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Gluco‐oligosaccharides (GlcOS) are potential prebiotics that positively modulate beneficial gut commensals like lactobacilli. For the rational design of GlcOS as prebiotics or combined with lactobacilli as synbiotics, it is important to establish the structure requirements of GlcOS and specificity toward lactobacilli. Herein, the utilization of 10 GlcOS with varied degrees of polymerization (DP) and glycosidic linkages by 7 lactobacilli strains (Levilactobacillus brevis ATCC 8287, Limosilactobacillus reuteri ATCC PTA 6475, Lacticaseibacillus rhamnosus ATCC 53103, Lentilactobacillus buchneri ATCC 4005, Limosilactobacillus fermentum FUA 3589, Lactiplantibacillus plantarum WCFS1, and Lactobacillus gasseri ATCC 33323) was studied. L. brevis ATCC 8287 was the only strain that grew on α/β‐(1→4/6) linked disaccharides, whereas other strains showed diverse patterns, dependent on the availability of genes encoding sugar transporters and catabolic enzymes. The effect of DP on GlcOS utilization was strain dependent. β‐(1→4) Linked cello‐oligosaccharides (COS) supported the growth of L. brevis ATCC 8287 and L. plantarum WCFS1, and shorter COS (DP 2–3) were preferentially utilized over longer COS (DP 4–7) (consumption ≥90% vs. 40%–60%). α‐(1→4) Linked maltotriose and maltodextrin (DP 2–11) were effectively utilized by L. brevis ATCC 8287, L. reuteri ATCC 6475, and L. plantarum WCFS1, but not L. fermentum FUA 3589. Growth of L. brevis ATCC 8287 on branched isomalto‐oligosaccharides (DP 2–6) suggested preferential consumption of DP 2–3, but no preference between α‐(1→6) and α‐(1→4) linkages. The knowledge of the structure‐specific GlcOS utilization by different lactobacilli from this study helps the structural rationale of GlcOS for prebiotic development. [ABSTRACT FROM AUTHOR]

• Cellooligosaccharides were synthesized from cellulose hydrolysis by sulfuric acid. • Separation of oligosaccharides by dead-end nanofiltration with commercial membranes. • Effects of applied pressure and feed (sugar and acid) concentration on separation performance. • Small-pore membrane to remove sulfuric acid and glucose from cellooligosaccharides. • Large-pore membrane for fractionation and further purification of cellooligosaccharides. Cellooligosaccharides (COS) as potential prebiotics have drawn increasing attention. They can be synthesized from cellulose via controlled hydrolysis by sulfuric acid (SA). However, it is challenging to efficiently separate COS from the hydrolysate. In this study, nanofiltration (NF) with commercial membranes was investigated to separate COS from cellulose hydrolysate by removing SA and non-prebiotic sugars (e.g., glucose) and further fractionating COS by size. Based on water permeability, pore size, and acid stability, two membranes (Trisep® XN45 and Synder® NFG) were selected from four candidates. The effects of operation conditions (membrane and applied pressure) and feed concentrations (sugars and SA) on the COS purification and fractionation were studied. It was found that the XN45 membrane with an estimated average pore size of 0.61 nm was efficient in removing SA and glucose from COS, while NFG with a larger pore size of 0.84 nm can be used to fractionate and further purify COS based on size (degree of polymerization, DP). Four sequential batch NF operations of cellulose hydrolysate through XN45 (×3) and NFG (×1) membranes recovered 80 % of the total COS in the hydrolysate and removed 99 % of SA and 95 % of glucose. NFG membrane can roughly separate COS into two fractions, one (retentate) with more larger COS (DP ≥ 9) and another (permeate) with more smaller COS (DP 2–8). This study successfully demonstrated the feasibility of NF to purify and fractionate COS from cellulose hydrolysate. [ABSTRACT FROM AUTHOR]

[Display omitted] • A facile method was developed to synthesize gluco-oligosaccharides (GlcOS) • Low-cost and abundant H 2 SO 4 solution was used as a medium for GlcOS synthesis. • The GlcOS synthesis was conducted under mild conditions with a high yield of 83% • The synthesized GlcOS had a DP of 2–9 with diverse glycosidic linkages. • The prebiotic activity of GlcOS was verified by select probiotic bacteria in vitro. Glucose-based short-chain oligosaccharides (gluco-oligosaccharides, GlcOS) have been established as functional food ingredients with health-promoting properties. Currently, GlcOS (e.g., isomalto-oligosaccharides, IMOs) are commercially produced via enzymatic processes, which face the challenges of low yield and high cost. Therefore, developing efficient technologies for large-scale production of prebiotic GlcOS is highly desirable. Herein, a facile chemical process was developed to synthesize GlcOS as potential prebiotics via enhanced dehydration condensation of glucose in concentrated sulfuric acid (60–92 %). The maximum GlcOS yield of 83 % was achieved under the optimal condition of 50 % initial glucose loading, 76 % H 2 SO 4 , 70 °C, and 20 min. Structural analysis revealed that the synthesized GlcOS are mainly short-chain oligomers with a degree of polymerization (DP) between 2 and 4 (46 % DP 2, 22 % DP 3, 12 % DP 4) and a small percentage of larger oligosaccharides (DP 5–9), which are linked by predominantly α- and β-(1→6) linkages along with (1→4), (1→ 3), (1→2), and (1↔1) linkages. In vitro fermentation experiments by probiotic Bifidobacterium bifidum ATCC 29521, Bifidobacterium animalis subsp. lactis DSM 10140, and Limosilactobacillus reuteri ATCC 6475 indicated that the GlcOS can be utilized as a carbon source for bacterial growth, and their promotion effect was overall comparable to three commercial prebiotic IMOs. GlcOS were also successfully synthesized from maltose and cellobiose with similar yield and structures to those from glucose, implying the possibility of synthesizing the prebiotic GlcOS directly from inexpensive starch and cellulose. [ABSTRACT FROM AUTHOR]