Development and application of a nanofiltration process as membrane bioreactor for the production of galacto-oligosaccharides with increased degree of polymerization

半乳糖寡糖（GOS）是由半乳糖与葡萄糖或半乳糖在还原端组成的β糖苷连接的不可消化的低聚糖，聚合度为3 ~ 10（主要为3、4和5）。这些低聚糖是通过半乳糖苷酶的转半乳糖基化活性从乳糖合成的。低聚半乳糖具有生物活性。作为益生元，它们促进肠道内共生菌的生长，调节免疫系统，抑制病原体在胃肠道上皮细胞表面的粘附。在膜生物反应器（MBR）中，酶促生产低半乳糖和纳滤分离残余的单糖和双糖可能是一种更有效的低半乳糖生产工艺。高纯度的低聚糖制剂可以在一个工艺步骤内获得。此外，高葡萄糖和半乳糖浓度对酶的抑制作用可以通过同时从葡萄糖中分离单糖来降低。可以合成聚合度较高的低聚半乳糖。研究工作的主要目标是开发和应用纳滤工艺作为膜生物反应器，提高聚合度生产低聚半乳糖。研究计划的里程碑是：建立2至3升规模的纳滤，以保留低聚糖，并通过渗透膜去除残留的单糖和双糖。采用纳滤系统作为膜生物反应器，提高了半乳糖低聚糖的聚合度。利用膜生物反应器制备半乳糖化甲壳素低聚糖，并提高壳聚糖低聚糖的聚合度。低聚糖的仪器分析及低聚糖对病原菌粘附的影响。计划研究工作的优势：将乳糖转化为具有生物活性的低聚糖可以导致双糖的增值。几丁质和壳聚糖生产成本低廉，具有多种生物活性（如抗菌、益生元、抗粘附活性），是半乳糖受体的理想选择。酶促β -转半乳糖基化生产低聚糖的分离工艺和在膜生物反应器中净化产品的纳滤相结合可能更有效。在膜生物反应器中制备低聚糖时，通过对单糖的渗透，可以提高单糖的产率和聚合度。

Beta galactooligosaccharides (GOS) are beta glycosidically linked non digestible oligosaccharides composed of galactose with glucose or galactose at the reducing end and a degree of polymerization of 3 to 10 (mostly 3, 4 and 5). These oligosaccharides are synthesized from lactose by transgalactosylation activity of the enzyme beta galactosidase. Galactooligosaccharides exhibit biological activities. As prebiotics they promote the growth of commensal bacteria in the intestine, they modulate the immune system and inhibit the adhesion of pathogens on the gastrointestinal epithelial cell surface. A combination of the enzymatically production of galactooligosaccharides and a nanofiltration for the separation of the residual monosaccharides and disaccharides in a membrane bioreactor (MBR) could be a more efficient process for galactooligosaccharide production. Highly pure oligosaccharide preparations could be achieved within one process step. Moreover, the inhibition of the enzyme by high glucose and galactose concentrations could be decreased by the simultaneously separation of the monosaccharides from the glucose. Galactooligosaccharides with higher degree of polymerization could be synthesized. The main goal of the research work is the development and application of a nanofiltration process as membrane bioreactor for the production of galactooligosaccharides with increased degree of polymerization.The milestones of the research plan are: The establishment of a nanofiltration on a 2 to 3 L scale for the retention of oligosaccharides and removal of residual mono- and disaccharides by permeation through the membrane. The use of a nanofiltration system as membrane bioreactor to produce galacto-oligosaccharides with increased degree of polymerization. The use of the membrane bioreactor to produce galactosylated chitin oligosaccharides, and chitosan oligosaccharides with increased degree of polymerization. The instrumental analysis of oligosaccharides and the effect of oligosaccharides on pathogen adhesion. Advantages of the planned research work: The conversion of lactose to oligosaccharides with biological activities can lead to a valorization of the disaccharide. Chitin and chitosan, which should be applied as galactosyl acceptors, are inexpensive to produce and exhibit various biological activities (e.g. antibacterial, prebiotic, antiadhesive activities). The combination of the separate processes for the oligosaccharide production by enzymatic beta transgalactosylation and the nanofiltration for the purification of the product within one process in a membrane bioreactor could be more efficient.By permeation of the monosaccharides during oligosaccharide production in the membrane bioreactor the yield and the degree of polymerization of these sugars could be increased.