Synthesis of potential prebiotic α-glucooligosaccharides using microbial glucansucrase and their in vitro fecal fermentation

Catalytic action of alternansucrase on sucrose under in vitro simulated gastric conditions

Alternansucrase, a glucosyltransferase, is currently used to produce slowly digestible alternan oligosaccharides or maltooligosaccharides from sucrose. These oligosaccharides are popular for food fortification to lower postprandial glucose levels. This study aimed to explore the enzymatic reaction of alternansucrase in simulated in vitro gastric reaction conditions. Under the studied conditions, SucroSEB (a model enzyme for alternansucrase) hydrolyzed the sucrose and transglycosylated the glucose to produce glucans, both in the absence and presence of acceptors. The preference of the acceptor was maltose˃ raffinose˃ lactose. The rate of sucrose hydrolysis was significantly higher in the presence of maltose (p = 0.024). The glucans formed during the reaction included oligomers (DP 3-10) and polymers (DP ≥ 11), both of which increased over time. These glucans contained α-1,3 and α-1,6 glycosidic linkages, confirmed by 1H and 13C NMR. They were slowly and partially digestible in the presence of rat intestinal extract in contrast to the complete and rapid digestion of starch. The glucans formed after a longer gastric reaction time exhibited higher dietary fiber potential (19.145 ± 4.77 %; 60 min) compared to those formed during the initial phase (2.765 ± 0.19 %; 15 min). Overall, this study demonstrated the efficacy of SucroSEB in converting sucrose to slowly and partially digestible glucans under simulated in vitro gastric conditions.

Biochemical characterization of glycoside hydrolase family 31 α-glucosidases from Myceliophthora thermophila for α-glucooligosaccharide synthesis

The transglucosidase activity of GH31 α-glucosidases is employed to catalyze the synthesis of prebiotic isomaltooligosaccharides (IMOs) using the malt syrup prepared from starch as substrate. Continuous mining for new GH31 α-glucosidases with high stability and efficient transglucosidase activity is critical for enhancing the supply and quality of IMO preparations. In the present study, two α-glucosidases (MT31α1 and MT31α2) from Myceliophthora thermophila were explored for biochemical characterization. The optimum pH and temperature of MT31α1 and MT31α2 were determined to be pH 4.5 and 65 °C, and pH 6.5 and 60 °C, respectively. Both MT31α1 and MT31α2 were shown to be stable in the pH range of 3.0 to 10.0. MT31α1 displayed a high thermostability, retaining 60 % of activity after incubation for 24 h at 55 °C. MT31α1 is highly active on substrates with all types of α-glucosidic linkages. In contrast, MT31α2 showed preference for substrates with α-(1→3) and α-(1→4) linkages. Importantly, MT31α1 was able to synthesize IMOs and the conversion rate of maltose into the main functional IMOs components reached over 40 %. Moreover, MT31α2 synthesizes glucooligosaccharides with (consecutive) α-(1→3) linkages. Taken together, MT31α1 and MT31α2, showing distinct substrate and product specificity, hold clear potential for the synthesis of prebiotic glucooligosaccharides.

Biofabrication, structure, and functional characteristics of a reuteran-like glucan with low digestibility

A novel reuteran-like glucan with low digestibility was fabricated using microbial glucanotransferase (GTase) treated maltodextrin. For GTase treated maltodextrin with DE 6, the molecular weight of reuteran-like glucan increased from 8.35 × 10⁴ to 5.14 × 10⁶ g/mol in the initial 6 h, increasing to 1.47 × 10⁷ g/mol at 72 h. The short chain fraction (DP 3-12) of reuteran-like glucan increased from 45.2 % to 100.0 %, accompanied by an increase in α-1,6 glycosidic linkage percentage from 3.9 % to 33.3 %. This reaction promoted rearrangements in glycosidic chains, leading to a substantial increase in resistant starch content (13.4 % to 37.4 %) in the reuteran-like glucan. During in vitro fecal fermentation for 48 h, the reuteran-like glucan yielded large amounts of short-chain fatty acids (212.33 mM), especially butyric acid (12.64 mM). Thus, reuteran-like glucan could be used as a low-digestible and highly fermentable fiber for controlling blood glucose levels and prebiotic potential.

Facile and efficient chemical synthesis of gluco-oligosaccharides (GlcOS) with diverse glycosidic linkages as potential prebiotics to promote the growth of probiotic bacteria

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 % H₂SO₄, 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.

Synthesis and biological characterization of low-calorie Schisandra chinensis syrup

Schisandra chinensis (Omija) is a well-known medicinal plant in East Asia. In this study, Omija oligosaccharide syrup was prepared from sucrose with Omija fruit extract using two glucansucrases of Leuconostoc mesenteroides B-512F/KM and L. mesenteroides B-1355CF10/KM. The degree of polymerization of Omija oligosaccharide syrup was ranged from 2 - 13 by MALDI-TOF-MS analysis. Compared to the Omija syrup, the Omija oligosaccharide syrup reduced 61% calories based on the enzymatic gravimetric method. It also reduced up to 96% insoluble glucan formation from sucrose by mutansucrase of Streptococcus mutans at 500 mg/mL. Additionally, it has 1.78-fold higher oxygen radical absorbance capacity value compared to Omija syrup. Using electronic tongue sensor system, Omija oligosaccharide syrup showed decreased sourness, astringency, and saltiness compared to Omija syrup. Thus, Omija oligosaccharides can be used as functional sweetener in nutraceutical industries.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-022-01061-8.

The bifidogenic effects and dental plaque deformation of non-digestible isomaltooligosaccharides synthesized by dextransucrase and alternansucrase

Non-digestible isomaltooligosaccharides (NDIMOS) are functional food and beverage ingredients that contributed to human health benefits through metabolism of gastrointestinal microorganism. In this study, NDIMOS were synthesized by combine dextransucrase from Leuconostoc mesenteroides B512F/KM and alternansucrase from L. mesenteroides NRRL 1355CF10/KM using sucrose as substrate and maltose as acceptor. Their digestibility was confirmed by using digestive enzymes including α-amylase and amyloglucosidase. NDIMOS inhibited insoluble glucan formation through mutansucrase from Streptococcus mutans. The bifidogenic effect of NDIMOS was investigated by growth of four strains of Bifidobacterium in MRS broth containing NDIMOS, compared with MRS broth contain glucose and negative control. Additionally, Bifidobacterium bifidum or Bifidobacterium adolescentis inhibited the growth of Salmonella enterica serovar typhimurium when they were co-cultivation in MRS broth containing NDIMOS. These results suggested that NDIMOS is potential functional ingredient for food, beverage, and pharmaceutical application.

Development of a prebiotic blend to influence in vitro fermentation effects, with a focus on propionate, in the gut

Short chain fatty acids (SCFAs) derived from the human gut microbiota, and in particular propionate, may beneficially influence metabolic processes such as appetite regulation. Development of prebiotics that induce high propionate levels during fermentation is desirable. A total of 11 candidate prebiotics were screened to investigate their fermentation characteristics, with a focus on propionate production in mixed anaerobic batch culture of faecal bacteria. Further to this, a continuous 3-stage colonic fermentation model (simulating the human colon) was used to evaluate changes in microbial ecology, lactate and SCFA production of three 50:50 blends, comprising both slow and rapidly fermented prebiotics. In mixed batch culture: xylo-oligosaccharide, polydextrose and α-gluco-oligosaccharide were associated with the greatest increase in propionate. Polydextrose, α-gluco-oligosaccharide, β-1,4 glucan and oat fibre induced the greatest reductions in the acetate to propionate ratio. The most bifidogenic prebiotics were the oligosaccharides. Fermentation of a 50:50 blend of inulin and arabinoxylan, through the continuous 3-stage colonic fermentation model, induced a substantial and sustained release of propionate. The sustained release of propionate through the colon, if replicable in vivo, could potentially influence blood glucose, blood lipids and appetite regulation, however, dietary intervention studies are needed. Bifidogenic effects were also observed for the inulin and arabinoxylan blend and an increase synthesis of butyrate and lactate, thus indicating wider prebiotic potential.

Reuteransucrase-catalytic kinetic modeling and functional characteristics for novel prebiotic gluco-oligomers

This work describes the reuteransucrase-catalyzed reaction and structural characterization as well as in vitro fermentation for the acceptor products of gluco-oligomers from sucrose and maltose. At a low concentration of sucrose, the production of gluco-oligomers was favored, resulting in a relatively large number of acceptor products (DP3-5). A mathematical model was also proposed to simulate gluco-oligomer production depending on the reaction conditions. The fine structures of major linear gluco-oligomer fractions for a sucrose : maltose ratio of 1 : 1 were assigned as follows: α-d-Glcp-(1→6)-α-d-Glcp-(1→4)-d-Glcp, α-d-Glcp-(1→4)-α-d-Glcp-(1→4)-α-d-Glcp-(1→4)-d-Glcp, α-d-Glcp-(1→4)-α-d-Glcp-(1→6)-α-d-Glcp-(1→4)-d-Glcp, and α-d-Glcp-(1→6)-α-d-Glcp-(1→4)-α-d-Glcp-(1→6)-α-d-Glcp-(1→4)-d-Glcp, respectively. Compared with dextran and GOS57, the results of fermentation selectivity indicated that gluco-oligomers promoted the proliferation of gut bacteria and total SCFA production with a higher concentration of propionate. These data suggested that the gluco-oligomers synthesized via the reuteransucrase acceptor reaction had a prebiotic effect on gastrointestinal health.