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This work concerns how starch-protein interplay affects the multi-scale structures (e.g., short- and long-range orders, nanoscale structure and morphology) of starch undergoing thermal processing (pasting) involving heating and cooling at high water content. An indica rice starch (IRS) and three proteins (whey protein isolate, WPI; soy protein isolate, SPI; casein, CS) were used. By inspecting rheological profiles of mixed systems before and after adding chemicals, IRS-WPI and IRS-CS showed mainly hydrophobic molecular interaction; and IRS-SPI exhibited hydrophobic, hydrogen bonding and electrostatic interactions. The RVA results revealed that, with starch and proteins as controls, starch-globular protein (WPI or SPI) interplay accelerated the swelling of starch granules (faster viscosity increase at initial pasting stage), and reduced the paste stability during heating (higher breakdown) and during cooling (higher setback); however, the starch-casein interactions resulted in opposed effects. Moreover, starch-protein interactions varied the multi-scale chain reassembly of starch into different structures during cooling. Observed could be fewer short- and long-range starch orders, and larger nonperiod structure (or colloidal clusters) on the nanoscale. On even larger scale to micron, IRS-globular protein molecules generated larger grids (with reduced number) in the gel network, and IRS-casein formed a more continuous gel network with less prominent tunnel-like features.

Colored brown rice shows better health benefits than polished rice, and there is great interest in the design of demanded cooking manners for brown rice. This investigation concerns how the change of cooking mode can slow starch digestion of colored brown rice by inspecting mainly starch structural changes during cooking. Compared to cooking Mode 1, the soaking of Mode 2, at higher temperature, probably enhanced water diffusion into rice matrices, thus strengthening starch lamellae without apparently altering rice morphology and ordered structures such as starch polymorphs and helices. The followed heating of Mode 2, with reduced time, more sufficiently disrupted rice structures, causing less prominent nonperiodic molecular organizations. At the final cooking stage, the braising of Mode 2, having faster temperature reduction for prolonged time, leading to similar rice morphology, reduced molecular orders (e.g., helices) and probably denser amorphous regions of nonperiodic organizations. Such features tended to increase packing density of molecular chains (mainly starch) in rice matrices, thus slowing the enzyme diffusion in rice matrices and associated binding and catalysis events. In this way, a reduced starch digestion rate and increased resistant starch (RS) and slowly digestible starch (SDS) were seen for the rice following Mode 2 cooking.

This study explored how microwave reheating (to about 73 °C at different power levels) affects the microstructure and digestion characteristics of cooked rice with different water contents (1.1 and 1.5 times that of rice in weight). Irrespective of water content, mainly the V-type crystallites remained after microwaving reheating, with slight changes in other multi-scale structural features. Only at a relatively high water content (1.5) and with a power level high enough could short-range order be reduced. Such microwave reheating increased the digestion resistance of cooked rice. At a water content of 1.1 times, increasing the microwave power led to a decreased rapid digestible starch (RDS) content and an increased resistant starch (RS) content. With a higher water content (1.5), the enhancement of digestion resistance with higher microwave power was less significant but still, a reduced slowly digestible starch (SDS) content and a higher RS content were observed.

With screening of Lactobacillus fermentum M9 and Candida santamariae Y11 from a natural fermentation broth (Jinjian) for rice noodle production, this work concerns how fermentation with M9:Y11 suspensions of different volume ratios affects the texture and sensory features of rice noodles. The M9:Y11 strains regulated rice structures and thus the physicochemical features of rice noodles. In particular, 5:5 and 8:2 v/v M9:Y11 strains endowed rice noodles with better texture and sensory performance than did Jinjian. The underlying mechanism regarding evolutions in rice noodle properties was discussed from a rice structural view. Specifically, the fermentation disrupted rice ordered structures (e.g., starch crystallites) and broke starch granules, which was preferable for the swelling and molecule leaching of rice noodle matrixes with enhanced molecule interactions. Such noodle matrixes were robust to resist imposed force, thus exhibiting increased hardness, chewiness and mouthfeel. More interestingly, the 5:5 and 8:2 v/v M9:Y11 strains less prominently altered starch granule integrity, contributing to increasing hardness, chewiness and mouthfeel of rice noodles associated with robustness of swollen granule shell within rice gel matrixes. These two ratios of M9:Y11 strains also improved the color, aroma and taste for rice noodles.

This work concerns the multi-scale supramolecular structures and physicochemical properties of two small adlay seed starches (Q-2 and P-6) and a big adlay seed starch (BW). Among the three starches, P-6 exhibited unique hierarchical structures and thus thermal and pasting properties. The underlying mechanism on starch property differences was discussed from a hierarchical (multi-scale) structural view. Specifically, P-6 possessed the lowest granule size, the intermediate lamellar thickness and compactness, and the highest contents of helices and crystallites with a relatively high flaw degree. These multi-scale structures were most susceptible to hydrothermal effects, eventually showing the lowest thermal transition and pasting temperatures. Also, this sample had the highest paste viscosities related to the swelling degree of starch granules and the water-holding ability of starch molecules. The shell of the fully swelled granules (granule ghosts) for P-6 were most robust under shearing and heating, resulting in the lowest breakdown viscosity (i.e., the highest paste stability during heating). The strongest assembly capacity for the starch chains of P-6, as indicated by its highest content of orders in untreated granules, induced a prominent increase in the paste viscosity during cooling. The results here indicate that P-6 may serve as functional agents such as thickeners with low pasting temperature as well as high viscosity and high paste stability under shearing and heating.

Using combined analytical techniques, this work discloses how citric acid (CA) treatment affects the pasting features of starch from a view of multi-scale structural evolutions. The treatment induced disruption events in starch multi-level structures and thus modulated the pasting behaviors. A structure-property relationship was proposed to rationalize CA effects on starch pasting properties. Specifically, CA disrupted starch structures from molecular scale to micron scale, eventually reducing pasting temperature and paste viscosities. Interestingly, unlike previous findings that acid hydrolysis normally reduces the breakdown viscosity, the CA here resulted in regulated breakdown viscosity (paste stability under shearing and heating) related to concurrent effects from granule surface corrosion and molecule degradation. Moreover, the molecule degradation of starch weakened its chain rearrangement tendency, allowing increased paste stability during cooling. Also, simply altering CA concentration effectively regulated starch structural and pasting features. Hence, compared to untreated counterpart, the CA-treated starch may serve as food agents with reduced paste viscosity, regulated paste stability under heating and increased paste stability during cooling.

The surface hydrophobicity of starch-based films could be regulated using a two-step surface modification method. Such modification was realized by grafting with alkanols of different chain lengths (hexanol, dodecanol and octadecanol) on the surface of starch-based films. The grafting of alkanol increased the mobility of glycerol as the plasticizer within the film surface. Also, this grafting increased the mass ratio of carbon to oxygen on the film surface but reduced the mass ratio of carbon to nitrogen. Under the same reaction conditions, there were fewer dodecyl chains grafted onto the film surface than hexyl or octadecyl chains. Furthermore, the results revealed that the surface hydrophobicity of starch-based films could be enhanced by simply increasing the alkyl chain length. Also, fewer alkyl chains tended to reduce the surface hydrophobicity of the films. These results are valuable for the rational design of starch-based materials with demanded hydrophobic properties.

This work discloses the multi-level structure and thermal behaviors of hydrophobic, propionylated starch-based films as affected by the amylose contents of starch materials used. Scanning electron microscopy results showed that amylose promoted the formation of more compact structure within the film matrices. Also, small and wide angle X-ray scattering analysis revealed that higher amylose content was preferable for the formation of new orders on nanoscale and crystallites. With these structural changes, the viscoelasticity of amorphous short chains was enhanced and the glass transition temperature was reduced by the increased amylose content; but the depolymerization of macromolecules and the decomposition of molecular bonds were postponed, since the increase in starch crystallites restricted the motion of adjacent amorphous regions. Hence, this work provides valuable information for rational design of hydrophobic starch-based films with desired thermal features by simply regulating the amylose content of starch raw materials.

Encapsulation systems have gained significant interest in designing innovative foods, as they allow for the protection and delivery of food ingredients that have health benefits but are unstable during processing, storage and in the upper gastrointestinal tract. Starch is widely available, cheap, biodegradable, edible, and easy to be modified, thus highly suitable for the development of encapsulants. Much efforts have been made to fabricate various types of porous starch and starch particles using different techniques (e.g. enzymatic hydrolysis, aggregation, emulsification, electrohydrodynamic process, supercritical fluid process, and post-processing drying). Such starch-based systems can load, protect, and deliver various food ingredients (e.g. fatty acids, phenolic compounds, carotenoids, flavors, essential oils, irons, vitamins, probiotics, bacteriocins, co-enzymes, and caffeine), exhibiting great potentials in developing foods with tailored flavor, nutrition, sensory properties, and shelf-life. This review surveys recent advances in different aspects of starch-based encapsulation systems including their forms, manufacturing techniques, and applications in foods.

The pasting and digestibility of a red adzuki bean starch were simultaneously modulated by heat-moisture treatment (HMT) through altering the multi-scale structure. HMT, especially at high moisture content, could disrupt the granule integrity, semicrystalline lamellae, molecular order (crystallites) and molecular chains. Also, certain rearrangement of starch molecules occurred to form ordered structures with increased thermal stability as shown by DSC. This concomitant disordering and reassembly in the multi-scale structure converted the fractions of resistant starch (RS) and rapidly digestible starch (RDS) into that of slowly digestible starch (SDS). Furthermore, the emergence of thermally-stable orders increased the pasting temperature but suppressed the swelling of granules during heating. Hence, HMT-modified red adzuki starch may serve as a potential thickener/gelling agent with slow digestion rate for various foods.

Starches were isolated from South China 5 (SC5) cassava harvested for 7, 8, 9, 10 and 11 months. During growth, the granule size, lamellar structure, crystalline structure and digestibility changed slightly, while the amylose content varied between 20.93% and 22.61%. However, the molecular weight showed an obvious increase as the harvesting time increased to 9 months, and then decreased during 9–11 months. The pasting behaviors were greatly affected by harvesting time. A shorter growth time led to higher pasting temperature, and lower peak, breakdown and setback viscosities. This trend became contrary when the growth time prolonged from 9 to 11 months. Hence, the starch harvested at 9 months showed the lowest pasting temperature (64.6 °C), but highest paste viscosity (2105 cP) and retrogradation tendency. All these results confirm that the growth time of 9 months was the turning point for the physicochemical features of SC5 during growth. This study provides fundamental data for rationally tailoring cassava starch properties by simply controlling the harvest time.

Here, we discovered that starch could be straightforwardly processed into optically-transparent electroconductive films, by compression molding at a relatively mild temperature (55 °C or 65 °C), much lower than those commonly used in biopolymer melt processing (typically over 150 °C). Such significantly-reduced processing temperature was achieved with the use of an ionic liquid plasticizer, 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]). A higher [C2mim][OAc] content, lower processing temperature (55 °C), and/or higher relative humidity (RH) (75%) during the sample post-processing conditioning, suppressed the crystallinity of the processed material. The original A-type crystalline structure of starch was eliminated, although small amounts of B-type and V-type crystals were formed subsequently. The starch crystallinity could be linked to the mechanical properties of the films. Moreover, the processing destroyed the original lamellar structure of starch, and the amorphous starch processed with [C2mim][OAc]/water could aggregate on the nanoscale. The films displayed excellent electrical conductivity (> 10−3 S/cm), which was higher with a lower processing temperature (55 °C) and a higher conditioning RH (75%). The incorporation of [C2mim][OAc] reduced the thermal decomposition temperature of starch by 30 °K, while the formulation and processing conditions did not affect the film thermal stability.\ud \ud

This work concerns the effects of concurrent ball milling (BM) and octenyl succinic anhydride (OSA) modification on the starch microstructure and physicochemical properties (swelling, emulsifying, and rheological). Unlike normal OSA-modified starches, the BM/OSA-modified starch displayed new features such as reduced viscosity and rigidity but increased paste stability during shearing, heating and cooling, regardless of the substitution degree. More interestingly, while the physicochemical properties could be regulated by simply altering the BM treatment time, BM/OSA was more efficient and effective at modulating starch properties during the initial period (approx. 10 h), as seen by the rapid evolutions in starch structural disruption and OSA esterification. Thus, the BM/OSA modification can serve as a viable and cost-effective approach for producing octenyl succinate starches where low viscosity (at relatively high concentrations) and high paste stability are desired.\ud \ud

This work concerns the multi-scale structures and digestion behaviors of indica rice starches with apparent amylose contents (AACs) of ca. 14%–24%. A higher AAC not always allowed a lower digestion rate (k), different from previous findings that starches containing more amylose normally show slowed digestion. Here, the proportion of stable molecular orders (melting temperature above ca. 73 °C) and AAC synergistically governed starch digestion rate. With a similar AAC, a higher amount of stable orders (Rh/l, ratio of enthalpy of stable orders to that of the rest) led to a lower k. Also, with a similar Rh/l, a larger AAC caused a lower k. Consistently, JPZ starch had almost the highest AAC and Rh/l, showing the lowest k. Regarding this, amylose and stable orders played roles in increasing the bulk density of starch structure matrices, and eventually slow the diffusion, absorption and catalysis events of digestion enzymes within the matrices.

Different characterization methods spanning length scales from molecular to micron scale were applied to inspect the microstructures and mechanical/hydrophilic features of agar/konjac glucomannan (KGM) films prepared under different drying temperatures (40 and 60 &deg, C). Note that the lower preparation temperature (40 &deg, C) could increase the strength and elongation of agar/KGM films at high KGM levels (18:82 wt/wt KGM-agar, or higher). This was related to the variations in the film multi-scale structures with the increment of KGM content: the reduced crystallinity, the increased perfection of nanoscale orders at some KGM amounts, and the negligibly-changed morphology and molecular chemical structure under 40 &deg, C preparation temperature. These structural changes initially decreased the film tensile strength, and subsequently increased the film strength and elongation with increasing KGM content. Moreover, under the higher drying temperature (60 &deg, C), the increased KGM content could concurrently reduce the strength and elongation for the films, associated with probable phase separations on nano and smaller scales. In addition, the increased KGM amount tended to make the film more hydrophilic, whereas the changes in the film structures did not dominantly affect the changing trend of hydrophilicity.

This work inspects the supramolecular/molecular structures and digestion rate of potato starches (BEM, C7H, CP2 and CP4) as affected by starch biosynthetic enzymes. Among the starches, CP2 had a lower digestion rate with a higher paste heating stability. Regarding this, predominantly enzyme-sets (i) and (ii) were revealed to produce amylopectin chains. For CP2, the reduced activity ratio of starch-branching enzymes to soluble starch synthases allowed more long amylopectin chains (polymerization degree ≥ 34). Such molecular features tended to increase the crystallites and thicken the lamellae. With similar surface morphology and amylose content, the bulk density of chain packing in CP2 supramolecular structures could be increased. Then, there were an increase in the resistance of starch structures to hydrothermal effects, and a reduction in the enzyme hydrolysis rate. Also, the increased long amylopectin chains played roles in increasing the paste stability during heating with shearing and in reducing the digestion rate.

From a supramolecular structure viewpoint, we concern how concurrent microwave and heat moisture treatment (M/HMT) tailors the pasting and digestion features of indica rice starch (IRS) and waxy rice starch (WRS), using combined analytical methods such as scanning electron microscopy and small-angle X-ray scattering. The results confirm that, for the starches (especially IRS), M/HMT led to a concave granule surface, weakened alignment of helices in lamellae, loosened packing of chains in amorphous regions, and somewhat disrupted crystallites. Consequently, the susceptibility of starch structures to hydrothermal effects was insignificantly altered, as reflected by unchanged pasting temperature; the enzyme absorption/hydrolysis could be properly accelerated, as affirmed by a modestly increased digestion rate and slightly reduced enzymatic resistance. Also, compared to WRS, IRS had more amylose with relatively long branches, which probably contributed to starch chain interactions during M/HMT. This tended to reduce the paste viscosity related to the swelling degree of starch granules, and increase the paste stabilities during heating and cooling related to the robustness of swelled granules and the reorganization of glucan chains.

Natural biopolymer materials have enormous potential in important, rapidly growing applications ranging from green electronics, dye and heavy metal removal, oil/water separation, therapeutic agent delivery, tissue engineering scaffolds, biological devices, optics, and sensing. However, the application of advanced functional biopolymer materials suffers from their poor processability and weak mechanical properties. Regarding this, there are enormous challenges to break the strong intermolecular interactions (hydrogen bonding) in their native forms, while re-establishing predominant hydrogen bonding in the processed materials in a cost-effective way. Here, we report our breakthrough to prepare biopolymer alloy materials based on chitosan and silk peptide (SP) with outstanding mechanical properties via a facile, "dry", melt processing method. The 1:1 (wt./wt.) chitosan-SP film had a toughness of 19.9 J cm, Young's modulus of 1855 MPa, and tensile strength of 95.9 MPa, which are similar to, or even better than, most engineering polymers. We propose that our method could maximize the molecular interactions between chitosan and SP via a simple and effective thermomechanical mixing, which resulted in considerably enhanced mechanical properties. Moreover, dehydration/rehydration can reversibly adjust the mechanical properties of the new biopolymer alloys, which demonstrates the dominant effect of hydrogen bonding in enabling the mechanical properties of these interesting alloys. Our simple approach to engineering high-performance biopolymer materials without resorting to complex chemistries and 3D-structural construction can be envisioned to bring about a new direction in the design of advanced functional materials where cost effectiveness is the priority.

The effects of anthocyanins on in vitro and in vivo digestibility of rice starch were evaluated in this study. Then, the effects of anthocyanins on physicochemical properties of rice starch and on starch digestive enzymes (α-amylase and α-glucosidase) were investigated to understand the mechanism of the effects of anthocyanins on starch digestibility. Characterization of physicochemical properties of rice starch indicates a structural change due to the presence of anthocyanins, hindering its access to starch digestive enzymes. Besides, anthocyanins inhibited the activities of starch digestive enzymes by binding to their active sites, competing with the substrates and changing the secondary structure of the enzymes. The above stated changes of rice starch and starch digestive enzymes due to the presence of anthocyanins both contributed to retarding the digestibility of rice starch. This study could offer some theoretical guidance to the development of new type rice-based food with low glycemic index.

This work revealed the influence of thermal processing on the microstructural, mesoscopic and molecular scale structures and thus the plasticizer migration of the starch ester films. Thermal processing promoted the permeation of water molecules to hinder the shrink of the amorphous macromolecules. That is, the swelling of the amorphous macromolecules diminished the ordered regions to a certain degree, resulting in the enlarged amorphous regions. Along with slight degradation of the macromolecules, the crystallites were partially disorganized, as indicated by a reduced relative crystallinity. These multi-scale structural changes of the films and the thermally enhanced mobility of plasticizer molecules synergistically enhanced the plasticizer migration. This study not only enables a well understanding of how thermal treatment alters the plasticizer migration of starch-based films from a multi-scale structural view, but also hints to our future work that rationally modulating the structural features of starch-based film may effectively control the migration of chemicals.

To rationalize the effects of heat-moisture treatment (HMT) on starch digestibility, the HMT-induced alterations in the mesoscopic and molecular scale structures of regular and high-amylose maize starches, as well as in their digestibility, were evaluated. Accompanying the supramolecular structural disorganizations and certain molecular degradation induced by HMT, somewhat molecular rearrangements occurred to probably form densely packed starch fractions, which eventually weakened starch digestion and thus transformed RDS into SDS and RS for regular and high-amylose starches. Interestingly, due to its larger amount of inter-helical water molecules that could be induced by HMT, B-polymorphic high-amylose starch was more susceptible to HMT (relative A-polymorphic regular starch), causing more prominent structural evolutions including molecular re-assembly and thus increasingly slowed digestion. In particular, the treated high-amylose starch with 30% moisture content showed a high SDS + RS content (48.3%). The results indicate that HMT-treated starch may serve as a functional ingredient with adjustable enzymatic digestibility for various food products.

Corn starch was treated by a dielectric barrier discharge plasma, and the changes in the granule morphology, crystalline structure, and molecular structure, as well as the rheological properties, were investigated using diverse techniques. Dielectric barrier discharge plasma could change not only the granule surface but also the internal structures of the starch granule through its pinholes. Specifically, after the plasma treatment, as the pinhole diameter increased, the relative degree of crystallinity decreased, accompanied by molecular chain oxidation, i.e., the generation of carboxyl groups, and degradation, i.e., molecular weight reduction. Therefore, the rheological behavior changed from pseudo-plastic to Newtonian with a decrease in the paste viscosity. The results indicate that dielectric barrier plasma could be used to produce modified starch with low viscosity at a high concentration for food and non-food applications. Industrial relevance As an eco-friendly and non-thermal physical technique, dielectric barrier discharge plasma has attracted great attention in polymer modification due to the interest in reducing generated wastes during modification and producing polymer products with high safety. Starch is traditionally a main material for foods and has been widely used in food and non-food industries. For improving the properties of starch and thus widening its industrial applications using a specific technique, it is indispensible to understand how the technique affects starch's structure and property. The present work revealed that not only was the surface of starch granules altered by the dielectric barrier discharge plasma but also the internal structure was affected, since the pinholes promoted the penetration of the plasma into granule interior. In particular, along with a reduced degree of crystallinity, molecular chain oxidation and degradation occurred, as confirmed by the generation of carboxyl groups and the molecular weight reduction. Then, the rheological behavior of starch paste changed from pseudo-plastic to non-Newtonian, together with a decreased paste viscosity. These results have demonstrated that dielectric barrier discharge plasma could be used as a new physical method to modulate the structure and rheological properties of starch, for the production of starchy food products with relatively low viscosity at a high concentration.

Supramolecular structural changes of maize starch as affected by hydrothermal treatment in excess water were investigated. At a temperature slightly higher than the onset (To) of gelatinization endotherm (G), an increase in the size of the cavity at the granule core and a sharp decrease in the ordering degree of the semi-crystalline lamellae occurred, together with the scattering objects apparently becoming looser. When the temperature approached close to the peak temperature (T-p) of endotherm G (70 degrees C), the semi-crystalline lamellae disappeared, accompanied by the emergence of a dual fractal structure. This suggests that the molecules of swollen maize starch displayed inhomogeneity on nanoscale, with a mass fractal structure at a higher scale level constituted by the scattering objects at a lower scale level. Additionally, it is proposed that a reduction in starch crystallites could enhance the degree of mixing between the crystalline and amorphous materials. The results enable a better understanding of starch supramolecular structural evolutions during the hydrothermal treatment in excess water.

Here, we tailored the multi-level structural and practical (mechanical/hydrophilic) features of gelatin films by varying the konjac glucomannan (KGM) content and the film-forming temperatures (25 and 40 &deg, C). The addition of KGM apparently improved the mechanical properties and properly increased the hydrophilicity. With the lower temperature (25 &deg, C), the increase in KGM reduced the gelatin crystallites of films, with detectable KGM&ndash, gelatin interactions, nanostructures, and micron-scale cracks. These structural features, with increased KGM and negligibly-occurred derivatizations, caused initially an insignificant decrease and then an increase in the strength, with a generally-increased elongation. The higher temperature (40 &deg, C) could reduce the strength and slightly increase the elongation, related to the reduced crystallites of especially gelatin. With this higher temperature, the increase in KGM concurrently increased the strength and the elongation, mainly associated with the increased KGM and crystallites. Additionally, the increase in KGM made the film more hydrophilic, the multi-scale structural changes of films did not dominantly affect the changing trend of hydrophilicity.

This work discloses the multi-scale structure and pasting/digestion behaviors of yam bean tuber starches (YB-GD and YB-SC). Compared to potato starch, YB starches exhibited varied pasting/digestion features that were understood from a multi-scale structural view. Especially, YB starches showed relatively polydisperse lamellae, less perfect crystallites, and fewer amylose molecules. These features should reduce the bulk density of starch chain packing, and could facilitate the water or enzyme diffusion in starch matrixes. Consistently, not only was starch’s resistance to hydrothermal effects weakened (shown by reduced pasting temperature), but also the enzyme absorption to starch chains and the subsequent hydrolysis events were accelerated. Furthermore, YB starch molecules had more short chains, which played roles in reducing the paste viscosity along with the reduced granule size and in enhancing the paste stabilities during heating and cooling. Also, those molecular features tended to speed up the enzyme diffusion and digestion events.

With synchrotron small/wide-angle X-ray scattering (SAXS/WAXS), we revealed that post-harvest hydration at ambient conditions can further alter the starch crystalline structure. The hydration process induced the alignment of starch helices into crystalline lamellae, irrespective of the starch type (A- or B-). In this process, non-crystalline helices were probably packed with water molecules to form new crystal units, thereby enhancing the overall concentration of starch crystallinity. In particular, a fraction of the monoclinic crystal units of the A-type starches encapsulated water molecules during hydration, leading to the outward movement of starch helices. Such movement resulted in the transformation of monoclinic units into hexagonal units, which was associated with the B-type crystallites. Hence, the hydration under ambient conditions could enhance the B-polymorphic features for both A-type and B-type starches. The new knowledge obtained here may guide the design of biopolymer-based liquid crystal materials with controlled lattice regularity and demanded features.\ud \ud

From a microstructural view, the focus of this work was on the water absorption rate of starch-based superabsorbent polymers (starch-SAPs) prepared under high starch concentration (0.27:1w/w starch:water). The effects of starch amylose/amylopectin ratio were disclosed. The increase in amylopectin reduced the amount (CPAM) of polyacrylamide (PAM) in starch-SAPs but increased the ratio of starch carbons grafted with PAM, which eventually decreased the average length (LPAM) of PAM chains. The shorter PAM chains could reduce starch-SAP chain flexibility, thus inducing larger mass fractal gels in swollen starch-SAPs. In general, the increases in CPAM and LPAM were preferable for a higher water absorbent capacity (WAC), whereas the denser fractal gels reduced WAC. Interestingly, all starch-SAPs had a dual-phase absorption process with the first stage showing a higher rate than the second phase (k1>k2). The shorter PAM chains caused increases in k1 and k2.

With increased awareness of global sustainability, there has been growing interest in the preparation of materials from natural, eco-friendly polymers (i.e., biopolymers). Nonetheless, despite their enormous application potential, biopolymers (starch, etc.) have a native semicrystalline structure with strong hydrogen bonding, and require use of solvents to improve their processability. However, the dissolution/processing of natural biopolymers such as starch often requires heating and thus significant energy input. Herein, we report an aqueous ionic liquid for fast and facile dissolution of starch, a typical semicrystalline natural polymer, under ambient conditions. The ionic liquid used is 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]). In particular, it is revealed that 0.15:1 mol/mol [C2mim][OAc]:water mixture disintegrates the sophisticated granule structure of native starch without apparently decreasing the molecular mass within 1 h at room temperature (i.e., 28 °C). In addition, this process did not result in any undesired derivatization. The discovery of this phenomenon could provide guidance for rationally designing “green” processes for chemical and biological engineering for the utilization of promising natural biopolymers.

This work concerns how the multi-scale supramolecular structure of starch relates to its digestion rate from a view of structural heterogeneity. The untreated granule starch displayed a dual-phase digestion pattern, ascribed to two digestible fractions within the heterogeneous multi-scale structure of starch, which had prominently different digestion rates. Not only amorphous starch but also part of molecular orders (crystallites with flaws) were digested at a same rate k1 at the first phase; densely-assembled starch including orders with fewer flaws was digested at a rather slow rate k2 (ca. 2/5 of k1) at the second phase. When alkali altered the heterogeneous supramolecular structure of starch, the digestion behaviors were also changed. The 0.1% (w/v) alkali solution slightly disrupted the starch multi-scale structure, which reduced the molecular orders, disrupted the lamellae, weakened the molecular organization within growth rings, and enlarged the granule pores. Then, part of resistant starch was transformed into slowly-digestible fraction with a digestion rate close to k2. In contrast, when stronger (0.5% w/v) alkali was used, the starch multi-scale structure was more apparently disrupted, causing even granule swelling. This structural change resulted in a triple-phase digestion with three different digestion rates. Moreover, especially with stronger alkali, along with the structural disruption, some orders with a higher thermal stability emerged and reduced the accessibility of starch molecules to the enzyme. In this case, the digestion rate decreased with the treatment time.\ud \ud

A fitting method combined with a linear correlation function was developed as an improved approach for the SAXS analysis of the semicrystalline lamellae of starch granules. Using a power-law function with two Gaussian plus Lorentz functions, the SAXS pattern was resolved into sub-patterns of the net lamellar peak and the power-law scattering plus scattering background (PL + B). The ratio of the net lamellar peak area (Apeak) to the total scattering area (Atotal) was proposed equal to the proportion of the lamellae within the starch granule (PSL). Along with this fitting method, we obtained a better profile of linear correlation function, with the elimination of the interference of non-lamellar amorphous starch (i.e., amorphous growth rings). Then, we could accurately calculate the lamellar parameters, e.g., PSL, the thicknesses of semicrystalline (d), crystalline (dc) and amorphous (da) lamellae, and the volume fraction (φc) of crystalline lamellae within semicrystalline lamellae. Quantitative analysis revealed that PSL was positively correlated with the crystallinity (Xc) of starch. It was confirmed that the distribution of lamellar thickness was more important than the starch botanical origin in affecting the validity of the developed fitting method. We also proposed a criterion to test the validity of the proposed method. Specifically, the total SAXS pattern should be mostly tangent to the profile of PL + B at a high q tail (close to 0.2 Å−1).\ud \ud

Here we concern the molecular fine structure of intermediate material (IM) fraction in regular maize starch (RMS) and Starpro 40 maize starch (S40). IM had a branching degree and a molar mass (Mw) somewhere between amylopectin (AP) and amylose (AM). Compared with AP, IM had more extra-long (Fr I) and long (Fr II) chains and fb3-chains (degree of polymerization (DP)>36), with a higher average chain length (CL). Also, IM contained less A-chains but more B-chains (both BS-chains with DP 3-25 and BL-chains with DP≥26), accompanied by longer B- and BL-chains, total internal chains (TICL) and average internal chains (ICL), and a similar average external chain length (ECL). Furthermore, relative to RMS-IM, the IM of S40 (with higher apparent amylose content than RMS) showed increases in relatively-long chains, e.g., Fr II, fb3-chains and BL-chains, but reductions in Mw, relatively-short chains (those with DP 6-12, etc.).

Multilevel structure and multiphase thermal transition of starch make its processing much more complex than that of synthetic polymers. This chapter discusses the unique structure and phase transition of native starch, as well as rheological properties of starch during thermal processing. The techniques used to study these characteristics are described. However, although starch can be processed using the conventional techniques designed for synthetic polymers, these techniques should be adapted along with optimized operational conditions and formulations. Regarding this, this chapter summarizes various processing techniques at laboratory and semi-industrial scales such as solution casting, extrusion, injection and compression moldings, as well as other innovative methods such as reactive extrusion. In particular, the most important aspects of starch processing pertaining to the use of plasticizers, blending with other polymers or ingredients, and orientation are discussed. Accordingly, native starch can be processed into different forms of plastic product such as films/sheets, foams and shaped articles for food packaging and other niche applications.

This work concerned the effects of amylose/amylopectin ratio on the structure and thermal stability of propionylated starches with high degree of substitution (DS). Four starches with different amylose content were used to obtain propionylated starches. Acylation partly disrupted granule morphology of native starches, and the imperfection and porous structures of starch granule were intensified along with the increased amylose content. It was noted that the crystalline structure of starch was destroyed and thus intense acylation occurred in both amorphous and crystalline regions. The acylated starch with high-amylose content displayed more ordered region compared to low-amylose starch. Acylation enhanced the thermal stability of starch, and this effect became more evident as the amylose content increased. Thus, the amylose/amylopectin ratio has been confirmed capable of affecting the structure and thermal behaviors of hydrophobic propionylated starch, which is of value for the design of starchy materials with tailored thermal stability.

The focus of this study was on the effects of plasticisers (the ionic liquid 1-ethyl-3-methylimidazolium acetate, or [Emim][OAc]; and glycerol) on the changes of starch structure on multiple length scales, and the variation in properties of plasticised starch-based films, during ageing. The films were prepared by a simple melt compression moulding process, followed by storage at different relative humidity (RH) environments. Compared with glycerol, [Emim][OAc] could result in greater homogeneity in [Emim][OAc]-plasticised starch-based films (no gel-like aggregates and less molecular order (crystallites) on the nano-scale). Besides, much weaker starch-starch interactions but stronger starch-[Emim][OAc] interactions at the molecular level led to reduced strength and stiffness but increased flexibility of the films. More importantly, [Emim][OAc] (especially at high content) was revealed to more effectively maintain the plasticised state during ageing than glycerol: the densification (especially in the amorphous regions) was suppressed; and the structural characteristics especially on the nano-scale were stabilised (especially at a high RH), presumably due to the suppressed starch molecular interactions by [Emim][OAc] as confirmed by Raman spectroscopy. Such behaviour contributed to stabilised mechanical properties. Nonetheless, the crystallinity and thermal stability of starch-based films with both plasticisers were much less affected by ageing and moisture uptake during storage (42 days), but mostly depended on the plasticiser type and content. As starch is a typical semi-crystalline bio-polymer containing abundant hydroxyl groups and strong hydrogen bonding, the findings here could also be significant in creating materials from other similar biopolymers with tailored sensitivity and properties to the environment.

The thermal property of cassava starch was regulated by the oxygen or helium glow-plasma treatment to change its supramolecular hierarchical structure. By investigating the microstructural and mesoscopic scale structural alterations and the thermal transition without and with the glow-plasma treatment, the underlying mechanism was explored through establishing a structure–thermal property relationship. Particularly, while there were negligible changes to the granule morphology, the glow-plasma predominantly disorganized the crystallites with low perfection and thermal stability, resulting in decreased alignment of double-helices within the crystalline lamellae, reduced relative crystallinity and thermal transition enthalpy, and increased transition temperatures accompanied by a narrowed gelatinization temperature range. The thermal transition parameters could be further modulated by simply changing the atmosphere type and treatment time. This is much different from our previous study which showed if glow-plasma disrupted the supramolecular structure of starch, the thermal transition temperatures would be reduced. These findings from present study indicate that the glow-plasma treatment can serve as a highly-safe physical method to rationally regulate the hierarchical structure of cassava starch and thus to realize the development of starch-based products with desired thermal behavior.\ud \ud

This work concerns how crosslinker amount (N, N'-methylene-bisacrylamide) affects the microstructural, absorbent and rheological features of one-step prepared starch-based superabsorbent polymers at a high starch concentration (0.27:1 w/w starch-water). The increased crosslinker amount evidently altered the microstructure and the absorbent and rheological features. Then, the variations in starch-based superabsorbent polymer properties were discussed from a microstructure viewpoint. Particularly, the higher crosslinker quantity rose the crosslinking density and the ratio (GR) of grafted anhydroglucose unit on starch backbone (from 27% to 52%), but short the average polyacrylamide (PAM) chain length (LPAM). These structural features suppressed the chain stretch within starch-based superabsorbent polymer fractal gels (confirmed by smaller Rg value) and promoted the formation of smaller chain networks, thus weakening the water absorption to the starch-based superabsorbent polymer chain networks. Also, the increased GR and reduced LPAM, with lowered chain extension and elevated crosslinking density, probably decreased the flexibility and mobility of chain segments in starch-based superabsorbent polymer gel matrixes. This caused the enhanced robustness and storage modulus of the gels with reduced chain energy dissipation ability.

We synthesized cobalt tetroxide (Co3O4) silica nanocomposites based on the conventional tetraethyl orthosilicate (TEOS) monomer and ethoxy polysiloxane (ES40) oligomer by sol-gel chemistry coupled with rapid thermal process (RTP). The physicochemical properties and structural formation of cobalt oxide silica nanocomposites were comprehensive characterized. By using ES40, well-controlled, homogeneous nanoparticle dispersion and size of Co3O4 with 5 nm within the silica matrix were achieved leading to fractal-like morphology. The concentration of the Co3O4 nanocatalyst was also significantly enhanced by more than 50 folds. Fenton-like HCO3−/H2O2 catalytic system using acid orange 7 and nanocomposites was examined for organic degradation. 98% AO7 and naphthalene intermediates degradation efficiency was achieved after 20 min with ES40-derived catalyst, which was three to ten folds faster than that of the TEOS-derived catalyst and the commercial Co3O4 catalyst. The combined use of ES40 sol-gel and RTP enabled a simple way to nanomaterial preparation and lowers overall processing time.