Molecular Structure of a Low-Amylopectin Starch and Other High-Amylose Maize Starches

The molecular structure of two commercially available high-amylose maize starches, HYLON® V starch and HYLON® VII starch, and of a newly developed low-amylopectin starch (LAPS) was examined. These high-amylose starches give three apparent fractions as determined by gel-permeation chromatography: a high-molecular weight (mol.wt) amylopectin fraction, a low-mol.wt amylose fraction, and an intermediate-mol.wt fraction which contains both linear and branched components. The low-mol.wt amylose fraction increases from 9·4% in HYLON V starch to 17·7% in HYLON VII starch and 26·5% in LAPS, whereas the high-mol.wt amylopectin fraction decreases from 31·1% in HYLON V starch to 13·8% in HYLON VII starch and 2·5% in LAPS. The percentage of linear components in HYLON V starch, HYLON VII starch, and LAPS are 42, 54, and 80%, respectively. High-amylose starches have a large proportion of long chains in their branched fractions compared to waxy-maize and normal-maize starch. Both HYLON VII starch and the LAPS give B plus V-type X-ray diffraction patterns, but the LAPS has even a higher gelatinization temperature, lower swelling power in hot water, and is more resistant to acid digestion. With the lack of amylopectin, amylose accounts for at least part of the double helical structure in the LAPS granules.     

Amylolysis of wheat starches. I. Digestion kinetics of starches with varying functional properties

The susceptibility of wheat (Triticum aestivum L.) starches to hydrolysis by pancreatic α-amylase in vitro was investigated using a series of 35 starches with slightly enriched amylose content within a narrow range (36–43%), but widely differing functional properties. After 2 h of incubation with α-amylase, native starch granules were digested to different extents, but there were no differences between any of the starches once they were gelatinized. Cooling the starch for 72 h at 4 °C after cooking reduced the susceptibility of all of the starches to enzymic digestion by a similar extent, whereas addition of monopalmitin decreased the digestibility of the starches that contained amylose, but did not affect the digestibility of waxy starches that were also included in the study. Amylopectin chain length distribution of partly digested starch granules displayed increased proportion of short and medium chains and decreased proportion of long chains in comparison to native granules. Separated large (A) and small (B) starch granules from three of the starches differed significantly in their susceptibility to in-vitro digestion. A predictive model of the susceptibility of starch in the different forms was developed from the physico-chemical and functional properties of the starches.     

Retrogradation of waxy and normal corn starch gels by temperature cycling

Gelatinized waxy and normal corn starches at various concentrations (20–50%) in water were stored under temperature cycles of 4°C and 30°C (each for 1 day) up to 7 cycles or at a constant temperature of 4°C for 14 days to investigate the effects of temperature cycling on the retrogradation of both starches. Compared to starches stored only at 4°C, both starches stored under the 4/30°C temperature cycles exhibited smaller melting enthalpy for retrogradation (ΔH_r), higher onset temperature (T_o), and lower melting temperature range (T_r) regardless of the starch concentration tested. Fewer crystallites might be formed under the temperature cycles compared to the isothermal storage, but the crystallites formed under temperature cycling appeared more homogeneous than those under the isothermal storage. The effect of starch content on the retrogradation was greater when the starch gels were stored under cycled temperatures. The reduction in ΔH_r and the increase in conclusion temperature (T_c) by retrogradation under 4/30°C temperature cycles became more apparent when the starch concentration was lower (20 or 30%). Degree of retrogradation based on melting enthalpy was greater in normal corn starch than in waxy corn starch when starch content was low.     

Processing and evaluation of heat moisture treated (HMT) amaranth starch noodles; An inclusive comparison with corn starch noodles

AS, HMT-AS and CS starches were studied for amylose content, swelling power, water absorption capacity, color, particle size (PSA), pasting profile (RVA) and thermal (DSC) properties. Based on the laboratory scale experiments, noodles with good expansion, minimum cooking time and firm texture were prepared. Noodles were successfully prepared from AS, HMT-AS and CS starches. Noodles prepared from native amaranth starch (AS) and heat moisture treated (HMT) were tested for different functional properties and compared to cornstarch noodles. Standardized noodles were evaluated for cooking loss, texture profile (TPA), sensory and micro-structural analysis by SEM. HMT-AS noodles had experience less cooking loss of 20.15 g/100 g in comparison to AS noodles (22.20 g/100 g). The HMT-AS based starch noodles shown firmer texture, along with augmented taste and distinct flavor in comparison to AS and CS noodles.     

The addition of corn fiber gum improves the long-term stability and retrogradation properties of corn starch

This study was designed to test the hypothesis that the stability and physical properties of starch gels could be improved by adding small amounts of corn fiber gum (CFG). In the differential scanning calorimeter measurement, the enthalpy of retrogradation was 7.30 J/g for starch without CFG and 4.30 J/g for starch composite gel with 1.0% CFG. The addition of 1.0% CFG to starch significantly (p < 0.05) decreased the degree of retrogradation during the long-term storage from 61.6% to 36.5%. The addition of CFG retarded the syneresis of the starch system from 17.97% and 34.93%–6.15% and 26.57% after storage for 7 and 14 days respectively. The crystallization peak of starch containing 0.5–1.0% CFG was quite diminished. When compared with the starch gel alone, the addition of CFG significantly lowered the hardness of the composite starch gel from 60.92 to 45.81 N after 14 days storage. The starch gel without CFG showed the lowest rapidly digestible starch content and the highest resistant starch content in comparison to starch/CFG composite gels after 7 and 14 days storage. Over all, the addition of CFG considerably inhibits the retrogradation of corn starch gels during long-term storage.     

Effects of polymerization changes in maize proteins during nixtamalization on the thermal and viscoelastic properties of masa in model systems

Although nixtamalization is widely used in the food industry, a comprehensive understanding of the influence of proteins on the viscoelastic behavior and thermal properties in masa is still lacking. In this work, the effect of protein changes and its influence on the masa viscoelastic behavior were studied using model systems. Mixtures of lime-starch, zein-starch and lime-zein-starch were cooked at 90 °C from 20 to 150 min. Zein changes during cooking were analyzed by SDS-PAGE. Thermal transition temperatures and enthalpies were determined using differential scanning calorimetry (DSC). Dynamic oscillatory tests were undertaken on model system samples with 50% (w/v) moisture content, using a strain-controlled rheometer. SDS-PAGE showed that zein polymerizes during cooking. In the zein-starch model system, no visible protein bands were found after 30 min cooking; however, when lime was present, five bands were observed in all samples. Thermal transitions were observed around 55–62 °C for all model systems, probably corresponding to starch retrogradation. Rheological studies showed that protein exhibited higher influence in the gel strength by increasing the elastic character of the system. It was hypothesized that the combined effects of lime on starch, zein polymerization and the formation of calcium-zein bonds during cooking, yield a stronger and more elastic gel structure.     

An innovative approach for significantly increasing enzyme resistant starch type 3 content in high amylose starches by using extrusion cooking

In this study effects of extrusion cooking on enzyme resistant starch (RS) formation in high amylose corn starches (Hylon V and VII) and the functional properties of RS preparations were investigated. Native starches were extruded at 50, 60, 70% feed moisture contents, at constant screw speed (100 rpm) and barrel temperature (140 °C). Among these samples, the highest RS contents were observed at 60% feed moisture. Therefore, feed moisture in the second and third extrusion cycles was set at 60%. There were significant increases in RS contents of both Hylon V and Hylon VII after the second extrusion cycle (p < 0.05). After the third extrusion, the RS levels reached to 40.0 and 45.1% for Hylon V and Hylon VII, respectively. Substantial loss of birefringence in these samples indicated that the increases in RS were mainly due to RS3 formation. The RS samples produced by extrusion did not have high emulsion capacity, but the ones produced from Hylon VII had high emulsion stability. Although, decreases in L* and increases in b* values of extruded samples were significant as compared to respective native starches, the changes were not substantial. Therefore, their incorporation is not expected to cause major changes in the colour of end-products.     

Properties of maize starch modified by ball milling in ethanol medium and low field NMR determination of the water molecular mobility in their gels

Ethanol as moisturizing agent and ball-milling treatment, has been combined in order to determine their impacts on the improvement of the properties of physically modified maize (Zea mays) starch granules. The content of ethanol has been set respecting a ratio of starch to ethanol varying from 1:0 to 1:3 (w:v), and the ball-milling time varied between 0 and 72 h. We observed that the increase of the amylose content varied in a more effective way with increase of the milling time (p < 0.05) than with the variation of the starch to ethanol ratios. As expected, modified starches were more transparent, more soluble, less crystalline, and presented damaged structures. In all cases, the starch granule sizes were better distributed at ratios of starch to ethanol of 1:0 and 1:3 (w:v) respectively. In addition, the impact of the combination of these treatments on the mobility of water molecules in starch gels characterized by the transverse relaxation time (T₂), as well as the abundance of protons (¹H T₂) in each populations were determined by low field NMR. Mobility of water molecules within starch gels increased at high temperature. Nonetheless, the proton population at T₂ > 10 ms (characterized by T₂₂) for the modified starch (starch/ethanol, 1:3 w:v) was fundamental in the different water concentrations, and accounts for 70 to 90% of total protons, at temperatures >60 °C.     

Water mobility,rheological and textural properties of rice starch gel

Three rice starches from indica (TNuS19), japonica (TNu67) and waxy (TCW70) were used as samples to investigate the water mobility, viscoelasticity and textural properties of starch gels using pulsed nuclear magnetic resonance (PNMR), dynamic rheometer and texture analyzer. The spin–spin relaxation time (T₂), showed water mobility of starch gels was detected with starch concentrations 10–30%. Generally, the TNuS19 and TNu67 at ≥20% showed two components (T_2a and T_2b) in water mobility, where T_2a and T_2b related to solid-like and liquid-like water molecules in starch gels, respectively. However, the TCW70 over the concentrations examined had only T_2b component, higher than those of corresponding TNuS19 and TNu67. The storage (G′) and loss (G″) moduli of starch gels were in the order of TNuS19 > TNu67 > TCW70. Texture analyzer analysis indicated that TNuS19 had higher hardness, stickiness and adhesiveness than did the TNu67 and TCW70, and changed significantly with the starch concentration increase. The value of T_2b was highly correlated with physical properties of starch gels, especially with dynamic rheological parameters. It is suggested that amylose content may play a major role to influence the water mobility of starch gels which affects the specific viscoelasticity and textural properties of starch gels.     

Rheological and textural properties of tef [Eragrostis tef (Zucc.) Trotter] grain flour gels

Interest in tef [Eragrostis tef (Zucc.)Trotter] grain in food applications has increased in recent years because of its nutritional merits and the absence of gluten. With the objective of evaluating the suitability of tef for making gel type food products, gel viscoelastic properties of three varieties of tef (one brown and two white) at different concentrations (6, 8, 10, 12 & 14% w/w) were evaluated at 25 °C and 90 °C. The texture and color evolution for 16% (w/w) gels were evaluated. Proximate compositions of the flours were quantified. Rice, refined and whole wheat flours were analyzed as reference. The minimum flour concentration required for gel formation from the three tef varieties was 6–8%, similar to wheat flour. All tef flour suspensions pre-heated to 95 °C led to gels with a solid-like behavior (G′ > G″), both at 25 °C and 90 °C, with higher consistency than wheat gels at the same concentration. The dependence of viscoelastic moduli with concentration fulfilled the power law. The Avrami model was successfully fitted to the textural evolution of tef gels. Important differences were observed among tef and rice and wheat flours, probably contributed by their differences in protein, starch, lipid and fiber constituents. Gelling properties characterized suggest that tef flours would be suitable ingredients in gel food formulations.     

Influence of amylopectin structure on rheological and retrogradation properties of waxy rice starches

A set of 13 waxy rice genotypes prepared by chemical-induced mutation of rice variety TNG67 and 7 waxy rice varieties widely grown in Taiwan were compared for structural, rheological and retrogradation characteristics of starches. Wide differences in retrogradation enthalpy (ΔH_ret), gel firmness and storage modulus (G’_ret) were observed for 2-week stored gels of 20 starches. Ratio of short-to-long amylopectin chains was significantly higher (p < 0.05) in starches from mutant genotypes than in commercial varieties. ΔH_ret and G’_ret of starch pastes stored over 4 weeks showed stronger correlation with amylopectin chain-profile compared to those stored for 2 weeks. Amount of long amylopectin chains was correlated positively (p < 0.05) with ΔH_ret and gel firmness. Overall, ratio of short-to-long amylopectin chains affected almost all the rheological and retrogradation parameters. Results of this study can be useful to plant breeders and food industry for quality improvement and selection of waxy rice mutants for various applications.     

Effects of amylose content,cooling rate and aging time on properties and characteristics of rice starch gels and puffed products

This study aimed at investigating the effects of amylose content (AC) of 0.12–19.00% w/w on dry basis, cooling rate (1, 3, 5, and 9 °C/min), and aging time (24, 48, and 72 h) on structure, physical properties and sensory attributes of rice starch-based puffed products. They had an influence upon the crystalline type, and the relative crystallinity (RC). The thermal and physical properties of starch gels were also determined. Amorphism was found for starch gels with 0.12% AC. The polymorphisms (B and V) and differential scanning calorimetric endotherms were found for those with AC ≥4.00%. The RC, retrogradation enthalpy (ΔH_r) and gel hardness increased with AC and aging time. The cooling rate did not affect RC, but increased ΔH_r and gel hardness. The higher AC and aging time resulted in higher hardness, fracturability, crispiness and bulk density, but lower expansion ratio and less oiliness of the puffed products. The hardness, fracturability, crispiness and bulk density of puffed products were well correlated with the RC of starch gel.     

Rheology and texture of starch gels containing iodine

The objective of this study was to investigate the textural and rheological properties of starch gels containing different levels of iodine. The research goal is to understand the architectural organization of granules by utilizing iodine as a marker. Corn (CS), wheat (WS), potato (PS) and tapioca (TS) starch gels containing varying concentrations of iodine were prepared in a Rapid Visco Analyser (RVA). The gels were analysed by using a rheometer for small-deformation properties and also by using a texture analyser for large deformation properties following storage for 1 or 7 days. With increasing concentration of iodine, the firmness of gels decreased and the extent of decrease varied for the different starches. The extent of change in complex modulus (G*) of the gels was highest in the A-type starch, CS, but was different from WS, which is also an A-type starch. The G* for PS gels (B-type) decreased with the addition of 0.1% iodine but there was no significant difference upon increasing the iodine concentration. The G* for the C-type TS gels was lower than 15 Pa. These observations suggest a difference in the microstructure of the starch gels formed, likely resulting from differential leaching of polymers.     

Study on melting and crystallization of short-linear chains from debranched waxy starches by in situ synchrotron wide-angle X-ray diffraction

In situ melting and crystallization of short-linear α-1,4-glucan (short-chain amylose, or SCA) from debranched waxy starches were investigated by synchrotron wide-angle X-ray diffraction. Amorphous SCA was prepared by dissolving completely debranched waxy starches in alkaline solution and neutralized by hydrochloric acid. When hydrated with 50% water at 25 °C, all amorphous SCA crystallized immediately and gave a B-type structure. The SCA from debranched waxy potato starch had a longer average chain length and a higher melting temperature but relatively lower crystallinity upon hydration; it was not completely melted at 100 °C and retained its original B-type structure during rapid cooling. In contrast, the SCA from debranched waxy wheat and waxy maize starches had a large portion of low molecular weight fractions, a higher crystallinity upon hydration, and a lower melting temperature. These differences suggest that amylopectin short chains crystallized more readily but their crystals were weaker than those of long chains. After the B-type crystals of hydrated SCA from waxy wheat and waxy maize starches melted, they reformed into the A-type polymorph upon rapid cooling. The thermal properties showed that the A-type polymorph of debranched waxy wheat and waxy maize starches had a higher melting temperature than their B-type structure.     

Investigation of the high-amylose maize starch gelatinization behaviours in glycerol-water systems

The effect of glycerol on gelatinization behaviours of high-amylose maize starch was evaluated by confocal laser scanning microscopy (CLSM), scanning electronic microscope (SEM), differential scanning calorimetry (DSC), texture analyzer (TPA) and rheometer. Gelatinization of the high-amylose maize starches with glycerol content of 10% (w/w) began at 95.4 °C (T_o), peaked at 110.3 °C (T_p), and completed at 118.9 °C (T_c). The birefringence began to disappear at around 100 °C and finished at 120 °C which corresponded well to the onset and conclusion temperatures obtained by DSC. The high-amylose maize starch granules maintained original morphological structure at 100 °C and swelled to a great degree at 110 °C. The high-amylose maize starch paste formed at 100 °C showed the lowest hardness (39.92 g), while at 120 and 130 °C, showed the highest hardness (610.89 g and 635.43 g, respectively). It should be noted that in going from 100 °C to 110 °C there is a significant increase in the viscosity of the slurry solution. The identical apparent viscosity was observed when the shear rate exceed 100 s⁻¹, resulting from the high-amylose maize starch granules were completely gelatinized at 120 °C, which was consistent with DSC analysis.     

Pasting,thermal and rheological properties of octenylsuccinylate modified starches from diverse small granule starches differing in amylose content

Waxy maize (a standard starch of normal granule size) and five small granule starches from different botanical sources (rice, wheat B type, oat, quinoa and amaranth) were subjected to 2-octenyl-1-succinic anhydride (OSA) modification. Changes of pasting, gel texture, thermal and rheological properties were investigated. Different small granule starches showed quite different property changes after OSA modification. Pasting viscosity was generally increased in OSA starches, among which OSA oat starch had notably high peak and breakdown viscosity but low setback viscosity. Gel hardness of rice, wheat B type, oat and quinoa starches was reduced by OSA treatment, whereas that of waxy maize and amaranth starches was increased. Amylose content was considered to be the major factor influencing pasting, gel and thermal property of OSA starches. Esterification increased pseudoplastic flow behavior of all starches, while OSA oat starch uniquely had reduced flow consistency coefficient. The dynamic rheological properties were also changed differentially among OSA starches. Viscoelastic properties of rice, wheat B type, oat and quinoa starches were increased after OSA treatment, whereas those of waxy maize and amaranth starches were decreased. This study showed that diverse functionalities from OSA small granule starches may fulfil different demands in product development.     

Partial-degradation and heat-moisture dual modification on the enzymatic resistance and boiling-stable resistant starch content of corn starches

Normal corn, Hylon V and Hylon VII starches were partially degraded by acid-ethanol treatment and applied to heat-moisture treatment (HMT) for improving the enzymatic resistance of starch. The weight-average degree of polymerization (DP_w) of acid-ethanol-treated (AET) corn starches ranged from 6.75 × 10⁵ to 181, 4.48 × 10⁵ to 121, and 1.94 × 10⁵ to 111 anhydrous glucose units for normal corn, Hylon V and Hylon VII starches, respectively. Starch retained its granular structure after AET and HMT, recovery of starch granules after modifications were higher than 92%. Resistant starch (RS) content and boiling-stable RS content of corn starch increased after dual modification, and the increment increased with increasing duration of AET. The boiling-stable RS content of dual-modified starch increased from 1.5 to 9.2, 12.2 to 24.1, and 18.0 to 36.2% for normal corn, Hylon V and Hylon VII starches, respectively. Increments of RS content and boiling-stable RS content of dual-modified starches were significantly correlated (r² > 0.700) with DP_w of starch, revealing that the enzymatic resistance of dual-modified corn starch granules increased with decreasing molecular size of starch. Result also suggested that starch granules partially degraded with AET could improve the molecular mobility and ordering during the consequent HMT.     

Morphologies and microstructures of cornstarches with different amylose–amylopectin ratios studied by confocal laser scanning microscope

The morphologies and microstructures of cornstarches with different amylose–amylopectin ratios (waxy: 0/100; maize: 23/77; Gelose 50: 50/50; and Gelose 80: 80/20) were studied by a confocal laser scanning microscope (CLSM). The temperature-induced changes of the cornstarch granules in excess of water were also studied under CLSM. Acid hybridization of starch by HCl was used to enhance the difference between amorphous and crystalline ranges. It was found that the high-amylose starches (G50 and G80) were brighter than those of low-amylopectin starches (waxy and maize) under confocal laser light, and the average (decreasing) fluorescence intensity sequence of the granules was G80 > G50 > maize > waxy. Waxy and maize starches showed clear internal cavities and channels, whilst G50 and G80 had bright cores. Sharp growth ring structures can be clearly observed for low-amylose starches (waxy and maize) after acid hydrolysis. Gelatinization of all starches starts at the hilum and the adjacent of the channels, and spreads rapidly to the periphery. This work is the first time that three-dimensional images of partly gelatinized granules have been constructed and presented from different confocal images, which allows further exploration of the mechanisms of gelatinization.     

Effects of added water and retrogradation on starch digestibility of cooked rice flours with different amylose content

Flours derived from rice varieties with different amylose content possess distinct physicochemical and molecular properties. The aim of this study was to determine optimal processing conditions for preparing rice flour-based foods with reduced starch digestibility. To do so, we evaluated the in vitro starch digestibility of rice flours with five varieties. Reducing the amount of water (from 10-fold to 4-fold of rice flour) used for cooking rice flour lowered its starch digestibility, and the magnitude of the decrease was positively correlated with amylose content. When retrogradation of cooked rice flour proceeded for 7 days, the digestibility of high-amylose rice flours declined rapidly in the first 3 days, whereas the digestibility of low-amylose rice flours declined continuously. Our analysis also demonstrated that the chain length distribution of starch molecules and the final and setback viscosity pasting properties were the most important parameters affecting the digestibility of rice flours. Based on our results, it appears possible to reduce rice starch digestibility by establishing optimum processing conditions for different varieties. We suggest a 7-fold addition of water and retrogradation for 1 day for high-amylose rice varieties and a 4-fold addition of water with 3 days of retrogradation for low-amylose rice.     

Viscoelastic properties and bubble structure of rice-gel made from high-amylose rice and its effects on bread

Rice gel is a novel form of processed rice, where gelatinized rice is sheared at high speed to create a gel with unique viscoelastic properties, which can partially replace wheat flour in bakery products. In this study, the viscoelastic properties and bubble structures of rice gels made from two high-amylose rice cultivars and two different ratios of rice to water were studied, focusing on the effect of cooling the gelatinized rice before high-speed shearing (cooled rice gel) as opposed to shearing the gelatinized rice while hot (hot rice gel). Increasing the water content and cooling the rice before high-speed shearing generally decreased the dynamic storage (E′) and loss moduli (E″) in the viscoelasticity measurement and introduced fewer but larger and uniform bubbles in the rice gel. In addition, breads made from cooled rice gel showed significantly higher volume than those made from hot rice gel. The application of mechanical shearing to gelatinized starch has a great potential in creating novel food materials with characteristic textures, and can also be used for the processing of cereals other than rice.