| Jerusalem artichoke is a kind of ecological and economic plant with the development potential, which is one of primary inulin resources. Inulin has exhibited many bioactivities, such as intestinal prebiotics, promotion of mineral absorption, antioxidant property and so on. The research of inulin has attracted more attention. As a plant polysaccharide, the degree of polymerization(DP) is an important factor affecting inulin’s activity. However, due to small difference of molecular weight between inulin, the separation of inulin with single DP is very difficult and so the report about this study is rare. In this paper, in order to improve the efficiency of inulin production from both the yield and the quality, we have studied the changes of content, DP, and bioactivity of inulin throughout the entire growth process of Jerusalem artichoke tubers. We also successfully obtained a series of inulin-type oligosaccharides with single DP by various analytical techniques, including gel chromatography, high performance liquid phase chromatography(HPLC) and mass spectrometry(MS). In addition, a preliminary study of the relationship between the degree of polymerization and bioactivity was investigated. The major research and results were as follows:At first, according to the study on the mobile phase, the flow rate, the column, the standard substances, and the standard curve, the DP of inulin was analyzed by Agilent 1260 HPLC with a differential refraction detector(RID). A Shodex GPC OHpak SB-804 column was used with ultrapure water as the mobile phase at a flow rate of 0.8 m L/min. The column temperature was set to 30℃ and injection volume was 20 μL. Dextran standard substances(Mw 1000, 5000, 12000, 25000, and 50000) were purchased from Sigma-Aldrich, and the curve was y =-2.405 + 1.827 x – 0.113x2. This test method was a technical support to our work.The changes of content, DP, and bioactivities of inulin throughout the entire growth process of Jerusalem artichoke tubers were investigated. We harvested the Jerusalem artichoke tubers from the initial to the maturation and extracted inulin. The results showed that the changes of inulin content and DP were related to the growth state of Jerusalem artichoke. They were almost the same, which increased rapidly at the beginning and then decreased gradually at a lower speed. Then the prebiotic effect and antioxidant activity were tested. It indicated that inulin with low DP had higher activity.In order to further clarify the relationship between inulin DP and its bioactivity, it was necessary to prepare inulin with single DP. Two common gels were assessed for inulin separation, and it was ultimately determined to use Bio-gel P-4 and Bio-gel P-2. HPLC and ESI-MS analysis revealed that the inulin-type disaccharide to octasaccharide was successfully obtained, and their purities were up to 98%.The prebiotic effect of the inulin-type oligosaccharides with well-defined DP was tested. The result suggested that the inulin-type disaccharide had the worst activity, whereas the inulin-type trisaccharide and tetrasaccharide had the best. The effects of the inulin-type pentasaccharide to octasaccharide weakened, but the differences among them were unconspicuous. This illustrated that the relationship between inulin DP and its bioactivity still followed the rule that inulin with low DP had higher activity, except disaccharide. The inulin-type trisaccharide and tetrasaccharide showed the best activity.In this work, the study on the changes of inulin content, DP, and activities throughout the entire growth process of Jerusalem artichoke tubers could be the theoretical instruction to produce inulin with high activity efficiently from Jerusalem artichoke tubers. Additionally, the separation of inulin-type oligosaccharides and their activity research preliminarily revealed the the relationship between inulin DP and its bioactivity, which is instructive to the further study. |
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