Starch/Staerke
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Kinetics and mechanism of thermal decomposition of cornstarches with different amylose/amylopectin ratios Abstract Thermal decomposition of cornstarches with different amylose/amylopectin ratios (waxy: 0/100, maize: 23/77, Gelose 50: 50/50, and Gelose 80: 80/20) under nitrogen condition was investigated by thermogravimetric analysis (TGA). Various decomposition models including Friedman, Kissinger, Flynn‐Wall‐Ozawa, and modified Coast‐Redfern methods were used to determine the apparent activation energy of different starches. Fourier transform infrared spectrometry (FTIR) and TGA‐FTIR were also used to study the mechanism of thermal decomposition process. The results show a multiple‐step mechanism for the thermal decomposition of all cornstarches. The sequence of activation energy for the cornstarches is waxy>maize>G50>G80, which corresponds to amylopectin content. FTIR results confirm that the thermal decomposition of cornstarch is due to the long‐chain scission. The higher activation energy for cornstarch with higher amylopectin content can be explained by its higher molecular weight and more α‐1,6 bonds.
Starch/Staerke - Tập 62 Số 3-4 - Trang 139-146 - 2010
High‐Speed Separation and Size Characterization of Wheat and Barley Starch Granules by Lift‐Hyperlayer Asymmetrical Flow Field‐Flow Fractionation in Synergy with SPLITT Fractionation Abstract The complementary employment of two separation techniques, one analytical‐scale, the other preparative‐scale, i.e. the lift‐hyperlayer asymmetrical flow field‐flow fractionation (AsyFlFFF) and the split flow‐thin cell (SPLITT) is presented for the first time as a methodology to size‐separate and rapidly characterize starch granules of different botanical origins. Very rapid separation and size characterization is achieved by AsyFlFFF and the techniques are mutually used to characterize and confirm data produced by the other. Light microscopy (LM) was used to test the quality of the performed SPLITT separations and consequently to evaluate the AsyFlFFF results. The procedure was applied to wheat and barley starch.
Starch/Staerke - Tập 58 Số 3-4 - Trang 140-154 - 2006
Properties and Flocculation Efficiency of Highly Cationized Starch Derivatives Abstract In this study the flocculation efficiency of cationic starch derivatives of varying degrees of substitution (DS) and different amylose/amylopectin ratios was investigated and compared to structural properties. The molar masses, M w , radii of gyration, R G , and the molar mass distributions of the starch samples were determined by applying the method of flow field‐flow‐fractionation combined with multi‐angle light scattering and interferometric refractometry. In dewatering experiments potato starch derivatives of differing DS have optimum dosages that correspond to their cationicity. The lowest flocculant dosage yielding maximum dewatering results was determined for the most strongly substituted sample (DS = 1.48), while the least substituted starch derivative (DS = 0.28) showed the highest flocculant demand. Furthermore, the molar mass distribution and coil dimensions of derivatives seem to have a great influence on flocculation efficiency, because a 1.5‐fold increase in molar mass can compensate a 1.5‐fold decrease in DS. Toxicological investigations on synthetic and natural flocculants employing hens fertile egg screening test (HEST) led to the conclusion that cationic starches of DS < 0.95 are less toxic than commercial synthetic flocculants. When the results of flocculation experiments and toxicological data were taken into account, a moderate DS of 0.6 was deemed to give the best compromise between dewatering efficiency, cost‐effectiveness and ecological safety.
Starch/Staerke - Tập 58 Số 3-4 - Trang 161-169 - 2006
Influence of Jet‐Cooking Temperature and Ionic Strength on Size and Structure of Cationic Potato Amylopectin Starch as Measured by Asymmetrical Flow Field‐Flow Fractionation Multi‐Angle Light Scattering Abstract Asymmetrical flow field‐flow fractionation (AsFlFFF) in combination with multi‐angle light scattering (MALS) was applied to cationic potato amylopectin (CPAP) to investigate how molar mass, root‐mean‐square (r.m.s.) radius and shape was influenced by different conditions of jet‐cooking. The effect of different jet‐cooking temperatures in the range 110°C – 140°C was studied in an excess steam jet‐cooker. This equipment is used in the industry for dissolution of starch and starch derivatives before technical application. The effect of different ionic strengths conditions was examined in the range of 10–200 mM. The weight‐average molar mass decreased from about 34×107 g/mol to 2.6×107 g/mol when the jet‐cooking temperature was increased from 110°C to 140°C. Concurrently the root‐mean‐square radius decreased from ca 380 nm to 90 nm. The decrease in size was reflected by a decrease in viscosity with increasing temperature. The root‐mean‐square radius was reduced when increasing the ionic strength. This decrease in size was correlated with a decrease in viscosity. Conformation and Kratky plots showed that at low ionic strength (≤ 10 mM) CPAP behaved as a flexible chain with high degree of branching, close to hyperbranching. Increase of the ionic strength gave a more compact structure and changes in the internal structure were observed as well. Consequently, by using AsFlFFF – MALS the effect of technical processing on the molar mass, molecular radius, conformational structure, and shape could be determined in a size region where standard methodology commonly fails.
Starch/Staerke - Tập 58 Số 2 - Trang 55-65 - 2006
Physicochemical Properties of Oxidized Cassava Starch Prepared under Various Alkalinity Levels Abstract The physicochemical properties of hypochlorite‐oxidized cassava starch as influenced by the alkalinity levels (pH 8 to 11) during modification process were investigated. Hypochlorite oxidation generally increased the contents of carbonyl and carboxyl groups in starch but decreased starch viscosity. The formation of carbonyl and carboxyl groups was more favorable under the milder alkaline conditions (pH 8 and 9). Oxidation conducted at higher alkalinity levels produced both functional groups at a much slower rate and to a lesser extent. Starch viscosity decreased markedly with increasing reaction time. The alkalinity levels during the modification process greatly influenced the initial viscosity of the oxidized starch paste and the viscosity stability of the paste during storage. Thermal behavior studies by differential scanning calorimetry (DSC) demonstrated that oxidation decreased both gelatinization temperature and enthalpy. The decrease in gelatinization temperature was strongly related to the carboxyl group content. The more carboxyl groups the oxidized starch contained, the lower was the gelatinization temperature. Retrogradation of amylopectin tended to increase slightly after oxidation. While the light transmittance of native starch paste drastically decreased during cold storage, the changes observed in oxidized starch pastes were less pronounced and appeared to depend on carboxyl content. The results from light transmittance studies suggested that carboxyl groups introduced into the starch molecules could effectively prevent retrogradation.
Starch/Staerke - Tập 61 Số 2 - Trang 92-100 - 2009
Physicochemical Properties of Banana Starch Oxidized under Different Conditions Abstract Starch isolated from unripe bananas was oxidized under different conditions and the physicochemical properties of the oxidized banana starches were characterized. It was found that pH was the dominating factor in the formation of carboxyl groups. Higher yields of carboxyl groups were found when oxidized starch was prepared at pH 11.5 as compared with 7.5. Longer reaction time also produced a higher carboxyl value. Maltese crosses were still visible in the polarized light micrographs of oxidized banana starch, indicating that the ordered arrangement of starch molecules was not altered. The diffraction pattern of both native and oxidized banana starches was a mixture of A‐ and B‐types. No difference was noted in the absorbance ratio as measured by infrared spectroscopy between the oxidized banana starches at both pHs. The onset and peak gelatinization temperatures increased and gelatinization range decreased with increasing pH during the oxidation. For pasting properties, viscosity significantly decreased during heating and cooling with the most drastic reduction noted for the sample oxidized at pH 11.5. All starches showed a non‐Newtonian shear‐thinning behavior. The oxidation reaction that incorporated chemical groups produced a softer system in banana starch due to the possible incorporation of more water molecules in its structure.
Starch/Staerke - Tập 61 Số 3-4 - Trang 206-213 - 2009
Oxidation of Potato Starch by Hydrogen Peroxide Abstract Potato starch was oxidized by hydrogen peroxide in alkaline and acidic reaction conditions with copper, iron and tungstate catalysts in order to introduce carboxyl and carbonyl groups to the starch molecule. Carbonyl contents up to 6.6 per 100 glucose units could be obtained, whereas carboxyl content remained low (up to 1.4). Starch yields in the alkaline and acidic reactions were 90 and 99%, respectively. The molecular weight decreased markedly with the degree of oxidation, and was dependent on the catalyst used. Rheological measurements revealed that when the molecular weight of the moderately oxidized starch was high, a very firm gel (G' = 40kPa) was obtained with 25% starch concentration. When the degree of oxidation increased, the storage modulus G' decreased. The more the oxidized starch contained carbonyl groups, the higher was the gelatinization temperature.
Starch/Staerke - Tập 47 Số 1 - Trang 19-23 - 1995
Studies on the Relationship Between Water‐satured State and Crystallinity by the Diffraction Method for Moistened Potato Starch Abstract Crystallinity was measured by X‐ray diffraction method and water‐saturated state was determined by means of the moisture contents calculated from the crystallinity for moistened cellulose and potato starch. In the X‐ray diffractograms the upper areas which were separated by the straight line joined the points of intensity at 37° and 4° (8°) of diffraction angle was the relative reflection area in the crystalline and amorphous portions, and the lower area was the background of the non‐relative reflection area. The upper area separated by the smooth curve joined the minimum intensity at 4° to 37° of diffraction angle corresponded to the crystalline portion and the lower area to the amorphous one. The ratio of the crystalline portion to sum of the crystalline and amorphous portions was considered to be crystallinity. Crystallinity of the air‐dried and the moisture‐saturated (28%) samples of cellulose were 0.68 and 0.71, resp. The crystallinity of the air‐dried and water‐saturated (49%) samples of potato starch were 0.24 and 0.32, resp.
Starch/Staerke - Tập 35 Số 12 - Trang 407-410 - 1983
Maize and teff starches modified with stearic acid as potential fat replacer in low calorie mayonnaise‐type emulsions Abstract Fat replacers have been developed to produce low‐calorie foods due to the association of fat‐rich diet to lifestyle diseases. Teff (an underutilized and under‐researched cereal), and maize starch pastes modified with stearic acid could be used as fat replacers because of their reduced gelling ability and higher viscosity. The effects of teff and maize starch pastes modified with stearic acid on the rheological properties, microstructure, freeze–thaw, and high temperature stability of low‐calorie mayonnaise type emulsions (LCMTE) were investigated. Starch suspensions (10% w/v) containing stearic acid (1.5%) were pasted and used to prepare LCMTE with 50 and 80% oil replacement. LCMTE with modified teff and maize starches had lower yield stress and viscosity and larger oil droplets compared to LCMTE with unmodified teff and maize starches. Increasing oil replacement level (50–80%) increased the viscosity. LCMTE with maize starch had higher yield stress and viscosity and smaller oil droplets than LCMTE with teff starch. All samples showed shear thinning behavior (n < 1). All the LCMTE were more stable to freeze–thaw cycles and high temperature storage than full fat mayonnaise. At 50% oil replacement, unmodified and modified teff and maize starch with stearic acid could produce LCMTE. When the oil content replacement was further increased to 80% only the LCMTE with modified starches were similar to the full fat. The LCMTE made with unmodified teff and maize starches (especially those with 80% oil replacement) did not flow like a mayonnaise compared to LCMTE made with stearic acid modified starches.
Starch/Staerke - Tập 65 Số 9-10 - Trang 773-781 - 2013
The Effect of pH on the Zeta Potential of Wheat and Potato Starch Abstract The facility with which starch is dispersed in aqueous media and the interactions of starch with other components are functions of the surface properties of starch granules. The zeta potentials of wheat and potato starch granules have been measured in the pH range 2 – 10 by microelectrophoresis. Removal of components from the surface of granules using appropriate reagents has enabled us to identify the contributions of the charged groups present on te surface of the granules. Results obtained from micropotentiometric titration of starch suspensions support the conclusions obtained from zeta potential measurements. At their isoelectric points, starch preparations flocculated, indicating that starch suspensions are charge‐stabilized.
Starch/Staerke - Tập 34 Số 5 - Trang 149-152 - 1982
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