glucose, rhamnose, xylose and galactose in the molar ratio of 3.7:1:2:1.2; glucose was the most abundant monosaccharide in IDFB, but also small amounts of arabinose, xylose, galactose in the molar ratio of 5.5:1: 1.2:1.3. |
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