High-amylose Maize Research Articles

Transplantation of High Hydrogen-Producing Microbiota Leads to Generation of Large Amounts of Colonic Hydrogen in Recipient Rats Fed High Amylose Maize Starch.

The hydrogen molecule (H2), which has low redox potential, is produced by colonic fermentation. We examined whether increased H2 concentration in the portal vein in rats fed high amylose maize starch (HAS) helped alleviate oxidative stress, and whether the transplantation of rat colonic microbiota with high H2 production can shift low H2-generating rats (LG) to high H2-generating rats (HG). Rats were fed a 20% HAS diet for 10 days and 13 days in experiments 1 and 2, respectively. After 10 days (experiment 1), rats underwent a hepatic ischemia–reperfusion (IR) operation. Rats were then categorized into quintiles of portal H2 concentration. Plasma alanine aminotransferase activity and hepatic oxidized glutathione concentration were significantly lower as portal H2 concentration increased. In experiment 2, microbiota derived from HG (the transplantation group) or saline (the control group) were orally inoculated into LG on days 3 and 4. On day 13, portal H2 concentration in the transplantation group was significantly higher compared with the control group, and positively correlated with genera Bifidobacterium, Allobaculum, and Parabacteroides, and negatively correlated with genera Bacteroides, Ruminococcus, and Escherichia. In conclusion, the transplantation of microbiota derived from HG leads to stable, high H2 production in LG, with the resultant high production of H2 contributing to the alleviation of oxidative stress.

Structural properties and prebiotic activities of fractionated lotus seed resistant starches

The objective of this study was to fractionate lotus seed resistant starch (LRS3) and investigate their structural properties and prebiotic activities. Two main fractions of resistant starch precipitated gradually by ethanol at concentrations of 20% and 30% were named as LRS3-20% and LRS3-30%, respectively. The swelling power and solubility of LRS3-20% were smaller compared to LRS3-30%, and their moisture and resistant starch contents were not significantly different. LRS3-20% and LRS3-30% had molecular weights mainly of 2.0 × 104–4.0 × 104 and 1.0 × 104–2.0 × 104 g/mol. Layered strips and gully shapes were evident on the rough surfaces of LRS3-20%, while LRS3-30% displayed a relatively smooth surface. Both LRS3-20% and LRS3-30% had a B-type crystalline structure with LRS3-20% containing more ordered structures and double-helices. Furthermore, LRS3-20% displayed higher prebiotic activities against Bifidobacterium adolescentis and Lactobacillus acidophilus compared to LRS3-30% and high amylose maize starch. This effect was related to its rough surface and double helix structure.

Comparison of a sports-hydration drink containing high amylose starch with usual hydration practice in Australian rules footballers during intense summer training

BackgroundFluid deficits exceeding 1.6% can lead to physical and cognitive impairment in athletes. Sport drinks used by athletes are often hyper-osmolar but this is known to be suboptimal for rehydration in medical settings and does not utilize colonic absorptive capacity. Colonic absorption can be enhanced by fermentative production of short chain fatty acids (SCFA) from substrates such as high amylose maize starch (HAMS). This study therefore compared, in elite Australian Football League (AFL) players at the height of outdoor summer training, a novel dual-action sports oral rehydration strategy that contained HAMS as well as glucose, to their usual rehydration practices (Control). The primary outcome markers of hydration were hematocrit and body weight.MethodsA randomized single-blind crossover study was undertaken in thirty-one AFL players; twenty-seven completed the study which was conducted on four days (two days in the Intervention arm and two in Control arm). The Intervention arm was comprised a 50-100 g evening preload of an acetylated HAMS (Ingredion Pty Ltd) followed by consumption of a specially formulated sports oral rehydration solution (SpORS) drink during intense training and recovery. Players followed their usual hydration routine in the Control arm. Quantitative assessments of body weight, hematocrit and urine specific gravity were made at three time-points on each day of training: pre-training, post-training (90 min), and at end of recovery (30–60 min later). GPS tracking monitored player exertion.ResultsAcross the three time-points, hematocrit was significantly lower and body weight significantly higher in Intervention compared to Control arms (p < 0.02 and p = 0.001 respectively, mixed effects model). Weights were significantly heavier at all three assessment points for Intervention compared to Control arms (Δ = 0.30 ± 0.13, p = 0.02 pre-training; Δ = 0.43 ± 0.14, p = 0.002 post training; and Δ = 0.68 ± 0.14, p < 0.001 for recovery). Between the pre-training and end-of-recovery assessments, the Control arm lost 0.80 kg overall compared with 0.12 kg in the Intervention arm, an 85% lower reduction of bodyweight across the assessment period.ConclusionThe combination of the significantly lower hematocrit and increased body weight in the Intervention arm represents better hydration not only at the end of training as well as following a recovery period but also at its commencement. The magnitude of the benefit seems sufficient to have an impact on performance and further studies to test this possibility are now indicated.Trial registrationTrial is listed on the Australian New Zealand Clinical Trials Registry (ACTRN 12613001373763).

Effects of dextrinization and octenylsuccinylation of high amylose starch on complex formation with ω-3 fatty acids (EPA/DHA)

High amylose maize starch (70% amylose) was dextrinized in an acid/alcohol solution (0.36% HCl in ethanol, 50 °C for 24 h), and the starch and its dextrin were octenylsuccinylated (DS 0.019) to be utilized as complex forming agents for ω-3 fatty acids (eicosapentaenoic acid and docosahexaenoic acid). A fish oil was used as the fatty acid sample and dispersion with starch and fish oil was stirred at 60 °C for 3 h and cooled at an ambient temperature for 3 h. The complex was isolated as the precipitates after centrifugation (25,000 × g, 25 °C for 30 min), and then the recovery of fatty acids in the complex and crystalline characteristics of the complex were examined. Dextrinization improved the efficiency of complex formation, increasing the recovery of fatty acids and decreasing the recovery of solid precipitates. Octenylsuccinylation, however, retarded the complex formation showing a decrease in fatty acid recovery. It was hypothesized that intermolecular complex between amylose and octenyl group in the substituents was formed during the reaction because the modified starch and dextrin without fatty acids showed a new endotherm (at around 100 °C) in their thermograms. Because of the possible competition between the substituents and fatty acids in complex formation, octenylsuccinylation hindered the complex formation between amylose and fatty acids. The fatty acid complex particles prepared with native starch or dextrin showed average particle size less than 400 nm with zeta potential below −40 mA, assuring the dispersion stability during an ambient storage.

Bivariate flow cytometric analysis and sorting of different types of maize starch grains.

Particle-size distribution, granular structure, and composition significantly affect the physicochemical properties, rheological properties, and nutritional function of starch. Flow cytometry and flow sorting are widely considered convenient and efficient ways of classifying and separating natural biological particles or other substances into subpopulations, respectively, based on the differential response of each component to stimulation by a light beam; the results allow for the correlation analysis of parameters. In this study, different types of starches isolated from waxy maize, sweet maize, high-amylose maize, pop maize, and normal maize were initially classified into various subgroups by flow cytometer and then collected through flow sorting to observe their morphology and particle-size distribution. The results showed that a 0.25% Gelzan solution served as an optimal reagent for keeping individual starch particles homogeneously dispersed in suspension for a relatively long time. The bivariate flow cytometric population distributions indicated that the starches of normal maize, sweet maize, and pop maize were divided into two subgroups, whereas high-amylose maize starch had only one subgroup. Waxy maize starch, conversely, showed three subpopulations. The subgroups sorted by flow cytometer were determined and verified in terms of morphology and granule size by scanning electron microscopy and laser particle distribution analyzer. Results showed that flow cytometry can be regarded as a novel method for classifying and sorting starch granules. © 2017 International Society for Advancement of Cytometry.

Manipulation of the internal structure of high amylose maize starch by high pressure treatment and its diverse influence on digestion

In this study, high amylose maize starch was mixed with different moisture contents, followed by high hydrostatic pressure (HHP) at 200, 400, 600, 800 and 1000 MP, respectively. Changes in starch physicochemical and digestion properties associated with HHP treatment were analyzed in terms of starch granular morphology, lamellar structures and crystalline characteristics. Results showed that, under the same pressure treatments, the starches with different moisture contents exhibited a similar pattern of the changes in the properties. The erosion of digestive enzymes on starch granules was enhanced with increased HPP pressures. Treatment with 200 and 400 MP led to a reduction of digestibility compared to its native one. However, digestion was gradually promoted when the treatment pressure reached up to 600 MP. Structural data acquired from SAXS and WAX indicated the treatment of HHP up to 600 MP partly destroyed the starch granules internally, resulting in a decreased degree of organized structure. These results may reveal the importance of starch lamellar structure and crystalline order as being the key structural parameters for influencing starch digestion properties. Changes in the electron density following the digestion indicated that digestion characteristics of the starch are highly related to the changes in its corresponding internal structure of amylopectin amorphous layer, amylose amorphous and amylopectin crystal layer caused by HPP. Further analysis of the changes in the relative crystallinity of the starch may suggest that starch digestion characteristics are highly related to lamellar structure but not relative crystallinity.

Rheological characterization of gum and starch nanoparticle blends

Commercial interest on the application of starch nanoparticles (SNP) in food is rapidly growing. Since gums are commonly used in food processing for their texturizing functionality, it is important to understand the influence of SNP on gum rheology. λ-Carrageenan and xanthan gum were selected in this study due to their wide range of applications in food systems. SNP isolated from waxy (0% amylose) and high amylose maize (71% amylose) were used. Binary blends consisting of 0.5% (w/v) gum and different concentrations of SNP were prepared and their flow behaviors evaluated using a rheometer. The starch source, concentration and thermal stability of the SNP influenced the viscosity and viscoelastic properties of the gum-SNP blends, in particular in the low elasticity λ-carrageenan. The blends containing high concentrations of high amylose maize SNP, when compared to waxy SNP, showed higher viscoelastic stability at temperatures up to 90°C, possibly due to their higher thermal stability.

Investigation of the high-amylose maize starch gelatinization behaviours in glycerol-water systems

The effect of glycerol on gelatinization behaviours of high-amylose maize starch was evaluated by confocal laser scanning microscopy (CLSM), scanning electronic microscope (SEM), differential scanning calorimetry (DSC), texture analyzer (TPA) and rheometer. Gelatinization of the high-amylose maize starches with glycerol content of 10% (w/w) began at 95.4 °C (To), peaked at 110.3 °C (Tp), and completed at 118.9 °C (Tc). The birefringence began to disappear at around 100 °C and finished at 120 °C which corresponded well to the onset and conclusion temperatures obtained by DSC. The high-amylose maize starch granules maintained original morphological structure at 100 °C and swelled to a great degree at 110 °C. The high-amylose maize starch paste formed at 100 °C showed the lowest hardness (39.92 g), while at 120 and 130 °C, showed the highest hardness (610.89 g and 635.43 g, respectively). It should be noted that in going from 100 °C to 110 °C there is a significant increase in the viscosity of the slurry solution. The identical apparent viscosity was observed when the shear rate exceed 100 s−1, resulting from the high-amylose maize starch granules were completely gelatinized at 120 °C, which was consistent with DSC analysis.

Structural characteristics and prebiotic effects of Semen coicis resistant starches (type 3) prepared by different methods

In order to investigate the effects of different preparation methods on Semen coicis resistant starch, the structural properties and prebiotic effects of autoclaving treatment–purified S. coicis resistant starch (GP-SRS3), ultrasonic-autoclaving treatment–purified S. coicis resistant starch (UP-SRS3), enzyme-autoclaving treatment–purified S. coicis resistant starch (EP-SRS3) and microwave-moisture treatment–purified S. coicis resistant starch (MP-SRS3) were studied compared to high-amylose maize starch (HAMS). Fourier transform infrared spectroscopy and Solid-state 13C NMR spectroscopy showed all of SRS3 displayed B-type crystallite structure, furthermore, MP-SRS3 and UP-SRS3 showed higher degree of ordered structure and degree of double helical structure compared to other samples. Field emission scanning electron microscopy showed MP-SRS3 displayed deeply layered strips and UP-SRS3 exhibited some cavities. Moreover, S. coicis resistant starch could promote the growth of Bifidobacteria adolescentis better compared to high-amylose maize starch, among these samples. MP-SRS3 exhibited best prebiotic effect, which was possible attributed to its rough surface and double helix structure. B. adolescentis displayed a higher survival rate to the simulated gastrointestinal tract environment in SRS3 medium than that in high-amylose maize starch medium, especially MP-SRS3 and UP-SRS3, which partly contributed to its strips and cavities. Overall, MP-SRS3 could be regarded as a potential prebiotic to promote the growth of B. adolescentis for its structural trait.

The effect of resistant starches on fat oxidation in healthy adults as measured by a 13CO2-breath test

ABSTRACTA resistant starch (RS) mixture (MIX) consisting of fibre of potatoes (FP) and wrinkled pea starch (WPS), and high amylose maize starch (HAMS) were supplemented in adults to evaluate their effects on fat oxidation by means of a 13CO2-breath test. Sixteen subjects received a regular diet either without or with the supplementation of MIX and HAMS in randomised order. After administration of a [U-13C]algal lipid mixture, exhaled air was collected over 14 h in 0.5- and 1-h intervals. The 13C abundances were measured by nondispersive infrared spectroscopy. In comparison to the dry run (DR), supplementation with MIX and with HAMS increased the cumulative percentage dose recovery: (DR: 16.7 %, MIX: 16.9 %, HAMS: 18.0 %), but without statistical significance. The colonic degradation of MIX and HAMS to short-chain fatty acids tends to lower the formation of carbohydrate-derived acetyl-CoA and contributes to a postprandial lipid oxidation increase by using fat-derived acetyl-CoA as a compensatory fuel source.

Glycaemic response to butyrylated high amylose maize starch

Glycaemic response to butyrylated high amylose maize starch

Beneficial Effects of Fermentation of Whole Grains (WG) and Whole Grain Resistant Starch (RS) in Lean Zucker Diabetic Fatty (ZDF) Rats

Whole grain components have been shown to have a beneficial role concurrent with and independent of purified resistant starch (RS2) through intestinal fermentation when delivered as a fermentable dietary fiber. As Americans consume less than half of the recommended amounts of fiber, determining if a lower fiber dose can still provide benefits through use of WG and RS may still allow for health benefits in the context of lower intake. The current study was designed to delineate optimal health effects from a whole grain prebiotic using a dose response, where the beneficial effects of fermentation were expected to be observed beginning at 5% (wt diet). Estimates for comparing fiber in humans vs. rats are ~10% for equivalence. Previous studies with obese ZDF rats showed robust effects of fermentation on gut microbiota with no reduction of abdominal fat when fed RS. Additionally, Sprague Dawley (SD) rats demonstrated a significantly increased fermentation, though not as robust as ZDF rats, when fed WG, RS, and WG+RS diets, but also statistically significant differences in abdominal body fat as compared to obese ZDF rats. Isocaloric moderate fat (3.7 kcal/g, ~30% of energy) diets were developed with the following starch sources: control starch with no WG or RS [CON], natural WG waxy corn flour with low RS (35.1 %WG) [WGC], or increasing levels of a whole grain high amylose maize resistant starch (WGRS) [HMWG: 5 (9.3), 10 (18.6), 15 (27.9), 20% (37.2%) RS (%WG)]. The six diets were fed to lean ZDF rats for eight weeks (n=11; n=12 for 5%, 10% HMWG). Single degree of freedom contrasts (WGC vs. CON, 5%, 10%, 15%, 20%) were performed at p&lt;0.05. Beginning at 5% HWMG, pH had significant reduction as compared to WGC. Cecum weight significantly increased from 10% HMWG on. All short chain fatty acid (SCFA) measurements were significantly different for WG vs. CON. SCFA acetate and propionate showed a significant increase at 5% and increased consecutively through 20%, while butyrate increased at 15% and 20%. No significant differences were observed for food and energy intake and percentage abdominal fat/emboweled body wt (gut contents removed). At 5% HMWG, fermentation effects differed overall from the WG control. An indirect comparison of lean ZDF rats and obese ZDF rats has shown similarity in fermentation and no changes in body fat. As WGRS dosage increased, gut health benefits (fermentation parameters) increased, but did not affect food and energy consumed or abdominal fat. WG flour alone promoted fermentation with RS1, a component of the WG kernel, and WGRS (RS1+RS2) promoted greater fermentation. Replacing traditional starch for a whole grain starch is beneficial, while replacing it with a whole grain with resistant starch, as low as 5%, is better. These results suggest that a lower level of intake of fermentable fiber as RS is beneficial, but show that substantial WG (35.1%) with only low RS1 (2%) also had beneficial effects.Support or Funding InformationUSDA–NIFA #2014–67017–21760, LSU AgCenter and Ingredion Incorporated.

Effect of acid-ethanol treatment and debranching on the structural characteristics and digestible properties of maize starches with different amylose contents

In this study, maize starches with different amylose contents were modified by acid-ethanol treatment (AET) to various degrees, followed by debranching and then recrystallization through temperature cycling to produce resistant starch type III (RS3). The structural characteristics and digestible properties of the AET-debranched starches were investigated. The result indicated significant reductions in amylose and long side-chain length in high-amylose maize starch (HMS) and normal maize starch (NMS), but minor variations in the chain-length distribution in waxy maize starch (WMS). All three maize starches exhibited increased relative crystallinities and RS levels following moderate AET; however, the increment varied according to starch types. The highest RS contents of HMS, NMS, and WMS at 66.8%, 58.7%, and 68.4% were obtained after 8 h, 24 h, and 14 h of AET, respectively. These results indicated that the appropriate reduction in chain length following AET and prior to debranching was beneficial to RS3 formation.

The effect of salt concentration on swelling power, rheological properties and saltiness perception of waxy, normal and high amylose maize starch.

The effect of salt concentration on swelling power, rheological properties and saltiness perception of waxy, normal and high amylose maize starch was investigated. The swelling power decreased with increasing salt concentration from 0% to 2.0% among all starch samples. Waxy starch showed the highest swelling power at different salt levels, while high amylose starch showed the least swelling power. The salt addition increased the gelatinization temperature of waxy starch and normal starch from 71.3 °C to 77.1 °C and from 72.3 °C to 78.2 °C. Their storage modulus (G'), loss modulus (G''), and viscosity values at lower salt concentration were greater than those at higher salt concentration. The increasing tan δ of waxy and normal starch against frequency sweep indicated liquid-like behavior, while high amylose starch exhibited decreasing tan δ indicating solid-like behavior as it was difficult to gelatinize. When sensory evaluation was conducted by trained panelists, it was found that high amylose starch displayed the highest initial saltiness and in-mouth saltiness intensity, accompanied by the greatest thickness, lubrication and stickiness, while waxy starch displayed the lowest values for saltiness perception and mouthfeel.

Effects of oligomeric procyanidins on the retrogradation properties of maize starch with different amylose/amylopectin ratios.

The effect of oligomeric procyanidins (OPCs) on the retrogradation of maize starch with different amylose/amylopectin ratios was investigated. The apparent amylose contents in high-amylose maize (HAM), normal maize (NM), and amylopectin maize (APM) starches are 79.05%, 25.43% and 0%. Structural characterizations of retrograded maize starches in the presence of OPCs were conducted by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and nuclear magnetic resonance (NMR). The results suggest that OPCs inhibit the retrogradation of maize starches in low concentrations (1.5-2.5%) with different inhibitory effects for HAM, NM and APM starches. It may be attributed to the variations on interaction ways and binding capabilities between different types of starches and OPCs. The in vitro enzymatic digestion result indicates HAM starch and OPCs have stronger interactions with the formation of resistant structures. These findings provide a further evidence for exploring the interactions between starches and phenolic compounds.

Morphologies and gelatinization behaviours of high-amylose maize starches during heat treatment

The granule morphologies and gelatinization behaviours of high-amylose maize starches during heating treatment were investigated by confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). Maltese crosses demonstrated that the high-amylose maize starches maintained a granular structure even at 120°C. The granules of high-amylose maize starches swelled slightly at 100°C and swelled remarkably at approximately 120°C. The destruction of the starch structure began at the centre and expanded rapidly to the periphery. The intense fluorescence of high-amylose maize starch granules gradually became feeble, and the darker region spread outward during heating at 130°C for 30min, indicating that the amylose component may have been damaged and shifted. The starch granules treated at 140°C were substantially destroyed, and the CLSM, normal light microscopy (NL) and SEM images displayed no discernible granules, which indicated that the original starch granules formed a continuous integrated matrix.

Anaerobic biodegradation, physical and structural properties of normal and high-amylose maize starch films

Abstract: Biodegradable plastics have attracted considerable attention in recent years due to their biodegradability, biocompatibility and non-toxicity. In this study, normal maize starch (containing 25% amylose) and high-amylose maize starch (containing 80% amylose) were served as model materials to prepare starch/polyvinyl alcohol (PVA) blends. To comprehensively study the effects of amylose contents on the film performances, the mechanical properties, water resistance and anaerobic biodegradability of the two films were examined. Moreover, the processes of anaerobic degradation were investigated by evolutions of biogas production, pH in reactors and the changes of film structures and compositions. The results indicated that amylose content played an important role in the microstructures of starch film as well as mechanical properties and water resistance, whereas it had no significant influence on anaerobic biodegradability of the films. Nonetheless, the structure of high-amylose maize starch/PVA film was more suitable and beneficial to the anaerobic biodegradation than that of the normal maize starch/PVA film, because it could effectively avoid accumulation of volatile fatty acids, which contributed to the stable biogas production, short fermentation period and non-souring in the reactor. Keywords: maize starch film, anaerobic biodegradation, polyvinyl alcohol(PVA), amylose content, biopolymer DOI: 10.3965/j.ijabe.20160905.2005 Citation: Liu W W, Xue J, Cheng B J, Zhu S W, Ma Q, Ma H. Anaerobic biodegradation, physical and structural properties of normal and high-amylose maize starch films. Int J Agric & Biol Eng, 2016; 9(5): 184－193.

Enhanced fluorescence of starch-fluorescence guest complexes enables evaluation of the encapsulation properties of maize starches

In this study, high-amylose maize starch (HAMS) was mixed with salicylic acid, 1-naphthol, and 2-naphthol, and the physical mixtures were then subjected to a sealed-heating procedure to prepare HAMS-fluorescence guest complexes. The results, obtained from wide angle X-ray scattering and thermogravimetric analysis, showed that all three fluorescence guests were encapsulated in the hydrophobic cavity of HAMS. After screening, salicylic acid was chosen as the most suitable fluorescent probe for evaluating the properties of the starch helix cavity. The formation of a starch-salicylic acid inclusion complex was accompanied by increased fluorescence from the salicylic acid molecules included in the complex. The hydrophobicity of the starch helix cavity and the capability of starch to form inclusion complexes could be evaluated from the increasing intensity of the fluorescence. Accordingly, the capabilities of maize starches to form inclusion complexes followed the order: high-amylose maize starch > normal maize starch > waxy maize starch.

Lytic polysaccharide monooxygenases and other oxidative enzymes are abundantly secreted by Aspergillus nidulans grown on different starches

BackgroundStarch is the second most abundant plant-derived biomass and a major feedstock in non-food industrial applications and first generation biofuel production. In contrast to lignocellulose, detailed insight into fungal degradation of starch is currently lacking. This study explores the secretomes of Aspergillus nidulans grown on cereal starches from wheat and high-amylose (HA) maize, as well as legume starch from pea for 5 days.ResultsAspergillus nidulans grew efficiently on cereal starches, whereas growth on pea starch was poor. The secretomes at days 3–5 were starch-type dependent as also reflected by amylolytic activity measurements. Nearly half of the 312 proteins in the secretomes were carbohydrate-active enzymes (CAZymes), mostly glycoside hydrolases (GHs) and oxidative auxiliary activities (AAs). The abundance of the GH13 α-amylase (AmyB) decreased with time, as opposed to other starch-degrading enzymes, e.g., the GH13 AmyF, GH15 glucoamylases (GlaA and GlaB), and the GH31 α-glucosidase (AgdE). Two AA13 LPMOs displayed similar secretion patterns as amylolytic hydrolases and were among the most abundant CAZymes. The starch-active AnLPMO13A that possesses a CBM20 carbohydrate-binding module dominated the starch-binding secretome fraction. A striking observation is the co-secretion of several redox-active enzymes with the starch-active AA13 LPMOs and GHs, some at high abundance. Notably nine AA9 LPMOs, six AA3 sub-family 2 (AA_2) oxidoreductases, and ten AA7 glyco-oligosaccharide oxidases were identified in the secretomes in addition to other non-CAZyme oxidoreductases.ConclusionsThe co-secretion and high abundance of AA13 LPMOs are indicative of a key role in starch granule deconstruction. The increase in AA13 LPMO abundance with culture time may reflect accumulation of a more resistant starch fraction towards the later stages of the culture. The identification of AmyR sites upstream AA13 LPMOs unveils co-regulation of LPMOs featuring in starch utilization. Differential deployment of amylolytic hydrolases and LPMOs over time suggests additional regulatory mechanisms. The abundant co-secretion of distinct AA3 and AA7 oxidoreductases merits further studies into their roles and possible interplay with LPMOs and other enzymes in the deconstruction of starchy substrates. The study reports for the first time the biological significance of LPMOs in starch degradation and the temporal interplay between these and amylolytic hydrolases.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0604-0) contains supplementary material, which is available to authorized users.

Characterization and Prebiotic Effect of the Resistant Starch from Purple Sweet Potato.

Purple sweet potato starch is a potential resource for resistant starch production. The effects of heat-moisture treatment (HMT) and enzyme debranching combined heat-moisture treatment (EHMT) on the morphological, crystallinity and thermal properties of PSP starches were investigated. The results indicated that, after HMT or EHMT treatments, native starch granules with smooth surface was destroyed to form a more compact, irregular and sheet-like structure. The crystalline pattern was transformed from C-type to B-type with decreasing relative crystallinity. Due to stronger crystallites formed in modified starches, the swelling power and solubility of HMT and EHMT starch were decreased, while the transition temperatures and gelatinization enthalpy were significantly increased. In addition, HMT and EHMT exhibited greater effects on the proliferation of bifidobacteria compared with either glucose or high amylose maize starch.