Development of Slowly Digestible Starch Derived α-Glucans with 4,6-α-Glucanotransferase and Branching Sucrase Enzymes

Abstract

Previously, we have identified and characterized 4,6-α-glucanotransferase enzymes of the glycosyl hydrolase (GH) family 70 (GH70) that cleave (α1→4)-linkages in amylose and introduce (α1→6)-linkages in linear chains. The 4,6-α-glucanotransferase of Lactobacillus reuteri 121, for instance, converts amylose into an isomalto/malto-polysaccharide (IMMP) with 90% (α1→6)-linkages. Over the years, also, branching sucrase enzymes belonging to GH70 have been characterized. These enzymes use sucrose as a donor substrate to glucosylate dextran as an acceptor substrate, introducing single -(1→2,6)-α-d-Glcp-(1→6)- (Leuconostoc citreum enzyme) or -(1→3,6)-α-d-Glcp-(1→6)-branches (Leuconostoc citreum, Leuconostoc fallax, Lactobacillus kunkeei enzymes). In this work, we observed that the catalytic domain 2 of the L. kunkeei branching sucrase used not only dextran but also IMMP as the acceptor substrate, introducing -(1→3,6)-α-d-Glcp-(1→6)-branches. The products obtained have been structurally characterized in detail, revealing the addition of single (α1→3)-linked glucose units to IMMP (resulting in a comb-like structure). The in vitro digestibility of the various α-glucans was estimated with the glucose generation rate (GGR) assay that uses rat intestinal acetone powder to simulate the digestive enzymes in the upper intestine. Raw wheat starch is known to be a slowly digestible carbohydrate in mammals and was used as a benchmark control. Compared to raw wheat starch, IMMP and dextran showed reduced digestibility, with partially digestible and indigestible portions. Interestingly, the digestibility of the branching sucrase modified IMMP and dextran products considerably decreased with increasing percentages of (α1→3)-linkages present. The treatment of amylose with 4,6-α-glucanotransferase and branching sucrase/sucrose thus allowed for the synthesis of amylose/starch derived α-glucans with markedly reduced digestibility. These starch derived α-glucans may find applications in the food industry.

Insights into Broad-Specificity Starch Modification from the Crystal Structure of Limosilactobacillus Reuteri NCC 2613 4,6-α-Glucanotransferase GtfB

“…For example, the GtfB from Streptococcus thermophilus was found to be suitable for converting wheat starch and potato starch. , Together, the different reaction specificities of GTs offer great opportunities to convert starches to different α-glucans, in particular, because introduction of α-1,3 and α-1,6 linkages decreases their digestibility in the upper human gastrointestinal tract. This property makes these α-glucans attractive as low-glycemic ingredients in food applications. − …”

An Innovative Short-Clustered Maltodextrin as Starch Substitute for Ameliorating Postprandial Glucose Homeostasis

“…Theoretically, slowly digested starch requires less insulin to regulate glucose homeostasis and brings potential benefits for diabetes management. Many researchers, therefore, have devoted considerable effort to producing slowly digested starch by altering starch structure with a series of methods. − These modified products were primarily evaluated using in vitro digestibility assays. Rather few studies have concentrated on the digestion of these slowly digested starches in vivo .…”

Approaches for development of functional and low gluten bread from sorghum: A review

“…Pongjaruvat et al (2014) developed jasmine rice‐based, gluten‐free bread using pre‐gelatinized tapioca starch and transglutaminase. The other enzyme of interest to industry is starch‐acting α‐glucanotransferase enzymes (Te Poele et al, 2020). However, the effect of enzymatic treatment and nixtamalization of flour on sorghum bread development is also less targeted research area, though Dai and Tyl (2021) in their review highlighted single and combined enzymes as dough conditioners for bread development.…”