Rheological and gelation properties of rice starch modified with 4-α-glucanotransferase

Heat- and shear-reversible networks in food: A review

While nature behaves like an irreversible network with respect to entropy and time, certain systems in nature exist that are, to some extent, reversible. The property of reversibility imparts unique benefits to systems that possess them, making them suitable for designing self-healing, stimuli-responsive, and smart materials that can be used in widely divergent fields. Reversible networks are currently being exploited for applications in tissue engineering, drug delivery, and soft robotics. They are also being utilized as low-calorie fat mimetics with melt-in-your-mouth textures, as well as being explored as potential scaffolds for three-dimensional (3D) printable food, among other applications. This review aims to gather representative examples of heat- and shear-reversible networks in the food science literature from the last 30 or so years, in other words, reversible food gels made either from linear biopolymers or from colloidal, particulate dispersions, including those that have been modified specifically to induce reversibility. An overview of the network mechanisms involved that impart reversibility, including a discussion of the strength and range of forces involved, will be highlighted. A model that explains why certain networks are thermoreversible while others are shear-reversible, and why others are both, will also be proposed. A fundamental understanding of these mechanisms will prove invaluable when designing reversible networks in the future, making possible the precise control of their properties, thus fostering innovative applications within the food industry and beyond.

Enhancing gel strength of Thermoproteus uzoniensis 4-α-glucanotransferase modified starch by amylosucrase treatment

4-α-glucanotransferase is used to produce thermoreversible starch gels to alleviate limitations to use of starch gels in repetitively heat-processed foods. However, the gel strength was weakened after this enzyme modification. In the present study, treatment by amylosucrase (NpAS) of corn starch and sucrose was applied to retain the gel thermoreversibility and eliminate the shortcoming caused by 4-α-glucanotransferase (TuαGT). Changes in molecular structure, rheological and retrogradation properties of modified starch were investigated after NpAS and TuαGT sequential and one-pot treatment, respectively. The apparent amylose content was reduced and increased by sequential and one-pot treatments, respectively, compared to single TuαGT modification. Chain length profiles showed higher proportion of degree of polymerization (DP) ≥ 13 by sequential treatment, whereas DP 6-12 was higher after one-pot treatment. All modified starches had reduced molecular weight. G' and G" increased by dual enzyme compared to single TuαGT treatment having little effect on retrogradation. Interestingly, starch subjected to 3 h one-pot treatment caused G' and G" temperature curves to cross-over, improving thermoreversible properties. The results indicate that NpAS treatment compensated for loss of starch gel strength caused by TuαGT and offered possibility to provide a wider range of thermoreversible starches.

Characterization of resistant starch nanoparticles prepared via debranching and nanoprecipitation

Cyperus esculentus starch was treated by pullulanase debranching and nanoprecipitation to prepare resistant starch nanoparticles. Amylose contents, rheological properties of debranched starch and the size, crystalline structure, resistant starch contents of the prepared starch nanoparticles were investigated. The results of amylose contents showed that enzymatic hydrolysis 4 h was the most appropriate enzymatic hydrolysis time. Dynamic light scattering analysis and scanning electron microscopy observations showed that when the starch solution was added to the ethanol, the larger the amount of ethanol, the more conducive to the formation of small size starch nanoparticles. When volume ratio of starch solution/ethanol was 1/5, the particle size was 271.1 nm, the content of resistant starch was higher (15.28%). X-ray diffraction results indicated that resistant starch nanoparticles had V-type crystalline structure. Pullulanase debranching and nanoprecipitation can be utilized to prepare smaller size of Cyperus esculentus resistant starch with higher efficiency.

Clean label starch: production, physicochemical characteristics, and industrial applications

Recently, health-conscious consumers have a tendency to avoid the use of modified starch in their food products because of reluctance regarding food additives or chemical processes. The present paper considers the characteristics and manufacturing methods of clean label starch, which is free from chemical modification. Clean label starch manufacturing is mainly dependent on starch blending, physical and enzymatic modification methods. Physical modifications include ultrasound, hydrothermal (e.g., heat-moisture treatment and annealing), pre-gelatinization (e.g., drum drying, roll drying, spray cooking, and extrusion cooking), high-pressure (high hydrostatic pressure), and pulsed electric field treatments. These physical processes allow variation of starch properties, such as morphological, thermal, rheological, and pasting properties. Enzyme treatment can change the properties of starch more dramatically. Actual use of clean label starch with such altered properties has occurred in industry and is described here. This review may provide useful information on the current status and future direction of clean label starch in the field of food science.

Improving the Stability and Curcumin Retention Rate of Curcumin-Loaded Filled Hydrogel Prepared Using 4αGTase-Treated Rice Starch

In this study, 4-α-glucanotransferase (4αGTase)-treated rice starch (GS) was added after 1-h (1 GS) and 96-h (96 GS) treatments to the aqueous phase of a curcumin-loaded emulsion to produce filled hydrogels (1 GS-FH and 96 GS-FH, respectively). The relative protective effects of the FH system, native rice starch-based filled hydrogel (RS-FH), and emulsion without starch (EM), on curcumin were evaluated based on ultraviolet (UV) stability and simulated gastrointestinal studies. The UV stability and curcumin retention after in vitro digestion of the filled hydrogels (FH) samples were greater than those of the EM samples. RS-FH showed a 2.28-fold improvement in UV stability over EM due to the higher viscosity of RS. 1 GS-FH and 96 GS-FH increased curcumin retention by 2.31- and 2.60-fold, respectively, and the microstructure of 96 GS-FH, determined using confocal laser microscopy, remained stable even after the stomach phase. These effects were attributed to the molecular structure of GS, with decreased amylopectin size and amylose content resulting from the enzyme treatment. The encapsulation of lipids within the GS hydrogel particles served to protect and deliver the curcumin component, suggesting that GS-FH can be applied to gel-type food products and improve the chemical stability of curcumin.

Properties of recombinant 4-α-glucanotransferase from Bifidobacterium longum subsp. longum JCM 1217 and its application

To determine the physiochemical properties of the 4-α-glucanotransferase from Bifidobacterium sp., the bllj_0114 gene encoding 4-α-glucanotransferase was cloned from Bifidobacterium longum subsp. longum JCM 1217 and expressed in Escherichia coli. The amino acid sequence alignment indicated that the recombinant protein, named BL-αGTase, belongs to the glycoside hydrolase (GH) family 77. BL-αGTase was purified using nickel-nitrilotriacetic acid affinity chromatography and characterized using various substrates. The enzyme catalyzed the disproportionation activity, which transfers a glucosyl unit from oligosaccharides to acceptor molecules, and had the highest activity at 40 °C and pH 6.0. In the presence of 5 mM metal ions, in particular Cu²⁺, Zn²⁺, and Fe²⁺, BL-αGTase activity was reduced. To determine whether BL-αGTase can be used to generate thermoreversible gels, potato starch was treated with BL-αGTase for various reaction times. The BL-αGTase-treated starches showed sol-gel reversibility and melted at 59.6-75.7 °C.

Complex formation of a 4-α-glucanotransferase using starch as a biocatalyst for starch modification

A 4-α-glucanotransferases from Thermus thermophilus (TTαGT) possesses an extra substrate binding site, leading to facile purification of the intact enzyme using amylose as an insoluble binding matrix. Due to the cost of amylose and low recovery yield, starch was replaced for amylose as an alternative capturer in this study. Using gelatinized corn starch at pH 9 with 36-h incubation in the presence of 1 M ammonium sulfate increased the TTαGT-starch complex formation yield from 2 to 56%. In preparative-scale production, TTαGT produced in Bacillus subtilis was recovered by 42.1% with the same specific activity as that of purified TTαGT. Structural and rheological analyses of the enzymatically modified starches revealed that the starch complex exhibited catalytic performance comparable to soluble TTαGT, suggesting that the starch complex can be used as a biocatalyst for modified starch production without elution of the enzyme from the complex.

Overproduction of a thermostable 4-α-glucanotransferase by codon optimization at N-terminus region

BACKGROUND

4-α-Glucanotransferases are useful enzymes to modify starch owing to their transglycosylation activity. In this study, codon optimizations were conducted to overproduce a thermostable 4-α-glucanotransferase from Thermus thermophilus (TTαGT).

RESULTS

Two variants, termed TTαGT-P4CCG and TTαGT-mut6, were constructed, which have the optimized codon at the first rare codon and optimized codons at all six chosen rare codons at the N-terminus of TTαGT, respectively. In the Escherichia coli system, the expression of both optimized genes was enhanced by about 100-fold relative to that of the original gene, whereas all six mutated codons contributed to the overall enhancement of TTαGT production in Bacillus subtilis. On the basis of the αGTase activity of the crude cell extracts, relative activities of 1:2.9:5.8 were determined for TTαGT, TTαGT-P4CCG and TTαGT-mut6, respectively, in B. subtilis. In addition, the activity of TTαGT-mut6 from B. subtilis grown without antibiotics was as much as that with the antibiotics. Finally, after heat treatment, the specific activity of TTαGT-mut6 from B. subtilis was 1.5-fold greater than that from E. coli.

CONCLUSION

The codon-optimized TTαGT that was produced in a GRAS microorganism, B. subtilis, without the selection antibiotics is potentially useful in the food industry as a food-grade enzyme.