Characterization Of Dietary Fiber And Pectin Extraction From Sweet Potato

Sweet potato is one of the main crops planted in china, the harvest area and production quantity of sweet potato in china are in the first place, the values are 3.69 millions ha. and 85.2 millions tonnes respectively (FAO, 2008). The major commercial utilization of sweet potatoes in china includes starch and starchy food production, which generates a huge volume of residue, which contain considerable residual starch, dietary fiber and pectin. Traditionally, the residue is used as animal feed or discarded as watste, which in turn causes environmental pollution and wastes the resources. The objective of this work was to characterize dietary fiber and pectin of sweet potato, as well as to investgate the physico-chemical properties of sweet potato dietary fiber and pectin, in order to analyze the feasibility of dietary fiber production from residues of sweet potato starch processing industry and its use for nutritional and technological applications.Dietary fiber were extracted from residues of ten varieties by sieving method, the average yield and purity of dietary fiber products were 9.97% and 75.19% respectively. The average content of cellulose, hemicellulose, lignin and pectin of dietaryfiber were 41.49%, 15.22%, 22.40% and 20.77%, respectively, the average value of swelling capacity, water holding capactiy, oil holding capacity and glucose absorption capactiy were 10.32mL/g, 4.82g/g, 1.95g/g and 0.87mmol/g, respectively, dietary fiber products with high pectin content had high water holding capactiy, and those with high cellulose content had high glucose absorption capacity. Sweet potato mainly composed of glucose, galacturonic acid, galctose, xylose, arabinose, glucuronic acid and rhamnose, the average content were 56.31%, 20.28%, 10.39%, 4.60%, 3.68%, 2.68% and 2.05%, respectively.In this work, pectin was extracted from sweet potato residue by acid solution. According to the results of one-factor experiment, the effects of pH value, extraction time, extraction time, and liquid-solid ratio on pectin yield and galacturonic acid content of pectin were investigated by quadratic regression orthogonal rotation combination desigen experiment, the optimal extraction technology was selected under integrative consideration the parameter of pectin yield and galacturonic acid content, the optimal technology was pH value 1.0, extraction temperature 95℃, extraction time 2.2h, liquid-solid ratio 30, Under this extraction condition, the yield of pectin was 5.11%, and the galacturonic acid content was 71.39% determination by carbazole and sulphuric acid spectrophotometric method.The molecular weight of sweet potato pectin preparation by optimal technology of acid solution method was 292.2 kDa, the results of Fourier transform infrared spectroscopy scanning showed that sweet potato belonged to low methoxyl pectin, degree of esterification was 28.26% calculation based on the data of FT-IR, which litte lower than the esterificaiton determination by titration method 31.71%. Sugar composition of sweet potato pectin was determined by high performance anoin exchange charomatogram, the result indated that galacturonic acid content was 72.94%, and the neutral sugar content was 23.30%, in which, the content of galactose and rhamnose were 7.48% and 9.48%, respectively. The fragment of pectin with high molecular weight had high galacturonic acid, low netural sugar content, and high esterificaiton.With increasing the pectin and Ca2+ concentration, the strength of sweet potato pectin gel increased, Ca2+ concentration was the main factor which influenced the formation of sweet potato pectin gel. The formation of sweet potato pectin gel and gel strength were influenced significantly by pH value, the pectin gel had highest strength at pH 5.0. The sweet potato pectin gel had highest strength at 20% sucrose concentration, but sucrose concentration was not the main factor which influenced sweet potato pectin gel formation and gel strength. When the pectin concentration was 1.5%, in the the optimal consititution of gel system, the Ca2+ concentration was 0.15, with pH 5.0 and sugar concentration was 20%.Sweet potato pectin had the capacity of emlsion formation and stabiliziation emulsion, the emulsion had small particle size and high stabilization with pectin concentration higher than 2.5%, oil-phase fraction range from 10-30%, pH 5.0. With increasing NaCl and Ca2+ concentration, particle size of emulsion increased, but emulsion activity and emulsion stabilization increased. The stabilization of pectin emulsion not only related to particle size of emulsion and pectin concentration adsorbed onto emulsion droplets, but also viscosity of emulsion. Pectin adsorbed onto emulsion droplets had high netrual sugar content (38.92%), low molecular weight (72.5kDa), which probably originated from the low molecular branch domain of pectin.