Effects of color protection and enzymatic hydrolysis on the microstructure, digestibility, solubility and swelling degree of chestnut flour.

Chestnuts, despite their nutritional value, pose challenges in starch processing, digestion, and absorption. This study employed various color-fixing formulations and processing methods to simulate the in vitro digestion of both untreated and enzymatically hydrolyzed chestnut flour. Changes in starch properties, digestion characteristics, and estimated glycemic index (eGI) were analyzed to understand how enzymatic hydrolysis affects chestnut flour properties. The results showed that the browning of chestnut flour was the least when the mass ratio of vitamin C, citric acid, and EDTA-Na2 was 9:1:0.3. Following treatment with pullulanase and glucoamylase, the content of rapidly digestible starch decreased to 10 %, while the content of slowly digestible starch and resistant starch increased to 62 % and 27 %, respectively. The eGI value of chestnut flour after enzymatic hydrolysis increased to 61.85-65.14, the hydrolysis rate was 78.37 %-89.20 %, the water holding capacity was 5.3-8.6, the solubility was 51.33 %-58.33 %, and the swelling degree decreased to 2.21-3.33 mL/g.

Effect of ethanol addition on the physicochemical, structural and in vitro digestive properties of Tartary buckwheat starch-quercetin/rutin complexes.

The effects of ethanol on the physicochemical, structural and in vitro digestive properties of Tartary buckwheat starch-quercetin/rutin complexes (e-TBSQ and e-TBSR) were investigated. Ethanol restricted the gelatinization of Tartary buckwheat starch (TBS), which resulted an increase in ∆H, G' and G" as well as a decrease in apparent viscosity of e-TBSQ and e-TBSR. The particle size, scanning electron microscopy and X-ray diffraction results showed that ethanol influenced the morphological structure of TBS granules and the starch crystalline structure in e-TBSQ and e-TBSR changed from B-type to V-type when the ethanol concentration was 25%. Saturation transfer difference-nuclear magnetic resonance results revealed that ethanol weakened the binding ability of quercetin/rutin to TBS in e-TBSQ and e-TBSR, leading to a change in the binding site on the quercetin structural unit. The residual ungelatinized TBS granules in e-TBSQ and e-TBSR induced a high slowly digestible starch content, and thus displayed a "resistant-to-digestion".

Interaction between starch and dietary compounds: New findings and perspectives to produce functional foods.

Due to the increased prevalence of overweight, obesity, diabetes, colon cancer, cardiovascular diseases, and metabolic syndrome, dietary approaches to reduce starch digestion and regulate glucose homeostasis have gained attention. Starch is a polysaccharide in most daily food consumed as bakery products, snacks, breakfast cereals, and pasta, which are often vilified. However, it is also present in beans, lentils, and oatmeal, which are considered healthy food products. The difference relays on the food matrix and the thermal process that can produce interactions between starch and dietary compounds (protein, lipid, non-starch polysaccharide, and bioactive compounds) or among starch chains (retrogradation). Such interactions produce structural changes so the digestive enzymes cannot hydrolyze them; additionally, the physical barrier of some macromolecules (proteins, hydrocolloids) restricts starch gelatinization and accessibility of the digestive enzymes to hydrolyze the starch. The interactions mentioned above and the use of some macromolecules as physical barriers could be explored as a pathway to develop functional foods. This review analyzes the interactions between starch and dietary compounds influenced by the processing of some food matrices to better understand their potential for developing functional foods.

Genotype-by-environment interactions for starch, mineral, and agronomic traits in pearl millet hybrids evaluated across five locations in West Africa.

Introduction: Pearl millet is a staple cereal grown in the harshest environments of arid and semi-arid regions of Asia and sub-Saharan Africa. It is the primary source of calories for millions of people in these regions because it has better adaptation to harsh environmental conditions and better nutritional traits than many other cereals. By screening the pearl millet inbred germplasm association panel (PMiGAP), we earlier reported the best genotypes with the highest concentration of slowly digestible and resistant starch in their grains. Methods: In the current study, we tested these 20 top-performing pearl millet hybrids, identified based on starch data, in a randomised block design with three replications at five locations in West Africa, viz. Sadore and Konni (Niger), Bambey (Senegal), Kano (Nigeria), and Bawku (Ghana). Phenotypic variability was assessed for agronomic traits and mineral traits (Fe and Zn). Results and discussion: Analysis of variance demonstrated significant genotypic, environmental, and GEI effects among five testing environments for agronomic traits (days to 50% flowering, panicle length, and grain yield), starch traits (rapidly digestible starch, slowly digestible starch, resistant starch, and total starch), and mineral trait (iron and zinc). Starch traits, such as rapidly digestible starch (RDS) and slowly digestible starch (SDS), showed nonsignificant genotypic and environmental interactions but high heritability, indicating the lower environmental influence on these traits in the genotype × testing environments. Genotype stability and mean performance across all the traits were estimated by calculating the multi-trait stability index (MTSI), which showed that genotypes G3 (ICMX207070), G8 (ICMX207160), and G13 (ICMX207184) were the best performing and most stable among the five test environments.

Effect of the Pasta Making Process on Slowly Digestible Starch Content.

The rate at which starch is digested in the human intestine elicits different glycemic responses and reflects the glycemic index (GI) of foods. In vitro measurement of starch digestibility can reflect the GI of food. Differences in starch digestibility among four durum wheat pasta samples, couscous, and bread were evaluated to better describe the role of the pasta making process in affecting starch digestibility. Statistical differences in RDS (rapidly digestible starch), SDS (slowly digestible starch), and RS (resistant starch) of products were found (p < 0.05). As expected, pasta samples showed the highest value of SDS/av starch compared to couscous and bread. Fusilli and cavatelli samples presented the highest SDS/av starch ratio (55.80 ± 3.06% and 53.91 ± 3.50%, respectively), then came spaghetti 49.39 ± 2.83% and penne 45.93 ± 1.19%, while couscous presented the lowest value of SDS/av starch (2.64 ± 0.50%), followed by bread (11.78 ± 2.63%). Our study confirmed that the pasta making process efficiently mediates an increase in SDS/Av starch content, which has been specifically quantified above 40%, therefore strongly related to a lowered glycemic response in vivo. Our results strengthened the concept that pasta is a good source of SDS, which makes it useful for glycemic control.

Yellow Mealworm (Tenebrio molitor) Powder Promotes a High Bioaccessible Protein Fraction and Low Glycaemic Index in Biscuits.

Traditional biscuits are considered products with poor nutritional value because of their large share of rapidly digested starch, which results in an elevated glycaemic index. This paper explores the improvement of the nutritional value of biscuits by adding yellow mealworm (Tenebrio molitor) powder. Four biscuit recipes containing 0%(R1), 10%(R2), 15%(R3), and 20%(R4) of yellow mealworm powder were prepared and subjected to sensorial analysis. The R3 biscuits were selected for further investigation, as they had the highest acceptability. Compared to the reference R1, the R3 biscuits showed an improved nutritional profile in terms of protein, fat, ash, minerals, fibres, essential amino acids, and unsaturated fatty acids, and lower amounts of carbohydrates and 5-hydroxymethylfurfural. The in vitro protein digestibility in R3 improved 1.12-fold compared to R1. No significant difference was found between the digestibility of the lipids released from R1 and R3. A higher fraction of slowly digestible starch was present in R3 compared to R1. The starch digestibility and estimated glycaemic index were 72.96% and 79.56% in R3, which can be compared to 78.79% and 90.14%, respectively, in R1. Due to their enhanced nutritional profile, higher bioaccessible protein fraction, and lower glycaemic index, yellow mealworm powder biscuits can be considered a more nutritious alternative to traditional biscuits.

Biochemical characteristics and potential application of a thermostable starch branching enzyme from Bacillus licheniformis.

Slowly digestible starch (SDS) has attracted increasing attention for its function of preventing metabolic diseases. Based on transglycosylation, starch branching enzymes (1,4-α-glucan branching enzymes, GBEs, EC 2.4.1.18) can be used to regulate the digestibility of starch. In this study, a GBE gene from Bacillus licheniformis (bl-GBE) was cloned, expressed, purified, and characterized. Sequence analysis and structural modeling showed that bl-GBE belong to the glycoside hydrolase 13 (GH13) family, with which its active site residues were conserved. The bl-GBE was highly active at 80 °C and a pH range of 7.5-9.0, and retained 90% of enzyme activity at 70 °C for 16 h. bl-GBE also showed high substrate specificity (80.88 U/mg) on potato starch. The stability and the changes of the secondary structure of bl-GBE at different temperature were determined by circular dichroism (CD) spectroscopy. The CD data showed a loss of 20% of the enzyme activity at high temperatures (80 °C), due to the decreased content of the α -helix in the secondary structure. Furthermore, potato starch treated with bl-GBE (300 U/g starch) showed remarkable increase in stability, solubility, and significant reduction viscosity. Meanwhile, the slowly digestible starch content of bl-GBE modified potato starch increased by 53.03% compared with native potato starch. Our results demonstrated the potential applications of thermophilic bl-GBE in food industries.

Genotype-by-Environment Interaction Analysis of Metabolites in Pearl Millet Genotypes with High Concentrations of Slowly Digestible and Resistant Starch in Their Grains.

Genotype × environment interactions (GEIs) should play an important role in the selection of suitable germplasm in breeding programmes. We here assessed GEI effects on pearl millet (Pennisetum glaucum L.) genotypes, selected to possess a high concentration of slowly digestible starch (SDS) and resistant starch (RS) in their grains. Entries were grown in a randomized complete block design with three replications at locations in Bawku-Ghana, Sadore-Niger, Bamako-Mali, Konni-Nigeria, and Gampella-Burkina Faso across West Africa. Harvested grains from these locations were metabolomically profiled using flow injection ionization-high-resolution mass spectrometry (FIE-HRMS). A total of 3144 mass features (m/z) (1560 negative ion mode and 1584 positive ion mode) were detected, of which, 475 m/z were linked to metabolites be involved in starch, antioxidant and lipid biosynthesis, and vitamin metabolism. Combined ANOVA revealed that the GEI was significantly evident for 54 health-benefiting metabolites, many associated with sugar, especially galactose, metabolism. Additive main effects and multiplicative interaction (AMMI) analysis examined genotype variation and GEI effects, which, when combined with principal component analysis (PCA), found that m/z 171.14864 (positive ionisation, propenyl heptanoate) accounted for 89% of the GEI variation along PC1. The AMMI-based stability parameter (ASTAB), modified AMMI stability value (MASV), and modified AMMI stability index (MASI) were then applied to identify stable and high-performing genotypes for all the health-benefiting metabolites. Similarly, the best-linear-unbiased-prediction (BLUP)-based stability estimation was also performed using the harmonic mean of genotypic values (HMGV), relative performance of genotypic values (RPGV), and harmonic mean of relative performance of genotypic values (HMRPGV), to identify genotype rankings across multiple environments. The multi-trait stability index (MTSI) was calculated and found that the genotypes G1 (ICMH-177111) and G24 (ICMX-207137) were the most stable and were the best mean performers across 52 health-benefiting metabolic traits. These findings demonstrate the potential of G × E assessments on the delivery of health-benefiting metabolite-rich grains in future varieties and hybrids of pearl millet.

Effects of dual modification of lysine and microwave on corn starch: In vitro digestibility and physicochemical properties.

The effects of lysine addition and microwave treatment (MC) on the digestibility, physicochemical properties and structure of corn starch were investigated. Among all uncooked samples, unmodified corn starch (CS), microwave modified corn starch (MC-CS) and corn starch mixed with lysine (CS-Lys) contained 15.09 %, 14.82 % and 18.86 % slowly digestible starch (SDS), while up to 30.28 % in microwave-lysine modified corn starch (MC-Lys). In contrast to CS, the peak viscosity, breakdown viscosity, setback viscosity and gel enthalpy of MC-Lys were decreased, while the relative crystallinity was increased. Scanning electron microscopy observation showed that corn starch aggregated with each other and was coated by lysine after MC, the particle size distribution range became wider, and the specific surface area decreased. The results showed that the interaction of starch with lysine in the microwave field increased the ordered and aggregated structure of corn starch, resulting in a significant change in the physicochemical properties and digestibility of corn starch. MC-Lys can be added to foods as a nutritional fortification to meet the needs of specific populations for lysine and low carbohydrate.

Fortification of Chinese steamed bread with flaxseed flour and evaluation of its physicochemical and sensory properties.

Flaxseed is a popular functional food ingredient that is widely used in various snack foods. In this study, we developed a Chinese steamed bread (CSB) enriched with flaxseed flour. We evaluated the relative nutritional quality of flours made from distinct parts of flaxseeds, and we investigated the effects of adding various amounts of flaxseed flour on the edible acceptance and nutritional quality of CSB. The results showed that with increased flaxseed flour, the crust and core of CSB became darker, hardness and chewiness increased, cohesiveness and springiness changed slightly, the essential amino acid and resistant starch (RS) content increased significantly. Chemical analysis indicated that the major volatile compounds of CSB were alcohols and nitrogen-containing compounds. The RS ranged from 34.89 ± 0.80 to 54.64 ± 0.23%. The antioxidant capacity increased nearly three-fold. In summary, our study showed that the addition of 10% flaxseed flour yielded CSB with increased nutritional value and popular edible acceptance.

Analysis of starch structure and functional properties of tetraploid wheat (Triticum turgidum L.) with differing waxy protein composition.

BACKGROUND: An increased demand for food has mirrored the increasing global population. Obesity and diabetes are two disorders induced by poor eating choices. Consequently, there is an urgent need to develop modified foods that can ameliorate such illnesses. The objective of this study was to explore the effect of Waxy genes on the structural and functional properties of starch, with the aim of improving food quality. Wild-type tetraploid wheat was compared with three mutants with different Waxy gene combinations. RESULTS: The proportion of B-type granules was higher in the mutants than in the wild-type (Wx-AB), and there were significant changes in the starch granule size, number, and phenotype in the Wx free mutant (Wx-ab). The lowest branch chain length was observed in Wx-ab, whereas Wx-AB had the highest branch chain length of DP ≥ 37. Wx-ab had the highest degree of crystallinity. The crystallinity trend followed the order Wx-ab>Wx-Ab>Wx-aB>Wx-AB. The amount of slowly digestible starch (SDS) was higher in native, gelatinized, and retrograded starch in the mutant. The amount of retrograded starch was closer to gelatinized starch than to native starch. CONCLUSION: Waxy proteins make a substantial contribution to starch structure. A lack of waxy proteins reduced the unit chains markedly compared with the control. Waxy proteins significantly affected the smaller and longer chains of starch. The lines with differing waxy composition had different effects on food digestion. The Wx-AB in native starch and Wx-Ab in gelatinized starch can control obesity and diabetes by slow-digesting carbohydrates and high resistance to digestion. © 2022 Society of Chemical Industry.

Calcium alginate/curdlan/corn starch@calcium alginate macrocapsules for slowly digestible and resistant starch.

This study aimed to enhance the content of slowly digestible starch (SDS) and resistant starch (RS) by designing a type of novel shell-controllable calcium alginate/curdlan/corn starch@calcium alginate (CA/CL/CS@CA) core-shell structured macrocapsule. These macrocapsules were obtained by coating calcium alginate/curdlan/corn starch beads with different concentrations of sodium alginate. The results of the swelling power indicated that as the concentration of sodium alginate in the shell increased from 0% to 0.5%, the swelling degree of the macrocapsules at 95 °C decreased from 5.64 ± 0.09 g/g to 4.30 ± 0.12 g/g. The in vitro digestion experiments indicated that the content of SDS and RS of the macrocapsules at a sodium alginate concentration of 0.5% reached 42.21 ± 1.04% and 28.82 ± 1.05%, respectively. These results suggest that the CA/CL/CS@CA core-shell structured macrocapsules have the potential to be used as functional foods for cardiovascular disease, diabetes, and obesity patients.

Investigating the Impact of Extruded Dehulled Adlay with Specific In Vitro Digestion Properties on Blood Lipids in Subjects with Mild to Moderate Dyslipidemia.

Dyslipidemia, a major risk factor for cardiovascular diseases (CVDs), is modifiable by diet and lifestyle changes. A large population with mild to moderate dyslipidemia is at risk of developing CVDs, and early initiation of preventive measures can avert advancing into severe medical conditions. Studies suggest increasing slowly digestible starch (SDS) in diets can help lower blood lipids. We processed dehulled adlay, a cereal rich in bioactive compounds, such as polyphenols and phytosterols, into an instant meal by extrusion and milling and then assessed its starch composition and in vitro digestibility. The dehulled adlay was found to consist of 32% SDS and resistant starch combined. Then, eligible subjects with dyslipidemia were recruited to explore the adlay's hypolipidemic potential, safety, and acceptability. Subjects consumed the dehulled adlay as the sole carbohydrate source in their breakfast, without changing other components in the diet or lifestyle, for 12 weeks. After intervention, serum total cholesterol (TC) decreased significantly in subjects with hypercholesterolemia. In addition, both TC and triglyceride levels decreased significantly in those above 50 years old. In conclusion, the extruded dehulled adlay displays potential for favorably modulating blood lipids, and the effect is more pronounced in the middle-aged population.

Enzyme kinetic approach for mechanistic insight and predictions of in vivo starch digestibility and the glycaemic index of foods.

BACKGROUND: Starch is a principal dietary source of digestible carbohydrate and energy. Glycaemic and insulinaemic responses to foods containing starch vary considerably and glucose responses to starchy foods are often described by the glycaemic index (GI) and/or glycaemic load (GL). Low GI/GL foods are beneficial in the management of cardiometabolic disorders (e.g., type 2 diabetes, cardiovascular disease). Differences in rates and extents of digestion of starch-containing foods will affect postprandial glycaemia. SCOPE AND APPROACH: Amylolysis kinetics are influenced by structural properties of the food matrix and of starch itself. Native (raw) semi-crystalline starch is digested slowly but hydrothermal processing (cooking) gelatinises the starch and greatly increases its digestibility. In plants, starch granules are contained within cells and intact cell walls can limit accessibility of water and digestive enzymes hindering gelatinisation and digestibility. In vitro studies of starch digestion by α-amylase model early stages in digestion and can suggest likely rates of digestion in vivo and expected glycaemic responses. Reports that metabolic responses to dietary starch are influenced by α-amylase gene copy number, heightens interest in amylolysis. KEY FINDINGS AND CONCLUSIONS: This review shows how enzyme kinetic strategies can provide explanations for differences in digestion rate of different starchy foods. Michaelis-Menten and Log of Slope analyses provide kinetic parameters (e.g., K m and k cat /K m ) for evaluating catalytic efficiency and ease of digestibility of starch by α-amylase. Suitable kinetic methods maximise the information that can be obtained from in vitro work for predictions of starch digestion and glycaemic responses in vivo.

Processing, digestion property and structure characterization of slowly digestible gorgon nut starch.

Slowly digestible gorgon nut starch (GN-SDS) was prepared by heating-cooling treatment (HCT), meanwhile its morphological and structural features were characterized in detail by SEM, DSC, XRD and IR detection. The optimized parameters of GN-SDS processing were as following: starch milk (20%) was heated at 100 °C for 20 min, and then cooled under 4 °C for 24 h. Under the optimized parameters, the SDS content increased from 20.49 to 61.74%. GN-SDS showed typical SDS characteristics in in vivo digestion with a low postprandial blood glucose. SEM images suggested that GN-S particles changed from uniform regular polyhedron with smooth surface to irregular gravel-like particles with coarse surface and obvious layered structure inside after HCT. The results of SEM, DSC, XRD and IR determination indicated that HCT changed the granule morphology, interior structure, gelatinization temperature and crystal type (A to B-type) of GN-S, and therefore made it hard to be digested accordingly. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10068-021-01007-6.

Association of Slowly Digestible Starch Intake with Reduction of Postprandial Glycemic Response: An Update Meta-Analysis.

Slowly digestible starch (SDS) has been shown to digest slowly throughout the entire small intestine, generating slow and prolonged release of glucose, according to the in vitro Englyst assay. The aim of this work was to conduct a meta-analysis of up-to-date evidence to evaluate the association between SDS consumption and a reduction in the postprandial glycemic response, including extended glycemic index (EGI) or glycemic profile (GP) parameters, during in vivo digestion. We searched the Web of Science, PubMed, Europe PMC, Cochrane Library, and Embase to identify related articles published up to September 2022. Human trials investigating the effect of the SDS amount on the postprandial glucose profile were estimated at the standard mean difference (SMD), with a 95% confidence interval (CI), using random effect models. The review followed the systematic reviews and meta-analyses (PRISMA) guidelines. The meta-analysis included a total of 65 participants. The results revealed that the EGI experienced a greater increase (SMD = 24.61, I2 = 79.2%, p < 0.01) after SDS intake, while the GP exhibited similar trends (SMD = 29.18, I2 = 73.3%, p < 0.01). High heterogeneity vanished in the subgroup and sensitivity analysis (EGI: I2 = 14.6%, p = 0.31; GP: I2 = 0.0%, p = 0.97). There was no evidence of publication bias for EGI (p = 0.41) or GP (p = 0.99).The present meta-analysis provides evidence that SDS intake is positively correlated with EGI and GP levels. The quantitative relationship of the reduction in the postprandial glycemic response and SDS consumption was used to quantify the slow digestion property on an extended time scale, and supplement the in vitro concept of SDS.

Research progress on the effects of parboiled rice on blood glucose / 中华老年医学杂志

After rice is processed into parboiled rice, it becomes a food with low glycemic index.Due to the effect of parboiled rice-preparing process on the rice, the changed starch structure and digestibility have induced a reduced hyperglycemic response to rice.After changes in starch structure, direct chain starch content increases with the result in digestive rate decrease.Furthermore, the proportion of the slowly digesting-starch(SDS)in the starch, and the content of the resistant starch(RS)go up, which induces an decreased digestive rate.In addition, parboiled rice also confers greater protection against oxidative stress.It also contains high fat and protein with strong sense of satiety, which reduces the level of blood glucose after eating.The parboiled rice is suitable for patients with diabetes and for the individuals with high risk for diabetes, and can also be applied to patients with hypertension, obesity and other metabolic diseases.

A single base change at exon of Wx-A1 caused gene inactivation and starch properties modified in a wheat EMS mutant line.

BACKGROUND: Wheat is an essential source of starch. The GBSS or waxy genes are responsible for synthesizing amylose in cereals. The present study identified a novel Wx-A1 null mutant line from an ethyl methanesulfonate (EMS)-mutagenized population of common wheat cv. SM126 using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and agarose gel analyses. RESULTS: The alignment of the Wx-A1 gene sequences from the mutant and parental SM126 lines showed only one single nucleotide polymorphism causing the appearance of a premature stop codon and Wx-A1 inactivation. The lack of Wx-A1 protein resulted in decreased amylose, total starch and resistant starch. The starch morphology assessment revealed that starch from mutant seeds was more wrinkled, increasing its susceptibility to digestion. Regarding the starch thermodynamic properties, the gelatinization temperature was remarkably reduced in the mutant compared to parental line SM126. The digestibility of native, gelatinized, and retrograded starches was analyzed for mutant M4-627 and the parental SM126 line. In the M4-627 line, rapidly digestible starch contents were increased, whereas resistant starch was decreased in the three types of starch. CONCLUSION: Waxy protein is essential for starch synthesis. The thermodynamic characteristics were decreased in the Wx-A1 mutant line. The digestibility properties of starch were also affected. Therefore, the partial waxy mutant M3-627 might play a significant role in food improvement. Furthermore, it might also be used to produce high-quality noodles. © 2021 Society of Chemical Industry.

Digestibility and structure changes of rice starch following co-fermentation of yeast and Lactobacillus strains.

Rice is sometimes fermented with microorganisms to develop health-promoting foods, but the contribution of a short-term fermentation (a necessary step for fermented rice cake-preparation) to properties of rice starch is not resolved yet. The effects of microorganism fermentation with different amount of starter cultures on multi-scale structures and digestibility of rice starch were investigated. The amount of starter cultures significantly affected structures and digestibility of fermented starch. The fermentation with a lower amount of starter cultures induced starch degradation (corrosion of starch granules, reduction of lamellar orders and compactness, decrease in crystallinity, double helix, short ranger-ordered structures, and molar mass) and a slightly reassembly, which increased the content of slowly digestible starch (SDS). While, the fermentation produced more starch fractions with Mw between 0.60 × 107 g/mol and 1.50 × 107 g/mol as the amount of starter cultures increased, and these starch molecules tended to reassemble and form more ordered multi-scale structures including double helical and short range-ordered structures, starch lamellar orders and compactness, which elevated SDS content. The SDS content of fermented starchy foods could be improved via controlling starch reassembly and multi-scale ordered structures through modulating the amount of starter cultures during fermentation.

Expression and characterization of 1,4-α-glucan branching enzyme from Microvirga sp. MC18 and its application in the preparation of slowly digestible starch.

Nutraceuticals containing modified starch with increased content of slowly-digestible starch (SDS) may reduce the prevalence of obesity, diabetes and cardiovascular diseases due to its slow digestion rate. Enzymatic methods for the preparation of modified starch have attracted increasing attention because of their low environmental impact, safety and specificity. In this study, the efficient glucan branching enzyme McGBE from Microvirga sp. MC18 was identified, and its relevant properties as well as its potential for industrial starch modification were evaluated. The purified McGBE exhibited the highest specificity for potato starch, with a maximal specific activity of 791.21 U/mg. A time-dependent increase in the content of α-1,6 linkages from 3.0 to 6.0% was observed in McGBE-modified potato starch. The proportion of shorter chains (degree of polymerization, DP < 13) increased from 29.2 to 63.29% after McGBE treatment, accompanied by a reduction of the medium length chains (DP 13-24) from 52.30 to 35.99% and longer chains (DP > 25) from 18.51 to 0.72%. The reduction of the storage modulus (G') and retrogradation enthalpy (ΔHr) of potato starch with increasing treatment time demonstrated that McGBE could inhibit the short- and long-term retrogradation of starch. Under the optimal conditions, the SDS content of McGBE-modified potato starch increased by 65.8% compared to native potato starch. These results suggest that McGBE has great application potential for the preparation of modified starch with higher SDS content that is resistant to retrogradation.