High-amylose Wheat Starch Research Articles

Dynamic rheological behavior of high-amylose wheat dough during various heating stages: Insight from its starch characteristics

The objective of this study was to understand how the dynamic rheological behaviors of high-amylose wheat (HAW) dough during various heating stages measured using a mixolab were affected by the starch properties. At the heating stage of 30 °C - 90 °C, low minimum (C2) and peak (C3) torques were observed for HAW doughs, which resulted from their reduced starch granule swelling. During holding at 90 °C, HAW doughs had low minimum (C4) and C3 - C4 torques, indicating a good resistance to mechanical shear and endogenous enzyme degradation. HAW doughs also had low final (C5) and setback (C5 - C4) torques, consistent with their low starch swelling power and solubility. The increased amylose in HAW starch formed long-chain double-helical B-type polymorph and amylose-lipid complex, which resulted in high starch gelatinization-temperatures and enthalpy change, low swelling power and solubility, low pasting viscosity, and high resistance of swollen granules to mechanical shear and enzyme degradation. The overall patterns of dough-rheological behavior of HAW doughs during heating were similar to their respective starch pasting profiles, indicating that starch was the dominant contributor to the dough rheology during heating. This study provides useful information for food applications and manufacturing of HAW-based products, especially none-fermented products requiring firm texture and low viscosity.

Characterization of structure-function properties relevant to copper-activated pyrite depression by different starches

Starches can adsorb on and depress copper-activated pyrite desirably during flotation, an important process in ore mineral extraction. In order to develop structure/function relationships, adsorption on and depression properties of copper-activated pyrite at pH 9 by normal wheat starch (NWS) and high-amylose wheat starch (HAW), dextrin, and a range of oxidized normal wheat starches (peroxide and hypochlorite treated) were investigated. Adsorption isotherms and bench flotation performance were compared with kinematic viscosity, molar mass distribution, surface coverage, and substituted functional groups assay. The differences in molar mass distribution and substituted functional groups among oxidized starches had little influence on the depression of copper-activated pyrite. However, the introduction of -C=O and -COOH substituents, combined with depolymerization, improved solubility and dispersibility, reduced aggregated structures, and strengthened surface binding of oxidized polymers, compared with NWS and HAW. At high concentrations, HAW, NWS, and dextrin were adsorbed onto the pyrite surface more than oxidized starches. However, at the low concentrations of depressant used in flotation, oxidized starches were more effective at selectively masking copper sites. This study suggests that a stable chelation between Cu(I) and starch ligands is necessary for depression of copper-activated pyrite at pH 9, which can be achieved with oxidized wheat starch.

High-amylose wheat tortillas with reduced in vitro digestion and enhanced resistant starch content

Increased nutritional functionality in bread and noodles have been reported with the incorporation of high amylose wheat flour (HAWF). Here, we broaden the application of HAWF and report structure-function-nutrition relationships for tortillas prepared with 50% and 100% incorporation of HAWF. The breaking force and extensibility of the HAWF tortillas were lower than controls resulting from incompletely gelatinized high-amylose wheat starch (HAWS). The digestion degree of tortillas was significantly reduced by increase of amylose content due to HAWS structural features and enzyme hindrance effects of greater protein content, with resistant starch (RS) content increasing from ∼3% in control (32% amylose) to ∼12% in tortillas with 71% amylose and ∼23% in tortillas with 84% amylose. In addition, tortillas showed lower starch digestion and higher RS than loaf bread or noodle counterparts. This demonstrates that wheat food in-vitro enzyme hydrolysis is not only a function of starch structure, but also the local density of the microstructure formed during food processing.

Amorphous packing of amylose and elongated branches linked to the enzymatic resistance of high-amylose wheat starch granules

To elucidate starch structural features underlying resistant starch formation, wheat starch granules with three (A-, B- and C- type) crystalline polymorphisms and a range of amylose contents were digested in vitro. The changes in multi-level structure of digestion residues were compared. In the residues of A- and C-type starches, the molecular fine structure (distributions of chain length and whole molecular size), as analyzed by size exclusion chromatography (SEC), remained similar during digestion. In contrast, B-type high amylose wheat starch (HAWS) showed distinct changes in multi-level structures of digestion-resistant fractions: (1) the peak of longer amylopectin branches shifted to a lower degree of polymerization (40 DP); (2) production of α-limit dextrin (~2 nm hydrodynamic radius) in the residues; (3) a small increase of double helix content during digestion, in contrast to 6 % reduction for the A-type starch; (4) a decrease (6 °C lower) in the melting temperature of amylose-lipid complexes. The comparison suggests that elongated branches in B-type starch contribute to the formation of resistant fraction (including α-limit dextrin) against α-amylase. The amorphous packing of starch polymers with elongated branches together with the absence of surface pores and channels is proposed to be the basis for the enzymatic resistance of granular HAWS.

Molecular-structure evolution during in vitro fermentation of granular high-amylose wheat starch is different to in vitro digestion

This study investigates the evolution of the distributions of whole molecular size and of chain length of granular wheat starches (37 ~ 93% amylose content), subjected to in vitro fermentation with a porcine faecal inoculum or digestion with pancreatic enzymes. The results showed that the molecular structures of high-amylose starch (HAS) unfermented residues largely remained unchanged during the fermentation process, while wild-type starch (37% amylose content) showed a preferential degradation of the amylopectin fraction. In contrast, under simulated digestion conditions, the undigested residues of HAS showed structural changes, including a decrease in amylose content, a shift of amylose peak position towards lower degrees of polymerisation, and an enzyme-resistant fraction. These changes of starch structure are likely to be dependent on the different starch-degrading enzyme activities present in pancreatic vs. microbial systems. Molecular changes in response to fermentation metabolism revealed by size-exclusion chromatography can help understand the microbial utilization of resistant starch.

Starch granular protein of high-amylose wheat gives innate resistance to amylolysis.

Granular protein is an important structural feature in determining starch digestibility. High-amylose wheat starch (HAWS) with >80% amylose content contains more granular protein than wild-type starch. As analyzed by mass spectrometry-based proteomics, granular-bound starch synthase (GBSS) is the major granular protein in isolated starch materials. GBSS content increases with amylose content (Spearman's correlation, p<0.05), whereas the abundance relative to other proteins is similar among starches. Multiple amylase inhibitors were also identified. From Michaelis-Menten analysis, HAWS has a similar Km (Michaelis constant) as wild type, suggesting initial enzymatic binding is similar. After the pre-digestion of proteins, wild type had a greater change in starch digestibility than HAWS, probably due to the latter having 'thicker' granular-protein layers and higher enzymatic resistance of substrate per se. Overall, the study suggests that the greater granular protein content in HAWS is a factor that contributes to slower amylolysis compared to wild type.

High-amylose wheat starch: Structural basis for water absorption and pasting properties

High-amylose wheat starch (HAWS) and flour (HAWF) have the potential to deliver food products with enhanced nutritional functionality, but structure/function relationships are not well understood. We report the structural bases for differences in water absorption and pasting properties for HAWS and HAWF (amylose contents 71–84 %) compared with wild-type (WTWS/WTWF). With higher amylose content, the proportion of longer amylopectin chains with DP > 25 increased. Both the degree of branching and the branch lengths of amylose were lower for HAWS than WTWS. Compared with WTWF, HAWF contained less total starch, more protein, had lower peak viscosity by high-temperature RVA, lower dough development time and stability time and higher water absorption by Farinograph. Water absorption by HAWS was ∼1.5 times greater than for WTWS, suggesting loose packing of polymers within HAWS granules. Consistent with this, crystallinity and birefringence of starch granules were lower in HAWS.

High-amylose wheat and maize starches have distinctly different granule organization and annealing behaviour: A key role for chain mobility

For regular starches, gelatinization occurs over a relatively narrow temperature range in excess water; however, high-amylose starches typically gelatinise over an extended temperature range by a process that is less understood. The present study compared granule organisation of high-amylose starches from wheat (HAWS) and maize (HAMS), and investigated the role of granule organization in determining the gelatinization heterogeneity and different responses to annealing. During gelatinization (starch/water = 1:2), the melting peaks of double helices and amylose-lipid complexes are merged in HAMS, whereas the peaks are separated for HAWS. It is hypothesized that the glucan chains in HAWS are relatively more mobile (i.e., fewer inter-chain interactions), compared to HAMS. Due to this mobility, hot water leaches amylose more readily from HAWS than from HAMS at similar levels of apparent amylose content. After two-step annealing, To (gelatinization onset temperature) of HAWS increased from 58 to 84 °C, while To of HAMS only increased from 70 to 82 °C. For HAWS, annealing apparently extended double helical lengths and made semi-crystalline lamellae more heterogeneous, but reduced double helix content. For HAMS with more organised granular structure, annealing has a relatively limited effect on lamellar layers and chain conformation. The study demonstrates that HAMS and HAWS have distinctly different granule organisation and behaviours during hydrothermal processing and that HAWS, with more mobile chains, has the potential to form thermostable molecular order. The molecular basis for these differences is proposed to be the greater proportion of very long chains/branches in HAWS than HAMS.

High amylose wheat starch structures display unique fermentability characteristics, microbial community shifts and enzyme degradation profiles.

A slower rate of starch digestion in the small intestine increases the amount of resistant starch (RS) entering the large intestine, which is associated with health benefits. Although increasing the amylose (AM) content of dietary starch intake is one way to increase RS, the processes involved in gut microbial hydrolysis and fermentation of high AM-RS substrates are poorly understood. In this study, five high AM wheat (HAW) starches ranging from 47% AM to 93% AM and a wild type (37% AM), in both native granular and cooked forms, were subjected to in vitro fermentation with a porcine faecal inoculum. Fermentation kinetics, temporal microbial changes, amylolytic enzyme activities and residual starch were determined. All granular starches showed similar fermentation characteristics, independent of AM level, whereas cooking accelerated fermentation of lower AM but slowed fermentation of high AM starches. HAW starches with a very high AM content (>85%) all had similar fermentation kinetics and short-chain fatty acid end-product profiles. Microbial α-amylase, β-amylase, pullulanase and amyloglucosidase enzymatic activities were all detected and followed fermentation kinetics. HAW starch promoted shifts in the microbial community, with increases of the family Lachnospiraceae and the genus Treponema observed, while the genera Prevotella and Streptococcus were reduced in comparison to 37% AM. Overall, these findings suggest that any HAW starch incorporated into high RS food products would be expected to have beneficial microbiota-mediated effects in terms of fermentation kinetics and end products.

Altering starch branching enzymes in wheat generates high-amylose starch with novel molecular structure and functional properties

Starch that escapes intestinal digestion (resistant starch, RS) is non-glycaemic and considered as dietary fibre. In planta increase of amylose content is a promising approach to make starch resistant to enzyme digestion. Compared to maize, little is known on the effect of amylose content at different length scales of high-amylose wheat (HAW) starch structure and properties. A range of starches with 37%–93% apparent amylose content (AM) were isolated from high-amylose bread wheat produced through non-transgenic breeding altering starch branching enzymes (SBE IIa and IIb). Compared to mutations only in SBEIIa, mutations of both SBE IIa and IIb resulted in higher amylose content with significantly increased proportion of long amylopectin chains (degree of polymerization ≳ 20) and amylose chains. The modified starch molecular structure has significant correlations with starch supramolecular structure and functionality. Compared with wild-type starch, HAW starches showed distinct granular morphology and crystalline pattern with a higher fraction of B-type and V-type polymorph (amylose complex). The peak temperature (Tp) was higher but the onset temperature (To) of gelatinization was not greatly raised (<3 °C) by the mutations. Pasting behaviour of HAW starches (AM<50%) remained similar to wild type, but was greatly reduced at higher AM levels. The data suggest that, depending on food processing condition requirements, different functional and RS properties can be selected based on wheat starch AM content.

High amylose wheat starch increases the resistance to deformation of wheat flour dough

High amylose wheat (HAW) starch has been the focus of a number of nutritional studies, but there is limited information around its effect on the mechanical properties of wheat flour dough. This study investigated the size, shape and packing volume of HAW starch and their effect on the microstructure and rheology of dough. Four flour blends were formulated by adding vital wheat gluten and either HAW or commercial wheat starch to HAW flour to achieve a constant 14% protein content, but varied amounts of HAW starch. A large number of small and irregularly shaped HAW starch granules resulted in a high packing volume per gram of starch. Confocal laser scanning microscopy of optimally mixed doughs correlated the degree of starch granule aggregation with the level of HAW starch in the bi-continuous dough network. Small deformation rheology demonstrated that increased quantities of HAW starch in the dough increased the elastic modulus G′ values. Uniaxial extension measurements highlighted a synergy between HAW starch and sources of gluten proteins resulting in increased strain hardening. The impact of HAW starch on dough rheology was attributed to its irregular shape and large number of small granules leading to greater granule-granule interactions.

Multi‐scale structural and digestion properties of wheat starches with different amylose contents

SummaryThe physicochemical and digestion properties of three wheat starches with different amylose contents were studied. Scanning electron microscopy (SEM) showed they displayed a spherical disc‐like form, a lenticular shape and an irregular morphology, respectively. Compared with waxy and normal wheat starches, high‐amylose wheat starch (HAWS) was characterised by the presence of lower molecular weight amylose fraction, and its granules demonstrated the highest resistance to the cooking. The changes in the IR ratio 1022/999–1047/1022 cm−1 following the gel storage suggested the molecules of HAWS are more readily to re‐associate and re‐organise into a more organised status than other two starches. The determination of glucose release showed that HAWS had the lowest digestion kinetics (P &lt; 0.001), and this difference in the digestion properties between HAWS and the other two starches might imply that starch molecular structure, in particular amylose structure is another key factor for manipulating starch digestion property rather than amylose content alone.

Contents and Heat-moisture Treatment Effect of Resistant Starch in High Amylose Wheat Starch

Contents and Heat-moisture Treatment Effect of Resistant Starch in High Amylose Wheat Starch

Physicochemical characteristics and fine structure of high-amylose wheat starches isolated from Australian wheat cultivars

High-amylose starch is a source of resistant starch (RS) which have great impact on human health like dietary fiber. Nowadays, high-amylose wheat has been produced by genetic backcrossing, which enhances apparent amylose content and generates altered amylopectin. In this study, the high-amylose wheat starches isolated from various high-amylose wheat cultivars grown in Australia were characterized for understanding their physicochemical properties and fine structure of starch. The physicochemical characteristics of the high-amylose wheat starches are significantly different among the cultivars. Amylose contents of these cultivars were in a range of 28.0–36.9%, which is significantly higher than that of the normal wheat starch (25.6%). The high-amylose wheat starches also had higher blue value but lower λ max than the normal wheat starch. Gelatinization temperature of the high-amylose wheat starches is higher than that of the normal wheat starch but transition enthalpy is lower. X-ray diffraction showed that the high-amylose wheat starch had C-type crystals close to A-type crystal. Pasting properties of the high-amylose wheat starches were varying depending on the cultivars. However, almost high-amylose wheat starches had lower peak and final viscosities and higher setback viscosity than did the normal wheat starch. Fine structure of amylose and amylopectin was different among the high-amylose wheat cultivars and related to the physicochemical properties of starch. These results help to understand well the characteristics of the high-amylose wheat starches before application for food processing.

Waxy and high-amylose wheat starches and flours—characteristics, functionality and application

Starch is a predominant component of wheat grain. It plays an important role in appearance, structure and quality of food products. Starch consists of two kinds of glucose polymers (amylose and amylopectin) with the ratio of amylose/amylopectin ranging between 25–28 and 72–75%, respectively. The isoforms of granule-bound starch synthase (GBSS) are responsible for the biosynthesis of amylose fraction, whereas amylopectin synthesis is more complicated with concerted activities of the soluble starch synthase together with branching and de-branching enzymes. Recently, waxy (amylose-free) and high-amylose wheats produced through the development of new physicochemical and biological techniques provide the unique starch functional properties. The starches of these wheats have the specific structures and unique characteristics that are believed to enhance the quality of food products. In this review, we will focus on recent advances in the studies of the characteristics of waxy and high-amylose wheat flours and starches and their application for food processing. In addition, we also propose further research ideas for clearer understanding of their characteristics and for their effective utilization.

Resistant starch and starch pasting properties of a starch synthase IIa-deficient wheat with apparent high amylose

The bread wheat (Triticum aestivum L.) analysed in this study has been produced by genetically eliminating the starch synthase IIa and shows apparent high amylose (HA) in the flour starch. Some starch properties of the HA wheat were analysed. The HA wheat contained 2.8–3.6% resistant starch (RS), much more than the normal (control) wheat, which contained almost no RS. Autoclaving the HA and normal wheat starches increased RS. The former contained 10.5% RS and the latter 5.9 or 6.8% RS. Swelling of the HA wheat starch and its pasting properties using Rapid ViscoAnalyzer (RVA) were investigated. Swelling power (g/g) of the HA wheat in 0.1% AgNO3 and swelling volume (mL/g) in urea solution were significantly less than those of the normal wheat. The RVA profile of the HA wholemeal and starch also differed from the normal. The peak viscosity, minimum viscosity, and final viscosity of HA were low, and breakdown (peak minus minimum viscosity) was very small. These findings show that amount of resistant starch and pasting properties are unique in the HA wheat starch, probably caused by lack of starch synthase IIa.