Effects of amylose and amylopectin molecular structures on the emulsification performance of starch nanoparticles

Starch nanoparticles have increasing applications as emulsion stabilizers in functional foods and drug delivery. The effects of amylose and amylopectin molecular structures on the emulsification performance of starch nanoparticles obtained from anti-solvent precipitation are explored here. From size-exclusion chromatography results, ten different starch nanoparticles with distinct molecular structures possessed a molecular size ranging from 63 nm to 111 nm. Rice-starch nanoparticles showed near-neutral wettability (contact angle 90.25°) with 100 % emulsifying stability index (ESI). Correlation analysis indicated that the maximum size of the amylopectin component was positively associated with ESI, while the amount of amylopectin long chains and the lengths of amylose short chains negatively correlated with ESI. Mechanistic reasons for these observations are put forward. These findings can help design new emulsifiers using starch nanoparticles, and development of "clean-label" (i.e. having relatively few ingredients, "natural" ingredients, and few synthetic additives) food emulsions.

Influence of γ irradiation on the physicochemical properties of tapioca granular starch-ascorbyl palmitate complexes

The original starch was irradiated with γ-rays at doses ranging from 0 to 10 kGy to investigate how irradiation influences the formation of tapioca granular starch-ascorbyl palmitate (TGS-AP) complexes. The results indicated that the pretreatment of tapioca starch with appropriate irradiation doses effectively increased the content of AP encapsulated in the complex, and the loading efficiency increased from 22.74 % (0 kGy) to a maximum of 32.95 % (2.5 kGy). Compared with the control complexes, the rapid visco analyzer (RVA) pasting profiles of the TGS-AP complexes changed significantly, with new viscosity peaks appearing during the cooling and holding stages. The swelling power, relative crystallinity, and thermal stability of the complexes were remarkably elevated to maximum increases of 116.50 %, 21.45 %, and 82.61 %, respectively, and the melting enthalpies of the complexes increased slightly after the native tapioca starch was subjected to irradiation. This study could serve as a basis for the development of a green and efficient process for the production of starch-lipid complexes.

Chromatographic analysis of branched and debranched starch structure: Variability of their results

Starch structure determination is crucial for understanding its properties and applications. However, method-dependent variations in size determination can lead to ambiguous interpretations. This study investigates the ambiguities in starch structure determination by evaluating the variation in size of four commercial branched starches as determined by average molar mass, gyration radius, hydrodynamic radius, and chain-length distribution. The starches were analyzed using high-performance size-exclusion chromatography (HPSEC) coupled with multi-angle laser light scattering (MALLS) and refractive index detector (RI), and after debranching by HPSEC-RI and high-performance anion-exchange chromatography (HPAEC) with pulsed amperometric detector (PAD). MALLS-derived MW values for amylose and amylopectin were higher than those obtained using the hydrodynamic volume method. The molecular weight of amylopectin chains, determined by the degree of polymerization (DP), ranged between 2.1 and 2.9 × 103 g/mol for short chains, and between 4.1 × 103 and 1.1 × 104 g/mol for long chains. Differences in amylopectin chain content were observed between HPSEC-RI and HPAEC-PAD, highlighting the complementary nature of these techniques. The study underscores the need for standardizing chromatography-based methodologies in starch research, particularly with the advent of new technologies.

Exploring urea as a prospective auxiliary for starch functionalization: A concise review on modified starch properties and the sustainable packaging films

Urea is also known as carbamide, an inexpensive and eco-friendly additive for starch functionalization. This article reviews the potential role of urea in starch modification, with the prominence of the mechanism of urea action, alterations in the starch structure and functional properties. In addition, current literature conveys the prospective effect of urea in fabricating starch films for food packaging, and the relevant areas that need to be covered in the forthcoming research are specified at the end of the article section. Urea can modify the diverse physico-chemical and functional properties of starch. Starch-based films exhibit pronounced effects on their mechanical and barrier properties upon the incorporation of urea, although this effect strongly depends on the urea content and degree of substitution (DS). Overall, urea holds great potential for use in the starch and bioplastic film industries, as it produces biocompatible derivatives with desirable performance.

Printable-Microencapsulated Ascorbic Acid for Personalized Topical Delivery

This study presents the successful development of printable-microencapsulated ascorbic acid (AA) for personalized topical delivery using laser printing technology. Rice flour with a 10% AA content was selected as an encapsulation material. Hydrophobic nanosilica was used to create negative electrostatic charges on the microencapsulated surfaces via a high-speed mixture. This process facilitated the microencapsulated AA fabrication using a commercial laser printer and produced a well-patterned design with some minor print defects, such as banding and scattering. The amount of encapsulated AA per area was 0.28 mg/cm2, and the RGB color code was 0,0,0. An emulsion carrier system comprising pentylene glycol (P5G) or diethylene glycol monoethyl ether (DEGEE), Tween 20, oleic acid, and deionized (DI) water at a ratio of 20:30:30:20 was developed to enhance AA transmission into the skin. The Franz diffusion cell technique was used to investigate topical absorption on Strat-M membranes using P5G and DEGEE as enhancers. The steady-state fluxes were 8.40 (±0.64) and 10.04 (±0.58) μg/h/cm2 for P5G and DEGEE, respectively. Cytotoxicity tests conducted on fibroblast cells revealed low cytotoxicity for the encapsulation products and carriers.

Starch chain-length distributions determine cooked foxtail millet texture and starch physicochemical properties

Starch chain-length distributions play an important role in controlling cereal product texture and starch physicochemical properties. Cooked foxtail millet texture and starch physicochemical properties were investigated and correlated with starch chain-length distributions in eight foxtail millet varieties. The average chain lengths of amylopectin and amylose were in the range of DP 24-25 and DP 878-1128, respectively. The percentage of short amylopectin chains (Ap1) was negatively correlated with hardness but positively correlated with adhesiveness and cohesion. Conversely, the amount of amylose intermediate chains was positively correlated with hardness but negatively correlated with adhesiveness and cohesion. Additionally, the amount of amylose long chains was negatively correlated with adhesiveness and chewiness. The relative crystallinity (RC) of starch decreased with reductions in the length of amylopectin short chains in foxtail millet. Pasting properties were mainly influenced by the relative length of amylopectin side chains and the percentage of long amylopectin branches (Ap2). Longer amylopectin long chains resulted in lower gelatinization temperature and enthalpy (ΔH). The amount of starch branched chains had important effects on the gelatinization temperature range (ΔT). These results can provide guidance for breeders and food scientists in the selection of foxtail millet with improved quality properties.

Synthesis, characterization, and antimicrobial activities of a starch-based polymer

Due to the rise of nosocomial infections and the increasing threat of antibiotic resistance, new techniques are required to combat bacteria and fungi. Functional antimicrobial biodegradable materials developed from low-cost renewable resources like polysaccharides would enable greater applications in this regard. Our group has developed and characterized a new antimicrobial polymer using commercially available N-ethyl piperazine and starch via simple one-pot method. The prepared antimicrobial polymer was characterized by FTIR and NMR. In addition, the thermal properties of the synthesized antimicrobial polymer were examined through TGA and DSC. The antimicrobial potential of the prepared material was investigated using the bacteria, Staphylococcus aureus, Escherichia coli, and Mycobacterium smegmatis and a fungi Candida albicans. The result indicates that, as the amount of polymer increases, the antimicrobial activity also increases. SA-E-NPz exhibited a zone of inhibition in the range of 8-13 mm, and the MIC was found to be < 0.625 mg against all four microbes. The antimicrobial activity of polymer coated on fabric was also studied. Furthermore, the cytotoxicity studied against human fibroblast cell lines showed that the prepared polymer is non-toxic to the cells. The study concluded that the synthesized polymer shows good antimicrobial activity, is non-toxic to human fibroblast cells, and thus can be used for wound dressing or textile applications.

Molecular insight into toughening induced by core-shell structure formation in starch-blended bioplastic composites

Binary and ternary blends with poly(lactic acid) (PLA), poly(butylene succinate) (PBS), and thermoplastic starch (TPS) were prepared by a melt process to produce biodegradable biomass plastics with both economical and good mechanical properties. The mechanical and structural properties of each blend were evaluated. Molecular dynamics (MD) simulations were also conducted to examine the mechanisms underlying the mechanical and structural properties. PLA/PBS/TPS blends showed improved mechanical properties compared with PLA/TPS blends. The PLA/PBS/TPS blends with a TPS ratio of 25-40 wt% showed higher impact strength than PLA/PBS blends. Morphology observations showed that in the PLA/PBS/TPS blends, a structure similar to that of core-shell particles with TPS as the embedding phase and PBS as the coating phase was formed, and that the trends in morphology and impact strength changes were consistent. The MD simulations suggested that PBS and TPS tightly adhered to each other in a stable structure at a specific intermolecular distance. From these results, it is clear that PLA/PBS/TPS blends are toughened by the formation of a core-shell structure in which the TPS core and the PBS shell adhered well together and stress concentration and energy absorption occurred in the vicinity of the core-shell structure.

Microstructures of Starch Granules with Different Amylose Contents and Allomorphs as Revealed by Scattering Techniques

In this study, as-is (ca. 12% moisture by mass) and hydrated (50% water by mass) granules of waxy potato (WP), waxy wheat (WW), waxy maize, normal maize, and high-amylose maize (HAM) starches were investigated by using small-angle neutron and X-ray scattering (SANS and SAXS), wide-angle X-ray scattering, and ultra-small-angle neutron scattering. The SANS and SAXS data were fitted using the two-phase stacking model of alternating crystalline and amorphous layers. The partial crystalline lamellar structures inside the growth rings of granules were analyzed based on the inter-lamellar distances, thicknesses of the crystalline lamellae and amorphous layers, thickness polydispersities, and water content in each type of layer. Despite having a longer average chain length of amylopectin, the WP and HAM starches, which had B-type allomorph, had a shorter inter-lamellar distance than the other three starches with A-type allomorph. The WP starch had the most uniform crystalline lamellar thickness. After hydration, the amorphous layers were expanded, resulting in an increase of inter-layer distance. The low-angle intensity upturn in SANS and SAXS was attributed to scattering from interfaces/surfaces of larger structures, such as growth rings and macroscopic granule surfaces. Data analysis methods based on model fitting and 1D correlation function were compared. The study emphasized─owing to inherent packing disorder inside granules─that a comprehensive analysis of different parameters was essential in correlating the microstructures with starch properties.

Tuning heterologous glucan biosynthesis in yeast to understand and exploit plant starch diversity

Background

Starch, a vital plant-derived polysaccharide comprised of branched glucans, is essential in nutrition and many industrial applications. Starch is often modified post-extraction to alter its structure and enhance its functionality. Targeted metabolic engineering of crops to produce valuable and versatile starches requires knowledge of the relationships between starch biosynthesis, structure, and properties, but systematic studies to obtain this knowledge are difficult to conduct in plants. Here we used Saccharomyces cerevisiae as a testbed to dissect the functions of plant starch biosynthetic enzymes and create diverse starch-like polymers.

Results

We explored yeast promoters and terminators to tune the expression levels of the starch-biosynthesis machinery from Arabidopsis thaliana. We systematically modulated the expression of each starch synthase (SS) together with a branching enzyme (BE) in yeast. Protein quantification by parallel reaction monitoring (targeted proteomics) revealed unexpected effects of glucan biosynthesis on protein abundances but showed that the anticipated broad range of SS/BE enzyme ratios was maintained during the biosynthetic process. The different SS/BE ratios clearly influenced glucan structure and solubility: The higher the SS/BE ratio, the longer the glucan chains and the more glucans were partitioned into the insoluble fraction. This effect was irrespective of the SS isoform, demonstrating that the elongation/branching ratio controls glucan properties separate from enzyme specificity.

Conclusions

Our results provide a quantitative framework for the in silico design of improved starch biosynthetic processes in plants. Our study also exemplifies a workflow for the rational tuning of a complex pathway in yeast, starting from the selection and evaluation of expression modules to multi-gene assembly and targeted protein monitoring during the biosynthetic process.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01408-x.

Microwave Cooking Enriches the Nanoscale and Short/Long-Range Orders of the Resulting indica Rice Starch Undergoing Storage

The chain reorganization of cooked starch during storage plays an important role in the performance of starchy products such as rice foods. Here, different analytical techniques (such as small-angle X-ray scattering) were used to reveal how microwave cooking influences the chain assembly of cooked indica rice starch undergoing storage for 0, 24, or 48 h. While stored, more short-range double helices, long-range crystallites, and nanoscale orders emerged for the microwave-cooked starch than for its conventionally cooked counterpart. For instance, after storage for 24 h, the microwave-cooked starch contained 46.8% of double helices, while its conventionally cooked counterpart possessed 34.3% of double helices. This could be related to the fact that the microwave field caused high-frequency movements of polar groups such as hydroxyls, which strengthened the interactions between starch chains and water molecules and eventually their assembly into double helices, crystallites, and nanoscale orders. This work provides further insights into the chain reassembly of microwave-cooked starch undergoing storage, which is closely related to the quality attributes of starch-based products.

Applications of infrared spectroscopy in polysaccharide structural analysis: Progress, challenge and perspective

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Functional properties of polysaccharides depend on their structural features.

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IR spectroscopy is widely used in polysaccharide structural analysis.

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Classical applications of IR spectroscopy in polysaccharide are reviewed.

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IR integrating techniques can considerably expand its application scope.

Polysaccharides are important biomacromolecules with numerous beneficial functions and a wide range of industrial applications. Functions and properties of polysaccharides are closely related to their structural features. Infrared (IR) spectroscopy is a well-established technique which has been widely applied in polysaccharide structural analysis. In this paper, the principle of IR and interpretation of polysaccharide IR spectrum are briefly introduced. Classical applications of IR spectroscopy in polysaccharide structural elucidation are reviewed from qualitative and quantitative aspects. Some advanced IR techniques including integrating with mass spectrometry (MS), microscopy and computational chemistry are introduced and their applications are emphasized. These emerging techniques can considerably expand application scope of IR, thus exert a more important effect on carbohydrate characterization. Overall, this review seeks to provide a comprehensive insight to applications of IR spectroscopy in polysaccharide structural analysis and highlights the importance of advanced IR-integrating techniques.

Methods for characterizing the structure of starch in relation to its applications: a comprehensive review

Starch is a major part of the human diet and an important material for industrial utilization. The structure of starch granules is the subject of intensive research because it determines functionality, and hence suitability for specific applications. Starch granules are made up of a hierarchy of complex structural elements, from lamellae and amorphous regions to blocklets, growth rings and granules, which increase in scale from nanometers to microns. The complexity of these native structures changes with the processing of starch-rich ingredients into foods and other products. This review aims to provide a comprehensive review of analytical methods developed to characterize structure of starch granules, and their applications in analyzing the changes in starch structure as a result of processing, with particular consideration of the poorly understood short-range ordered structures in amorphous regions of granules.

Starch granule size: Does it matter?

Nature has developed starch granules varying in size from less than 1 μm to more than 100 μm. The granule size is an important factor affecting the functional properties and the applicability of starch for food and non-food applications. Within the same botanical species, the range of starch granule size can be up to sevenfold. This review critically evaluated the biological and environmental factors affecting the size of starch granules, the methods for the separation of starch granules and the measurement of size distribution. Further, the structure at different length scales and properties of starch-based on the granule size is elucidated by specifying the typical applications of granules with varying sizes. An amylopectin cluster model showing the arrangement of amylopectin from inside toward the granule surface is proposed with the hypothesis that the steric hindrance for the growth of lamellar structure may limit the size of starch granules.

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.

Impact of ultrasonic treatment on rice starch and grain functional properties: A review

As a green, nonthermal, and innovative technology, ultrasonication generates acoustic cavitation in an aqueous medium, developing physical forces that affect the starch chemistry and rice grain characteristics. This review describes the current information on the effect of ultrasonication on the morphological, textural, and physicochemical properties of rice starch and grain. In a biphasic system, ultrasonication introduced fissures and cracks, which facilitated higher uptake of water and altered the rice starch characteristics impacting textural properties. In wholegrain rice, ultrasonic treatment stimulated the production of health-related metabolites, facilitated the higher uptake of micronutrient fortificants, and enhanced the palatability by softening the rice texture. This review provides insights into the future direction on the utilization of ultrasonication for the applications towards the improvement of rice functional properties.

Rheological, thermal, and structural properties of high-pressure treated Litchi (Litchi chinensis) kernel starch

Starch isolated from litchi kernel was subjected to high-pressure (HP) treatment at selected pressures (300, 450 and 600 MPa) for 10 min, and evaluated for its rheological, morphological, thermal and structural properties. The amylose content of native litchi kernel starch (LKS) was 17.4%, which increased significantly upon pressurization. The temperature sweep test of the untreated starch sample resulted in the peak G' and G″ values of 3417 and 283 Pa, respectively, and those values decreased after pressurization. Oscillatory rheological measurements showed the frequency dependency of tested starch pastes. Furthermore, the mechanical rigidity of the starch pastes improved with pressure treatment. Morphological studies revealed that starch granule structure remained intact after pressurization; however, pressure >450 MPa resulted in surface roughness and small cavities. HP treatment significantly influenced thermal properties of LKS, in particular at 450 and 600 MPa, where a significant drop in the transition temperatures and enthalpy values were recorded. The HP-treated starch samples exhibited distinct X-ray diffraction pattern of native LKS i.e. the blend of A- and B-type allomorphs with a predominating A-type crystalline structure. Upon pressure treatment, the disappearance of 2θ peak at 5.6° and significant changes in peak intensities confirmed the structural change in the starch matrix.

Parameterizing starch chain-length distributions for structure-property relations

Understanding starch structure-property relationship is important for the development of new generation of starch-based foods with desirable functions. Recent developments of methodologies on the characterisation of starch molecular structures, especially how to parameterize the starch chain-length distribution (CLD) by few biologically meaningful parameters have brought new insights to explain starch physicochemical properties from molecular levels. Especially, it has shown that gelatinization temperatures are largely controlled by amylopectin short chains, while the retrogradation rate of starch molecules is controlled by amylose content, amylose short to medium chains, amylopectin external and internal chain length. Starch pasting and digestion properties are also controlled to a significant extent by its CLD. With extensive discussion of correlative and casual relations between starch CLD with its physicochemical properties, this review aims to establish a holistic starch structure-property relationship. It enables food producers to develop functional foods based on a precise understanding of starch structure-property relations.

Competition between Granule Bound Starch Synthase and Starch Branching Enzyme in Starch Biosynthesis

BACKGROUND

Starch branching enzymes (SBE) and granule-bound starch synthase (GBSS) are two important enzymes for starch biosynthesis. SBE mainly contributes to the formation of side branches, and GBSS mainly contributes for the synthesis of amylose molecules. However, there are still gaps in the understanding of possible interactions between SBE and GBSS.

RESULTS

Nineteen natural rice varieties with amylose contents up to 28% were used. The molecular structure, in the form of the chain-length distribution (CLDs, the distribution of the number of monomer units in each branch) was measured after enzymatic debranching, using fluorophore-assisted carbohydrate electrophoresis for amylopectin and size- exclusion chromatography for amylose. The resulting distributions were fitted to two mathematical models based on the underlying biosynthetic processes, which express the CLDs in terms of parameters reflecting relevant enzyme activities.

CONCLUSIONS

Finding statistically valid correlations between the values of these parameters showed that GBSSI and SBEI compete for substrates during rice starch biosynthesis, and synthesis of amylose short chains involves several enzymes including GBSSI, SBE and SSS (soluble starch synthase). Since the amylose CLD is important for a number of functional properties such as digestion rate, this knowledge is potentially useful for developing varieties with improved functional properties.

Molecular structure-property relations controlling mashing performance of amylases as a function of barley grain size

In brewing, amylases are key enzymes in hydrolyzing barley starch to sugars, which are utilized in fermentation to produce ethanol. Starch fermentation depends on sugars produced by amylases and starch molecular structure, both of which vary with barley grain size. Grain size is a major industrial specification for selecting barley for brewing. An in-depth study is given of how enzyme activity and starch structure vary with grain size, the impact of these factors on fermentable sugar production, and the underlying mechanisms. Micro-malting and mashing experiments were based on commercial methodologies. Starch molecular structural parameters were obtained using size-exclusion chromatography, and fitted using biosynthesis-based models. Correlation analysis using the resulting parameters showed larger grain sizes contained fewer long amylopectin chains, higher amylase activities and soluble protein level. Medium grain sizes released most sugars during mashing, because of higher starch utilization from the action of amylases, and shorter amylose chains. As starch is the substrate for amylase-driven fermentable sugars production, measuring its structure should be a prime indication for mashing performance, and should be used as an industry specification when selecting barley grains for brewing.

Functional cationic derivatives of starch as antimicrobial agents

Antimicrobial polymers with a broad spectrum of action and high selectivity towards pathogens (versus mammalian cells) provide the opportunity to combat infections with only a limited chance of resistance development.

Characterizing Starch Molecular Structure of Rice

A better understanding of the nutritional properties of rice starch is important because of the rapid rise of diet-related health complications, particularly obesity, type 2 diabetes, and colorectal cancers. Rice starch that is slowly digested to glucose, and where significant quantities of starch which reach the lower gut ("resistant starch"), can mitigate, and also delay the onset of, these diseases. These digestibility properties depend to some extent on starch molecular structure. The characterization of this structure is therefore significant for understanding and developing healthier slower digestible rice. In this chapter, a series of techniques used for characterizing starch structure are reviewed and the procedure for preparing rice starch samples with minimum degradation for characterizing starch chain length distribution (CLD) and overall molecular structure is given. Some methods for choosing or developing plants showing desirable structural characteristics are briefly summarized.

Instrumental measurement of cooked rice texture by dynamic rheological testing and its relation to the fine structure of rice starch

Increasing demands for better instrumental methods to evaluate cooked rice texture is driving innovations in rice texture research. This study characterized cooked rice texture by descriptive sensory analysis and two instrumental methods (texture profile analysis (TPA) and dynamic rheological testing) using a set of 18 varieties of rice with a wide range in amylose content (0-30%). The panellists' results indicated that hardness and stickiness were the two most discriminating attributes among 13 tested textural attributes. The consistency coefficient (K(*)) and loss tangent (tan δ) from a dynamic frequency sweep were used to compare with hardness and stickiness tested by TPA and sensory panellists, showing that using K(*) to express hardness, and tan δ to express stickiness, are both statistically and mechanistically meaningful. The instrumental method is rationalized in terms of starch structural differences between rices: a higher proportion of both amylose and long amylopectin branches with DP 70-100 causes a more elastic and less viscous texture, which is readily understood in terms of polymer dynamics in solution.

Characterization of multi-scale structure and thermal properties of Indica rice starch with different amylose contents

Fully understanding the relationship between multi-scale structure and thermal properties of rice starch is important for starch-based food processing.

Progress in controlling starch structure by modifying starch-branching enzymes

This paper reviews the progress of development of plants with desirable starch structure by modifying starch branching enzymes. Starch-branching enzyme (SBE) is responsible for the creation of branches during starch biosynthesis in plastids, and is a major determinant of the final fine structure and physical properties of the starch. Multiple isoforms of SBE have been found in plants, with each playing a different role in amylopectin synthesis. Different methods have been used to develop desirable starch structures by modifying the SBE activity. These can involve changing its expression level (either up-regulation or down-regulation), genetically modifying the activity of the SBE itself, and varying the length of its transferred chains. Changing the activity and the transferred chain length of SBE has been less studied than changing the expression level of SBE in vivo. This article reviews and summarizes new tools for developing plants producing the next generation of starches.

The importance of amylose and amylopectin fine structure for textural properties of cooked rice grains

Statistically and causally meaningful relationships are established between starch molecular structure (the molecular distribution of branched starch and the chain length distribution of debranched starch) and texture (hardness and stickiness) of cooked rice grains. The amounts of amylose chains with degree of polymerization (DP) 100-20,000, and of long amylopectin chains, positively correlated with hardness, while amylopectin chains with DP<70 and amylose molecular size both showed negative correlations with hardness (p<0.05). There was also a significant negative correlation between stickiness and the amounts of long amylopectin chains (p<0.01). For rices with similar amylose content, the amount of amylose chains with DP 1000-2000 positively correlated with hardness while size negatively correlated with hardness (p<0.05). This indicates for the first time that, regardless of amylose content, rice varieties with smaller amylose molecular sizes and with higher proportions of long amylose chains have a harder texture after cooking.

Roles of GBSSI and SSIIa in determining amylose fine structure

This study examines the relationships between genetics (single nucleotide polymorphisms (SNPs) in GBSSI and SSIIa genes), starch structure (amylose and amylopectin fine structures), and starch properties (relating to gelatinization). GBSSI and SSIIa SNPs did not alter the starch content of rice grains. GBSSI SNPs can affect the amylose content, but they are incapable of altering the chain-lengths of amylopectin and amylose. The amounts of both long and short amylose branches changed with the same trend as amylose content, and they appeared to affect starch gelatinization properties. SSIIa synthesizes intermediate single-lamella amylopectin chains (DP 16-21), and consequently impacts the gelatinization temperature. Mathematical modelling suggests that the reduction in SSIIa activity significantly increases the activity of SBEII, resulting in a decreased activity ratio of SS to SBE in the enzyme set governing an appropriate chain-length distribution range. This application of the genetics-structure-property paradigm provides selection strategies to produce rice varieties with improved qualities.

New perspectives on the role of α- and β-amylases in transient starch synthesis

Transient starch in leaves is synthesized by various biosynthetic enzymes in the chloroplasts during the light period. This paper presents the first mathematical model for the (bio)synthesis of the chain-length distribution (CLD) of transient starch to aid the understanding of this synthesis. The model expresses the rate of change of the CLD in terms of the actions of the enzymes involved. Using this to simulate the experimental CLD with different enzyme combinations is a new means to test for enzymes that are significant to the rate of change of the CLD during synthesis. Comparison between the simulated CLD from different enzyme combinations and the experimental CLD in the leaves of the model plant Arabidopsis thaliana indicate α-amylase, in addition to the core starch biosynthetic enzymes, is also involved in the modification of glucans for the synthesis of insoluble starch granules. The simulations suggest involvement of β-amylase, in the absence of α-amylase in mutants, slows the rate of attaining a crystalline-competent CLD for crystallization of glucans to form insoluble starch. This suggests a minor role of β-amylase in shaping normal starch synthesis. The model simulation predicts that debranching of glucans is an efficient mechanism for the attainment of crystalline-competent CLD; however, attaining this is still possible, albeit slower, through combinations of α- and β-amylase in the absence of isoamylase-type debranching enzyme. In Arabidopsis defective in one of the isoamylase-type debranching enzymes, the impact of α-amylase in starch synthesis is reduced, while β-amylase becomes significantly involved, slowing the rate of synthesis in this mutant. Modeling of transient starch CLD brings to light previously unrecognized but significant effects of α- and β-amylase on the rate of transient starch synthesis.