The Production Of Different Degree Of Polymerization Of Inulin And Its Effection On Lactobacillus Growth

Inulin is a mixture of fructooligosaccharide (FOS) and polyfructose. Its degree of polymerization ranges from2to60. Inulin, which has lots of physiological function, hardly be degraded in the upper gastrointestinal and reaches the large intestine. Inulin can be used as prebiotics to promote the proliferation of intestinal bifidobacteria, lactobacilli and other beneficial bacteria. Because of the different degree of polymerization of inulin, its manufacturability and some functional are different. This study producted a series of inulin with different degree of polymerization by the fractional precipitation method. Part of these inulin’s physical properties were studied. And we had explored the utilization effect of lactobacillus and bifidobacterium on inulin with different degree of polymerization as a sole carbon source. The main results were as follows:We divided the raw materials inulin into14parts with different degree of polymerization with fractional precipitation by using ethanol of different concentration. The content of inulin, precipitated out under40%～85%ethanol concentration, was more than others and accounted for80.86%. Inulin precipitated out under70%ethanol concentration was the most,10.43%. The average molecular weight of inulin raw material and inulin with different degree of polymerization was determined by viscosity method. Then we got the values of degree of polymerization. The average degree of polymerization of raw material was11, while the degree of polymerization of the inulin fraction was different from1to34.We tested the special viscosity of inulin with Ubbelohde viscometer. As the degree of polymerization reduced, the levels of characteristic viscosity of inulin decreased. When water was used as the pure solvent, all levels of inulin’s solubility increased with temperature rised. The nature of inulin raw material was most obvious for its larger DP span. Under the same temperature, the smaller degree of polymerization inulin has, the bigger solubility it owns. In different concentration of ethanol solvent under25℃, solubility of all levels inulin decreased with the increasing of concentration of ethanol.Glucose and fructose had effective stress on the growth of four kinds of lactobacillus. As polymerization degree increased, this stress gradually reduced. When the degree of polymerization was greater than12, the bacteria could not grow. The effect of the same carbon source on lactobacillus was obvious, while plant lactobacillus was weaker. When the four kinds of lactobacillus were cultivated, the growth promoting effect was superior than their pure culture. When polymerization degree less than4, inulin’s growth promoting effect on bifidobacteria was more obvious than that of glucose and fructose. When polymerization degree greater than5, inulin’s growth promoting effect on bifidobacteria decreased with the increase of the degree of polymerization.The greater degree of polymerization inulin has, the worse effect of fermentation. As polymerization degree of inulin increased, the logarithmic phase of the lactobacillus became shorter, A630value of stable phase was smaller, and the content of residual sugars growing at the same time was higher. Different lactic acid bacteria’s fermentation conditions on the same inulin was different while Bifidobacterium’s was better than lactobacillus. When Bifidobacterium used inulin with degree of polymerization less than5as a carbon source, the number and proliferation rate of bacterial on ogarithmic phase were superior than the control group. When inulin with DP less than3was used as a carbon source, we measured that the amount of residual sugar was lower than the control group after48hours.