Retrogradation of corn starch after thermal treatment at different temperatures

Multi-endotherms of the gelatinization of corn starch, such as G, M1, M2, and Z endotherms, have been detected by DSC. The retrogradation of corn starch after initial thermal treatment at different temperatures was studied by DSC; in particular, the effect of thermal treatment before and after each endotherm of gelatinization on retrogradation was determined as a function of annealing time. The effect of thermal treatment at a certain temperature on the residual gelatinization endotherm at a higher temperature is also discussed. It was found that the higher temperature of thermal treatment always removed all the endotherms below that temperature. However, a certain thermal treatment temperature could affect the residual endotherm above this treatment temperature. The time-dependent retrogradation of corn starch is mainly due to G and M1 endotherms. The temperature and enthalpy of the melting of amylose–lipid complexes M2 and nonlipid complex amylose Z were not affected by aging time. The final enthalpy of retrogradation was found to be lower than that of gelatinization.     

State diagram of potato starch–water mixtures treated with high hydrostatic pressure

Potato starch–water mixture was treated with high hydrostatic pressure (HHP) of up to 1.2 GPa, and effect of starch content (10–70% (w/w)) on HHP-gelatinization was investigated by differential scanning calorimetry (DSC). Depending on the treatment pressure and potato starch content, DSC thermograms showed decrease in enthalpy change of heat gelatinization reflecting the progress of HHP-gelatinization and increase in enthalpy change of re-gelatinization of retrograded starch. From the viewpoint of the enthalpy changes, physically modified state of HHP-treated potato starch–water mixtures was classified as follows: no change, partial gelatinization, complete gelatinization, partial gelatinization and retrogradation, and complete gelatinization and retrogradation. A state diagram of potato starch–water mixtures (treatment pressure vs. starch content) was presented.     

Identification of the thermal transitions in potato starch at a low water content as studied by preparative DSC

The aim of this work was to identify the transitions in the complex DSC profiles of potato starch at a low water content. Preparative DSC involves the thermal processing of samples in stainless steel DSC pans in a way that allows their subsequent structural characterization. The low temperature (LT), dual melting (M1–M2), and high temperature (HT) endotherms observed in DSC profiles of potato starch with 16% water were assigned to enthalpy relaxation, melting with preservation of granular identity, and transition of the melted granules into a molecular melt, respectively. Granular melting was accompanied by a strong reduction of swelling capacity. Significant molecular degradation was observed after the HT transition. There is evidence that HT does not represent a true thermodynamic transition, but is due to a volume change in the sample. In contrast to potato starch, maize starch with 16% water gave inhomogeneous samples after processing, presumably because of its low packing density.     

The Pasting and Gel Textural Properties of Corn Starch in Glucose,Fructose and Maltose Syrup

The pasting and gel textural properties of corn starch in syrup at different concentrations were investigated by Rapid Visco Analyzer (RVA) and Texture profile analysis (TPA) tests. The results showed that the pasting temperatures of corn starch greatly increased, especially at higher sugar concentration. Increasing concentration of syrup caused an increase in peak, trough and final viscosity of corn starch. Peak viscosity and the disintegration rate of starch increased in the following order: fructose syrup> maltose syrup> glucose syrup. Increasing syrup concentration to 13%, 25% and 50% resulted in a lower retrogradation rate than the control. When the maltose syrup concentration increased to 50%, the retrogradation rate decreased to 14.30% from 33.38%. The highest hardness was observed when the syrup concentration was 25%. There was a particular low hardness when the concentration of syrup was 50%. The springiness of starch gels in syrup was similar at different concentrations.     

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.     

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.     

Microstructural characterization of yam starch films

Yam starch films were produced by thermal gelatinization of starch suspensions using different starch and glycerol concentrations and were compared to control samples without glycerol. Films were characterized by polarized light microscopy, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermomechanical analysis (TMA), X-ray diffraction, water vapor permeability (WVP) and water sorption isotherms. The polarized light microscopy and DSC data showed that starch gelatinization for film formation was complete. Plasticized films have a homogeneous structure as observed by SEM. At water activities >0.43, glycerol increased the equilibrium moisture content of the films due to its hydrophilic character. X-ray pattern of the yam films could be assigned to a B-type starch; during storage this pattern remained almost the same, however a slight recrystallization process could be observed. Amylopectin retrogradation was not observed by DSC with storage time of the films. Glass transition temperatures of films with glycerol were lower than those of control films as measured by DSC and TMA. WVP of yam starch films increased with the presence of glycerol.     

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.     

Use of (1)H cross-relaxation nuclear magnetic resonance spectroscopy to probe the changes in bread and its components during aging

(1)H nuclear magnetic cross-relaxation spectroscopy was used to probe the molecular mobility/rigidity in bread and its components during storage. The Z-spectra lineshapes, attributed to the solid-like polymer fractions of the samples, differed for the bread, gelatinized waxy starch (GX), gelatinized wheat starch (GW), heated flour (HF), and heated gluten (HG). Upon storage, no change was observed in the Z-spectrum of the bread sample, while the Z-spectra for GX, GW, and HG increased in the width at half height of the decomposed broad component (increased rigidity). These trends in the Z-spectra detected by NMR were contradictory to the DSC results that showed an increase in amylopectin retrogradation enthalpy for all samples containing starch, including bread. These trends in the Z-spectra detected by NMR were not reflected by the DSC results that showed an increase in amylopectin retrogradation enthalpy for all samples, including bread. The differences in molecular mobility could not be therefore, due to recrystallized amylopectin and may be attributed to the role of gluten and/or redistribution of water in the amorphous regions of the samples.     

A photographic approach to the possible mechanism of retrogradation of sweet potato starch

Although the subject of starch retrogradation has been studied for about 20 years, the mechanism of starch retrogradation seems not yet to be completely established. In this paper, the possible retrogradation mechanism of sweet potato starch was postulated from four optical micrographs at the stages of melting of the starch granules, autoclaving treatment and aging. The possible process of retrogradation consists of three stages. Firstly, starch granules was swelled and melted with loss of X-ray crystallinity and formation of both crystalline and amorphous lamellae; secondly, in crystalline lamellae, amylopectin began to form nucleation when they were autoclaved; finally, the nucleus grew up to great rod-like crystals as the result of congregating of amylose on plates which were composed of and prolongated by amylopectin.     

Influence of spent brewer’s yeast β-glucan on gelatinization and retrogradation of rice starch

The effects of β-glucan (BG) prepared from spent brewer’s yeast on gelatinization and retrogradation of rice starch (RS) were investigated as functions of mixing ratio and of storage time. Results of rapid visco-analysis (RVA) indicated that addition of BG increased the peak, breakdown, setback, and final viscosities, but decreased the pasting temperatures of the rice starch/β-glucan (RS/BG) mixtures. Differential scanning calorimetry (DSC) data demonstrated an increase in onset (T_o), peak (T_p), and conclusion (T_c) temperatures and a decrease in gelatinization enthalpy (ΔH₁) with increasing BG concentration. Storage of the mixed gels at 4 °C resulted in a decrease in T_o, T_p, T_c, and melting enthalpy (ΔH₂). The retrogradation ratio (ΔH₂/ΔH₁) and the phase transition temperature range (T_c − T_o) of the mixed gels increased with storage time, but this effect was reduced by the addition of BG. BG addition also slowed the syneresis of the mixed gels. Results of dynamic viscoelasticity measurement indicated that the addition of BG promoted RS retrogradation at the beginning and then retarded it during longer storage times. The added BG also retarded the development of gel hardness during refrigerated storage of the RS/BG mixed gels.     

Influence of Soy Protein Isolate Hydrolysates Obtained under High Hydrostatic Pressure on Pasting and Short-Term Retrogradation Behavior of Maize Starch

The influences of soy protein isolate hydrolysate (SPIH) obtained during different pressure treatments for 4 h on pasting and short-term retrogradation behaviors of maize starch (MS) were investigated. The results showed solubility of MS markedly increased, whereas swelling power decreased with increased SPIH concentration and pressure. Compared with native MS, the addition of SPIH led to decrease of peak viscosity, final viscosity, setback, and breakdown, whereas pasting temperature was increased. Meanwhile, differential scanning calorimetry (DSC) analysis also showed an increase in gelatinization temperature. In addition, low-field nuclear magnetic resonance (LF-NMR) analysis indicated that the tight association of water and starch molecules was observed with increasing pressures and additions of SPIH. Confocal laser scanning microscopy (CLSM) and atomic force microscope (AFM) images indicated that SPIH obtained at 200 MPa dispersed in the MS gel system to block the formation of hydrogen bonds and inhibit the recrystallization of MS. Fourier transform infrared (FTIR) spectroscopy analysis demonstrated that the addition of SPIH resulted in a decrease in hydrogen bonds within the starch molecules and the result supported above CLSM and AFM measurement results. The results proved that the addition of SPIH could effectively influence pasting characteristics and inhibit the short-term retrogradation of MS, which can be helpful to the application of SPIH in starch-based functional foods.

     

Gelatinization and freeze-concentration effects on recrystallization in corn and potato starch gels

Freeze-concentration of starch gels was controlled by temperature and gelatinization with glucose and lactose. The aim of the study was to evaluate the effects of freezing temperature and gel composition on starch recrystallization behaviour of corn and potato starch gels (water content 70%, w/w) in water or glucose or lactose (10%, w/w) solutions. Starch gels were obtained by heating in differential scanning calorimetry (DSC). Samples of starch gels were frozen at -10 degrees C, -20 degrees C and -30 degrees C for 24h and, after thawing, stored at +2 degrees C for 0, 1, 2, 4 and 8 days. The extent of starch recrystallization was taken from the enthalpy of melting of the recrystallized starch by DSC. Freezing temperatures, glucose, lactose and the origin of the starch affected the recrystallization behaviour greatly. The recrystallization of amorphous starch during storage was enhanced by freeze-concentration of gels at temperatures above T'(m). Molecular mobility was enhanced by unfrozen water and consequently molecular rearrangements for nucleation could take place. Further storage at a higher temperature enhanced the growth and the maturation of crystals. In particular, glucose decreased the T'(m) of the gels and consequently lower freezing temperatures were needed to reduce enhanced recrystallization during storage. Freeze-concentration temperatures also showed a significant effect on the size and the perfection of crystals formed in starch recrystallization.     

Modification of maize starch by thermal processing in glacial acetic acid

Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) methods were used to determine if corn starch–glacial acetic acid mixtures can be melted and thermally processed at reasonable temperatures. DSC studies showed that the melting temperature of dry starch was reduced from about 280 to 180°C in the presence of >30% acetic acid. Glass transition temperatures varied from 110 to 40°C at 15 and 45% acetic acid, respectively. XRD showed the loss of native starch crystallinity and the formation of V-type complexes. Addition of 10% water decreased the melting temperatures to 140–150°C while addition of a base (sodium acetate) had little effect. Some possible applications of processing starch in glacial acetic acid will be discussed.     

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.     

The retrogradation of waxy maize starch extrudates: effects of storage temperature and water content

The effects of water content and storage temperature on the kinetics of the retrogradation of nonexpanded waxy maize starch extrudates were studied using (1)H pulsed NMR and wide-angle X-ray diffraction. The increase in crystallinity observed by XRD was accompanied by a decrease in the relaxation times of the solid-like component of the NMR free induction and the spin-echo decays, and an increase in the contribution of the solid-like component to the total signal. The dependence of the rate of starch retrogradation on the storage temperature showed the typical "bell-shaped" behavior, which was successfully modeled using the Lauritzen-Hoffman theory of crystallization of chain-folded polymers. This theory was extended to model the effect of water content on the rate of isothermal crystallization by exploiting the ten-Brinke and Karasz, and the Flory equations to describe the dependence of the glass-transition and the melting temperatures on water content.     

Studies of the retrogradation process for various starch gels using Raman spectroscopy

The retrogradation of untreated wild-type starches (potato, maize, and wheat), waxy maize starches, and one pregelatinized, modified amylose-rich starch was investigated continuously using Raman spectroscopy. The method detects conformational changes due to the multi-stage retrogradation, the rate of which differs between the starches. The pregelatinized, modified amylose-rich starch shows all stages of retrogradation in the course of its Raman spectra. In comparison to amylose, the retrogradation of amylopectin is faster at the beginning of the measurements and slower in the later stages. The untreated starches can be ranked in the order of their rate of retrogradation as follows: potato>maize>wheat.     

Pasting viscosity and in vitro digestibility of retrograded waxy and normal corn starch powders

Pasting viscosity and in vitro digestibility of oven-dried powders of waxy and normal corn starch gels (40% solids) retrograded under an isothermal (4 °C) or temperature cycled (4/30 °C) storage were investigated. Temperature cycling induced higher onset temperature for melting of amylopectin crystals than isothermal storage under a differential scanning calorimeter whereas little difference in crystalline type was observed under X-ray diffraction analysis. Temperature cycling caused higher pasting temperature and viscosity for the retrograded starches than isothermal storage. The retrograded waxy corn starch powders exhibited pasting behaviors similar to that of native waxy corn starch. However, the retrograded normal corn starch powders showed very much different pasting patterns with lower pasting viscosity but higher pasting temperature than native starch counterpart. The retrogradation increased slowly digestible starch content without changing resistant starch content, more effectively by the temperature cycling than the isothermal storage.     

Detection of synergistic interactions of polyvinyl alcohol–cassava starch blends through DSC

The synergistic interaction of polyvinyl alcohol (PVOH) and cassava starch was studied by differential scanning calorimetry (DSC) method. Film of the PVOH–cassava starch blends were prepared by solution cast method. Originally, cassava starch film did not show presence of any endothermic peaks in DSC thermogram. However, after adding PVOH to cassava starch, the PVOH–cassava starch blend films showed obvious endothermic peaks with onset and end-point temperatures higher than neat PVOH film. In addition, the PVOH–cassava starch blends have experimental enthalpy of melting higher than theoretical values. This evidence shows that the interactions between PVOH and cassava starch molecules are extensively strong. Due to the synergistic interactions of PVOH and cassava starch, it is postulated that incorporation of 65–75 wt.% of PVOH in cassava starch blend has physical bonding equivalent to neat PVOH.     

Structure function relationships of transgenic starches with engineered phosphate substitution and starch branching

Potato tuber starch was genetically engineered in the plant by the simultaneous antisense suppression of the starch branching enzyme (SBE) I and II isoforms. Starch prepared from 12 independent lines and three control lines were characterised with respect to structural and physical properties. The lengths of the amylopectin unit chains, the concentrations of amylose and monoesterified phosphate were significantly increased in the transgenically engineered starches. Size exclusion chromatography with refractive index detection (SEC-RI) indicated a minor decrease in apparent molecular size of the amylose and the less branched amylopectin fractions. Differential scanning calorimetry (DSC) revealed significantly higher peak temperatures for gelatinisation and retrogradation of the genetically engineered starches whereas the enthalpies of gelatinisation were lower. Aqueous gels prepared from the transgenic starches showed increased gel elasticity and viscosity. Principle component analysis (PCA) of the data set discriminated the control lines from the transgenic lines and revealed a high correlation between phosphate concentration and amylopectin unit chain length. The PCA also indicated that the rheological characteristics were primarily influenced by the amylose concentration. The phosphate and the amylopectin unit chain lengths had influenced primarily the pasting and rheological properties of the starch gels.