Small-granule starch has many advantages for advanced food applications. Annealing could expand the advantages of small-granule starch by modifying their properties without disrupting the granular integrity. The study compared the annealing of three small-granule starches (from amaranth, quinoa, and taro) with that of conventional starches (from potato and maize). The impacts of annealing on the properties were diverse among small-granule starches and also the controls. The diversity was collectively affected by the molecular and supramolecular structures of these starches. The role of the branched backbone of amylopectin in modulating the annealing-induced changes, in addition to that of shortand long-range ordered structures, was revealed by a novel method developed based on the building block backbone model and branch scattering theory. Taro starch exhibited interesting changes in supramolecular structure and physicochemical properties (thermal properties and temperature-dependent viscoelastic properties), which were associated with a unique modification in the distribution of branches in its granules. The proportion of small branched building blocks in the Naegeli dextrins increased in taro starch after the annealing. The results provided novel insight into the barely changed shortrange order but improved long-range order of taro starch upon annealing. The study demonstrated that variations in molecular structure strongly influence the extent and nature of annealing-induced changes in starch supramolecular order and functionality.

C-type starch has a mixed crystalline structure with B-type in the central region of the granules and A-type in the periphery region, though the polymorph distribution remains to be better studied. This study used 90 % dimethyl sulfoxide (DMSO) solution as a chemical gelatinization agent to treat granular pea and chickpea starches (C-type). Morphological observations showed that the periphery layer of pea and chickpea starch granules did not undergo an ideal peeling of surface gelatinization. X-ray diffraction on granular residues indicated that more A-type starch fraction was maintained after the chemical gelatinization. The starch granules were partly gelatinized from the surface and partly gelatinized from the central region upon the disintegration of starch granules. Temperature-dependent rheological properties of the native starches showed two-phase swelling, while that of chemical gelatinized starches did not. For most starches (except for small-granule pea starch), amylose chain length was significantly shorter in the granular residues after the chemical gelatinization compared to their native counterpart. The results suggested that DMSO selectively gelatinized starch granules, in which the structure of amylose made a difference. The present study highlighted the possibility of separating A- and B-type fractions in individual starch granules.

Structural nature of glucan chains in the amorphous part of granular starch was examined by iodine vapor treatment and lintnerization. Four iodine-stained amylose-containing normal starches and their waxy counterparts were examined under a microscope before, during, and after lintnerization. The presence of amylose retarded the lintnerization rate. The degree of retardation correlated with the structural type of the amylopectin component, suggesting that potato amylopectin (type 4 structure) interacts with amylose in the granules, whereas in barley granules (type 1 structure) the interaction is very weak. The inclusion complexes with iodine were not degraded by the acid treatment. Therefore, the iodine-glucan chain complex formation could be used to study the structural nature of the flexible, amorphous parts of the starch granules. Indeed, at the end of lintnerization, when 20%-30% of the granules remained, substantial amounts of blue-stained complexes were washed out from the granules especially from amylose-containing barley and maize starch, but also from both normal and waxy cassava and potato starch. The complexation with iodine did not affect the rate of lintnerization. This suggested that single helical structures were present during lintnerization also in the absence of iodine and this conformation was the reason for the acid resistance.

This investigation validated iodine binding in combination with lintnerization for studying the structural nature of the amorphous areas in starch granules. Lintners of four iodine vapor-stained and non-stained amylose-containing starches and their waxy counterparts were analyzed by high-performance anion-exchange chromatography (HPAEC). The composition of the lintners was strongly affected by the absence of amylose in barley and potato starch but not in maize and cassava starch. Iodine-stained waxy lintners possessed increased number of long B2 chains. β-Limit dextrins of the lintners were very variable in composition. Iodine inclusion complexes washed out from the granular residues in the lintners (mostly from amylose-containing barley and maize starches) were also analyzed. Acid-soluble complexes from both amylose-containing and waxy starches possessed a lot of material with a degree of polymerization (DP) around 60 and a periodicity in size of DP 8-12. Such long chains were only minor components in water-soluble complexes of amylose-containing barley and maize starch lintners, and they lacked the size periodicity. Models of the principal structure of the acid and water-soluble complexes are suggested. It is concluded that acid hydrolysis of iodine-stained starch granules is a useful tool in structural analyses of the molecular composition of amorphous parts of starch granules.

Understanding functionality of polysaccharides such as starch requires molecular representations that account for their functional characteristics, such as those related to gelatinization, gelation, and crystallization. Starch macromolecules are inherently very complex, and precise structures can only be deduced from large data sets to generate relational models. For amylopectin, the major, well-organized, branched part of starch, two main molecular representations describe its structure: the classical cluster model and the more recent backbone model. Continuously emerging data call for inspection of these models, necessary revisions, and adoption of the preferred representation. The accumulated molecular and functional data support the backbone model and it well accommodates our present knowledge related to the biosynthesis of starch. This Perspective focuses on our current knowledge of starch structure and functionality directly in relation to the backbone model of amylopectin.

High amylose and waxy starches from maize and potato were incubated with plasma-activated water (PAW) at 25 degrees C, 60 degrees C, and 80 degrees C temperatures to investigate PAW treatment effects on the starches' properties. At 60 degrees C incubation temperature, the starches were basically annealed with PAW. Annealing starches with PAW signifi-cantly increased (p < 0.05) the gelatinization parameters except for the enthalpy of gelatinization of waxy potato starch. Furthermore, starch swelling power significantly decreased while the water absorption capacity and solubility increased significantly when incubated at 80 degrees C. X-ray photoelectron spectroscopy (XPS) analysis showed the oxidation of C-C/C-H and C-O into carboxyl groups in waxy and high amylose maize starches incubated with PAW at 60 degrees C and 80 degrees C, respectively. In addition, cross-linking was observed in waxy maize and high amylose potato incubated with PAW at 80 degrees C and 25 degrees C, respectively. Overall, the results indicated PAW temperature is an important factor in modifying cereals and tuber starches with PAW.

This review systematically documents the major different strategies of generating high-amylose (HAS) starch mutants aiming at providing high resistant starch, by engineering the starch biosynthesis metabolic pathways. We identify three main strategies based on a new representation of the starch structure: ‘the building block backbone model’: i) suppression of starch synthases for reduction of amylopectin (AP) side-chains; ii) suppression of starch branching enzymes (SBEs) for production of AM-like materials; and iii) suppression of debranching enzymes to restrain the transformation from over-branched pre-AP to more ordered AP. From a biosynthetic perspective, AM generated through the second strategy can be classified into two types: i) normal AM synthesized mainly by regular expression of granule-bound starch synthases, and ii) modified linear AP chains (AM-like material) synthesized by starch synthases due to the suppression of starch branching enzymes. The application of new breeding technologies, especially CRISPR, in the breeding of HAS crops is also reviewed.

Starch is a major energy store in many plants and microorganisms. Semi-crystalline starch granules consist of two major glucans known as amylose and amylopectin. Amylose is a linear or slightly branched polymer with a comparatively simple structure that forms helical inclusion complexes with a range of ligands, such as fatty acids and iodine. Amylopectin, which is the major polymer in most starch granules, is extensively branched. It is considerably larger and has a more complex structure than amylose. In addition, some starch granules, notably those from mutant plants, contain materials with structures intermediate between amylose and amylopectin. The cluster model, originally proposed in the early 1970s, suggests that short chains of amylopectin are clustered and form double helices that constitute crystalline lamellae in the starch granules. However, more recent structural analyses of isolated -dextrins have challenged the accuracy of this traditional model. Instead, the so-called building block backbone model offers a rational platform that not only explains the semi-crystalline structure of the starch granules, but also systematically organizes the starches based on four distinct structural types of amylopectin

The relationship between molecular structure and crystalline and lamellar structures of fifteen types of rice starches was studied. GPC and HPAEC were used for the molecular chain analysis and WAXS, SAXS, and CP/MAS 13C NMR were employed for aggregation structural analysis. The amylopectin content and the average lengths of fb1-chains (the degree of polymerization (DP) 13-24) were positively correlated with the amount of double helices (r2 = 0.92 and 0.57, respectively). In contrast, amylose content was positively correlated with the amounts of amorphous materials in starch (r2 = 0.77). The amount of double helices, which constitute a major part of the crystalline matrix, was positively correlated with the lamellar ordering (r2 = 0.81), and negatively correlated with the thickness of crystalline lamellae (r2 = 0.90) and lamellar repeat distance (r2 = 0.84). Conversely, the amount of the amorphous matrix was correlated with these parameters in the opposite way (r2 = 0.50, 0.75, and 0.75, respectively).

Starch from bananas/plantains, belonging to the genus Musa spp, is gaining prominence given its great potential as a healthy food ingredient made from an inexpensive raw material. Recent works highlight the outstanding potential of Musa starch to develop enzyme-resistant structures upon retrogradation. However, despite the wide variety of Musa cultivars (due to both natural mutation and breeding selection), there is no comparative investigation of the starch molecular structure from the most commonly cultivated Musa genotypes. In this work, the starch from six Musa cultivars harvested during the same growing season from the same parcel, was purified and analyzed for amylose ratio, amylose chain length distribution, and amylopectin unit and internal chain length distribution. Results showed significant differences between the fine structure of all Musa amylopectin molecules, which were structurally categorized as type 4 (consisting of a high number of B3-chains, few BS- and B-fp-chains, and low S:L and BS:BL ratios). Moreover, the different Musa starches exhibited dramatic differences in amylose ratio (17.7-27.6%), amylose branching degree (as evidenced by differences in the population of short chains of approximately 260 glucose units, GU) and a shorter average length (approximately 1000 GU) of the population of long amylose unit chains. Remarkably, these differences in amylose structure resulted in the cultivar Manzano (Musa AAB, silk subgroup) to possess a dramatically lower extension of in vitro starch digestion (C-90 = 4.70%) than the rest of the cultivars (C-90 = 17-18%) after full gelatinization and retrogradation for 7 days.

Starch is a water-insoluble polymer of glucose synthesized as discrete granules inside the stroma of plastids in plant cells. Starch reserves provide a source of carbohydrate for immediate growth and development, and act as long term carbon stores in endosperms and seed tissues for growth of the next generation, making starch of huge agricultural importance. The starch granule has a highly complex hierarchical structure arising from the combined actions of a large array of enzymes as well as physicochemical self-assembly mechanisms. Understanding the precise nature of granule architecture, and how both biological and abiotic factors determine this structure is of both fundamental and practical importance. This review outlines current knowledge of granule architecture and the starch biosynthesis pathway in relation to the building block-backbone model of starch structure. We highlight the gaps in our knowledge in relation to our understanding of the structure and synthesis of starch, and argue that the building block-backbone model takes accurate account of both structural and biochemical data.

A structure-digestion model is proposed to explain the formation of α-amylase-slowly digestible structures during amylopectin retrogradation. Maize and potato (normal and waxy) and banana starch (normal and purified amylopectin through alcohol precipitation), were analyzed for amylose ratio and size (HPSEC) and amylopectin unit- and internal-chain length distribution (HPAEC). Banana amylopectin (BA), like waxy potato (WP), exhibited a larger number of B3-chains, fewer BS- and Bfp-chains and lower S:L and BS:BL ratios than maize, categorizing BA structurally as type-4. WP exhibited a significantly greater tendency to form double helices (DSC and 13C-NMR) than BA, which was attributed to its higher internal chain length (ICL) and fewer DP6-12-chains. However, retrograded BA was remarkably more resistant to digestion than WP. Lower number of phosphorylated B-chains, more S- and Bfp-chains and shorter ICL, were suggested to result in α-amylase-slowly digestible structures through further lateral packing of double helices (suggested by thermo-rheology) in type-4 amylopectins.

In this study, the molecular and aggregation structures of nine types of pure amylopectin (waxy) starches from sorghum (WSS), wheat (WWS) and millet (WMS) were combinedly studied by Gel-Permeation Chromatography (GPC), Fluorophore-Assisted Carbohydrate Electrophoresis (FACE), Wide Angle X-ray Scattering (WAXS), and Small Angle X-ray Scattering (SAXS). The chain lengths (CL) and contents of amylopectin chain fractions were mainly related to the genotype. Pearson correlation analysis suggests that short amylopectin chains 1 (S1 chains, DP 6–18) were the main contributors to crystalline lamella; longer S1 chains resulted in decreased thickness (dc) of the crystalline lamellae. However, also the lengths of the short amylopectin chains 2 (S2, DP 19–30) related to dc showing a positive correlation. Therefore, WWS samples, with the highest average CL of the S2 chains and lowest CL of S1 chains, displayed the thickest crystalline lamellae and longest long period distance i.e. the sum of the crystalline and amorphous lamellar thickness, dac. Among the different starches, WMS exhibited the thinnest crystalline lamellae and shortest dac, and consequently had the second-highest CL of S1 chains and lowest CL of S2 chains of the samples. The dc and dac of WSS were intermediate and related to its medium length of S1 chains and S2 chains. Our study provides information of structural parameters of different types of amylopectin starches and specifically provides evidence of the importance of S2 chains on the lamellar structure. Importantly, our data demonstrate that the total CLD of amylopectin can reflect internal CL of importance for starch granule lamellar features.

Four different types of amylopectin structure have been reported in our earlier work based on the internal unit chain profile obtained from limit dextrins of amylopectin and data strongly suggested that chain length and organization of internal unit chains of amylopectin influence the gelatinization and retrogradation properties of the starch. Another important functional attribute is granule swelling that mainly contributes to the viscosifying property of starches. In this study, unmodified defatted amylose-containing starch granules possessing amylopectin of four types were subjected to swelling in warm water. The swelling pattern of the granules was related to the structural type of the amylopectin component. Granules having amylopectin of Type 1 structure started to swell at lower temperature (about 55 degrees C) and possessed more restricted swelling than most of the other starches. Type 1 starches lost their integrity at temperatures above 85 degrees C, whereas starch granules with Type 2 and 3 amylopectin were still intact at 95 degrees C. Starches with Type 4 amylopectin were heterogeneous with respect to their swelling: Lesser yam starch possessed comparatively restricted swelling between 75 and 95 degrees C, whereas canna and potato starch swelled extensively and disintegrated already before 95 degrees C. Some waxy samples were also included in the investigation and these were generally more sensitive to swelling than their non-waxy counterparts, showing that amylose restricts the swelling and stabilizes the granular structure, albeit there was no correlation between the apparent amylose content and the swelling of tested samples. Instead, the result suggested a correlation between the structure of amylopectin and the deposition of amylose in the starch granules.

The use of carbon dioxide-argon gas radio frequency cold plasma in modifying waxy rice, maize and potato was explored in this paper. Treatment with plasma at 120 W or 0 W (carbon dioxide-argon gas mixture only) resulted in significant increases in the enthalpy of gelatinization of all three waxy starches. Treatment with plasma or gas resulted in a significant increase in the resistant starch content of maize and potato with rice increasing only after gas treatment. Significant decreases were observed in the setback and final viscosities after 120 W treatment in all starches. Plasma and gas treatment resulted in a 5.5% and 2.8% decrease in crystallinity of potato but not rice and maize starch. NMR results showed the presence of V-type single helices in mostly maize and rice starches. Carbon dioxide-argon radio frequency cold plasma served as a useful tool in modifying the properties of all three waxy starches.

Retrogradation is the re-association and recrystallization process of glucan chains in gelatinized starch. The objective of the study was to investigate the effect of amylopectin structure on re-association of glucan chains during retrogradation. Amylopectin retrogradation of 17 starches from four different structural types was examined by differential scanning calorimetry (DSC). Gelatinized starches were stored for 10 days at 4 degrees C and then scanned from 10-120 degrees C at 10 degrees C/min. The structural type of amylopectin influenced the transition temperatures (T-m and T-c), melting temperature range (T-c-T-o) and enthalpy change of transition (Delta H). Correlation analysis between different chain length categories and the melting parameters of recrystallized amylopectin revealed a strong correlation of the external chain length (ECL) with T-m (r = 0.90, p < 0.01), T-c (r = 0.95, p < 0.01), T-c-T-o (r = 0.89 p < 0.01), and Delta H (r = 0.89, p < 0.01) showing the importance of the external chains of amylopectin in the recrystallization process. Chains with very short external length (ECL 6-8) showed negative relationship with retrogradation behavior. However, also the inter-block chain length (IB-CL; distance between tightly branched units) showed positive correlation with transition temperatures (T-c: r = 0.96, p < 0.01, T-c-T-o: r = 0.97, p < 0.01), and Delta H (r = 0.91, p < 0.01) suggesting that longer internal chain segments also play an important role, possibly by contributing to a flexible amylopectin structure. The retrogradation behavior of amylopectin types can be systematically interpreted with the backbone model of amylopectin. (C) 2018 Elsevier Ltd. All rights reserved.

Starch is a major food supply for humanity. It is produced in seeds, rhizomes, roots and tubers in the form of semi-crystalline granules with unique properties for each plant. Though the size and morphology of the granules is specific for each plant species, their internal structures have remarkably similar architecture, consisting of growth rings, blocklets, and crystalline and amorphous lamellae. The basic components of starch granules are two polyglucans, namely amylose and amylopectin. The molecular structure of amylose is comparatively simple as it consists of glucose residues connected through α-(1,4)-linkages to long chains with a few α-(1,6)-branches. Amylopectin, which is the major component, has the same basic structure, but it has considerably shorter chains and a lot of α-(1,6)-branches. This results in a very complex, three-dimensional structure, the nature of which remains uncertain. Several models of the amylopectin structure have been suggested through the years, and in this review two models are described, namely the “cluster model” and the “building block backbone model”. The structure of the starch granules is discussed in light of both models.

The impact of diurnal photosynthetic activity on the fine structure of the amylopectin fraction of starch synthesized by normal barley (NBS) and waxy barley (WBS), the latter completely devoid of amylose biosynthesis, was determined following the cultivation under normal diurnal or constant light growing conditions. The amylopectin fine structures were analysed by characterizing its unit chain length profiles after enzymatic debranching as well as its φ,β-limit dextrins and its clusters and building blocks after their partial and complete hydrolysis with α-amylase from Bacillus amyloliquefaciens, respectively. Regardless of lighting conditions, no structural effects were found when comparing both the amylopectin side-chain distribution and the internal chain fragments of these amylopectins. However, the diurnally grown NBS and WBS both showed larger amylopectin clusters and these had lower branching density and longer average chain lengths than clusters derived from plants grown under constant light conditions. Amylopectin clusters from diurnally grown plants also consisted of a greater number of building blocks, and shorter inter-block chain lengths compared to clusters derived from plants grown under constant light. Our data demonstrate that the diurnal light regime influences the fine structure of the amylopectin component both in amylose and non-amylose starch granules.