Deciphering the structural and functional characteristics of an innovative small cluster branched α-glucan produced by sequential enzymatic synthesis

Synergistic Amylase and Debranching Enzyme Catalysis to Improve the Stability of Oat Milk

Oat starch plays a crucial role in the stability of oat milk. Enzyme-hydrolyzed oat starch has been demonstrated to be an effective means of improving the stability of oat milk. The effects of different enzyme combinations on the stability of oat milk and the properties of starch in oats were investigated by adding α-amylase, amyloglucosidase, and different ratios of pullulanase and isoamylase. The results showed that as the degree of hydrolysis increased, the molecular weight, amylose content, and side chain length distribution of the starch decreased significantly. Moreover, compared with oat starch, the rheological and emulsifying properties of the starch hydrolysates were improved, and the characterization of emulsion stability showed that a 1:2 ratio of pullulanase to isoamylase promoted effective debranching and thus improved the stability of oat milk. This study demonstrated that debranching enzymes enhance the enzymatic hydrolysis of beverages and improve the physicochemical properties and stability of oat milk.

Structural and property characterization of low-molecular-weight novel reuterans synthesized from pea starch by Limosilactobacillus reuteri N1 GtfB with 4,6-α-glucanotransferase II activity

Promising novel α-glucanotransferases with starch-converting activity have recently emerged from the CAZy GH70 GtfB subfamily. In this study, we thoroughly investigated and elucidated the impact of the newly characterized 4,6-α-glucanotransferase II Limosilactobacillus reuteri N1 GtfB (LrN1 GtfB), which was capable of synthesizing linear (α1 → 6) and branched (α1 → 4,6) linkages, on the fine structure, rheology, and retrogradation properties of pea starch (PS). The results revealed that as the reaction time increased, the total (α1 → 6) linkages in linear chains and branching points of PS increased from 5.6 % to 18.7 %, the molecular weight decreased from 7.3 × 106 g/mol to 7.4 × 104 g/mol, and the percentage of short chains (DP ≤ 12) increased from 47.4 % to 92.7 %, thereby producing low-molecular-weight, short-clustered novel reuterans with new (α1 → 6) linkages in both linear chains and branches. Additionally, LrN1 GtfB-modified PS exhibited lower storage/loss modulus and weaker creep property, indicating a significant attenuation of the strength and rigidity of the modified gel structure. Moreover, products derived from pea starch and LrN1 GtfB exhibited notably low retrogradation properties. These findings provide insights into the potential application of GtfB-type α-glucanotransferases in starch-based products, thereby producing unique-structured α-glucans with versatile properties from starch.

Structural elucidation and functional characteristics of novel potential prebiotics produced from Limosilactobacillus reuteri N1 GtfB-treated maize starches

The recently characterized Limosilactobacillus reuteri N1 GtfB (LrN1 GtfB) from glycoside hydrolase family 70 is a novel 4,6-α-glucanotransferase acting on starch/maltooligosaccharides with high enzyme activity and soluble protein yield (in heterogenous system). In this study, the influence of the treatment by LrN1 GtfB on the fine structure and functional characteristics of three maize starches were furtherly investigated and elucidated. Due to the treatment of LrN1 GtfB, the starch molecules were transformed into reuterans containing linear and branched (α1 → 6) linkages with notably smaller molecular weight and shorter chain length. Moreover, the (α1 → 6) linkage ratios in the GtfB-modified high-amylose maize starch (GHMS)/normal maize starch (GNMS)/waxy maize starch (GWMS) increased by 18.3 %/12.6 %/9.0 % as compared to their corresponding controls. In vitro digestibility experiment revealed that the resistant starch content of GHMS, GNMS and GWMS increased by 16 %, 18 % and 25 % as compared to the starch substrates. Furthermore, the butyric acid yielded from GHMS, GNMS and GWMS in the in vitro fermentation experiments were 1.4, 1.5 and 1.4 times higher than those of commercial galactose oligosaccharides. These results indicated that the highly-branched short-clustered reuteran synthesized by LrN1 GtfB might serve as novel potential prebiotics, and provide insights for the synthesis of promising prebiotic dietary fiber from starch.

Macromolecular, thermal, and nonthermal technologies for reduction of glycemic index in food-A review

Consumers rely on product labels to make healthy choices, especially with regard to the glycemic index (GI) and glycemic load (GL), which identify foods that stabilize blood sugar. Employing both thermal and nonthermal processing techniques can potentially reduce the GI, contributing to improved blood sugar regulation and overall metabolic health. This study concentrates on the most current advances in GI-reduction food processing technologies. Food structure combines fiber, healthy fats, and proteins to slow digestion, reducing GI. The influence of thermal approaches on the physical and chemical modification of starch led to decreased GI. The duration of heating and the availability of moisture also determine the degree of hydrolysis of starch and the glycemic effects on food. At a lower temperature, the parboiling revealed less gelatinization and increased moisture. The internal temperature of the product is raised during thermal and nonthermal treatment, speeds up retrogradation, and reduces the rate of starch breakdown.

Analysis of the action pattern of sequential α-amylases from B. stearothermophilus and B. amyloliquefaciens on highly concentrated soluble starch

Hydrolysis of highly concentrated soluble starch (60%, w/w) was performed using sequential α-amylases from Bacillus stearothermophilus (T, 0.2%, w/w) and Bacillus amyloliquefaciens (B, 0.1%, w/w) to identify their possible action patterns. We found that T reduced the average molecular weight (Mw) of soluble starch from 52,827 Da to 31,914 Da and significantly affected its branched chain length. Compared with soluble starch, the chains with DP 6-12 and DP ≥ 13 in the T samples were diminished by 46% and 96%, respectively. This resulted in an attenuation in the proportions of exterior and inner chains, as well as low iodine binding capacity of the hydrolysates. In contrast, a slower decrease in the average Mw of soluble starch occurred after TB incubation, and the level of DP 6-12 further lowered, causing a gradual decline in the iodine binding capacity of the hydrolysates. Gathered data revealed an unusual action pattern of sequential α-amylase treatment at high substrate concentrations. Bacillus stearothermophilus α-amylase exhibited more pronounced endo-hydrolysis of amylopectin, whereas the attack of Bacillus amyloliquefaciens α-amylase on the exterior chains was enhanced in amylopectin residues. These findings suggest that the synergy of various α-amylases is an effective strategy to promote the dextrinization of highly concentrated starch and finely modify the molecular structure of starch.