Starch Recrystallization Research Articles

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 °C, −20 °C and −30 °C for 24 h and, after thawing, stored at +2 °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.

Recrystallization of waxy maize starch during manufacturing of starch microspheres for drug delivery: Influence of excipients

The formation of ordered structure, such as crystallites, in starch was studied by means of differential scanning calorimetry (DSC). The influence of time/temperature treatment and additives such as polyethylene glycol (PEG), bovine serum albumin (BSA) and a carbonate buffer on the formation was investigated. The experiments were planned with a CCC (Central Composite Circumscribed) design. For all three investigated systems it could be concluded that the incubation time at 6 °C was the decisive factor for the amount of ordered structure obtained during the incubation, while the incubation time at 37 °C was the decisive factor for the thermal stability of the crystallites as expressed by T on, T m and T c. The additives seemed to mainly affect the nucleation phase of crystallization process. The additives decreased the time required in order to obtain a certain level of ordering in the incubated starch samples. The carbonate buffer decreased the amount of ordered structure in starch as judged by DSC enthalpy values, while increasing the melting temperature of these structures. The additives PEG and BSA lowered the melting temperatures of the starch in the systems but increased the enthalpy values. By optimization procedure a specific amount of ordered structure with desired thermal characteristics could be predicted.

Recrystallization of waxy maize starch during manufacturing of starch microspheres for drug delivery: Optimization by experimental design

Gelatinized starch/water dispersions with a water content of 70% w/w were studied in order to evaluate the influence of the incubation time at two fixed temperatures (6 and 37 °C) on the recrystallization behavior. The starch material was produced from waxy maize starch by acid hydrolysis followed by a mechanical treatment, i.e. a high pressure homogenization. Empirical models for the recrystallization of the model starch dispersions were investigated by using a central composite circumscribed (CCC) design in two factors involving 11 trials. The rebuilt crystalline structure was estimated by measuring the melting transition parameters with differential scanning calorimetry (DSC). The designed models for the melting enthalpy, the melting transition temperatures, and the melting interval as the responses were reproducible and predictable and the results were analyzed by using a response surface modeling. Operative conditions for the formation of the most thermally stable crystalline structure with the highest possible crystallinity were determined. It was also concluded that the decisive factor for the crystallinity of the given starch material was a prolonged storage at 6 °C, while thermal characteristics of the crystallites could be controlled by storage at 37 °C. An interaction effect was observed between the incubation time at these two experimental temperatures regarding enthalpy values and the melting interval of the samples.

Thermoplastic Starch Plasticized by Glycerol as Solid Polymer Electrolytes

AbstractSummary: Melt extrusion can be used to prepared GPTPS mixed with alkali metal chlorides (LiCl, NaCl and KCl) as a potential solid polymer electrolytes. SEM reveals that excess salt results in the congregation of salt crystals, which affects the mechanical properties and conductivities of GPTPS. FT‐IR spectroscopy shows that alkali metal ions can interact with starch, which restrains starch recrystallization, as proved by XRD. The introduction of salts improves the elongation at break, but reduces the tensile stress of GPTPS. Both salt content and water content have an effect on the conductance of GPTPS. The introduction of salts increases the conductance by a factor of 1–2, while the conductance increases about 5 orders of magnitude as the water content increases from 0.05 to 0.55 wt.‐%. The relationship of conductance versus water content can be well described by a second‐order polynomial, with R2 > 0.96. The type of salt has no obvious effect on the correlation between the conductance and water contents.SEM micrographs of native starch granules and fractured surfaces of GPTPS filled with different types and amounts of alkali metal chlorides per 100 g starch.magnified imageSEM micrographs of native starch granules and fractured surfaces of GPTPS filled with different types and amounts of alkali metal chlorides per 100 g starch.

Fly ash-reinforced thermoplastic starch composites

As a by-product from the combustion of pulverized coal, fly ash was, respectively, used as the reinforcement for formamide and urea-plasticized thermoplastic starch (FUPTPS) and glycerol-plasticized thermoplastic starch (GPTPS). The introduction of fly ash improved tensile stress from 4.56 MPa to 7.78 MPa and Youngs modulus increased trebly from 26.8 MPa to 84.6 MPa for fly ash-reinforced FUPTPS (A-FUPTPS), while tensile stress increased from 4.55 MPa to 12.86 MPa and Youngs modulus increased six times from 76.4 MPa to 545 MPa for fly ash-reinforced GPTPS (A-GPTPS). X-ray diffractograms illustrated that fly ash destroyed the formation of starch ordered crystal structure, so both A-GPTPS and FUPTPS could resist the starch re-crystallization (retrogradation). Also fly ash improved water resistance of TPS. As shown by rheology, during the thermoplastic processing, the extruder screw speed effectively adjusted the flow behavior of A-FUPTPS, while the increasing of the processing temperature effectively ameliorated the flow behavior of A-GPTPS. However, superfluous ash contents (e.g., 20 wt%) worsened processing fluidity and resulted in the congregation of fly ash in FUPTPS matrix (tested by SEM) rather than in GPTPS matrix. This congregation decreased the mechanical properties and water resistance of the materials.

The Effects of Citric Acid on the Properties of Thermoplastic Starch Plasticized by Glycerol

The effects of citric acid on the properties of glycerol-plasticized thermoplastic starch (GPTPS) were studied. In the presence of citric acid and glycerol, native cornstarch granules are transferred to a continuous phase as shown by scanning electron microscopy (SEM). As shown by thermogravimetric analysis (TGA), the improvement in thermal stability confirms that the adhesion between citric acid, glycerol, water and starch in TPS was enhanced with the addition of citric acid. It was proven by Fourier transform infrared (FTIR) spectroscopy that citric acid can form stronger hydrogen-bond interactions with starch than glycerol. Both FTIR spectroscopy and X-ray diffractometry of citric acid-modified GPTPS (CATPS) revealed that citric acid can effectively inhibit starch re-crystallization (i.e. retrogradation), because of the strong hydrogen-bond interaction between citric acid and starch. Rheology studies revealed that citric acid can obviously decrease the shear viscosity and improve the fluidity of TPS. Citric acid can also improve the elongation of GPTPS and ameliorate the water resistance of GPTPS at high relative humidities, but decreased the tensile stress.

Radiation Graft Co-polymerization of Methacrylic Acid (MAA) onto Sago Starch Films

In this work, the factors that may affect the gamma radiation-induced grafting of methacrylic acid monomer (MAA) onto sago starch films were investigated. The graft copolymers were characterized by tensile mechanical testing, dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and infrared spectroscopy. The results showed that the highest grafting yield was obtained within the irradiation dosage level of 10–20 kGy and by using monomer concentration range of 15–20 wt%. The highest tensile mechanical properties were observed for sago starch films having 66% graft yield of MAA. The DSC thermograms indicated a decrease in the gelatinization temperature (temperature at which the disruption of the molecular orders in the starch granules occurs) of sago starch as a result of grafting. This behavior was explained on the basis that radiation grafting prevents the retrograddation process of starch (starch re-crystallization). On the other hand, the IR spectra indicate an increase in the intensity of the absorption band due to C˭O stretching, confirming the occurrence of grafted chains of MAA.

Ethanolamine as a novel plasticiser for thermoplastic starch

Ethanolamine plasticised thermoplastic starch (ETPS) was prepared using a novel plasticiser ethanolamine. SEM images show that the native starch granules were destroyed, and the ethanolamine made them come into a uniform continuous phase. FTIR spectroscopy showed that the hydrogen bonds between the ethanolamine and starch molecules weakened the strong effect of starch intermolecular and intramolecular hydrogen bonds. The ETPS successfully restrains the re-crystallization of traditional thermoplastic starch plasticised by glycerol (GTPS), which was proved by XRD. The mechanical properties of ETPS, such as Young's modulus and breaking energy and the water absorption were improved. The glass-transition temperature ( T g) and thermal stability were also studied by DSC and TGA.

Water Redistribution and Structural Changes of Starch During Storage of a Gluten-free Bread

The objective of the present work was to analyze molecular and supramolecular changes of bread starch and to relate bread firmness increase during storage with starch recrystallization and water hydration levels and migration in gluten-free bread. At the studied conditions starch was in the supercooled region of the state diagram, at a temperature between Tg (glass transition temperature) and Tm (melting temperature), feasible to crystallize. The crystalline degree during storage was followed by the intensity increase in the X-ray diffraction peaks. During bread storage, water migration occurred from the crumb towards the crust. Water amount and redistribution affected the kind of starch crystallites formed and firmness of aged bread. It was not the total amount of crystalline fraction that determined bread firmness, but the type of crystallites formed. These observations are a further evidence that bread firmness development and starch recrystallization, although being related phenomena, are obviously separate events.

High performance biodegradable thermoplastic starch—EMMT nanoplastics

Nanoplastics were prepared using the formamide/ethanolamine-plasticized thermoplastic starch (FETPS) as the matrix and ethanolamine-activated montmorillonite (EMMT) as the reinforcing phase. Wide angle X-ray diffraction (WAXD), scanning electron microscope (SEM) and transmission electron microscope (TEM) revealed that FETPS was successfully intercalated into the layers of EMMT and formed the intercalated nanoplastics with EMMT. When EMMT content was 5 wt%, the mechanical testing indicated that the tensile stress of the nanoplastics achieved 7.5 MPa, and the tensile strain achieved 85.2%, Young's modulus increased from 47.2 MPa of pure FETPS to 145.1 MPa of FETPS/EMMT nanoplastics, and the breaking energy increased from 1.34 to 1.81 N m after being stored at RH=25% for 14 days. Comparing with FETPS, the nanoplastics effectively restrained the recrystallization of starch. In contrast to pure FETPS, the strength of nanoplastics obviously improved, and the thermal stability and water resistance also improved.

Effect of Different Enzymes on the Textural Stability of Shelf‐Stable Bread

ABSTRACTThree enzyme systems (2 amylase‐based and 1 protease‐based) were tested in shelf‐stable bread to determine effectiveness in preserving texture during storage for eight weeks. Each enzyme was tested in formulations without glycerol or with 6% glycerol. Bread samples were analyzed to determine physical properties (crumb density, crust‐to‐crumb ratio, rate of moisture distribution from crumb to crust), mechanical properties (modulus, and a parameter [C1] describing resistance to high levels of deformation obtained by fitting stress‐strain data to a three‐parameter function), and thermal properties (thermal stability and enthalpy of transitions) as a function of storage time. Mechanical properties were further analyzed to predict asymptotic firmness. Bread firmness after storage as evaluated in terms of modulus and C1 were lower in all enzyme‐added systems, the effect of protease being the most significant. Enzymes had less effect on glycerol‐containing systems with no apparent trend. The breads had complex thermal behavior and exhibited multiple transitions. Both amylase preparations in the presence of glycerol reduced the amount of starch recrystallization.

Effects of sugars and sugar alcohols on thermal transition and cold stability of corn starch gel

Various sugars and sugar alcohols (ribose, xylose, glucose, fructose, mannose, sucrose, maltose, isomaltose, trehalose, xylitol, mannitol, and sorbitol) were compared in their effects on thermal transitions and cold-storage stability of a corn starch–sugar gel (40% starch, starch:sugar=10:1 or 10:3 dry solids basis) using a differential scanning calorimetry. As the molar concentration of sugar increased, the onset temperature and enthalpy for starch melting were increased. Among the sugars, the samples with disaccharides exhibited higher onset temperature and enthalpy than those with monosaccharides at the same molar concentration. Under cold storage (4 or −20 °C), the sugars facilitated amylopectin recrystallization. Fructose and isomaltose produced higher degrees of amylopectin recrystallization than did other sugars. Sugar alcohols produced slightly greater recrystallization than did the corresponding sugars. Ice melting temperature and glass transition temperature ( T′ g) of the freeze-concentrated phase were decreased as the molar concentration of sugars increased, and there was no or little dependence on the chemical structure of sugars. Ice melting enthalpy for the gels showed no clear dependence on sugar concentration or structure. Sucrose addition lowered the ice melting enthalpy (ice formation by rapid freezing), whereas isomaltose or trehalose addition raised it. By cold storage, the T′ g of the starch gels was increased, whereas the ice melting enthalpy was decreased, as a result of water consumption for starch recrystallization. In the gel system (40% starch), sugar addition (10 or 30% based on starch) enhanced starch recrystallization, but decreased the ice melting and glass transition temperatures.

Effects of Sucrose Ester, Dough Conditioner, and Storage Temperature on Long‐Term Textural Stability of Shelf‐Stable Bread

ABSTRACTThe effectiveness of a dough conditioner containing an amylase enzyme, surfactants, and a reducing compound on preserving the textural stability of shelf‐stable bread was compared with that of sucrose ester. Military‐specification Meal, Ready‐to‐Eat bread was formulated to contain sucrose ester alone, the dough conditioner alone, both in combination, or neither additive. Samples were also stored at 4, 21, and 38°C for 12 weeks. Instrumental texture, as determined by uniaxial compression and mathematically fitted stress‐strain relationships, and sensory texture, as determined by a trained texture panel, were assessed periodically between 0 and 12 weeks. Both sucrose ester and the dough conditioner yielded stored samples that were softer than the control; sucrose ester was slightly more effective than the dough conditioner in preserving instrumental texture, and the additive combination yielded the lowest firmness parameters. Thermal analysis results were consistent with mechanical and sensory evaluations in showing slightly increased recrystallization of starch in the noadditive formulation. Panelists perceived the samples containing sucrose ester to be much closer to an “ideal” texture compared with those containing the dough conditioner. A partial substitution of the lower cost dough conditioner for higher cost sucrose ester may be possible.

Freeze–thaw stabilization of sweet potato starch gel by polysaccharide gums

Nine polysaccharide gums (sodium alginate, carboxymethyl cellulose, curdlan, gellan, guar gum, gum arabic, κ-carrageenan, locust bean, and xanthan) were compared for their stabilizing effects in sweet potato starch gel against repeated freeze–thawing (FT) treatments. The gums were added in starch gel at 0.3 or 0.6% (w/w, based on total gel weight), and total solid content in the gel was adjusted to 7% (w/w) with starch. The gels containing starch and gum were repeatedly freeze–thawed up to five times by storing at −18 °C for 20 h and then at 25 °C for 4 h. Water release (syneresis) was measured by vacuum-filtering the freeze–thawed gels. Among the gums tested, alginate, guar gum, and xanthan were highly effective in reducing the syneresis. For example, guar gum, at 0.6%, showed the least syneresis (33.0%, w/w based on initial water content) after five FT cycles, which was less than half that of pure starch gel. At 0.3%, however, xanthan was more effective than guar gum in reducing syneresis. Xanthan reduced paste viscosity significantly, whereas guar gum and alginate increased the viscosity, but there was little relation between pasting viscosity and syneresis. The gums remained in the gel matrix during the syneresis without a significant loss. Recrystallization of starch (retrogradation) induced by FT treatment was also retarded by the presence of gums, and sodium alginate was more effective in retarding the retrogradation than xanthan or guar gum.

A Fresh Perspective on Staling: The Significance of Starch Recrystallization on the Firming of Bread

ABSTRACT: Storage stability of standard white bread (SWB) and Meal, Ready‐to‐Eat (MRE) breads were studied in terms of texture firming, amylopectin recrystallization, and water relations. SWB showed a more rapid increase in firmness during storage mainly due to the loss of moisture to the crust and surrounding environment. The MRE, a long shelf‐life military bread, firmed much slower due to the moisture loss inhibition (hermetic pouch) and plasticization (by formulation). This work confirmed previous findings that in some cases, firming of a bread can be strongly influenced by factors other than amylopectin crystallization. This is possible through controlling changes in the amorphous domains earlier described from thermomechanical studies.

Comparison in glass transition and enthalpy relaxation between native and gelatinized rice starches

Native and gelatinized rice starches were compared in their glass transition and enthalpy relaxation at various water contents using a differential scanning calorimetry (DSC). In a low moisture content range (8–18%), the glass transition temperature ( T g) of native starch was higher (up to 20°C) than that of gelatinized starch, and the difference became greater as the moisture content decreased. Heat capacity change (Δ C p) at T g became substantially higher by gelatinization. Plasticizing effect of water on the glass transition in the low moisture content range followed the Couchman–Karasz equation. The glass transition temperature ( T g′) of native starch with sufficient moisture (40 or 60%) also appeared higher (−6.8 or −6.0°C) than that of gelatinized starch (−10.0 or −7.7°C), but ice-melting occurred in broader temperature range with smaller Δ H when the starch was gelatinized. Upon extended storage up to 14 days at 4°C, the gelatinized starch showed increased T g′ but decreased ice-melting enthalpy due to the water incorporation in recrystallization of starch. Enthalpy relaxation appeared only when the moisture was <20% regardless of gelatinization. The relaxation peak increased in magnitude as the moisture content increased, and appeared as ‘ T g overshoot’ at a moisture content above 12% due to superimposed glass transition, whereas at a moisture content below 12%, it located in a temperature range far below glass transition, showing a ‘sub- T g endotherm’.

Biodegradable Corn Starch Loose-Fill. II. The Effect of Storage at Different Relative Humidities on the Physical Properties of Loose-Fill

The physical properties of corn starch loose-fill were examined at various relative humidities (r.h.). After 48 h of storage at both 25 and 50% r.h., only a slight change in the dimension and physical properties of the corn starch loose-fill was apparent. A wet environment (75% r.h. for 48 h), however, caused significant shrinkage and the loss of physical properties. The tensile properties, particularly tensile modulus, sharply increased, while the resilience gradually decreased with storage time. Amorphous X-ray diffraction patterns of corn starch loose-fills were transformed into crystalline patterns due to aging at 75% r.h. after 48 h. These changes were attributed to the structural relaxation, which was accelerated by moisture gain. The Tg of corn starch loose-fill decreased with increasing the moisture content in expanded starch. Our proposed model based on Avrami equation was able to describe the time-dependent recrystallization of corn starch by modifying the time-dependent tensile modulus. The growth parameter (n) and time constant (k) for the recrystallization process of corn starch loose-fill were about 3.2 and 8.87 × 10−18 s−1, respectively. If the growth parameter of 3.2 is considered, spherulitic growth of crystallization occurred in the corn starch loose-fill in the wet environment.

Effect of Moisture Level on the Crystallinity of Wheat Starch Aged at Different Temperatures

AbstractDifferential Scanning Calorimetry (DSC) was used to study retrogradation of wheat starch. For storage at 4°C, enthalpy (ΔH) values of retrogradation endotherm (recrystallization) of wheat starch containing various moisture levels (25–80%) slowly continued to increase except in samples with moisture level of 50, 60 and 70%. For storage at 26°C and 32°C, most recrystallization of wheat starch occured within one and two weeks of storage time, while recrystallization with a moisture level of 50% at 26°C occurred for 4 weeks. The peak temperatures of retrogradation endotherm at various moisture levels (25–80%) after 4 weeks of storage time increased largely as the storage temperatures increased from 4 to 32°C. The enthalpy values of retrogradation endotherm after 4 weeks of storage occurred to a greater extent at a lower storage temperature. The glass transition temperature and starch recrystallization have a close relationship. In the recrystallization of wheat starch, the nucleation and propagation rate after 4 weeks of storage can be converted into enthalpy and peak temperature of retrogradation endotherm.

A DSC study of the effects of sugars on thermal properties of rice starch gels before and after aging

Thermal characterization of gelatinized binary rice starch-water and ternary starch-sugar-water gels before and after aging was carried out using differential scanning calorimetry. The glass transition temperature of the maximally freeze-concentrated solution (T′g) in both fresh and aged gels was observed to decrease progressively with increasing sugar concentration. Aging of the gels generally shiftedT′g to higher temperatures, but had little or no effect on the ice melting peak temperature (T m). The presence of various sugars could either accelerate or retard starch (amylopectin) recrystallization, depending on the type and concentration of sugar, as well as on starch/water ratio. A hypothesis based on the dual antiplasticizing-plasticizing effects of sugars was postulated to explain the observed effects. Of the sugars studied, xylose and fructose appeared to display exceptional retardative and accelerative effects, respectively, on retrogradation.

Enzymatic hydrolysis of oat and soya lecithin: Effects on functional properties

AbstractEnzymatic hydrolysis of oat and soy lecithins and its effects on the functional properties of lecithins were investigated. The phospholipase used was most efficient at low enzyme and substrate concentrations. More fatty acids were released from soy lecithin than from oat lecithin. The maximum degree of hydrolysis was 760 μmol free fatty acids per gram soy lecithin and 170 μmol free fatty acids per gram oat lecithin. On the basis of the total carbohydrate and phosphorus contents in the polar fractions of the lecithins, oat lecithin contained more glycolipids and less phospholipids than soy lecithin. With regard to functional properties, the stability of oil‐in‐water emulsions was enhanced by hydrolyzed soy lecithin and by crude and hydrolyzed oat lecithins, but only hydrolyzed soy lecithin prevented the recrystallization of barley starch. The dissociation enthalpy of amylose‐lipid‐complex (AML‐complex) was significantly higher when hydrolyzed soy lecithin was present. Hydrolyzed oat lecithin slightly affected the dissociation enthalpy of AML‐complex. The other lecithins had no effect on recrystallization or dissociation enthalpies in the barley‐starch matrix.