Relationship between branching density and crystalline structure of A- and B-type maize mutant starches

GBSS mutations in an SBE mutated background restore the potato starch granule morphology and produce ordered granules despite differences to native molecular structure

Potato starch with mutations in starch branching enzyme genes (SBEI, SBEII) and granule-bound starch synthase gene (GBSS) was characterized for molecular and thermal properties. Mutations in GBSS were here stacked to a previously developed SBEI and SBEII mutation line. Additionally, mutations in the GBSS gene alone were induced in the wild-type variety for comparison. The parental line with mutations in the SBE genes showed a ∼ 40 % increase in amylose content compared with the wild-type. Mutations in GBSS-SBEI-SBEII produced non-waxy, low-amylose lines compared with the wild-type. An exception was a line with one remaining GBSS wild-type allele, which displayed ∼80 % higher amylose content than wild-type. Stacked mutations in GBSS in the SBEI-SBEII parental line caused alterations in amylopectin chain length distribution and building block size categories of whole starch. Correlations between size categories of building blocks and unit chains of amylopectin were observed. Starch in GBSS-SBEI-SBEII mutational lines had elevated peak temperature of gelatinization, which was positively correlated with large building blocks.

Glucan, water dikinase (GWD) penetrates the starch granule surface and introduces C6 phosphate in the vicinity of branching points

Starch phosphorylation mediated by α-glucan, water dikinase is an integral part of starch metabolism. So far however, it is not fully understood. For getting deeper insights, several in vitro assays and intensive mass spectrometry analyses were performed. Such analyses allowed us to determine the phosphorylation position within the amylopectin in detail. Thus, unique features of the starch structure and GWD action were correlated. Therefore, recombinant potato GWD (Solanum tuberosum L.; StGWD) was used for detailed analyses of the phosphorylation pattern of various starches. Additionally, oil palm (Elaeis guineensis Jacq.; EgGWD) GWD was cloned and characterized, representing the first characterization of GWD of a monocot species. The distribution patterns of single phosphorylated glucan chains catalyzed by both GWDs were compared. The phosphorylation distribution patterns of both GWDs varied for different starches. It was proven that GWD phosphorylates different positions within the amylopectin of native starch granules. GWD enters the starch granule surface and phosphorylates the glucosyl units in the proximity of branching points to convert the highly ordered glucan chains into a less ordered state and to render them accessible for the downstream acting hydrolases. This enables deciphering the GWD actions and the related structural properties of starch granules.

The effect of non-thermal physical modification on the structure, properties and chemical activity of starch: A review

Non-thermal physical treatments has obvious advantages in regulating the structure and properties of starch compared with chemical treatment. Hance, this article summarized and compared the effects of three kinds of non-thermal physical treatments including grinding and ball milling, high hydrostatic pressure and ultrasonic on the structure, properties and chemical activity of starches from different plants. The potential applications of non-thermal physical modified starch were introduced. And strategies to solve the problems in the current research were put forward. It is found that although starch has a dense structure, the starch granules could be deformed under three kinds of non-thermal physical treatments, which could damage the granule morphology, microstructure, and crystal structure of starch, reduce particle size, increase solubility and swelling power, and promote starch gelatinization. Three kinds of non-thermal physical treated starch could be used as flocculant thickener, starch based edible films and fat substitutes. Non-thermal physical treatments caused the structure of starch to undergo three stages, which were similar to mechanochemical effects. When starch was in the stress stage and the transition stage from aggregation to agglomeration, its active sites significantly increase and move inward, ultimately leading to a significant increase in the chemical activity of starch.

Dual cross-linked starch hydrogel for eugenol encapsulation and the formation of hydrogen bonds on textural hydrogel

Physical and chemical cross-linked hydrogels combining N, N'-Methylenebisacrylamide (MBA)-grafted starch (MBAS) and sorbitol were successfully prepared and encapsulated with eugenol in this work. The dense porous structure with diameter of 10-15 μm and strong skeleton after restructuring inside the hydrogel was confirmed by SEM. The band shifts between 3258 cm^-1 and 3264 cm^-1 clarified the presence of a large number of hydrogen bonds in physical and chemical cross-linked hydrogels. The robust structure of the hydrogel was confirmed by mechanical and thermal property measurements. Molecular docking techniques were used to help understand the bridging pattern between three raw materials and to assess the advantageous conformation, which demonstrate sorbitol is beneficial to improve the characteristics of textural hydrogel by the formation of hydrogen bonds, creating a denser network, structural recombination and new intermolecular hydrogen bonds between starch and sorbitol afforded considerably junction zones. Compared to ordinary starch-based hydrogels, eugenol-loaded starch-sorbitol hydrogels (ESSG) exhibited a more attractive internal structure, swelling properties, viscoelasticity. Moreover, the ESSG showed excellent antimicrobial activity for typical undesired microorganisms in foods.

Structural and Functional Properties of Porous Corn Starch Obtained by Treating Raw Starch with AmyM

Porous starch is attracting considerable attention for its high surface area and shielding ability, properties which are useful in many food applications. In this study, native corn starch with 15, 25, and 45% degrees of hydrolysis (DH-15, DH-25, and DH-45) were prepared using a special raw starch-digesting amylase, AmyM, and their structural and functional properties were evaluated. DH-15, DH-25, and DH-45 exhibited porous surface morphologies, diverse pore size distributions and pore areas, and their adsorptive capacities were significantly enhanced by improved molecular interactions. Structural measures showed that the relative crystallinity decreased as the DH increased, while the depolymerization of starch double helix chains promoted interactions involving disordered chains, followed by chain rearrangement and the formation of sub-microcrystalline structures. In addition, DH-15, DH-25, and DH-45 displayed lower hydrolysis rates, and DH-45 showed a decreased C∞ value of 18.9% with higher resistant starch (RS) content and lower glucose release. Our results indicate that AmyM-mediated hydrolysis is an efficient pathway for the preparation of porous starches with different functionalities which can be used for a range of applications.

Cluster Size of Amylopectin and Nanosized Amylopectin Fragments Characterized by Pyrene Excimer Formation

Amylopectin from waxy corn and the three nanosized amylopectin fragments (NAFs)—NAF(56), NAF(20), and NAF(8)—from waxy corn starch with a hydrodynamic diameter of 227, 56, 20, and 8 nm, respectively, were randomly labeled with 1-pyrenebutyric acid. The efficiency of these pyrene-labeled amylopectin-based polysaccharides (Py-AbPS) for pyrene excimer formation (PEF) upon diffusive encounter between an excited and a ground-state pyrene increased with increasing concentration of unlabeled NAF(56) in Py-AbPS dispersions in DMSO. Fluorescence decay analysis of the Py-AbPS dispersions in DMSO prepared with increasing [NAF(56)] yielded the maximum number (N_blob^exp) of anhydroglucose units (AGUs) separating two pyrene-labeled AGUs while still allowing PEF. Comparison of N_blob^exp with N_blob^theo, obtained by conducting molecular mechanics optimizations on helical oligosaccharide constructs with HyperChem, led to a relationship between the interhelical distance (d_h-h) in a cluster of oligosaccharide helices, [NAF(56)], and the number of helices in a cluster. It was found that the AbPSs were composed of building blocks made of 3.5 (±0.9) helices that self-assembled into increasingly larger clusters with increasing [NAF(56)]. The ability of PEF-based experiments to yield the cluster size of AbPSs provides a new experimental means to probe the interior of AbPSs at the molecular level.

How Does Starch Structure Impact Amylolysis? Review of Current Strategies for Starch Digestibility Study

In vitro digestibility of starch is a common analysis in human nutrition research, and generally consists of performing the hydrolysis of starch by α-amylase in specific conditions. Similar in vitro assays are also used in other research fields, where different methods can be used. Overall, the in vitro hydrolysis of native starch is a bridge between all of these methods. In this literature review, we examine the use of amylolysis assays in recent publications investigating the complex starch structure-amylolysis relation. This review is divided in two parts: (1) a brief review of the factors influencing the hydrolysis of starch and (2) a systematic review of the experimental designs and methods used in publications for the period 2016–2020. The latter reports on starch materials, factors investigated, characterization of the starch hydrolysis kinetics and data analysis techniques. This review shows that the dominant research strategy favors the comparison between a few starch samples most frequently described through crystallinity, granule type, amylose and chain length distribution with marked characteristics. This strategy aims at circumventing the multifactorial aspect of the starch digestion mechanism by focusing on specific features. An alternative strategy relies on computational approaches such as multivariate statistical analysis and machine learning techniques to decipher the role of each factor on amylolysis. While promising to address complexity, the limited use of a computational approach can be explained by the small size of the experimental datasets in most publications. This review shows that key steps towards the production of larger datasets are already available, in particular the generalization of rapid hydrolysis assays and the development of quantification approaches for most analytical results.

Changes in fine structure of amylopectin and internal structures of starch granules in developing endosperms and culms caused by starch branching enzyme mutations of japonica rice

BEIIb plays a specific role in determining the structure of amylopectin in rice endosperm, whereas BEIIa plays the similar role in the culm where BEIIb is absent. Cereals have three types of starch branching enzymes (BEs), BEI, BEIIa, and BEIIb. It is widely known that BEIIb is specifically expressed in the endosperm and plays a distinct role in the structure of amylopectin because in its absence the amylopectin type changes to the amylose-extender-type (ae-type) or B-type from the wild-type or A-type and this causes the starch crystalline allomorph to the B-type from the wild-type A-type. This study aimed to clarify the role of BEIIa in the culm where BEIIb is not expressed, by using a be2a mutant in comparison with results with be2b and be1 mutants. The results showed that the amylopectin structure exhibited the B-type in the be2a culm compared with the A-type in the wild-type culm. The starch granules from the be2a culm also showed the B-type like allomorph when examined by X-ray diffraction analysis and optical sum frequency generation spectroscopy. Both amylopectin chain-length profile and starch crystalline properties were found to be the A-type at the very early stage of endosperm development at 4-6 days after pollination (DAP) even in the be2b mutant. All these results support a view that in the culm as well as in the endosperm at 4-6 DAP, BEIIa can play the role of BEIIb which has been well documented in maturing endosperm. The possible mechanism as to how BEIIa can play its role is discussed.

Multi-scale structure of A- and B-type granules of normal and waxy hull-less barley starch

The multi-scale structure of combined (A- and B- type granules), A-type, and B-type granules from normal (NHB) and waxy hull-less barley (WHB) starch was studied, including crystalline structure, molecular branching, nanostructural and fractal characteristics. Particle size distribution was applied to determine the separation purity (>95%), and micrography was used to distinguish between the A-type and B-type granules. Lacking amylose, WHB had higher relative crystallinity, gelatinization temperature, enthalpy, level of scattering intensity and uniformity of orientation of double helices than NHB starch. Generally, B-type granules had higher gelatinization temperature, lower enthalpy, greater relative crystallinity, higher ratio of crystalline to amorphous region, more fa chains in amylopectin, and thicker semi-crystalline lamellae than A-type and combined granules. The results showed that the multi-scale structure of A-type and B-type granules differed greatly, and the characteristics of combined granules were not the same as those of its two constituent granule fractions.

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.

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Michaelis-Menten kinetics determines catalytic efficiency of amylase action on starch.

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Kinetic parameters K_m and k_cat/K_m are useful for estimating ease of digestibility.

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Log of slope analysis can quantify starch fractions digested at different rates.

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Categorisation of Resistant Starch can be based on types of interaction with amylase.

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Enzyme kinetic studies of amylolysis are useful for predicting postprandial glycaemia.

Effects of BEIIb-Deficiency on the Cluster Structure of Amylopectin and the Internal Structure of Starch Granules in Endosperm and Culm of Japonica-Type Rice

It is known that one of starch branching enzyme (BE) isoforms, BEIIb, plays a specific role not only in the synthesis of distinct amylopectin cluster structure, but also in the formation of the internal structure of starch granules in rice endosperm because in its absence the starch crystalline polymorph changes to the B-type from the typical A-type found in the wild-type (WT) cereal endosperm starch granules. In the present study, to examine the contribution of BEIIb to the amylopectin cluster structure, the chain-length distributions of amylopectin and its phosphorylase-limit dextrins (Φ-LD) from endosperm and culm of a null be2b mutant called amylose-extender (ae) mutant line, EM10, were compared with those of its WT cultivar, Kinmaze, of japonica rice. The results strongly suggest that BEIIb specifically formed new short chains whose branch points were localized in the basal part of the crystalline lamellae and presumably in the intermediate between the crystalline and amorphous lamellae of amylopectin clusters in the WT endosperm, whereas in its absence branch points which were mainly formed by BEI were only located in the amorphous lamellae of amylopectin. These differences in the cluster structure of amylopectin between Kinmaze and EM10 endosperm were considered to be responsible for the differences in the A-type and B-type crystalline structures of starch granules between Kinmaze and EM10, respectively. The changes in internal structure of starch granules caused by BEIIb were analyzed by wide angle X-ray diffraction, small-angle X-ray scattering, solid state ¹³C NMR, and optical sum frequency generation spectroscopy. It was noted that the size the amylopectin cluster in ae endosperm (approximately 8.24 nm) was significantly smaller than that in WT endosperm (approximately 8.81 nm). Based on the present results, we proposed a model for the cluster structure of amylopectin in WT and ae mutant of rice endosperm. We also hypothesized the role of BEIIa in amylopectin biosynthesis in culm where BEIIb was not expressed and instead BEIIa was the major BE component in WT of rice.

A Review of Starch Biosynthesis in Relation to the Building Block-Backbone Model

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.

Polyglucosan body structure in Lafora disease

Abnormal carbohydrate structures known as polyglucosan bodies (PGBs) are associated with neurological disorders, glycogen storage diseases (GSDs), and aging. A hallmark of the GSD Lafora disease (LD), a fatal childhood epilepsy caused by recessive mutations in the EPM2A or EPM2B genes, are cytoplasmic PGBs known as Lafora bodies (LBs). LBs result from aberrant glycogen metabolism and drive disease progression. They are abundant in brain, muscle and heart of LD patients and Epm2a^-/- and Epm2b^-/- mice. LBs and PGBs are histologically reminiscent of starch, semicrystalline carbohydrates synthesized for glucose storage in plants. In this study, we define LB architecture, tissue-specific differences, and dynamics. We propose a model for how small polyglucosans aggregate to form LBs. LBs are very similar to PGBs of aging and other neurological disorders, and so these studies have direct relevance to the general understanding of PGB structure and formation.

Effects of BEIIb-Deficiency on the Cluster Structure of Amylopectin and the Internal Structure of Starch Granules in Endosperm and Culm of Japonica-Type Rice

It is known that one of starch branching enzyme (BE) isoforms, BEIIb, plays a specific role not only in the synthesis of distinct amylopectin cluster structure, but also in the formation of the internal structure of starch granules in rice endosperm because in its absence the starch crystalline polymorph changes to the B-type from the typical A-type found in the wild-type (WT) cereal endosperm starch granules. In the present study, to examine the contribution of BEIIb to the amylopectin cluster structure, the chain-length distributions of amylopectin and its phosphorylase-limit dextrins (Φ-LD) from endosperm and culm of a null be2b mutant called amylose-extender (ae) mutant line, EM10, were compared with those of its WT cultivar, Kinmaze, of japonica rice. The results strongly suggest that BEIIb specifically formed new short chains whose branch points were localized in the basal part of the crystalline lamellae and presumably in the intermediate between the crystalline and amorphous lamellae of amylopectin clusters in the WT endosperm, whereas in its absence branch points which were mainly formed by BEI were only located in the amorphous lamellae of amylopectin. These differences in the cluster structure of amylopectin between Kinmaze and EM10 endosperm were considered to be responsible for the differences in the A-type and B-type crystalline structures of starch granules between Kinmaze and EM10, respectively. The changes in internal structure of starch granules caused by BEIIb were analyzed by wide angle X-ray diffraction, small-angle X-ray scattering, solid state ¹³C NMR, and optical sum frequency generation spectroscopy. It was noted that the size the amylopectin cluster in ae endosperm (approximately 8.24 nm) was significantly smaller than that in WT endosperm (approximately 8.81 nm). Based on the present results, we proposed a model for the cluster structure of amylopectin in WT and ae mutant of rice endosperm. We also hypothesized the role of BEIIa in amylopectin biosynthesis in culm where BEIIb was not expressed and instead BEIIa was the major BE component in WT of rice.

Understanding Starch Structure: Recent Progress

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.

Starch as a source, starch as a sink: the bifunctional role of starch in carbon allocation

Starch commands a central role in the carbon budget of the majority of plants on earth, and its biological role changes during development and in response to the environment. Throughout the life of a plant, starch plays a dual role in carbon allocation, acting as both a source, releasing carbon reserves in leaves for growth and development, and as a sink, either as a dedicated starch store in its own right (in seeds and tubers), or as a temporary reserve of carbon contributing to sink strength, in organs such as flowers, fruits, and developing non-starchy seeds. The presence of starch in tissues and organs thus has a profound impact on the physiology of the growing plant as its synthesis and degradation governs the availability of free sugars, which in turn control various growth and developmental processes. This review attempts to summarize the large body of information currently available on starch metabolism and its relationship to wider aspects of carbon metabolism and plant nutrition. It highlights gaps in our knowledge and points to research areas that show promise for bioengineering and manipulation of starch metabolism in order to achieve more desirable phenotypes such as increased yield or plant biomass.

Analysis of the functional interaction of Arabidopsis starch synthase and branching enzyme isoforms reveals that the cooperative action of SSI and BEs results in glucans with polymodal chain length distribution similar to amylopectin

Starch synthase (SS) and branching enzyme (BE) establish the two glycosidic linkages existing in starch. Both enzymes exist as several isoforms. Enzymes derived from several species were studied extensively both in vivo and in vitro over the last years, however, analyses of a functional interaction of SS and BE isoforms are missing so far. Here, we present data from in vitro studies including both interaction of leaf derived and heterologously expressed SS and BE isoforms. We found that SSI activity in native PAGE without addition of glucans was dependent on at least one of the two BE isoforms active in Arabidopsis leaves. This interaction is most likely not based on a physical association of the enzymes, as demonstrated by immunodetection and native PAGE mobility analysis of SSI, BE2, and BE3. The glucans formed by the action of SSI/BEs were analysed using leaf protein extracts from wild type and be single mutants (Atbe2 and Atbe3 mutant lines) and by different combinations of recombinant proteins. Chain length distribution (CLD) patterns of the formed glucans were irrespective of SSI and BE isoforms origin and still independent of assay conditions. Furthermore, we show that all SS isoforms (SSI-SSIV) were able to interact with BEs and form branched glucans. However, only SSI/BEs generated a polymodal distribution of glucans which was similar to CLD pattern detected in amylopectin of Arabidopsis leaf starch. We discuss the impact of the SSI/BEs interplay for the CLD pattern of amylopectin.

Structure and physicochemical properties of starches in lotus (Nelumbo nucifera Gaertn.) rhizome

The type and content of starch are believed to be the most critical factors in determining the storage and processing quality of lotus rhizome species, and the intention of this study is to survey the structure and properties of starches isolated from rhizomes of two lotus cultivars using X-ray powder diffraction, solid-state nuclear magnetic resonance spectroscopy, attenuated total reflectance-Fourier transform infrared spectroscopy, scanning electron microscope, differential scanning calorimetry, and rapid viscosity analyzer (RVA). Starch in rhizome of cultivar Meirenhong exhibited C-type X-ray diffraction pattern, while starch in rhizome of cultivar Wawalian showed A-type pattern. ¹³C cross-polarization magic-angle spinning nuclear magnetic resonance (¹³C CP-MAS NMR) also confirmed the polymorphs. The relative crystallinity of two starches was quantitatively estimated from two methods and compared. Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) results indicated that the external regions of the starch granules had a great level of ordered structure. Starch granules in Meirenhong showed oval-shaped granules, while starch granules in Wawalian were elongated and oval in shape with relatively large size. Gelatinization temperatures of starch in Meirenhong and Wawalian were 330.5 and 342.4 K, respectively, and the gelatinization temperature range of Meirenhong was significantly wider than that of Wawalian. Starch in rhizome of cultivar Meirenhong showed lower pasting temperature, lower hot and cool viscosities, lower setback, and higher peak viscosity and breakdown than those of Wawalian in RVA pasting profiles at 6% starch concentration.

Glucose release of water-soluble starch-related alpha-glucans by pancreatin and amyloglucosidase is affected by the abundance of alpha-1,6-glucosidic linkages

This study tested the hypothesis that an increased branch density (i.e., the percentage of alpha-1,6-glucosidic linkage) in water-soluble, starch-related alpha-glucans leads to reduced glucose release by pancreatin and amyloglucosidase. Malto-oligosaccharides and phytoglycogens were structurally analyzed and compared for their susceptibility to the enzymes. Malto-oligosaccharides were prepared by subjecting starch to alpha-amylase and beta-amylase followed by ultrafiltration to enrich alpha-1,6-glucosidic linkages. The branch density of the oligosaccharide products reached up to 17%, determined by (1)H NMR. Phytoglycogens were extracted from six sweet corn lines, and analysis showed similar chain length distributions and a branch density range from 8.8 to 9.5%, as compared with 4.6% for normal corn starch and 5.7% for waxy corn starch. The digestion behavior of these alpha-glucans was correlated to branch density: Highly branched malto-oligosaccharides had much reduced glucose release as compared with starch, whereas the reduction of glucose release from phytoglycogen was relatively low. Particularly, the reduction of glucose release associated with enhanced branch density was caused by reduced hydrolysis by amyloglucosidase.

Branching Features of Amylopectins and Glycogen Determined by Asymmetrical Flow Field Flow Fractionation Coupled with Multiangle Laser Light Scattering

The aim of this work was to characterize starch polysaccharides using asymmetrical flow field flow fractionation coupled with multiangle laser light scattering. Amylopectins from eight different botanical sources and rabbit liver glycogen were studied. Amylopectins and glycogen were completely solubilized and analyzed, and high mass recoveries were achieved (81.7-100.0%). Amylopectin Mw, RG, and the hydrodynamic coefficient nuG (the slope of the log-log plot of RGi vs Mi) were within the ranges 1.05-3.18 x 10(8) g mol(-1), 163-229 nm, 0.37-0.49, respectively. The data were also considered in terms of structural parameters. The results were analyzed by comparison with the theory of hyperbranched polymers (Flory, P. J. Principles of Polymer Chemistry; Cornell University Press: Ithaca, NY, 1953; Burchard, W. Macromolecules, 1977, 10, 919-927). This theory, based upon the ABC model, has been shown to underestimate the branching degrees of amylopectins. However, quantitative agreement with the data in the literature was found for amylopectins when using the ABC model modified by the introduction of a multiplying factor, determined from previously described amylopectin structures in terms of the number of branching point calculations.