基于右旋糖酐合成与降解的两步法制备低聚异麦芽糖

Two-step preparation of isomalto-oligosacchrides:Synthesis and degradation of dextran

低聚异麦芽糖(isomalto-oligosacchrides,IMOs)是一类由α-1,6糖苷键连接的寡聚糖,主要成分是异麦芽糖、异麦芽三糖(isomaltotriose,IG3)和潘糖等,因其具有可提高免疫力、预防龋齿等益生性能被广泛研究和应用。研究表明IMOs中可促进双歧杆菌的增殖主要归因于IG3。由于传统制备工艺产率低且产品中益生成分含量低,高效生产IMOs仍存在瓶颈。该研究提出使用来源于Lactobacillus fermentum的4,6-α-葡萄糖基转移酶(4,6-α-glycosyltransferases,LfGT)合成右旋糖酐,再使用来源于Brevibacterium fuscum的异麦芽三糖右旋糖酐酶(isomaltotrio-dextranase,BfIMTD)降解右旋糖酐的两步法制备IMOs的工艺,由此提高IMOs产率和IG3比例。在37℃,pH 6.0,反应时长为24 h的条件下,使用LfGT与普鲁兰酶和异普鲁兰酶复配可将200 g/L DE2麦芽糊精转化为产物占比为66.3%的右旋糖酐,其α-1,6糖苷键比率可达99.3%;在40℃,pH 7.5,反应10 h的条件下,BfIMTD水解右旋糖酐(终质量浓度100 g/L)可产出98.3 g/L的IG3,两步法IG3最终产率为65.2%。此两步法工艺为制备IMOs提供新思路,为IMOs链长可控性提供新策略。

Isomalto-oligosaccharieds(IMOs)are a kind of oligosaccharides withα-1,6 glycosidic linkages,mainly including isomal-tose,isomaltotriose(IG3)and panose,and they have been widely studied and applied because of the probiotic characteristics such as en-hancing human immunity,preventing dental caries,etc.It was reported that IG3 in IMOs mainly contributed to the promotion of Bifidobacterium proliferation.However,due to the low production yield and low probiotics content of traditional preparation process,there is still a bottleneck in the efficient production of IMOs.To enhance IMOs production and increase IG3 proportion,we proposed a two-step method to produce IMOs,which combined dextran synthesis by 4,6-α-glycosyltransferase(4,6-α-GT,LfGT)from Lactobacillus fermen-tum with the following dextran degradation by isomaltotrio-dextranase(BfIMTD)from Brevibacterium fuscum.Under the condition of 37℃and pH 6.0 for 24 h,using LfGT with pullulanase and isopullulanase,could produce dextran with 66.3%yield from 200 g/L maltodex-trins,and theα-1,6 glycosidic linkage ratio of the generated dextran was up to 99.3%.Then 98.3 g/L IG3 was finally produced(65.2%from maltodextrins)when BfIMTD reacted with dextran(100 g/L final concentration)at 40℃and pH of 7.5 for further 10 h.Therefore,this study suggests that the above two-step process can provide not only a new insight into the production of IMOs,but also an innovative strategy for the length controllability of IMOs.