Functionality of chemically modified wild-type,partial waxy and waxy starches from tetraploid wheats

Partial waxy (reduced-amylose) and fully waxy (amylose-free) tetraploid durum wheats (Triticum turgidum L. var durum) were developed by introgression of null alleles at the Wx-A1 and Wx-B1 loci from common hexaploid wheat (Triticum aestivum L.). Purified starches were obtained from each genotype, and chemically modified by: 1) cross-linking with phosphorus oxychloride, 2) substitution with propylene oxide, and 3) sequential cross-linking with phosphorus oxychloride followed by substitution with propylene oxide. Functional properties were compared to blends of waxy and wild-type durum starches of known amylose contents. Significant differences in functionality were observed amongst the genotypes and blends after each modification. Waxy (0% amylose) and wild-type (30% amylose) typically were at the extremes of the observed ranges of functional properties. In general, the functional properties of the chemically modified starches were dependent upon amylose content. Starches from Wx-B1 null lines (24% amylose), were an exception. After substitution, such starches had the significantly highest value for RVA final viscosity, and generally performed in a manner similar to starch blends of 12–18% amylose.     

Effect of wx genes on amylose content,physicochemical properties of wheat starch,and the suitability of waxy genotype for producing Chinese crisp sticks

The effect of wx genes on amylose content, physicochemical properties of wheat starches, and the quality of Chinese crisp stick were investigated using near-isogenic lines (NILs) with null wx alleles in Yangmai 17 and Yangmai 01-2 backgrounds. wx genes showed significant effects on amylose content and other traits. The triple-null genotype had the lowest amylose content among eight genotypes, followed by double-null, single-null, and wild-type genotypes. The triple-null also showed lower flour yield, higher percentage of type B-granules on a volume basis and higher crystallinity than non-waxy genotypes, and showed significant differences in all pasting and thermal transition parameters compared to non-waxy genotypes, except for degree of retrogradation at day 14. For the quality of Chinese crisp stick, the hardness, crispness, fracturability, and specific volume of waxy genotype were 3.91 kg, 11.0, 1.85 mm and 104.4 ml, whereas the corresponding ranges for non-waxy genotypes were 5.39–5.70 kg, 0.5–0.9, 0.69–0.86 mm and 49.5–57.6 ml, respectively, in Yangmai 17 background. This indicates that waxy genotypes showed significantly better crisp stick quality than non-waxy genotypes. A similar trend was also observed in Yangmai 01-2 background. This indicated the potential utilization of waxy wheat for producing traditional products.     

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.     

Amylolysis of wheat starches. II. Degradation patterns of native starch granules with varying functional properties

Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were employed to investigate degradation patterns of native starch granules from wheat (Triticum aestivum L.) by different starch-degrading enzymes. The starches examined were from a waxy wheat and four varieties with slightly elevated amylose content, but with different functional properties. Differences in the digestion patterns after partial α-amylolysis of starch granules were noted between the starches. The waxy starch seemed to be degraded by endocorrosion, whereas the amylose-rich starches followed a slower mode of hydrolysis starting from the granular surface. X-ray diffractograms of the amylose-rich starches were not significantly altered by 2 h of α-amylolysis, whereas partial hydrolysis of the waxy starch decreased scattering intensity at higher 2θ angles, consistent with a different mode of attack by α-amylase in the initial digestion stages of granules of waxy and amylose-rich starches. We propose these differences are due to the combined effects of the change in packing density and partial preference for hydrolysis of amorphous material. The native starch granules were also attacked by beta-amylase, isoamylase and amyloglucosidase, which indicates that α-amylase is not the only starch-degrading enzyme that is able to initiate starch hydrolysis of native granules.     

Variation in amylose concentration to enhance wheat flour extrudability

Composition and functionality of five waxy wheat (Triticum aestivum L.) genotypes were elaborately investigated and related to end-product attributes of extrudates. As such, the interaction between starch biopolymers and protein in extrusion processing could be studied. Furthermore, the effect of an increasing amylose-concentration was studied by the use of blends. Waxy genotypes absorbed more water, gave rise to stiffer doughs and had higher onset and peak gelatinization temperature. In contrast, a lower pasting temperature and final viscosity and higher peak viscosity and breakdown could be observed. The volume percentage of small starch granules showed to be negatively correlated with peak temperature and positively with final viscosity and holding strength as well as with extrudate hardness. This was also positively correlated with amylose concentration. Expansion index was highest at a slightly decreased amylose concentration of 16.6%. Markedly higher moisture content for all amylose-free extrudates was attributed to a combination of increased solubility of amylopectin and reduced water evaporation at die emergence. It was hypothesized that an interplay with protein content and composition was laying at the basis of the observed differences. Moreover, the altered pasting behavior of waxy wheat may enhance the extrudability of gluten containing wheat flour.Starch granule size distribution is related to extrudate texture. Amylose content affects expansion index, water absorption and texture of extrudates. Interaction between starch content and protein composition and quality was observed. Waxy genotypes are strongly varying in their protein composition and functionality. Maximum expansion was obtained for blends containing 25% waxy flour.     

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.     

Effect of repeated heating and cooling cycles on the pasting properties of starch

The properties of starch and starch–lipid pastes have been explored using a novel extended Rapid Visco Analyser (RVA) profile, in which the heating and cooling cycles are repeated five times. Starches from four wheat varieties with amylose content ranging from 23 to 27%, and waxy starches of wheat, rice and maize were tested, alone and in mixtures with lauric acid and monopalmitin (glyceryl-1-monopalmitin). Gels of all of the starches formed and melted reproducibly during repeated heating and cooling in the RVA. The addition of lauric acid to the waxy starches had no effect on the multiple RVA profile. Monopalmitin caused an increase in viscosity during the heating stage of the second to the fifth cycles with the waxy starches, which was attributed to the presence of monopalmitin aggregates. Changes in the multiple cycle viscosity traces observed when monopalmitin or lauric acid was added to the amylose-containing starches were complex. It was concluded that RVA paste viscosities were determined by starch–lipid interactions, as well as by free lipid in the starch mixtures. The water solubility of the lipid and association of proteins with starch granules influence these interactions.     

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.     

Physicochemical properties and amylopectin fine structures of A- and B-type granules of waxy and normal soft wheat starch

This work fractionated waxy and normal wheat starches into highly purified A- and B-type granule fractions, which were representative of native granule populations within parent native wheat starches, to accurately assess starch characteristics and properties of the two granule types. Wheat starch A- and B-type granules possessed different morphologies, granule specific surface area measurements, compositions, relative crystallinities, amylopectin branch chain distributions, and physical properties (swelling, gelatinization, and pasting behaviors). Within a genotype, total and apparent amylose contents were greater for A-type granules, while lipid-complexed amylose and phospholipid contents were greater for B-type granules. B-type (relative to A-type) granules within a given genotype possessed a greater abundance of short amylopectin branch chains (DP_n < 13) and a lesser proportion of intermediate (DP_n 13–33) and long (DP_n > 33) branch chains, contributing to their lower relative crystallinities. Variation in amylose and phospholipid characteristics appeared to account for observed differences in swelling, gelatinization, and pasting properties between waxy and normal wheat starch fractions of a common granule type. However, starch granule swelling and gelatinization property differences between A- and B-type granules within a given genotype were most consistently explained by their differential amylopectin chain-length distributions.     

Microwave irradiation differentially affect the physicochemical properties of waxy and non-waxy hull-less barley starch

Waxy and non-waxy hull-less barley kernels and their isolated starches were irradiated under different microwave conditions (power 640, 720, and 800 W, time 60, 120 and 180 s). Changes in physicochemical properties were studied to investigate the effects of microwave irradiation (MWI) on in-kernel starches and isolated starches. For in-kernel starch, microwave reduced the ratio of 1047/1022 cm⁻¹ wavelengths, gelatinization enthalpy (ΔH_g) and relative crystallinity (RC), indicating that microwave of starch within the cells disrupted the crystalline regions. For isolated starch, microwave decreased the ratio of 1047/1022 cm⁻¹ wavelengths but increased ΔH_g of isolated starch, indicating that microwaving resulted in disruption of amorphous structure and an increase in the amount of remaining double helix structure. Moreover, viscosities of in-kernel starches decreased as microwave power and time increased, but this was not observed in isolated starches. Microwave treatment induced an enhancement of gelatinization temperature for non-waxy starches (NWS) but decreased in waxy starches (WS). Microwave had a greater effect for swelling power and solubility on in-kernel MWI-WS than MWI-WS, whereas the reverse results were found between in-kernel MWI-NWS and MWI-NWS. The results indicated that amylose plays a profound role in the properties of isolated and in-kernel starches during microwaving.     

The Effect of Heat–Moisture Treatment on the Structure and Physicochemical Properties of Normal Maize,Waxy Maize,Dull Waxy Maize and Amylomaize V Starches

Normal maize, waxy maize, dull waxy maize and amylomaize V starches were heat treated at 100 °C for 16 h at a moisture content of 30%. The results showed that the X-ray intensities of the major d-spacings of all starches increased on heat–moisture treatment (waxy maize > normal maize > dull waxy maize > amylomaize V). This treatment decreased the apparent amylose content (amylomaize V > normal maize), swelling factor (amylomaize V > waxy maize > dull waxy maize > normal maize), amylose leaching (amylomaize V > normal maize), pasting viscosities (amylomaize V > normal maize), acid hydrolysis (amylomaize V > normal maize > waxy maize > dull waxy maize), enzyme hydrolysis (amylomaize V > normal maize > dull waxy maize > waxy maize) and syneresis (amylomaize V > normal maize > waxy maize ≈ dull waxy maize). The gelatinization transition temperatures of all starches increased on heat–moisture treatment (amylomaize V > normal maize > waxy maize > dull waxy maize). However, the gelatinization temperature range increased only in normal maize and amylomaize V starches (amylomaize V > normal maize), while it remained unchanged in both the waxy starches. The enthalpy of gelatinization remained unchanged on heat–moisture treatment in all starches and the pasting viscosities of the two waxy starches were also unaffected. The foregoing data showed that starch chains within the amorphous and crystalline regions of the granule associate during heat–moisture treatment. However, the extent of this association was of a greater order of magnitude within the amorphous regions. DSC studies have indicated associations involving amylose chains (amylose–amylose and amylose–native starch lipids) resulted in the formation of new crystallites of different stabilities. In contrast, associations involving amylopectin chains (amylopectin–amylopectin) did not lead to crystallite formation.     

Starch digestibility and the estimated glycemic score of different types of rice differing in amylose contents

Three types of rice cultivars (indica, japonica and hybrid rice) with four levels of amylose were selected for assessing variability in starch digestibility. A vitro enzymatic starch digestion method was applied to estimate the glycemic index in vivo based on the kinetics of starch hydrolysis in vitro. The results indicated that significant differences in term of glycemic response were observed in three types of rice. Amylose content had an obviously impact on the estimated glycemic score (EGS) value and resistant starch (RS) content. The contents of RS were increased with the increasing amylose in the same type of rice. Japonica rice was significantly lower in RS content compared to indica rice and hybrid rice with similar amylose. The high amylose rice cultivar ZF201, which was characterized by low major RVA parameters, i.e. peak viscosity (PKV), hot paste viscosity (HPV) and cool paste viscosity (CPV), were obviously higher in RS content and lower in EGS. The retrogradation of cooked rice led to a reduction of HI and EGS of all varieties. Starch hydrolysis tends to be more quick and complete for the waxy and low amylose rice than for the intermediate and high amylose rice.     

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.     

Effect of process conditions and amylose/amylopectin ratio on the pasting behavior of maize starch: A modeling approach

The effects of different process conditions on the pasting behavior of the 14%, w/w suspensions of high amylose, waxy and normal maize starches at mixing speeds of 50, 160 and 250 rpm with the heating rates of 2.5, 5 and 10 °C/min were investigated. In addition, the impact of the starch mixture with an amylose-amylopectin ratio of 0–70% at 160 rpm and a heating rate of 5 °C/min on the pasting parameters was studied. According to the results, when stirring speed decreased from 250 rpm to 50 rpm, the peak viscosity dramatically increased. Furthermore, both heating and stirring rates significantly affected the pasting properties (p < 0.05). The amylose content of maize starch had a negative correlation with peak viscosity, trough viscosity, breakdown viscosity, final viscosity, and setback viscosity. Besides, syneresis values decreased as amylose content decreased from 70% to 0%. According to the kinetic modelling of pasting curves, starch coefficients were found to be higher than 1 for all starches, indicating that the penetration of water into starch granules increased granule swelling rate. The findings of the present study confirmed that both process conditions and amylose/amylopectin ratio can be optimized without necessity of starch modification to obtain the products with the desired quality.     

The Null-4A Allele at the Waxy Locus in Durum Wheat affects Pasta Cooking Quality

Granule-bound starch synthase, also known as the waxy protein catalyses the synthesis of amylose in wheat endosperm starch. In durum wheats, the genes encoding GBSS are present at the two Wx loci on chromosome 7A and 4A (a segment of 7B that has been translocated). Several null Wx-B1 (missing GBSS protein from chromosome 4A) durum lines were produced from crosses with null-4A bread wheats backcrossed to durum wheats. Semolina milled from 4 normal and 7 null-4A durum wheat lines grown over two seasons (1999 and 2000) in South Australia were analysed for amylose content, starch pasting properties as measured by the Rapid Viscoanalyzer (RVA), swelling power and starch damage, protein content and electrophoretic protein analysis. Spaghetti was prepared with a micro-scale extruder and the cooked pasta evaluated for cooking loss, firmness, stickiness and water absorption. The null-4A lines had significantly lower (ca. 5%) amylose content, higher starch peak viscosities and semolina swelling power. The pasta derived from the null-4A lines had lower cooking loss and in 1999 was more adhesive than the non-waxy lines. Cooking loss was correlated with amylose content, peak starch viscosity, swelling power of semolina and cooked pasta adhesiveness. Semolina swelling power was highly correlated with RVA peak viscosity. Waxy durum wheats appear to have an advantage over the normal types in terms of lower cooking loss, widely used as an indicator of pasta cooking quality.     

Characterisation of Starch from Inner and Peripheral Parts of Normal and Waxy Barley Kernels

A previous microscopical examination of barley kernels indicated an uneven distribution of amylose in the waxy cultivar SW7142-92, where the subaleurone layer was strongly stained by iodine. To explain these results, starch was isolated from fractions of inner and peripheral parts of kernels of the waxy cultivar and a cultivar with normal starch. Analyses of amylose content showed a higher concentration of amylose in starch from the outer part of the waxy barley kernel, where the amylose, determined by a colorimetric method, made up 8·6% of the starch compared with 5·9% in the middle and 2·2% in the innermost part of the waxy kernel. This difference in amylose distribution was not observed in the normal starch kernel. The results were confirmed by gel permeation chromatography. No differences in amylopectin chain length distribution were detected by size exclusion HPLC and HPAEC-PAD of amylopectins from different parts of the barley kernels.     

Genetic and Environmental Variation in Sorghum Starch Properties

Starch was isolated from eight local Zimbabwean landrace varieties, an improved cultivar (SV2) and a hybrid (DC-75) of sorghum grown in four environments. Amylose content, pasting (peak (PV), hot-paste (HPV), cool-paste (CPV) viscosity), textural and thermal (gelatinisation peak temperature (T_p) and gelatinisation energy (ΔH)) properties of the starches were determined. The F -tests from analyses of variance detected significant (p<0·001) differences among genotypes and growing environments for the starch properties measured. The results indicate that a range of genetic and environmental variability exists for these traits in sorghum genotypes although the latter could be greater than varietal effects. Hybrid DC-75 largely differed in starch amylose content, pasting PV, and gel hardness from the local landrace varieties. Environments used for local landrace varieties caused significant differences in starch properties, hence selection and monitoring of growing conditions is essential if a particular genotype is to maintain minimum variation in the desired pasting, textural or thermal properties. Genotype×environment interactions indicate that in breeding programmes, selection for starch properties at a single location would be misleading.     

Glass transition temperature of starches with different amylose/amylopectin ratios

The glass transition temperatures (T_g) of starch with different amylose/amylopectin ratios were systematically studied by a high-speed DSC. The cornstarches with different amylose contents (waxy 0; maize 23, G50 50 and G80 80) were used as model materials. The high heating speed (up to 300 °C/min) allows the weak T_g of starch to be visible and the true T_g was calculated by applying linear regression to the results from different heating rates. It is confirmed for the first time, that the higher the amylose content is, the higher the T_g is for the same kind of starch. The sequence of true T_g of cornstarch is G80 > G50 > maize > waxy when samples contain the same moisture content, which corresponds to their amylose/amylopectin ratio. It was found that T_g was increased from about 52 to 60 °C with increasing amylose content from 0 to 80 for the samples containing about 13% moisture. The microstructure and phase transition were used to explain this phenomenon, in particular the multiphase transitions that occur in high-amylose starches at higher temperatures, and the gel-ball structure of gelatinized amylopectin.     

Nucleotide polymorphisms in the waxy gene of NaN3-induced waxy rice mutants

Spontaneous and induced waxy phenotype, associated with endosperm containing little or no amylose, has been recognized in rice (Oryza sativa L.). Mutation of a dominant gene Wx into a recessive gene wx, which causes the inactivation or absence of granule bound starch synthase, is believed to be responsible for the change in endosperm starch leading to the waxy grain. In the present study, the nucleotide polymorphism in the Wx gene of rice genotype Tainung 67 (wild type) and its 35 NaN₃-induced wx mutants were examined. Iodine staining confirmed that all the mutants had waxy grain trait. The G-to-T single base substitution analysis indicated that the wild type genotype Tainung 67 and its waxy mutants carried Wx^b allele. Moreover, 23-bp duplication in exon 2 was detected in all the waxy mutants. Microsatellite polymorphism (CT)_n was also detectable on the Wx gene of the tested genotypes and mutants, with at least 5 classes of (CT)_n microsatellites identified at the Wx locus. Electrophoretic analyses also confirmed the observed nucleotide polymorphsim. Thus, nucleotide polymorphsim exist among NaN₃-induced waxy mutants in rice. However, only the 23-bp duplication in exon 2 may be used as a molecular marker to characterize waxy grain trait in rice genotypes.