The influence of amylose and amylopectin characteristics on gelatinization and retrogradation properties of different starches

Physico-chemical properties of starch from wheat, rye, barley (waxy, high-amylose and normal-amylose), waxy maize, pea and potato (normal-amylose and high-amylopectin) were studied. Emphasis was given to the amylose (total, apparent and lipid-complexed) and amylopectin characteristics as well as to the gelatinization and retrogradation properties measured using differential scanning calorimetry. The total amylose content varied from ca. 1 % for waxy maize to 37% for high-amylose barley. The amylopectin characteristics were determined by high-performance size-exclusion chromatography after debranching with isoamylase. The weight-average degree of polymerization ( _w) was 26, 33 and 27 for the A-, B-, and C-type starches, respectively. In general, the potato starches exhibited the highest retrogradation enthalpies and the cereal starches the lowest, while the pea starch showed an intermediate retrogradation enthalpy. The data were analysed by principal component analysis (PCA). The _w showed positive correlation to the melting interval, the peak minimum, the offset temperatures of the retrogradation-related endotherm as well as to the gelatinization and retrogradation enthalpies. However, the high-amylose barley retrograded to a greater extent than the other cereal starches, despite low _w (24). The amylose content was negatively correlated to the onset and the peak minimum temperatures of gelatinization.     

Effect of acid–alcohol treatment on the molecular structure and physicochemical properties of maize and potato starches

The molecular structure and physicochemical properties of acid–alcohol treated maize and potato starches (0.36% HCl in methanol at 25 °C for 1–15 days) were investigated. The yields of the modified starches were ranging from 91 to 100%. The average granule size of modified starches decreased slightly. The solubility of starches increased with the increase of treatment time, and the pasting properties confirmed the high solubility of modified starches. The gelatinization temperatures and range of gelatinization increased with the increase of treatment time except T_o (onset temperature) of maize starch. Molecular structures of modified starches suggested the degradation of starches occurred mostly within the first 5 days of treatment, and degradation rate of potato starch was higher than maize starch both in amylopectin and in amylose. Maize starch was found less susceptible to acid–alcohol degradation than potato starch.     

Structural and physicochemical characterisation of rye starch

The gelatinisation, pasting and retrogradation properties of three rye starches isolated using a proteinase-based procedure were investigated and compared to those of wheat starch isolated in a comparable way. On an average, the rye starch granules were larger than those of wheat starch. The former had very comparable gelatinisation temperatures and enthalpies, but slightly lower gelatinisation temperatures than wheat starch. Under standardised conditions, they retrograded to a lesser extent than wheat starch. The lower gelatinisation temperatures and tendencies of the rye starches to retrograde originated probably from their higher levels of short amylopectin (AP) chains [degree of polymerisation (DP) 6–12] and their lower levels of longer chains (DP 13–24) than observed for wheat starch. The rapid visco analysis differences in peak and end viscosities between the rye starches as well as between rye and wheat starches were at least partly attributable to differences in the levels of AP short chains and in average amylose molecular weight. The AP average chain lengths and exterior chain lengths were slightly lower for rye starches, while the interior chain lengths were slightly higher than those for wheat starch.     

Succinyl and acetyl starch derivatives of a hybrid maize: physicochemical characteristics and retrogradation properties monitored by differential scanning calorimetry

Starch isolated from a hybrid maize (8535-23) was chemically modified by succinylation and acetylation. No pronounced difference was observed between the X-ray pattern of native starch and modified starch samples, and the samples gave the characteristic A pattern of cereal starches. Onset temperature (T(o)), peak temperature (T(p)), concluding temperature (T(c)) and enthalpy of gelatinisation (DeltaH), reduced after succinylation and acetylation, but gelatinisation temperature range increased following starch modifications. Modifications reduced starch retrogradation.     

Effects of an added inclusion-amylose complex on the retrogradation of some starches and amylopectin

The effects of added cetyltrimethylammonium bromide (CTAB)-amylose complex on retrogradation of some starches (waxy-maize, maize, and potato starch) and on amylopectin from potato have been studied by differential scanning calorimetry (DSC). The starches and amylopectin samples with added CTAB-amylose complex received four different heat treatments prior to storage and DSC measurements that either melted the complex or left the complex intact. The calorimetry measurements showed that intact CTAB-amylose complex had much less effect on decreasing the retrogradation of the starches and the amylopectin than samples with melted complex prior to measurements. This is discussed in relation to possible complex formation of amylopectin and lipids and the effects of adding uncomplexed lipids on the retrogradation of waxy starches and amylopectin.     

Changes in color and texture of wheat noodles during chilled storage

Wheat noodles cooked for different periods of time were stored at 5 °C, and color changes in their cross sections were quantitatively assessed by digital image analysis. The color of noodles with flattened moisture distributions whitened greatly during the early stages of chilled storage due to the retrogradation of starch, with the color change showing a significant correlation with the changes in noodle fragility. Color changes were also measured for wheat noodles and noodles containing modified starch with internal moisture distributions, and local changes within the noodles were kinetically analyzed. The addition of modified starch significantly reduced the color change in the noodle interior, where the moisture content was relatively low. Scanning calorimetric measurements indicated differences in the gelatinized state of modified starch and original wheat starch at low moisture contents, which affected the rate of color change in the interior of noodles containing modified starch.     

Effect of annealing and pressure on microstructure of cornstarches with different amylose/amylopectin ratios

This work focuses on the effect of annealing and pressure on microstructures of starch, in particular the crystal structure and crystallinity to further explore the mechanisms of annealing and pressure treatment. Cornstarches with different amylose/amylopectin ratios were used as model materials. Since the samples covered both A-type (high amylopectin starch: waxy and maize) and B-type (high amylose starch: G50 and G80) crystals, the results can be used to clarify some previous confusion. The effect of annealing and pressure on the crystallinity and double helices were investigated by X-ray diffraction (XRD) and ¹³C CP/MAS NMR spectroscopy. The crystal form of various starches remained unchanged after annealing and pressure treatment. XRD detection showed that the relative crystallinity (RC) of high amylopectin starches was increased slightly after annealing, while the RC of high amylose-rich starches remained unchanged. NMR measurement supported the XRD results. The increase can be explained by the chain relaxation. XRD results also indicated that some of the fixed region in crystallinity was susceptible to outside forces. The effect of annealing and pressure on starch gelatinization temperature and enthalpy are used to explore the mechanisms.     

Amylose content and chemical modification effects on thermoplastic starch from maize – Processing and characterisation using conventional polymer equipment

A design of experiments was performed on extruded starch based materials studied in a recently published article [Chaudhary, A. L., Miler, M., Torley, P. J., Sopade, P. A., & Halley, P. J. (2008). Amylose content and chemical modification effects on the extrusion of thermoplastic starch from maize. Carbohydrate Polymers, 74(4), 907–913] highlighting the effects of amylose content, chemical modification and extrusion on a range of maize starches. An investigation into the effects of starch type (unmodified 0–80% amylose starch; hydroxypropylated 80% amylose starch), screw speed and ageing after moulding on final product properties such as mechanical properties (Young’s modulus, maximum stress and strain at break), moisture absorption, morphology and retrogradation are included. A full factorial design was used to study these starch type, processing and final product property relationships. Microscopy was used to observe any morphological difference between the various starch types in thermoplastic starch (TPS) blends and X-ray diffraction (XRD) was used to observe changes in crystallinity over time (retrogradation). The results show that 0% amylose (waxy maize) and hydroxypropylated 80% amylose thermoplastic starches have mechanical properties comparable to that of low density polyethylene (LDPE) and high density polyethylene (HDPE), therefore these materials have the potential to be an environmentally friendly alternative to current polymer resins.     

Determination of the maximum water solubility of eight native starches and the solubility of their acidic-methanol and -ethanol modified analogues

The maximum water solubilities of eight native starches from potato, shoti, tapioca, maize, waxy maize, amylomaize-7, wheat, and rice and their acid-methanol and acid-ethanol modified analogues have been determined. Maximum solubilities of 18.7 and 17.4 mg/mL were obtained for waxy maize and tapioca and 12.4 mg/mL for potato and maize starches by autoclaving 220 mg/10 mL at 121 degrees C; 8.7 mg/mL was obtained for shoti starch by stirring in 85:15 (v/v) Me(2)SO-H(2)O at 20 degrees C; and 7.0 and 5.2mg/mL for rice and amylomaize-7 starches by stirring in 1M NaOH at 20 degrees C. The acid-alcohol treated starches were 4-9 times more soluble than their native starches. The compositions of the solubilized starches had, in general, much higher ratios of amylose to amylopectin than the ratios in their native granules. A major exception to this was the acid-methanol treated potato, shoti, and rice starches that had much lower ratios of amylose to amylopectin than the ratios in their granules.     

Determination of the botanical origin of starch using direct potentiometry and PCA

A new approach for the determination of the botanical origin of starch is presented based on the formation of starch-triiodide complexes. The starch samples were extracted from wheat (Srpanjka), potato, maize, rye (Barun), barley (Conduct), rice, tapioca and a commercial modified starch. The amylose/amylopectin ratios of starches, among various other properties, differ between starches of different botanical origins. Triiodide ions bind characteristically to the amylose and amylopectin of the starch depending on the starch's origin. The new technique includes direct potentiometric measurements of the response of free triiodide ions in starch-triiodide solutions where the data is analysed by principal component analysis (PCA). PCA gave graphical results for statistical differentiation between starches of different botanical origins.     

In situ starch degradation of different feeds in the rumen

The in situ starch degradation of 5 feeds (barley, maize, pea, oats and wheat bran) has been measured (trial 1), and the influence of particle size on starch degradation investigated with 3 feeds (barley, maize, pea) (trial 2). The starch degradability of barley, oats and wheat bran was found to be higher than that of pea, and higher again than that of maize: 98, 97, 96, 90 and 58% respectively. For barley, oats and wheat bran, starch was degraded more rapidly than the other dry matter (pm) components. Maize and pea starches were degraded at the same rate as non-starchy components. The particle size variations between feeds ground on the same screen may partly explain variations in starch degradability. When the particle size increased from 0.8 to 6.0 mm screen grinding, in situ starch degradability decreased; the decrease was higher for maize (13.8 points) than for barley (7.4 points) or pea (10.4 points).     

Organisation of the external region of the starch granule as determined by infrared spectroscopy

Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) was used to study the external regions of starch granules. Native starches (wheat, potato, maize, waxy maize and amylomaize) were analysed and compared to gelatinised and acid-hydrolysed starches. The IR spectra of potato and amylomaize starches were closer to that of highly ordered acid-hydrolysed starch than the other starches. FTIR was not able to differentiate between A- and B-type crystallinity so the difference observed between starches was not related to this factor. The variation between starch varieties was interpreted in terms of the level of ordered structure present on the edge of starch granules with potato and amylomaize being more ordered on their outer regions. This could explain the high resistance of both these starches to enzyme hydrolysis.     

Determination of the structural changes by FT-IR, Raman, and CP/MAS C NMR spectroscopy on retrograded starch of maize tortillas

The nixtamalization, production and storage of tortillas in refrigeration cause several changes on the starch structure, resulting in an increased crystallinity and therefore a higher content of resistant starch. The IR analysis for resistant starch (RS) showed a band at 1047 cm⁻¹ associated to the retrogradation process; this band was due to the weakening of the intermolecular H-bonds. These associated together to form ordered regions. The Raman analysis shows a characteristic band at 856 cm⁻¹ corresponding to C-C skeletal modes of glucose of α-1,4 glycosidic linkage starches, and a band at 480 cm⁻¹ attributed to skeletal vibrations of the pyranose ring in the glucose unit of starches. These changes may be related to the polymerization degree of the starch molecules, as well as to the retrogradation of amylose and amylopectin. The spectrum of ¹³C CP-MAS/NMR for RS3 supports the results obtained by IR and Raman. Lipidic and proteic groups were observed which may be in the form of complexes with amylose. One can proclaim that the existence of the salt form is induced and stabilized by the interactions dominating the V amylose structure in the solid state.     

A rheological comparison between the effects of sodium caseinate on potato and maize starch

The differences in response of 1% potato and 4% maize starch pastes to sodium caseinate inclusion were investigated. Pasting of the starches was performed at 95 °C for l h in a range of concentrations of sodium caseinate. Caseinate levels as low as 0.01% dramatically reduced the swelling volume of potato starch and hence the viscosity of the system. Since sodium chloride addition shows similar effects, it appears that caseinate acts through a non-specific ionic strength effect. The influence of caseinate on maize starch was less clear since it depended on the solvent medium. In distilled, deionized water, there was an increase in viscosity with increasing caseinate concentration, which may simply be explained by a contribution of the caseinate to the viscosity of the continuous phase. However, in 0.1M, pH 7.0 buffer the results suggest that caseinate may inhibit retrogradation as the viscosity of the system after ageing is reduced by its inclusion. It is suggested that phase separation between starch and caseinate is encouraged at high salt concentrations. As a consequence, both starch granule swelling and subsequent retrogradation are discouraged by caseinate in the buffer system, but not when pasting is carried out in distilled, deionized water.     

Starch modification by iterated syneresis

Potato, tapioca, corn and wheat starches were solubilised in water and isolated from the solution by iterated syneresis and the effect of this physical modification on the physicochemical properties and structure was studied. The experimental starches were examined by chemical analysis, the Brabender rheological method, scanning electron or light microscopy, X-ray diffractometry, infrared spectroscopy, and differential scanning calorimetry. Physical modification was evidenced to the change starch–water interaction and the structure of starches. Pasting temperature shifted to lower values and the gelatinisation mechanism changed. All modified starches had a B-type of X-ray diffraction pattern. The melting temperature of starch crystallites was typical of retrograded starch, but the enthalpy change was higher. The correlation between the resistant starch content of modified starches and their crystal structure was discussed together with the thermal properties.     

Physicochemical characteristics and fine structure of high-amylose wheat starches isolated from Australian wheat cultivars

High-amylose starch is a source of resistant starch (RS) which have great impact on human health like dietary fiber. Nowadays, high-amylose wheat has been produced by genetic backcrossing, which enhances apparent amylose content and generates altered amylopectin. In this study, the high-amylose wheat starches isolated from various high-amylose wheat cultivars grown in Australia were characterized for understanding their physicochemical properties and fine structure of starch. The physicochemical characteristics of the high-amylose wheat starches are significantly different among the cultivars. Amylose contents of these cultivars were in a range of 28.0–36.9%, which is significantly higher than that of the normal wheat starch (25.6%). The high-amylose wheat starches also had higher blue value but lower λ_max than the normal wheat starch. Gelatinization temperature of the high-amylose wheat starches is higher than that of the normal wheat starch but transition enthalpy is lower. X-ray diffraction showed that the high-amylose wheat starch had C-type crystals close to A-type crystal. Pasting properties of the high-amylose wheat starches were varying depending on the cultivars. However, almost high-amylose wheat starches had lower peak and final viscosities and higher setback viscosity than did the normal wheat starch. Fine structure of amylose and amylopectin was different among the high-amylose wheat cultivars and related to the physicochemical properties of starch. These results help to understand well the characteristics of the high-amylose wheat starches before application for food processing.     

Effects of structural imperfection on gelatinization characteristics of amylopectin starches with A- and B-type crystallinity

The aim of the present work was to investigate the effect of physical structures on the properties of starch granules. Starches with a high amylopectin content possessing A- and B-type crystallinity were chosen for the study. The gelatinization temperature decreased in the following order: maize (A) > potato (B) > wheat (A) > barley (A), which did not reflect a correlation with the type of crystallinity. Low values of gelatinization temperature were accompanied with high free surface energy of the crystallites. It is proposed that these data are caused by different types of imperfections in starch crystals. Annealing resulted in an enhancement of the gelatinization temperature and a decrease of the free surface energy of the crystallites for all starches reflecting a partial improvement of crystalline perfection. A limited acid hydrolysis (lintnerization) of the starches decreased the gelatinization temperature because of a partial disruption of the crystalline lamellae and an increase of the amount of defects on the edges of the crystallites. Annealing of the lintnerized starches improved the structure of maize and potato starch, giving them similar structural and physicochemical parameters, which was opposite the behavior of the annealed sample from wheat. The possible nature of removable and nonremovable defects inside the crystalline region of the starch granules is discussed. It is concluded that, besides the allomorphic A- and B-types of crystal packing, physical defects in the crystals possess a major impact on starch gelatinization.     

Physico-chemical and morphological characteristics of New Zealand Taewa (Maori potato) starches

The physico-chemical, morphological, thermal, pasting, textural, and retrogradation properties of the starches isolated from four traditional Taewa (Maori potato) cultivars (Karuparera, Tutaekuri, Huakaroro, Moemoe) of New Zealand were studied and compared with starch properties of a modern potato cultivar (Nadine). The relationships between the different starch characteristics were quantified using Pearson correlation and principal component analysis. Significant differences were observed among physico-chemical properties such as phosphorus content, amylose content, swelling power, solubility and light transmittance of starches from the different potato cultivars. The starch granule morphology (size and shape) for all the potato cultivars showed considerable variation when studied by scanning electron microscopy and particle size analysis. Starch granules from Nadine and Moemoe cultivars showed the presence of large and irregular or cuboid granules in fairly high number compared with the starches from the other cultivars. The transition temperatures (T_o; T_p; T_c) and the enthalpies (ΔH_gel) associated with gelatinization suggested differences in the stability of the crystalline structures among these potato starches. The Moemoe starch showed the lowest T_o, while it was higher for Tutaekuri and Karuparera starches. Pasting properties such as peak, final and breakdown viscosity and texture profile analysis (TPA) parameters of starch gels such as hardness and fracturability were found to be higher for Nadine and Huakaroro starches. The Nadine and Huakaroro starch gels also had lower tendency towards retrogradation as evidenced by their lower syneresis (%) during storage at 4 °C. Principal component analysis showed that the Tutaekuri and Nadine cultivars differed to the greatest degree in terms of the properties of their starches.     

Changes in morphological, thermal and pasting properties of yam (Dioscorea alata) starch during growth

This study was carried out in order to compare and establish the changes in physicochemical properties of starch from four different cultivars of yam at various stages of maturity during growth. The results showed that the starch content of the four yam tubers increased as growth progressed and were in the range of 70.5–85.3% on a dry basis. The shapes of the starch granules were round to oval or angular in the four yams and the size of starch granule increased with growth time ranging from 10 to 40 μm. The X-ray diffraction patterns could be classified as typical of B-type starch for the four cultivars of yam starch. The transition temperature of gelatinization of the four yam starches decreased during maturity. The RVA parameters suggested that yam starch paste showed a lower breakdown at an early harvest time. It appeared to be thermo-stable during heating but had a high setback after cooling, which might result in a tendency towards high retrogradation. The results for pasting behaviors showed that higher amylose content was associated with a lower pasting temperature and a higher peak viscosity in these starches.     

Digestion of starch and glycaemic response to mixed meals in pigs.

The digestion in the proximal intestine of mixed meals (5,160 kJ) containing either native (NS) or pregelatinized (PS) maize starches (approximately 200 g), and the postprandial glycaemic responses they induced were compared in pigs. For both meals, approximately 25% of the ingested starch was assimilated above the duodenal cannula (positioned 75 cm beyond the pylorus). Larger amounts of starch were collected for NS than for PS during the first 30 min. The glycaemic responses, however, indicated a higher rate of glucose absorption for PS during the first 30 min, which could be explained by the higher susceptibility of PS to hydrolysis, as we observed in vivo. Indeed, malto-oligosaccharides (G1-G3) represented almost 80% of the total alpha-glucans collected at 150 min in the duodenum after the PS meal. At that time, after the NS meal, only 30% of the alpha-glucans were malto-oligosaccharides. Thus, even after a mixed meal, the starch digestion rate can alter the observed postprandial glycaemic response.