Preparation Of High-purity Fructooligosaccharides Using Membrane Technique

The general grade fructooligosaccharides containing a small amount of by-products (glucose and sucrose) are usually lack of health-promoting effect, and can't be applied in diabetic patients or eurodonticus. Thus, the development of high-purity fructooligosaccharide is of great significance in aspect of physiological effect, nutrition, strengthening the comprehensive utilization of agricultural products, extending of the agricultural industrial chain and improving the added values of products. Based on this aim, nanofiltration with the advantage of separating small moleculars was used to purify fructooligosaccharides, and the coupling of membrane separation technology and enzymatic reactions was used to prepare high purity fructooligosaccharides production in this article.The objective rejection rates of specific sugar contents in low purity fructooligosaccharides and membrane flux, which depend on syrup concentration and transmembrane differential pressure, were calculated in fitting methods, while other model parameters were investigated in the same way. The structural parameters of nanofiltration membrane were estimated in membrane pore structure model. The results were consistent with the structural parameters of other nanofiltration membrane which were reported previously.In this study, the transmembrane pressure, feed concentration and operating temperature had significant influences on membrane flux and rejection rates, while circulation flow rate and pH didn't show any notable effects under the experiment conditions. The optimum conditions for nanofiltration are filtration pressure 1.1 MPa, feed concentration 10 g/100 g, temperature 40℃, circulation flow rate 6 L/min, and pH 6.0.After the nanofiltration process, the purity of FOS was increased to 85.05%,compared with 53.49% previously. However, the rejection rate of surcose in the nanofiltration membrane was still very high, thus a further improvement of purity of FOS couldn't be achieved. In order to obtain higher purity fructooligosaccharides, monosaccharides and sucrose were filtered and transformed by the combinations of membrane separation and enzyme reaction in this study. And the purity of FOS was raised to 93.79%. This method was compared to others which were listed in other literature. Compared with other methods reported, the yield of FOS got remarkable improved without introducing any by-products in this method . Moreover, this method was very simple, and suitable for industrial production.Feed concentration was key factor in membrane fouling, and temperature had limited impact on membrane fouling, while the other three factors has little impact on membrane pollution. In this article, two membrane cleaning program were investigated. Experimental results show that both options have their advantages, thus the choice should be made according to the actual situation.