Study On The Preparation, Purification And Structure Characterization Of The Peanut Non-starch Polysaccharides

The polysaccharide is one of the most important bioactive compounds in peanut.In recent years, it has been drawing close attention because of its bioactive function in hepatoprotective effect and antioxidant activities. In order to study the peanut polysaccharide comprehensive and enhance the utilization of peanutby-products,the composition and content of carbohydrate in the peanut has been researched in this paper. This study optimized the hot water extraction process for polysaccharides from defatted peanut cake by response surface methodology (RSM), based on the single factor experiments of extraction temperature, extraction time and ratio of material to liquid. What’s more, considering of the cogeneration mode of polysaccharides and peptides, the protease was used to treat the defatted peanut cake. Then, single factor experiments and RSM were used to optimize the hot water extraction process. Otherwise, the amylase was used to remove the starch. The one purified fraction was separated and purified by Sephadex G-100chromatography. Their structural characteristics were investigated primarily.The content of total sugar was32.45%of defatted peanut cake. The main monosaccharides were fructose (0.12%) and glucose (0.19%). Oligosaccharides content was higher. The main sweet matter of peanut is sucrose, its content was9.83%. The other oligosaccharides were maltose (0.74%) and stachyose (0.42%). The content of lactose was less than0.1%. Otherwise, the starch and fiber contents of defatted peanut cake were8.01%and3.64%repectively.A five level, three variable Central Composite Design (CCD) was applied to determine the best combination of variables for the highest extraction rate of polysaccharides from defatted peanut cake. Three variables considered for this research were extraction temperature (X1), extraction time (X2) and ratio of water to raw material (X3) while the proper ranges of three variables were set based on single-factor experiments for the polysaccharides production. The analysis of variance of the quadratic regression model demonstrated that the model was highly significant, as the F-test had a very low probability value (p<0.0001), and the lack of fit was not significant (p=0.0628>0.05). The total determination coefficient (R2) was0.9538, and the adjusted coefficient of determination (R2adj) was0.9957, indicating a reasonable fit of the model to the experimental data. It was found that the optimum technical conditions were as follows:extraction at91℃for4h with ratio of material to solvent1:30(g/mL). The polysaccharides extraction rate could achieve to39.47%, agreed with the predicted value. The content of polysaccharide was83.34±0.7%and the starch was62.47±0.55%。The effect of pretreatment on removing protein from peanut cakes was compared between single neutral protease and the complex method, with adding Neutrase and Protamex successively. The coefficient protease of Neutrase and Protamex was finally chosen to hydrolyze peanut cakes. Moreover, the co-production of polypeptide can be realized by this technology and the content of total sugar was51.04%in final peanut polysaccharide obtained, with starch content15.54%. The hot water was used to extract the non-starch polysaccharides from residue after the hydrolysis of peanut cakes. The effect of temperature, extraction time and rate of solution to solid on extraction ratio of non-starch polysaccharides was investigated. On the basis of single factor experiments, the extraction conditions were optimized by response surface methodology design experiment. The regression model built reached a significant level (p<0.0001) and the lack of fit was not significant (p=0.0735>0.05). The total determination coefficient of regression equation was R2=0.9995, with modified determination coefficient R2adj=0.9987, indicating the model had a high imitation degree. The optimum non-starch polysaccharides extraction conditions by hot water were as follows:temperature85℃, extraction time3h, the rate of solution to solid1:20(g/mL). Under these conditions, the actual extraction ratio of non-starch polysaccharides was34.49±0.15%, which corresponding to the model. The a-amylase and glucoamylase were used to remove the starch in the peanut polysaccharides. The contents of total sugar and starch were44.40%and4.19%repectively. But, there was still have little protein (40.73%). The non-starch polysaccharide was sequentially purified by chromatography of Sephadex G-100, and one purified fraction was obtained. The contents of total sugar and protein were70.20%and2.90%repectively.The non-starch peanut polysaccharide was characterized by FT-IR, HPAEC, SEC-MALLS. The average molecular weights for purified fraction was2.383×105Da. The polysaccharide was mainly composed of glucose (Glu), galactose (Gal), arabinose (Ara), xylose (Xyl). And there were littler rhamnose (Ram), galacturonic acid (GalA) and glucuronic acid (GluA). The purified fraction was found to be present in a molar ratio of Glu:Gal:Ara:Xyl:Rha:GalA:GluA=35.16:22.10:24.95:10.44:3.69:3.10:0.56.The peanut polysaccharide has the typical absorption of polysaccharide. The structure has been changed after enzymatic hydrolysis by SEM. The images revealed that the structure was loose and honeycomb-like.