Structurally diverse arabinoxylan hydrolyzates: Their activity as immunomodulators and their effect on growth of bacteroidetes

Arabinoxylan (AX) is a plant polysaccharide which consists of a xylan backbone on which arabinose is substituted. Thirty structurally different wheat arabinoxylan hydrolyzates (AXH) were prepared by means of different combinations of xylanase (Cellvibrio japonicas xylanase (CJX) and Aspergillus niger xylanase (ANX)) and arabinofuranosidase (Bifidobacterium adolescentis arabinofuranosidase (BAF) and Clostridium thermocellum arabinofuranosidase (CAF)). The AXH were analyzed using GC-FID, GC-MS, 1H-NMR and SEC-MALS techniques. In general, the AXH had high proportion of unsubstituted xylose and lesser amount of di- or mono-substituted xylose. The average molecular weights of the AXH varied between 0.78-5.64 million Da. Between the two xylanases, ANX might be an enzyme of choice for the production of arabinoxylan hydrolyzates with simple structural details while the enzyme CJX might be selected for the production of arabinoxylan hydrolyzates with more complex structural features. Addition of BAF followed by CAF was more effective in generating AXH with higher amount of unsubstituted xylose as well as lesser amount of disubstituted xylose. The structural contribution to the immunomodulatory properties of the AXH was also evaluated using LPS induced macrophage cell line. The AXH being tested exhibited both pro- and anti-inflammatory properties. Structure-function relationship of arabinoxylan hydrolyzates as immunomodulators was further assessed using LPS induced colon cancer cell lines: Caco-2 and HT-29. Fine structural details had a strong correlation with the immunological properties of the AXH. The influence of the fine structural details of AXH on the growth of human gut Bacteroides strains was also evaluated. In general, B. cellulosilyticus DSM 14830 had the highest growth while B. eggerthii DSM 20697 had the lowest growth on AXH. Interestingly, B. cellulosilyticus DSM 14830, B. ovatus 3_1_23, B. ovatus ATCC 8483 and B. xylanisolvens XB1A displayed clearly distinguishable phase shifts along the growth curves indicating their ability to tune in their gene expressions to overcome the hindrances to growth exerted by structural details on the substrate polysaccharide. This research confirmed the ability of Bacteroides to utilize structurally diverse arrays of polysaccharides. Overall, the current study indicates that there might be a structure- function relationship between AXH and their immunomodulatory properties as well as prebiotic properties.