Influence of molecular structure on the susceptibility of starch to α-amylase

Mechanism analysis for the differences in multi-level structure, enzyme accessibility and pasting properties of starch granules caused by different hydrolysis pathways of maltogenic α-amylase

The effect of pores distribution on the multi-scale structure, enzyme accessibility, and pasting properties of the waxy maize starch granules with the same degree of hydrolysis were examined. Increased maltogenic α-amylase (MA) dosage obviously increased the shallow pores number and the roughness, whereas extended time increased the holes depth. Despite achieving the same hydrolysis degree and specific surface area, samples with numerous shallow holes exhibited a higher mass fractal dimension, a lower, peak viscosity, final viscosity and setback. Besides, increased dosage prompted a sustained decrease in the number of short chains with DP 10-17; whereas prolonging time encouraged the continuous catalyzation in the same chains. Enzymatic probe profiles showed MA was more accessible to the amorphous region on the periphery of starch granules, rather than the inside. This finding provides a more valuable understanding of the catalytic mechanism for MA in heterogeneous systems and an accurate guidance for the industrial production.

New insights into EGCG retards the digestion of wheat starch by α-amylase in ternary system: Comparison with binary systems

This study was to investigate the mechanism of the action of epigallocatechin gallate (EGCG) on α-amylase in the ternary simulated system and explore the changes in enzyme structure during the digestion process. Enzymatic kinetics, fluorescence spectroscopy, surface hydrophobicity, fluorescence microscopy, and molecular docking were used to compare (in the presence and absence of EGCG) the structural changes of α-amylase and α-amylase-starch complex, as well as the binding characteristics among EGCG and the α-amylase and starch. The results showed that EGCG had a significant inhibitory effect on α-amylase, and it exhibited a coexistence of competitive and anti-competition inhibition type, and predominantly competitive inhibition. In the ternary and binary systems, the inhibitory mechanisms of EGCG on α-amylase were distinct. In the ternary system, EGCG preferably bound to α-amylase to form α-amylase-EGCG binary complexes rather than α-amylase-starch-EGCG ternary complexes, and altered the structure of α-amylase, leading to unfolding of the enzyme's secondary structure and exposing more non-catalytic site aromatic amino acids.

A review of in vitro antioxidant and antidiabetic polysaccharides: Extraction methods, physicochemical and structure-activity relationships

Nowadays, various plant polysaccharides have been successfully extracted which exhibited strong biological activities and might be useful for diabetes management. However, the effect of extraction methods, physicochemical and the structural-activity relationships of polysaccharides to exhibit antioxidants and antidiabetics were inadequate to explain their mechanism in action. The uses of advance extraction methods might be preferred to obtain higher antioxidants and antidiabetic activities of polysaccharides compared to conventional methods, but the determination of optimal extraction conditions might be crucial to preserve their structure and biological functions. Other than that, the physicochemical and structural properties of polysaccharides were closely related to their biological activities such as antioxidant and antidiabetic activities. Therefore, this review addressed the research gap of the influence of extraction methods, physicochemical and structural relationships of polysaccharides to biological activities, pointing out the challenges and limitations as well as future prospects to the current findings.

Porous corn starch granules as effective host matrices for encapsulation and sustained release of curcumin and resveratrol

Type 2 Diabetes Mellitus (T2DM) is a carbohydrate-rich diet-regulated ailment with carbohydrates digested and absorbed rapidly. Hence, modulating carbohydrate digestion is warranted; to this end, polyphenols from plant sources are handy. However, polyphenols' instability and low bioavailability limit their wholesome use, and thus, encapsulating them into an inexpensive and suitable wall material would be the best strategy. Herein, the potential of porous starch granules is demonstrated. Curcumin and resveratrol were chosen as the test polyphenols due to their proven health benefits, and porous corn starch granules were chosen as the wall material. Porous corn starch granules were prepared through enzymatic modification with 11, 22, and 33 units of amyloglucosidase at three reaction times of 2, 4, and 6 h. The polyphenols were loaded at 100, 200, and 500 mg concentrations in 1 g of starch for 21 days and were characterized through Scanning Electron Microscope (SEM) and Fourier Transform Infrared spectroscopy (FTIR) analyses. The encapsulation efficiency was determined, the rate of starch digestion was calculated through the Englyst test, and polyphenols' in vitro release behavior in gastric and intestinal fluids was measured. Results suggest that 33 enzyme units for a 2 h reaction time were optimal for forming spherical-oval pores on corn starch granules with the maximum encapsulation efficiency of 80.16 % and 88.33 % for curcumin and resveratrol, respectively. The FTIR results suggest the entrapment of polyphenols inside the starch matrix. The inclusion significantly reduced starch digestion and increased the percentage of resistant starch up to 41.11 % and 66.36 % with curcumin and resveratrol, respectively. The in vitro release behavior demonstrated good stability in the simulated gastric fluids and sustained release in simulated intestinal fluids. The encapsulated polyphenols showed a complex Fickian type of diffusion mechanism. Overall, the results suggest that porous corn starch granules could be a potential delivery system for curcumin and resveratrol and will aid in developing novel functional foods to address the T2DM concerns.

Enhancing the anti-thixotropic properties of waxy maize starch modified by different α-amylases and its underlying molecular mechanism

The large thixotropy of the starch-thickened foods is often unfavorable in many applications. This study examined the contribution of the proportion of amylopectin chain length to time-dependence of starch gels. The α-amylase (AM) from Bacillus stearothermophilus and maltogenic α-amylase (MA) from Bacillus subtilis were used to trim amylopectin in different reaction patterns. HPLC, HPAEC and IBC data suggested AM attacked B-chains (DP 12-36), causing an increment in number of the chains with DP 6-12, whereas MA primarily trimmed the short B-chains (DP 12-18) and partial A-chains (DP 9-12) to generate short chains with DP 6-9. Interestingly, the recovery of AM-gels was faster than MA-gels at the same degree of hydrolysis when subjected to shear according to the linear correlation analysis. When releasing the same mass of sugar, shortening of the long internal chains played an important role in reducing time dependence of starch gel rather than the external side chains. Possible models were proposed to illustrate the differences in the mechanism of rapid-recovery caused by different side-chain distributions. The outcome provided a new perspective to regulate the thixotropy behavior of starch through enzyme strategies in the granular state.

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.

Maltogenic amylase: Its structure, molecular modification, and effects on starch and starch-based products

Maltogenic amylase (MAA) (EC3.2.1.133), a member of the glycoside hydrolase family 13 that mainly produces α-maltose, is widely used to extend the shelf life of bread as it softens bread, improves its elasticity, and preserves its flavor without affecting dough processing. Moreover, MAA is used as an improver in flour products. Despite its antiaging properties, the hydrolytic capacity and thermal stability of MAA can't meet the requirements of industrial application. However, genetic engineering techniques used for the molecular modification of MAA can alter its functional properties to meet application-specific requirements. This review briefly introduces the structure and functions of MAA, its application in starch modification, its effects on starch-based products, and its molecular modification to provide better insights for the application of genetically modified MAA in starch modification.

Impact of a Starch Hydrolysate on the Production of Exopolysaccharides in a Fermented Plant-Based Dessert Formulation

Plant-based desserts are becoming increasingly popular with and appreciated by consumers. However, they are limited by the choice of ingredients, which are often expensive and unstable with a random texture. Therefore, the aim of the research is to propose a new product that offers an advantageous texture and flavour in a fermented dessert based on a flour mix supplemented with an enzymatic hydrolysate. This study involved the development of two processes: (i) an enzymatic hydrolysis of oat flour and (ii) a fermentation of a flour mixture (oat, chickpea, and coconut) by lactic acid bacteria (Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus). The result of the oat flour hydrolysate shows a significant decrease in starch after 60 min of reaction, followed by an increase in sugar content. During 23 days of storage at 4 °C, the formulations used showed post-acidification, water retention capacity decrease, and hardness increase related to the hydrolysate rate (p < 0.05). All formulations allowed the viability of lactic bacteria (over 5 log10 CFU/mL) and verified their ability to produce exopolysaccharides (0.23-0.73 g/100 g). The prototyping of such a product represents a key step in meeting the growing demand for plant-based alternatives, with qualitative sensory characteristics without additives.

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

Highly branched α-glucan (HBAG) proved to be a promising material as an osmotic agent in peritoneal dialysis solutions. However, high resistance of HBAG to amylolytic enzymes might be a potential drawback for peritoneal dialysis due to its high degree of branching (20-30 %). To address this issue, we designed a small-clustered α-glucan (SCAG) with a relatively low molecular weight (Mw) and limited branching. Structural characteristics revealed that SCAG was successfully synthesized by modifying waxy rice starch (WRS) using sequential maltogenic α-amylase (MA) and starch branching enzyme (BE). The Mw of SCAG was 1.40 × 10⁵ Da, and its (α1 → 6) bonds ratio was 8.93 %, which was below that of HBAG. A relatively short branch distribution was observed in SCAG (CL = 6.27). Short-range orderliness of WRS was reduced from 0.749 to 0.322 with the MABE incubation. Additionally, SCAG had an extremely low viscosity (~12 cP) and nearly no retrogradation. Although the resistance of SCAG to amylolytic enzymes was enhanced by 15.22 % compared with native WRS, the extent was significantly lower than that of HBAG in previous studies. These new findings demonstrate the potential of SCAG as a novel functional α-glucan in food and pharmaceutical applications.

The effect of thiolation process with l-cysteine on amylolysis efficiency of starch-cysteine conjugate by α-amylase

l-Cysteine (l-Cys) pre-treatment at two concentrations (150 mg/kg; PC1 and 300 mg/kg; PC2) on potato starch was conducted to produce starch-cysteine conjugates. Afterward, the effect of α-amylase on starch digestibility of potato native (PE) and starch-cysteine conjugates (PC1E and PC2E) were examined. Thiolation not only damaged starch according to the formation of pore and blister-like spots on the surface of starch granules, but also provided the functional group to immobilize α-amylase. Starch-cysteine conjugates showed a significantly greater degree of hydrolysis 24.1 % (PC1E) and 36.5 % (PC2E) in comparison with (16.8 %; PE). Destroying the granules integrity were accompanied with decreased crystallinity from 37.7 % to 33.1 % (PC1), 31.1 % (PC2), 27.6 % (PC1E) and 22.4 % (PC2E) with increasing thiol content (%) on surface from 2.3 %; PC1 to 3.4 %; PC2. The ratio of 1047/1022 cm^{- 1} reduced from 1.112 (native potato starch) to 0.974 (PC1E) and 0.867 (PC2E) after being subjected to α-amylase. Additionally, substantially low pasting viscosities (determined by RVA) along with the thermal properties (determined by DSC) of starch-cysteine conjugates treated with α-amylase could confirm the degradation of molecular structures containing low swelling power.

Designing liquefaction and saccharification processes of highly concentrated starch slurry: Challenges and recent advances

Starch-based sugars are an important group of starch derivatives used in food, medicine, chemistry, and other fields. The production of starch sugars involves starch liquefaction and saccharification processes. The production cost of starch sugars can be reduced by increasing the initial concentration of starch slurry. However, the usage of the highly concentrated starch slurry is characterized by challenges such as low reaction efficiency and poor product performance during the liquefaction and saccharification processes. In this study, we endeavored to provide a reference guide for improving high-concentration starch sugar production. Thus, we reviewed the effects of substrate concentration on the starch sugar production process and summarized several potential strategies. These regulation strategies, such as physical field pretreatment, complex enzyme-assisted, and temperature control, can significantly increase the starch concentration and mitigate the challenges of using highly concentrated starch slurry. We believe that highly concentrated starch sugar production will achieve a qualitative leap in the future. This review provides theoretical guidance and highlights the importance of high concentration in starch-based sugar production. Further studies are needed to explore the fine structure and enzyme attack mode during the liquefaction and saccharification processes to regulate the production of more targeted products.

Comparison of structural and functional properties of maize starch produced with commercial or endogenous enzymes

To explore an effective and economic method to prepare higher contents of resistant starch (RS), different enzyme treatments including single pullulanase (PUL), commercial α-amylase (AA) or/and β-amylase (BA) with PUL, and malt endogenous amylase (MA) with PUL were used and the structural, physicochemical properties and digestibility of all modified starches (MS) were compared. All the enzyme-treated starches displayed a mixture of B and V-type diffraction patterns. The MA/PUL-MS showed higher V-type diffraction peak intensity as compared to other modified starches. Compared to the combination of commercial enzyme treatment, the combination of malt enzyme treatment led to higher apparent amylose contents (45.56%), RS content (53.93%) and thermal stability (302 °C), whereas it possessed lower solubility indices and predicted glycaemic index. The apparent viscosity and shear resistance of MA/PUL-MS were lower than that of AA/PUL-MS, whereas that of MA/PUL-MS was higher than that of BA/PUL-MS and BA/AA/PUL-MS. These findings would provide a theoretical and applicative basis to produce foods with lower GI in industrial production.

Microparticle prepared by chitosan coating on the extruded mixture of corn starch, resveratrol, and α-amylase controlled the resveratrol release

Microcapsule was developed by chitosan coating on the microparticle which was prepared by smashing the extruded mixture of corn starch, resveratrol, and α-amylase. In the preparation process, the low-temperature extrusion and α-amylase were employed to overcome the disadvantages of low gelatinization, dissolution, and poor hydration of extruded starch. Chitosan-coating retarded starch aging, improved the stability of microcapsules, delayed the release of resveratrol. Considering the bioactive functions of chitosan, microcapsules also obtained the functions of chitosan by chitosan coating. The chitosan coating and α-amylase addition improved the release ratio of resveratrol. CESRA (chitosan solution (2%) coating on the extruded mixture of corn starch, resveratrol, and α-amylase) released 86.8% resveratrol at 25 °C in six days chasing, and 85.3% resveratrol at 37 °C in 48 h chasing. Chitosan coating slightly improved the free radical scavenging activity of ABTS⁺. The particle size variation, SEM, XRD, and FT-IR were also employed to investigate the variation of morphology, crystal structure, and chemical composition.

Biochemical and synergistic properties of a novel alpha-amylase from Chinese nong-flavor Daqu

Background

Daqu is the most important fermentation starter for Chinese liquor, with large number of microbes and enzymes being openly enriched in the Daqu system over thousands of years. However, only a few enzymes have been analyzed with crude protein for total liquefying power and saccharifying power of Daqu. Therefore, the complex enzymatic system present in Daqu has not been completely characterized. Moreover, their pivotal and complicated functions in Daqu are completely unknown.

Results

In this study, a novel α-amylase NFAmy13B, from GH13_5 subfamily (according to the Carbohydrate-Active enZYmes Database, CAZy) was successfully heterologous expressed by Escherichia coli from Chinese Nong-flavor (NF) Daqu. It exhibited high stability ranging from pH 5.5 to 12.5, and higher specific activity, compared to other GH13_5 fungal α-amylases. Moreover, NFAmy13B did not show activity loss and retained 96% residual activity after pre-incubation at pH 11 for 21 h and pH 12 for 10 h, respectively. Additionally, 1.25 mM Ca²⁺ significantly improved its thermostability. NFAmy13B showed a synergistic effect on degrading wheat starch with NFAmy13A (GH13_1), another α-amylase from Daqu. Both enzymes could cleave maltotetraose and maltopentaose in same degradation pattern, and only NFAmy13A could efficiently degrade maltotriose. Moreover, NFAmy13B showed higher catalytic efficiency on long-chain starch, while NFAmy13A had higher catalytic efficiency on short-chain maltooligosaccharides. Their different catalytic efficiencies on starch and maltooligosaccharides may be caused by their discrepant substrate-binding region.

Conclusions

This study mined a novel GH13_5 fungal α-amylase (NFAmy13B) with outstanding alkali resistance from Nong-flavor (NF) Daqu. Furthermore, its synergistic effect with NFAmy13A (GH13_1) on hydrolyzing wheat starch was confirmed, and their possible contribution in NF Daqu was also speculated. Thus, we not only provide a candidate α-amylase for industry, but also a useful strategy for further studying the interactions in the complex enzyme system of Daqu.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-021-01571-w.

Microstructure of Whole Wheat versus White Flour and Wheat-Chickpea Flour Blends and Dough: Impact on the Glycemic Response of Pan Bread

Whole foods are generally considered healthier choices compared to processed foods. For nutritional consideration, whole wheat bread is recommended over the white bread. However, it has a similarly high effect on glycemic response (GR) as the white bread. This study is aimed at assessing the microstructure of whole wheat flour (WWF), white flour (WF), chickpea flour (BF), their blends, and dough and the GR of the bread made thereof. Scanning electron microscope analysis showed clear distinctions in the microstructure of the three flours. WWF particle size distribution had the widest spread with a polydispersity index (PDI) of 1.0 (±0.0) and wider average diameter, with z value of 1679.5 (±156.3) compared with the particle size of 658.9 (±160.4) and PDI of 0.740 (±0.04) for WF followed by BF with the particle size of 394.1 (±54.9) and PDI of 0.388 (±0.07) (p < 0.05). The falling number was significantly (p < 0.05) lower for WWF compared to WF or BF, indicating higher alpha-amylase activity. Thus, bread made from WWF without BF substitution exhibited a higher glycemic response similar to the bread made from WF. When partly replaced with BF, the GR of the bread made with WWF or WF reduced significantly (p < 0.05) in healthy individuals.