Oxidized and acid thinned starch derivatives of hybrid maize: functional characteristics, wide-angle X-ray diffractometry and thermal properties

Starch isolated from hybrid maize (8535-23) was subjected to oxidation and acid thinning. Proximate analyses revealed that moisture, ash, protein, fat, fibre, and pH reduced after oxidation and acid thinning. Percentage amylose content reduced from 20.42% in native starch to 18.76 and 17.65% in oxidised and acid thinned starch derivatives, respectively. Wide-angle X-ray diffraction patterns indicated strong peaks at 15.9 degrees, 17.2 degrees, 18.8 degrees, and 25.0 degrees 2theta. No significant difference was observed between the X-ray pattern of the native and modified starches. Both swelling power and solubility increased with increase in temperature. Oxidation and acid thinning reduced swelling power and increased solubility starch. At all pHs, both oxidation and acid thinning reduced the swelling capacity of the native starch. Oxidation increased water and oil absorption capacity of the native starch, while both hydrophilic and hydrophobic properties reduced following acid thinning. Least gelation concentration reduced in acid thinned starch but increased in oxidised derivative. Pasting temperature (Tp), peak viscosity (Pv), hot paste viscosity (Hv), and viscosity after 30 min holding at 95 degrees C (H(v30)) reduced following both modifications. However, values for cold paste viscosity (Cv) and setback (SB) reduced in oxidised derivative and increased in acid thinned starch. Light transmittance of the starch pastes reduced with increase in storage days, however, reduction was more pronounced in native and acid thinned starches. Onset temperature (To), peak temperature (Tp) and conclusion temperature (Tc) of gelatinisation reduced in modified starches compared with native hybrid maize starch. Also, gelatinisation enthalpy reduced after oxidation and acid thinning. Enthalpy of regelatinisation increased as days of storage of starch paste increased.     

Gelatinisation of sago starch in the presence of sucrose and sodium chloride as assessed by differential scanning calorimetry

The inhibitory effect of sucrose and sodium chloride on sago starch gelatinisation was investigated by differential scanning calorimetry (DSC). The temperature of gelatinisation of starch in the presence of low levels of water and high levels of sucrose was found to increase in the presence of sucrose, whereas the gelatinisation enthalpy was unaffected. The gelatinisation temperature range was not as broad in the presence of sucrose as without sucrose. Furthermore, the shape of the gelatinisation endotherm was changed by the addition of sucrose. The double endotherm obtained in limited water:starch systems was changed into a single endotherm, similar to the endotherm obtained in excess water:starch systems at a higher temperature. DSC was also used to examine the effects of water and sodium chloride content on the phase transitions of sago starch. Samples were adjusted to starch:water ratios of 2:3 and 3:2 in sodium chloride concentrations of 0.0, 1.0, 2.0, 3.0, 4.0, 5.0 M. The gelatinisation temperatures of sago starch increased and then decreased as the sodium chloride concentration increased. Sodium chloride created similar effects on the endotherms in excess water content and on the first endotherm with limited water content. In the presence of sucrose and sodium chloride, gelatinisation shifted to higher temperatures, and enthalpy associated with the endothermic process decreased. The extent of temperature shift and enthalpy change was dependent on the water to starch to solutes ratios.     

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.     

Effect of hydrostatic pressure on starch gelatinisation

Samples of wheat and potato starches, mixed with water to four concentrations were subjected to preselected hydrostatic pressures (in the range 200–1500 MPa) and temperatures. Subsequent examination in a polarising microscope revealed that the effect of high hydrostatic pressure was to lower the gelatinisation temperature. With the exception of the low water content samples, the samples did not appear to be greatly affected in any other way by hydrostatic pressure (as evidenced by staining behaviour, appearance in the polarising microscope and subsequent gelatinisation behaviour at ambient pressure). Reduction in gelatinisation temperature was a non-linear function of pressure, being greatest at high pressure. The effect was also more pronounced at the higher water contents. The significance of these results with respect to thermodynamic models of starch gelatinisation is discussed.     

Effect of microwave radiation on physico-chemical properties and structure of potato and tapioca starches

The time-temperature profiles of selected starch-water systems subjected to microwave processing were established and the effect of microwave radiation on the physico-chemical properties and structure of potato and tapioca starches was studied. The experimental starch samples were examined by the Brabender rheological method, light microscopy, scanning electron microscopy and X-ray diffractometry. Microwave radiation was evidenced to affect the temperature and moisture contents of the experimental starches, with a strong correlation between the moisture content and the rate of temperature rise. An isothermal transformation was revealed with the samples of moisture contents over 20%, causing a rise in the gelatinisation temperature of the starch and a drop in its solubility in water. The most pronounced change was observed in the case of potato starch: its crystal structure changed from type B to type A. The tapioca starch underwent similar but less marked changes.     

Consequences of antisense RNA inhibition of starch branching enzyme activity on properties of potato starch

Antisense constructs containing cDNAs for potato starch branching enzyme (SBE) were introduced into potato (Solanum tuberosum L.). A population of transgenic plants were generated in which tuber SBE activity was reduced by between 5 and 98% of control values. No significant differences in amylose content or amylopectin branch length profiles of transgenic tuber starches were observed as a function of tuber SBE activity. Starches obtained from low SBE activity plants showed elevated phosphorous content. ³¹P n.m.r. analysis showed that this was due to proportionate increases in both 3- and 6-linked starch phosphates. A consistent alteration in starch gelatinisation properties was only observed when the level of SBE activity was reduced to below ˜5% of that of control values. Starches from these low SBE activity plants showed increases of up to 5 °C in d.s.c. peak temperature and viscosity onset temperature. Studies on melting of crystallites obtained from linear (1 → 4)-- -glucan oligomers suggest that an average difference of double helix length of about one glucose residue might be sufficient to account for the observed differences in gelatinisation properties. We speculate that the modification of gelatinisation properties at low SBE activities is due to a subtle alteration in amylopectin branch patterns resulting in small changes in double helix lengths within granules.     

Studies on the hydrothermal modifications of new cocoyam (Xanthosoma sagittifolium) starch

Native new cocoyam starch (nNCS) was subjected to annealing (aNCS) and heat moisture treatment at 18% moisture level (h₁₈NCS), 21% moisture level (h₂₁NCS), 24% moisture level (h₂₄NCS) and 27% moisture level (h₂₇NCS) as hydrothermal treatments. Scanning electron and light microscopy revealed round and polygonal shapes with sizes ranging from 15 to 40 μm for native and modified starches. nNCS showed “A” pattern X-ray diffraction and no significant differences were observed in the X-ray pattern of the modified starches. Swelling power and solubility reduced following heat moisture treatment. At all pH studied (2–12), unmodified new cocoyam starch exhibited higher swelling capacity and solubility than the modified derivatives. Hydrothermal modifications improved water absorption capacity but reduced oil absorption capacity. Pasting temperature of native starch shifted to higher values following annealing and heat moisture treatment. Hot paste viscosity (Hv), viscosity after 30 min holding at 95 °C (Hv₃₀) and cold paste viscosity (Cv) reduced after annealing and heat moisture treatment. The result also indicates that hydrothermal treatments reduced the tendency for setback. As the number of days of storage of starch paste increased from 1 to 10, light transmittance of all the starches reduced but marked reduction of light transmittance was observed in native starch. DSC studies revealed increase in gelatinization temperature following annealing and heat moisture treatment. Starch hydrothermal modifications reduced retrogradation as enthalpies of regelatinization reduced following modifications. The regelatinization peak in the second day scanning shifted to lower temperature than the gelatinization peak in first run heating DSC curve for all samples. The regelatinization peak also became larger and shifted to higher temperature range when the storage days increased from 2 to 7.     

SANS study of the distribution of water within starch granules

This study describes contrast variation small angle neutron scattering (SANS) experiments which focus on the role which the intra-granular room temperature distribution of water and carbohydrate plays in determining the native structure and subsequent functionality of starch. It is shown that variations in botanical origin and amylose content do not correlate with significant differences in room temperature composition of A-type starch granules. In turn, variations in the gelatinisation behaviour of A-type starches do not correlate with variations in room temperature water distribution. In contrast, the room temperature water content is found to differ significantly between granules of potato (B-type) and a range of A-type starch cultivars. A correlation is found between these compositional differences and variations in crystal structure, which has implications for biological growth conditions and gelatinisation behaviour.     

Endocytosis and breakdown of ribonuclease oligomers by sinusoidal rat liver cells in vivo. II. Effect of charge.

Experiments presented in this paper suggest that sinusoidal rat liver cells recognize basic groups on proteins and that this recognition results in endocytosis of the proteins. Evidence for involvement of basic groups was obtained in two ways. Firstly, we changed the positively charged amino groups of the cross-linked ribonuclease molecules to neutral or negative by acetylation or succinylation, respectively. The modified proteins did not contain easily reducible disulfide bonds and they were not very sensitive to endoproteases, suggesting that they were not denatured by the acetylation procedures. Acetylation and succinylation reduced uptake of the injected cross-linked ribonuclease derivatives by liver and spleen and abolished their rapid clearance from plasma. In nephrectomized rats about 75% of the polymer, 36% of the acetylated polymer and 32% of the succinylated polymer were endocytosed by liver after 6 h. For the dimer fractions these values were 59%, 23% and 27%, respectively. Autoradiography and subcellular fractionation of liver 30 min post-injection localized the acetylated polymer in the lysosomal/microsomal fraction of sinusoidal liver cells, probably endothelial cells. Secondly, a positive correlation was found between binding of a number of ribonuclease derivatives to the cation exchanger SP-Sephadex G-25 and the rate of endocytosis by sinusoidal liver cells.     

Endocytes and breakdown of ribonuclease oligomers by sinusoidal rat liver cells in vivo: II. Effect of charge

Experiments presented in this paper suggest that sinusoidal rat liver cells recognize basic on proteins and that this recognition results in endocytosis of the proteins. Evidence for involvement of basic groups was obtained in two ways.Firstly, we changedd the opsitively charged amino groups of the cross-linked ribonuclease molecules to neutral or negative by acetylation or succinylation, respectively. The modified proteins did not contain easily reducible disulfide bonds and they were not very sensitive to endoproteases, suggesting that they were not denatured by the acetylation procedures. Acetylation and succinylation reduced uptake of the injected cross-linked ribonuclease derivatives by liver and spleen and abolsihed their rapid clearance from plasma. In nephrectomized rats about 75% of the polymer, 36% of the acetylated polumer and 32% of the succinylated polumer were endocytosed by liver after 6 h. For the dimer fraction these values were 59%, 23% and 27%, respectively. Autoradiography and subcellular fractionation of liver 30 min post-injection localized the acetylated polumer in the lysosomal/microsomal fraction of sinusoidal liver cessls, probably endothelial cells.Secondly, a positive correlation was found between binding of a number of ribonuclease derivatives of the cation exchanges SP-Sephadex G-25 and the rate of endocytosis by sinusoidal liver cells.     

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.     

High moisture twin-screw extrusion of sago starch: 1. Influence on granule morphology and structure

Effects of barrel temperature (81–149°C) and screw speed (315–486rpm) on extrusion processing of sago starch in a co-rotating twin-screw extruder under a high moisture system (34–47%) were investigated using response surface methodology. Structural changes were characterised by measuring water solubility index (WSI), water absorption index (WAI), degree of gelatinisation (DG), dextrose equivalent (DE) and high performance size-exclusion chromatography (HPSEC) profiles of the extradates. Thermomechanical processing of sago starch in the twin-screw extruder at the high moisture (34–47%) system led to shearinduced limited degradation and starch phase transitions (a composite melting gelatinisation process). Strong positive correlations between WAI, WSI and DG showed that gelatinisation was the fundamental mechanism in this high moisture system rather than dextrinisation. Processing-induced solubility increased at the expense of water absorption. Low WSI (4.5–18.1%) is ascribed to the presence of structures of either granular crystallite remnants or rearrangement of bonds during extrusion.     

蛋白质赖氨酸残基的琥珀酰化修饰

蛋白质的琥珀酰化修饰是一种普遍存在于真核生物和原核生物中的翻译后修饰。修饰的蛋白质遍及细胞膜、细胞质基质、各种细胞器及细胞核等细胞的各个部分,它们参与了细胞内包括糖代谢、三羧酸循环和脂肪酸代谢等各种代谢反应,与生命体的活动息息相关。本文综述了琥珀酰化蛋白质活性变化、修饰位点周围氨基酸的特异性及空间结构的分析、亚细胞分布情况、琥珀酰化与乙酰化之间的相互作用及碳源和生长阶段对蛋白质琥珀酰化水平的影响等内容,以期为后续蛋白质的琥珀酰化科研提供一定的参考。     

Effects of annealing on the polymorphic structure of starches from sweet potatoes (Ayamurasaki and Sunnyred cultivars) grown at various soil temperatures

Starches extracted from the sweet potato cultivars Sunnyred and Ayamurasaki grown at 15 or 33 degrees C (soil temperature) were annealed in excess water (3 mg starch/mL water) for different times (1, 4, 8 or 10h) at the temperatures 2-3 degrees K below the onset melting temperature. The structures of annealed starches, as well as their gelatinisation (melting) properties, were studied using high-sensitivity differential scanning calorimetry (HSDSC). In excess water, the single endothermic peak shifted to higher temperatures, while the melting (gelatinisation) enthalpy changed only very slightly, if any. The elevation of gelatinisation temperature was associated with increasing order/thickness of the crystalline lamellae. The only DSC endotherm identified in 0.6 M KCl for Sunnyred starch grown at 33 degrees C was attributed to A-type polymorphic structure. The multiple endothermic forms observed by DSC performed in 0.6M KCl for annealed starches from both cultivars grown at 15 degrees C provided evidence of a complex C-type (A- plus B-type) polymorphic structure of crystalline lamellae. The A:B-ratio of two polymorphic forms increased upon annealing due to partial transformation of B- to A-polymorph, which was time dependent. Long heating periods facilitated the maximal transformation of B- to A-polymorph associated with limited A:B ratio.     

Comparison of potato amylopectin starches and potato starches — influence of year and variety

Starches from three potato varieties and their respective transformants producing amylopectin starch were studied over a period of 3 years. The gelatinisation, swelling and dispersion properties were studied using differential scanning calorimetry (DSC), X-ray diffraction, swelling capacity measurements and a Brabender Viscograph.

The potato amylopectin starches (PAP) exhibited higher endothermic temperatures as well as higher enthalpies than the normal potato starches (NPS). PAP samples gave rise to an exceptionally sharp viscosity peak during gelatinisation and a relatively low increase in viscosity on cooling. Swelling capacity measurements showed that PAP granules swelled more rapidly, and that the dispersion of the swollen granules occurred at a lower temperature (85°C). Analysis of variance (ANOVA) also revealed that the year influenced the DSC results, and that both year and variety affect some of the Brabender parameters. Furthermore, the PAP and NPS samples were subjected to heat–moisture treatment at three different moisture levels, and the Brabender viscosity properties were studied.     

The effect of lintnerisation on wheat and potato starch granules

Wheat and potato starches were hydrolysed with 2·2 n hydrochloric acid at 35°C for a period of time up to 15 days. The residues (lintnerised starches) were washed and freeze dried, and studied by differential scanning calorimetry (DSC), wide-angle X-ray scattering (WAXS), small-angle light scattering (SALS), small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS). These techniques showed that profound changes took place in the first day of hydrolysis (during which time the extent of hydrolysis was 7·7% for potato starch and 12·5% for wheat starch). In particular, the gelatinisation enthalpy (ΔH) decreased, the X-ray crystallinity increased and the SANS and SAXS peaks (indicative of a regular spacing between crystalline and amorphous regions) virtually disappeared. The reduction in ΔH is surprising and is discussed at length. It was also shown that freeze drying results in a considerable lowering of the gelatinisation temperature of potato starch (and also of ΔH) while that of wheat starch is only slightly affected.     

Comparison of methods to determine the degree of gelatinisation for both high and low starch concentrations

A general procedure was developed to measure the degree of gelatinisation in samples over a broad concentration range. Measurements based on birefringence, DSC (Differential scanning calorimetry), X-ray and amylose–iodine complex formation were used. If a 10 w/w % wheat starch–water mixture was used, each method resulted in approximately the same degree of gelatinisation vs. temperature curve. In case the gelatinisation of a 60 w/w % wheat starch–water mixture was followed as a function of the temperature, each method resulted in a different degree of gelatinisation vs. temperature curve. DSC and X-ray measurements are preferred, because they can be used to determine when the final stage of the gelatinisation process has been completed. Birefringence and amylose–iodine complex formation measurements are suitable alternatives if DSC and X-ray equipment is not available, but will lead to different results. The differences between the methods can be explained by considering the phenomena that take place during the gelatinisation at limiting water conditions.

Based on the experimental data obtained with DSC and X-ray measurements, the gelatinisation of 10 w/w % and 60 w/w % wheat starch–water mixtures started at the same temperature (approximately 50 °C). However, complete gelatinisation was reached at different temperatures (approximately 75 °C and 115 °C for, respectively, 10 w/w % and 60 w/w % wheat starch–water mixtures) according to the experimental DSC and X-ray data. These results are in accordance with independent DSC measurements that were carried out.

The Flory equation was adapted to provide a quantitative explanation for the curves describing the degree of starch gelatinisation as a function of the starch–water ratio and the temperature. The gelatinisation curves that were obtained with the model are in good agreement with the experimentally determined curves. The parameters , ΔH_u and χ₁₂ that resulted in the lowest sum of the squared residuals are 291 ± 63 °C, 29.2 ± 3.9 kJ/mol and 0.53 ± 0.05 (95% confidence interval). These values agree with other values reported in literature.     

Effect of modification of cytochrome c on its reactions with superoxide and NADPH:cytochrome P-450 reductase

Acetylation and succinylation of cytochrome c decrease its rate of reaction with superoxide. The effect of succinylation is greater than that of acetylation. As predicted by the Brönsted-Debye-Hückel relationship, the effect of modification of cytochrome c is more pronounced at low ionic strength. Modification of cytochrome c causes a much greater decrease in its reaction with NADPH-cytochrome P-450 reductase, compared to its reaction with superoxide. This data forms the quantitative basis for the enhanced specificity of modified cytochrome c for superoxide detection previously described by other investigators. Additionally, a greatly simplified version of the trinitrobenzenesulfonic acid method for estimation of free amino groups is presented.     

Effect of hydrostatic pressure on starch gelatinisation,as determined by DTA

A study of starch gelatinisation over the pressure range 0·1–400 MPa has been performed using high pressure differential thermal analysis (HPDTA). The results show that the gelatinisation temperature first increases by a few degrees, becomes constant at 150–250 MPa and then decreases slightly. ΔH decreases with an increase in pressure, with the decrease being more rapid for wheat and smooth pea starches than for potato starch. Using the Clapeyron equation it can be deduced that ΔV is initially positive, but decreases with an increase in pressure to become zero at 150–250 MPa and eventually just negative.