Action of transglucosidase from Aspergillus niger on maltoheptaose and [U–13C]maltose

Retrogradation inhibition and intragranular distribution in cooked rice by addition of α-glucosidase (AG) and branching enzyme (BE)

The effect of inhibiting retrogradation and changes in chain length distribution by AG and BE, which are texture-modifying enzymes, has been clarified. To ascertain in which part of the rice grain retrogradation occurs and which enzymes is most effective, the degree of retrogradation in each part of the rice grain was measured from the surface to the core of the same rice grain using a synchrotron radiation X-ray beam with a beam size of 100 μm. Retrogradation was effectively suppressed at all measurement sites by enzyme addition, although the effect of enzymes was greater at the surface. Rice grain sections were stained with iodine and eosin. A starch layer that does not easily form a complex with iodine was observed inside the protein layer at the surface of cooked rice. A starch layer with a long molecular chain that forms complexes with iodine was observed inside the rice grain.

Slow digestion properties of long-sized isomaltooligosaccharides synthesized by a transglucosidase from Thermoanaerobacter thermocopriae

Isomaltooligosaccharides (IMOs) are widely used as prebiotic ingredients that promote colon health; however, recent studies revealed that these are slowly hydrolyzed to glucose within the small intestine. Here, novel α-glucans with a higher number of α-1,6 linkages were synthesized from maltodextrins using the Thermoanaerobacter thermocopriae-derived transglucosidase (TtTG) to decrease susceptibility to hydrolysis and improve slow digestion properties. The synthesized long-sized IMOs (l-IMOs; 70.1% of α-1,6 linkages), comprising 10-12 glucosyl units, exhibited slow hydrolysis to glucose when compared to commercial IMOs under treatment with mammalian α-glucosidase level. In male mice, the ingestion of l-IMOs significantly decreased the post-prandial glycemic response compared to other samples (p < 0.05). Therefore, enzymatically synthesized l-IMOs can be applied as functional ingredients for the modulation of blood glucose homeostasis in obesity, Type 2 diabetes, and other chronic diseases.

Synthesis of improved long-chain isomaltooligosaccharide, using a novel glucosyltransferase derived from Thermoanaerobacter thermocopriae, with maltodextrin

Isomaltooligosaccharide (IMO), considered to be a prebiotic, reportedly has health effects, particularly in terms of digestion; however, the prebiotic effects of IMOs depend largely on the degree of polymerization. Currently, IMOs are commercially produced using transglucosidase (TG) derived from Aspergillus niger. Here, we report a novel Thermoanaerobacter thermocopriae-derived TG (TtTG) that can produce long-chain IMOs (L-IMOs) using maltodextrin as the main substrate. A putative carbohydrate-binding gene comprising carbohydrate-binding module 35 and glycoside hydrolase family 15 domain was cloned and successfully overexpressed in Escherichia coli BL21 (DE3) cells. The resulting purified recombinant enzyme (TtTG) had a molecular mass of 94 kDa. TtTG displayed an optimal pH of 4.0 (higher than that of commercial TG) and an optimal temperature of 60 °C (same as that of commercial TG). TtTG also enabled the synthesis of oligosaccharides using various saccharides, such as palatinose, kojibiose, sophorose, maltose, cellobiose, isomaltose, gentiobiose, and trehalose, which acted as specific acceptors. TtTG could also produce a medium-sized L-IMO, different from that by dextran-dextrinase and TG, from maltodextrin, as the sole substrate. Thus, the novel combination of maltodextrin and TtTG shows potential as an effective method for commercially producing L-IMOs with improved prebiotic effects.

Novel glucoamylase-resistant gluco-oligosaccharides with adjacent α-1, 6 branches at the non-reducing end discovered in Japanese rice wine, sake

Sake, a traditional Japanese rice wine, contains various oligosaccharides (Sake oligosaccharides; SAOs) derived from rice starch. We previously found that SAOs reach a high degree of polymerization (DP). In this study, we developed a hydrophilic interaction liquid chromatography-time-of-flight/mass spectrometry (HILIC-TOF/MS) based analytical method to separate isomeric SAOs. Isomers of SAOs with DP = 6, 7, and 8, which were named DP6-1, DP7-1, DP8-1 and DP8-2, respectively, were purified from sake and their structures were determined by two-dimensional NMR spectroscopy. These were novel oligosaccharides containing two α-1, 6 bonded branches on an α-1, 4-linked glucose main chain. Interestingly, adjacent double α-1, 6 branches that have not been identified in starch, were found in DP6-1, DP7-1, and DP8-1, suggesting the presence of the branching pattern in starch. DP6-1 was poorly digested by fungal glucoamylase, and this may be attributed to its adjacent double branches at the non-reducing end.

Does high pressure have any effect on the structure of alpha amylase and its ability to binding to the oligosaccharides having 3-7 residues? Molecular dynamics study

Studies have shown that deletion of amino acids from the C-terminus of amylase do not alter its amylolytic activity. Although high pressure is used to modify the structure and function of this enzyme, the effects of high pressures on the structures of the wild-type and truncated amylases have not yet been understood at the molecular level. Using molecular dynamic simulations and docking, we studied the structures of wild-type and truncated Taka-amylases at high pressures (1000-4000 bar). To construct the truncated Taka-amylase, 50 and 100 C-terminal residues were removed in two separate steps. Results of simulation showed that, although the overall shape partly agglomerates with rise in pressure, high pressure fails to modify the structure of the barrel-like region of the β-sheet in the wild-type and truncated enzymes. A comparison of contact graphs revealed that the changes at the N-terminus were less extensive than those at the C-terminus. Further analysis showed that 10 regions of the secondary structures changed due to pressure change in wild-type amylase, of which 6 regions were associated with the loops and 4 with helix, while the structure of β-sheets remained unchanged. The docking of maltotriose, maltotetraose, maltopentaose, maltohexaose, and maltoheptaose with the averaged structures obtained from different simulations was conducted to characterize the influence of pressure on the activities of the wild-type and truncated enzymes. The results showed that maltoheptaose made hydrophobic contacts with residues Tyr238-Asp117-Tyr82-Leu166-Leu232-Tyr155 and hydrogen contacts with residues Asp233-Gly234-Asp206-Arg204-His296-Glu230. Similar results were obtained for other malto-oligosaccharides.

Isomalto/malto-polysaccharide, a novel soluble dietary fiber made via enzymatic conversion of starch

Dietary fibers are at the forefront of nutritional research because they positively contribute to human health. Much of our processed foods contain, however, only small quantities of dietary fiber, because their addition often negatively affects the taste, texture, and mouth feel. There is thus an urge for novel types of dietary fibers that do not cause unwanted sensory effects when applied as ingredient, while still positively contributing to the health of consumers. Here, we report the generation and characterization of a novel type of soluble dietary fiber with prebiotic properties, derived from starch via enzymatic modification, yielding isomalto/malto-polysaccharides (IMMPs), which consist of linear (α1 → 6)-glucan chains attached to the nonreducing ends of starch fragments. The applied Lactobacillus reuteri 121 GTFB 4,6-α-glucanotransferase enzyme synthesizes these molecules by transferring the nonreducing glucose moiety of an (α1 → 4)-glucan chain to the nonreducing end of another (α1 → 4)-α-glucan chain, forming an (α1 → 6)-glycosidic linkage. Once elongated in this way, the molecule becomes a better acceptor substrate and is then further elongated with (α1 → 6)-linked glucose residues in a linear way. Comparison of 30 starches, maltodextrins, and α-glucans of various botanical sources, demonstrated that substrates with long and linear (α1 → 4)-glucan chains deliver products with the highest percentage of (α1 → 6) linkages, up to 92%. In vitro experiments, serving as model of the digestive power of the gastrointestinal tract, revealed that the IMMPs, or more precisely the IMMP fraction rich in (α1 → 6) linkages, will largely pass the small intestine undigested and therefore end up in the large intestine. IMMPs are a novel type of dietary fiber that may have health promoting activity.

Biotechnological approaches for the production of prebiotics and their potential applications

Worldwide interest in prebiotics have been increasing extensively both as food ingredients and pharmacological supplements, since they have beneficial properties for human health. Prebiotics not only stimulate the growth of healthy bacteria such as bifidobacteria and lactobacilli in the gut but also increase the resistance towards pathogens. In addition to this, they also act as dietary fiber, an energy source for intestinal cells after converting to short-chain fatty acids, a stimulator of immune systems, sugar replacer etc. Moreover, due to heat resistant properties, they are able to maintain their intact form during the baking process and allow them to be incorporated into every day food products. Thus, they can be interesting and useful ingredients in the development of novel functional foods. This review provides comprehensive information about the different biotechnological techniques employed in the production of prebiotics and their potential applications in different areas.