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.     

Controlled peeling of the surfaces of starch granules by gelatinization in aqueous dimethyl sulfoxide at selected temperatures

Microscopic examination of starch granules in 90:10 (v/v) Me(2)SO-H(2)O indicated that the granules were slowly being gelatinized from their surfaces. The rate of gelatinization was dependent on two variables: (1) the amount of water in Me(2)SO and (2) the temperature. An increase of water in Me(2)SO and/or an increase in temperature increased the rate of gelatinization and vice versa. Specific ratios of Me(2)SO and H(2)O (85:15-95:5) and temperatures (0-15 degrees C) were found to give controlled sequential peeling/gelatinization of eight kinds of starch granules in 1-12h, with amounts of 10-25% gelatinization per hour. It was observed that the percent of starch granule remaining versus time gave curves that were linear and others that had linear parts separated by one or more abrupt changes. No two starches had a similar gelatinization curve for the same two conditions of the amount of water and the temperature. It is hypothesized that these curves reflect different structural characteristics for the individual kinds of starch granules.     

Effect of sodium chloride on the gelatinization of starch: a multimeasurement study.

The effect of sodium chloride on the gelatinization and rheological properties of wheat and potato starches has been studied using differential scanning calorimetry, dynamic mechanical thermal analysis, and electron spin resonance techniques. All samples contained 60% water (w/w wet starch basis) and the salt content ranged from 0 to 16% (g/100 g starch-water). The presence of salt affected the onset (T(o)), peak (T(p)), and end (T(e)) temperatures of gelatinization, gelatinization enthalpy (DeltaH), storage modulus (G'), and rotational mobility coefficient (D(rot)), and the effect differed by salt concentration. 1H-NMR was used in parallel in order to elucidate how salts affect the properties of water in starch suspensions and in aqueous salt solutions according to their position on the Hofmeister series classification. The obtained results suggest that the mechanism of starch gelatinization in salt solutions can be attributed to the effect of solute on water properties and direct polymer-solute interactions. These two effects conflict with one another and result in complex effect patterns depending on the concentration of the salts.     

On the effect of surface active agents and their structure on the temperature-induced changes of normal and waxy wheat starch in aqueous suspension. Part II: A confocal laser scanning microscopy study

The location and penetration patterns of two fluorescently labelled, surface active molecules into normal and waxy wheat starch granules prior, during and after the temperature-induced gelatinization were studied by means of confocal laser scanning microscopy (CLSM). Amphiphilic dyes were found to have a tendency to penetrate wheat starch granules in aqueous suspension. The penetration patterns were however found to be dependent on the contact time, type of starch and the chain length (C₁₂ vs. C₁₆) of the amphiphilic dye. The penetration of amphiphilic dyes through the starch granule matrix proved to be less restricted in waxy than in normal wheat starch. For a given type of starch, the penetration of the longer chain dye was more constrained than that of the shorter chain one. The extent to which the dye diffuses into the granule matrix as it gelatinizes is also affected by the chain length of the dye, diffusion of the shorter chain dye occurring more profusely and at lower temperatures than for the longer chain one. These differences are suggested to be related to the dissociation temperature of the AM-amphiphilic dye complexes.     

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.     

Imaging of high-amylose starch tablets. 3. Initial diffusion and temperature effects

The penetration of water into cross-linked high amylose starch tablets was studied at different temperatures by nuclear magnetic resonance (NMR) imaging, which follows the changes occurring at the surface and inside the starch tablets during swelling. It was found that the swelling was anisotropic, whereas water diffusion was almost isotropic. The water proton image profiles at the initial stage of water penetration were used to calculate the initial diffusion coefficient. The swelling and water concentration gradients in this controlled release system show significant temperature dependence. Diffusion behavior changed from Fickian to Case II diffusion with increasing temperature. The observed phenomena are attributed to the gelatinization of starch and the pseudo-cross-linking effect of double helix formation.     

Gelatinization of starch in excess water: beyond the melting of lamellar crystallites. A combined wide- and small-angle X-ray scattering study

The gelatinization of waxy rice, regular rice, and potato starch suspensions (66% w/w moisture) was investigated by real-time small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) during heating and by fast ramp differential scanning calorimetry (DSC). The high-angle tail of the SAXS patterns suggested the transition from surface to mass fractal structures in the DSC gelatinization range. Amylose plays a major role in determining the dimensions of the self-similar structures that develop during this process as the characteristic power-law scattering behavior extends to lower scattering angles for regular than for waxy starches. Crystallinity of A-type starches is lost in the temperature region roughly corresponding to the DSC gelatinization range. At the end of the gelatinization endotherm, the B-type potato starch showed residual crystallinity (WAXD), while SAXS-patterns exhibited features of remaining lamellar stacks. Results indicate that the melting of amylopectin crystallites during gelatinization is accompanied by the (exothermic) formation of amorphous networks.     

Synthesis and characterization of starch-modified polyurethane

Corn starch was reacted with urethane prepolymer in order to modifying starch and preparing new hydrophobic copolymers. These copolymers were prepared by two-step reactions. The polycaprolactone terminated hexamethylene diisocyanate (HDI) (as prepolymer) was prepared by introducing diisocyanate on both ends of PCL at a molar ratio of 1:2 (PCL:HDI). The grafting was performed by addition of polycaprolactone based prepolymer to starch solution of DMSO with different weight ratio of starch and prepolymer. The samples were characterized and examined by FTIR and ¹H NMR spectroscopy, DSC analysis, and scanning electron microscopy (SEM). By introducing NCO groups onto the PCL terminals, the FTIR spectrum shows a new sharp peak, representing the NCO groups and formation of prepolymer. By grafting this prepolymer onto starch a NH and urethane band were appeared. The effect of prepolymer percentage on hydrophobicity was measured through contact angle and it was found that increases with increasing amount of prepolymer. Glass transition temperature (T_g) is also affected with increasing amount of urethane linkages. Surface morphology of modified starch was studied by SEM. It was observed that the surfaces of modified starch are rougher and disordered than the surface of unmodified starch particles. This confirms the grafting and modification of starch. This modified starch can be used as filler in biodegradable starch based polymers.     

Starch Gelatinization at Different Temperatures as Measured by Enzymic Digestion Method

The gelatinization process of potato starch was isothermally investigated at 52.5∽65.3°C. The degree of gelatinization was measured by an enzymic digestion method using glucoamylase. When the starch–water suspension was incubated at a definite temperature the gelatinization reached a limit at each temperature after 30∽60 min incubation. So, it can be supposed that starch gelatinization reached an equilibrium state. It was found that gelatinization of potato starch occurred even at 52.5°C, a temperature which is lower than the so-called gelatinization temperature generally reported. Starch gelatinization was found to follow first order kinetics, and from the temperature dependence of the rate constants obtained, the activation energy was calculated to be 22±5 kcal/mol. The relationship between the degree of gelatinization of the starch whose gelatinization reached an equilibrium state at a definite temperature and the incubation temperature gave a transition curve expressed, by the fraction of gelatinized potato starch granules as a function of temperature, and the half-transition temperature was found to be 59.1°C. From the transition curve.the van’t Hoff enthalpy for gelatinization was determined to be +130±3 kcal/mol.     

Functional properties of pregelatinized and cross-linked cassava starch obtained by extrusion with sodium trimetaphosphate

Cassava starch was cross-linked with sodium trimetaphosphate (STMP) on a Cerealtec single-screw extruder at different extrusion temperatures and concentrations of STMP and NaOH. The effect of variables on functional properties of the products was analysed by the response–surface methodology. The degree of substitution (DS) was influenced by NaOH and phosphorus level, and increased when their concentration increased. Extrusion temperature affected water absorption, cold viscosity and gel characteristics. The introduction of phosphate groups by cross-linking, with maximum DS of 1.5×10⁻⁴, increased the gel strength, water absorption index, resistance to high temperature and shear, and decreased gel cohesiveness, starch clarity and water solubility index. The products had different DS and degree of gelatinization and thus can be applied in several kinds of foods.     

Influence of drying temperature on functional properties of wet-milled starch granules

Relationships between swelling capacities, pasting properties, rotational flow behaviour and textural properties of hydro-thermally heated wet-milled starch granules from corn dried between 60 and 130 °C were investigated. High-drying temperatures applied during the corn drying process conferred to the wet-milled starch granules (WSG) such a rigidity which reduced their swelling capacities, their water binding capacities and their water solubility index after gelatinization. These granules changes affected their pasting characteristics, their flow behaviour and several textural parameters of gel formed from the wet-milled starch granule after gelatinization. The rigidity of granules was a major factor determining the formation of either starch pastes or gels.     

Arsenic-lipid complex formatinon during the active transport of arsenate in yeast

In studying formation of an arsenic-lipid complex during the active transport of (74)As-arsenate in yeast, it was found that adaptation of yeast to arsenate resulted in cell populations which showed a deficient inflow of arsenate as compared to the nonadapted yeast. Experiments with both types of cells showed a direct correlation between the arsenate taken up and the amount of As-lipid complex formed. (74)As-arsenate was bound exclusively to the phosphoinositide fraction of the cellular lipids. When arsenate transport was inhibited by dinitrophenol and sodium azide, the formation of the As-lipid complex was also inhibited. Phosphate did not interfere with the arsenate transport at a non-inhibitory concentration of external arsenate (10(-9)m). The As-adapted cells but not the unadapted cells were able to take up phosphate when growing in the presence of 10(-2)m arsenate.     

Contribution of the net charge to the regulatory effects of amino acids and epsilon-poly(L-lysine) on the gelatinization behavior of potato starch granules

The effects of lysine (Lys), monosodium glutamate (GluNa), glycine, alanine and epsilon-poly(L-lysine) (PL) with different degrees of polymerization on the gelatinization behavior of potato starch granules were investigated by DSC, viscosity and swelling measurements, microscopic observation, and measurement of the retained amino acid amount to clarify the contribution of the net charge to their regulatory effects on the gelatinization behavior. The amino acids and PL each contributed to an increase in the gelatinization temperature, and a decrease in the peak viscosity and swelling. These effects strongly depended on the absolute value of their net charge. The disappearance of a negative or positive net charge by adjusting the pH value weakened the contribution. The swelling index and size of the potato starch granules changed according to replacement of the swelling medium. The amino acids and PL were easily retained by the swollen potato starch granules according to replacement of the outer solution of the starch granules.     

Surface effects in the acetylation of granular potato starch

The occurrence of surface effects in the acetylation of granular potato starch with acetic anhydride to degrees of substitution 0.04-0.2 was studied by two different approaches. The first approach involved the fractionation of granular starch acetates into five different size classes and analysis of their acetate content. Alternatively, two narrow size fractions of potato starch acetate granules were surface-peeled by chemical gelatinization in 5M CaCl(2), and the remaining cores were analyzed for acetyl content at different peeling levels. It was established that true surface peeling occurs in this medium and that the ester linkages are stable under the conditions applied. Both approaches led to the conclusion that the acetylation of potato starch granules is accompanied by a pronounced surface effect. The surface peeling method allows determination of the extent of substitution as a function of the radial position in the starch granule.     

秸秆还田对旱作马铃薯块茎淀粉合成关键酶活性及基因表达的影响

为探讨秸秆还田下旱作马铃薯块茎形成过程中淀粉合成关键酶活性及基因表达特性,以马铃薯栽培品种"青薯9号"为材料,以露地栽培为对照,设置秸秆还田处理,研究了马铃薯块茎形成过程中淀粉合成关键酶活性、基因表达、淀粉糊化及累积指标。结果表明:秸秆还田显著提高了旱作马铃薯SSS酶活性,降低了AGPP、GBSS酶活性,而对SBE酶活性没有显著影响;显著提高了SSⅡ、SSⅢ基因表达量,降低了AGPase、GBSSⅠ、SBEⅠ、SBEⅡ基因表达量;显著增加了淀粉崩解值,减少了淀粉各阶段粘度、回生值,而对淀粉糊化温度没有显著影响;显著增加了直链淀粉含量及直/支链淀粉比,减少了总淀粉含量; GBSS酶活性与AGPase、SBEⅠ基因表达量呈显著正相关,与直链淀粉含量、直/支链淀粉比呈显著负相关; SBE酶活性与SSⅡ基因表达量、峰值粘度、低谷粘度、最终粘度、总淀粉含量呈显著正相关,与崩解值、糊化温度呈显著负相关; AGPase基因表达量与直链淀粉含量呈显著负相关;GBSSⅠ基因表达量与最终粘度、回生值呈显著正相关,与糊化温度呈显著负相关;淀粉糊化与累积无显著相关性。     

A new insight into the gelatinization process of native starches

The gelatinization characteristics of seven different food starches (regular corn, high-amylose corn, waxy corn, wheat, rice, potato, and tapioca) were investigated. Each starch sample type was heated to 35, 40, 45, etc. up to 85 °C at 5 °C intervals, and freeze-dried. The treated samples were analyzed using light microscopy, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and high-performance size exclusion chromatography (HPSEC). When heated, granules underwent structural changes prior to the visible morphological changes that took place during gelatinization. The nature of these structural changes depended on starch type. These results indicate that the starch gelatinization process is more complex than a simple granular order-to-disorder transition.     

Locations of hypochlorite oxidation in corn starches varying in amylose content

The general oxidation mechanism by hypochlorite on starch has been well studied, but the information on the distribution of the oxidation sites within starch granules is limited. This study investigated the locations where the oxidation occurred within corn starch granules varying in amylose content, including waxy corn starch (WC), common corn starch (CC), and 50% and 70% high-amylose corn starch (AMC). Oxidized corn starches were surface gelatinized by 13 M LiCl at room temperature to different extents (approximately 10%, 20%, 30%, and 40%). The surface-gelatinized remaining granules were separated and studied for structural characteristics including carboxyl content, amylose content, amylopectin chain-length distribution, thermal properties, and swelling properties. Oxidation occurred mostly at the amorphous lamellae. More carboxyl groups were found at the periphery than at the core of starch granules, which was more pronounced in oxidized 70% AMC. More amylose depolymerization from oxidation occurred at the periphery of CC. For WC and CC, amylopectin long chains (>DP 36) were more prone to depolymerization by oxidation. The gelatinization properties as measured by differential scanning calorimetry also supported the changes in amylopectin fine structure from oxidation. Oxidized starches swelled to a greater extent than their unmodified counterparts at all levels of surface removal. This study demonstrates that the locations of oxidation and physicochemical properties of oxidized starches are affected by the molecular arrangement within starch granules.     

Effect of salts on pasting, thermal, and rheological properties of rice starch in the presence of non-ionic and ionic hydrocolloids

Effects of salts on pasting, thermal, and rheological properties of rice starch (RS) in the presence of non-ionic (guar gum; GG) or ionic (xanthan; XT) hydrocolloid were studied. Rapid visco-analysis (RVA) showed that addition of salts significantly increased peak, breakdown, and final viscosities, and pasting temperatures of RS/XT blends, whereas those of RS/GG blends were varied depending on the type of salts added. Differential scanning calorimetry (DSC) demonstrated that salt addition significantly increased gelatinization temperatures of either RS/GG or RS/XT blend, whereas gelatinization enthalpy was less affected. Dynamic viscoelastic tests revealed that addition of salts had a more pronounced effect on enhancing structure formation of RS/XT gels than that of RS/GG gels. The steady shear viscosity was generally in line with the values of final viscosity obtained during pasting. These results would be used as a guideline for developing starch-based food products containing salts.     

Synthesis, analysis and reduction of 2-nitropropyl starch

Granular 2-nitropropyl potato starch was synthesized by reaction with 2-nitropropyl acetate in an aqueous suspension. Nitroalkylation occurs preferentially with the amylose fraction of potato starch, as was confirmed by leaching experiments and digestion of the modified starch with alpha-amylase. The 2-nitropropyl substituent is a mixture of the nitroalkane and nitronic acid tautomer. Some grafting occurs and to a lesser extent additional reactions (formation of carbonyls and oximes) of the nitro group take place. After catalytic hydrogenation of water soluble 2-nitropropyl starch only a small amount of the nitro functionality was reduced to the corresponding amine. Reduction of granular 2-nitropropyl starch with sodium dithionite did not go to completion and led to a complex mixture of starting material, several intermediates and side products (for example sulfamates).     

Trehalase activity in extracts of Phycomyces blakesleeanus spores following the induction of germination by heat activation

The heat activation of trehalase in extracts of sporangiospores of Phycomyces blakesleeanus, following the induction of germination by heat activation and the gelatinization of potato starch granules were studied under different conditions in order to discriminate between several phenomena as possible triggers in the activation of trehalase.Short-chain alcohols (from methanol to pentanol) lower the activation temperature of trehalase while long-chain alcohols (from heptanol to nonanol) raise it. Short-chain alcohols also lower the gelatinization temperature of potato starch granules, while long-chain alcohols, hexanol and heptanol have hardly any influence on the gelatinization temperature. Octanol raises the gelatinization temperature. More polar phenols lower the activation temperature of trehalase, while more apolar phenols will raise it. The gelatinization temperature of starch granules is more lowered by the polar polyphenols than by the more apolar phenols.The effect of high pressure on starch gelatinization was investigated in order to compare data from such a model system with the data on trehalase activation.The gelatinization temperature of starch granules is shifted upwards with about 3–5 K/1000 atm (1.013×10⁵ kPa). Pressures higher than 1500 atm do not further increase the gelatinization temperature. However, no reversal of the effect, as occurs with protein conformational changes, is seen with pressure up to 2500 atm. Also for trehalase activation we find a continuous upward shift of the activation temperature with about 5–9 K/1000 atm. These data are in agreement with a thermal transition in a polysaccharide matrix, being the trigger in the heat activation of trehalase.