Thermal and viscoelastic properties of starch gels from maize varieties (original) (raw)
Related papers
The aim of this work was to characterize the thermal (gelatinization temperature and melting enthalpy of retrograded starch) and rheological (viscoelasticity and viscosity in Bravebder Units) properties of starch isolated from different corn hybrids grown in Mexico. The gelatinization temperatures of the starches ranged from 71.5 to 74.7 °C. Melting temperatures of the retrograded starches were lower than the gelatinization temperature at the 7th and 14th day of storage, while the melting enthalpies of retrograded samples were usually higher only after 14 days. The rheological profiles showed that pastes formed during the first two stages (heating-cooking) of a heating/cooling kinetics, behaved as " weak " viscoelastic gels, with greater elastic modulus than viscous modulus (G'>G''). However, at the third (cooling) stage, all starch samples showed the behavior of " elastic " gels (G'>>G''). Viscoamylograms showed that 5 (w/v) % total solids starch pastes reached peak viscosity at about 93 ºC, whereas for 10 (w/v) % total solids pastes the peak was registered at about 87 ºC. According to the statistical analysis, there were significant differences among starches regarding their chemical features, as well as their thermal and rheological properties. In view of their high tendency to retrograde and their " weak " gel viscoelastic properties during processing, the starches may have applications in non-processed foods. RESUMEN: El objetivo de este trabajo fue caracterizar las propiedades térmicas (temperatura de gelatinización y temperatura de fusión del almidón retrogradado) y reológicas (viscoelasticidad y viscosidad en unidades Bravender) del almidón aislado de diferentes maíces híbridos cultivados en México. La temperatura de gelatinización de los almidones fluctuó de 71,5 a 74,7 °C. La temperatura de fusión del almidón retrogradado fue menor a los 7 y 14 días de almacenamiento que la temperatura de gelatinización, mientras que la entalpía de fusión fue, en general, mayor sólo a los 14 días de almacenamiento. El perfil reológico para las pastas formadas durante las primeras dos etapas (calentamiento-cocimiento) de una cinética de tres etapas de calentamiento/enfriamiento, correspondió al de geles viscoelásticos débiles, con el módulo elástico mayor que el módulo viscoso (G'>G''), mientras que en la tercera etapa (enfriamiento), las pastas se comportaron como geles mayormente elásticos (G'>> G''). El viscoamilograma de las pastas de almidón mostró viscosidades máximas alrededor de los 93 °C para mezclas al 5% (p/v) de sólidos y 87 °C para mezclas con 10 (p/v) % de sólidos. El análisis estadístico mostró diferencias significativas entre los almidones con respecto a su composición química, así como en sus propiedades térmicas y reológicas. Los resultados sugieren que estos almidones podrían utilizarse en alimentos no procesados, por su alta tendencia a retrogradar y su comportamiento de geles viscoelásticos " débiles " durante el procesamiento.
Food Hydrocolloids, 2006
Starches separated from five types of maize (two normal, one sugary and two waxy) were investigated for physicochemical, thermal, amylopectin structure and viscoelastic properties. Kisan and Paras were normal maize while Parbhat and LM-6 were waxy maize type. Apparent amylose content of normal and sugary maize was 29.5-32.6 and 41.0%, respectively. Swelling power of normal, sugary and waxy maize starches was 11.6-15.2, 7.8 and 30.2-39.2 (g/g), respectively. X-ray diffraction of maize starches indicated typical A-pattern. Maize starch showed a single broad peak at 2qZ23.28 and a dual peak 2qZ178-18.1, respectively. Waxy maize starches showed the presence of greater crystallinity than other starches while sugary maize starch showed the presence of lower crystallinity and a large amount of amylose-lipid complex. Intrinsic viscosity [h] of starches in 90% DMSO at 25 8C was 79.7-119.5 ml g K1 for normal, 70.5 ml g K1 for sugary and 107.2-118.1 ml g K1 for waxy starches. Branch chain-length distribution of amylopectin revealed that the apparent amylose, long side chain-and short side chain-amylopectin proportion ranged between 0.0-41%, 13.4-31.5% and 41.5-66.8%, respectively, among the various maize starches. Maize sugary showed the highest apparent amylose content and the least amount of short-and long-side chains of amylopectin. LM-6 and Parbhat showed higher proportion of both longand short-chain amylopectin as compared to other starches. Distribution of a-1, 4-chains of amylopectin (short-/long-chain) ranged between 2.1 and 3.4, the least for LM-6 and the highest for Paras starch. The transition temperatures (T o-T c) ranged between 60.5 and 76.1 8C for sugary, 63.5-76.3 8C for normal and 64.4-81.3 8C for waxy maize starch. The enthalpy of gelatinization (DH gel) of sugary, normal and waxy maize starches was 2.47, 3.7-4.75 and 4.15-5.4 J/g, respectively. Normal and sugary maize starches showed higher G 0 and G 00 than waxy type starches. The change in the moduli during cooling and reheating of pastes cooked at different temperatures revealed low disintegration of granular structure in starch with higher amylose and amylose-lipid complex as well as low crystallinity. The changes in moduli during 10 h at 10 8C revealed highest retrogradation in maize sugary followed by Paras and Kisan starch.
Rheological changes in nixtamalised maize starch
Journal of Central South University of Technology, 2007
In Mexico, a great deal of maize lines are growth, most of them go through the process of nixtamalisation (lye treatment at boiling temperature) to produce masa, which is used to mainly elaborate tortillas. During this process, the heat treatment brings about biochemical reactions, cross-links and molecular interactions that modify the physicochemical, structural and rheological properties of the masa as well as those of the tortillas produced. A high percentage of these changes is due to modifications in the structure of starch, the main chemical component of maize. Control starch (S) was isolated from a lot of maize and another lot of the same maize sample was subjected to lye treatment to obtain nixtamalised starch (NS). Rheological studies were carried out to determine its amylographic profile (Bravender), following a heating-cooking-cooling kinetics. Flow curves were carried out at 25 ℃ and 40 ℃ (heating-cooling, 25 ℃−90 ℃−40 ℃), using a strain controlled rheometer (TA Instruments AR-1000) with a cone and plate system, angle of 1˚. The dynamic oscillatory tests were carried out in a heating-cooling kinetics (25 ℃−90 ℃−25 ℃) with the same geometry (angle of 1˚), in dispersions with 10%(w/V) of total solids. Maximum viscosity and molecular dissociation were higher in the control starch. The flow curves show that all samples (S and NS) behave as Newtonian fluids at 25 ℃, which shifts to a shear-thinning behaviour at 40 ℃ and show a more pronounced tendency. In the dynamic tests, all starch gels obtained present weak viscoelastic gel-like behaviour predominating the elastic or storage modulus (G′) over the viscous or loss modulus (G″) during the three stages of the heating-cooling kinetics. According to tanδ values, nixtamalised starch forms amorphous gels, while control starch starch produces gels with a crystalline structure.
Food Chemistry, 1995
A comparative study was undertaken to examine the effect of sugars on the thermal and mechanical properties of ageing waxy maize, wheat, potato and pea starch gels. The addition of sugars, at a ratio of 1 : 0.5 : 1.5 (w/w) for starch-sugar-water mixtures, inhibited chain reorganization in starch gels, as followed by differential scanning calorimetry and dynamic rheometry in the order, ribose > sucrose > maltotriose > water alone, glucose > fructose. Kinetic experiments on the evolution of storage modulus (G) at 8°C indicated a progressive transition from a sigmoid curve (waxy maize) to a hyperbolic G' -time relationship (potato and pea starches), consistent with an increasing proportion of amylose in the composite gels. The effects of sugars on the development of the retrogradation endotherm (AH) and gel rigidity (0) were less pronounced for potato and pea starches than for waxy maize or wheat starches, presumably because of their higher amylose content, which dominates the gel network properties.
Effect of Amaranthus and buckwheat proteins on the rheological properties of maize starch
Food Chemistry, 1999
The relationship between pasting properties (determined with a Rapid Visco-Analyser) of maize starch and the texture of the resulting gel was examined after addition of Amaranthus and buckwheat proteins. An increase in the peak viscosity due to the addition of protein concentrates was observed, and a lesser increase from the addition of protein hydrolysates. The increase in starch pasting viscosity was related to protein solubility, and could be attributed to the starch granule stabilizing action of proteins. The interactions between starch and proteins were further investigated using oscillation and creep/recovery rheological tests. Generally, the proteins weakened starch gel structure, shown by the lower elastic modulus (G′) and higher phase degree (δ) compared to gels without any proteins added. The same results were obtained from creep/recovery experiments. It seemed that, since native proteins interact more with the granules, they act as a barrier to the release of amylose molecules; hence the resulting gels became weak. If desired, such effects could be lessened by partially hydrolyzing the proteins. ©
International Journal of Polymer Science, 2018
The influence of roasting conditions on the potato starch (PS) composition, solubility, crystallinity, gel-forming thermal profiles, and texture of the corresponding gels was studied. Thermorheological testing of roasted starches with (RPS) and without (RPSI) the soluble fraction was conducted on a stress-controlled rheometer. Texture profile analysis (TPA) was used to determine the RPS final gel texture. Solubility tests showed equivalent effects of starch roasting for samples treated at 190°C for 8 h (RPS190-8), 210°C for 6 h (RPS210-6), and 230°C for 4 h (RPS230-4). The apparent amylose content of RPS linearly increased with the decreasing degree of crystallinity. Elastic (G′) and viscous (G″) properties of RPS depended markedly on apparent amylose content and crystallinity. G′gel values of roasted starches linearly increased with the amylose content suggesting a promotion of the amylose breakdown with roasting temperature. Gels prepared with RPS roasted between 120 and 170°C exh...
Combined rheological and optical investigation of maize, barley and wheat starch gelatinisation
Carbohydrate Polymers, 2008
Microstructural and rheological changes during gelatinisation are important indicators of starch functionality. A combined rheometer and optical microscope system (Rheoscope 1, Thermo Haake) was used to monitor the gelatinisation of different starches (maize starch containing 0%, 24%, 55% and 85% amylose; wheat starch and barley starch) suspended in a 0.1% guar solution (to minimise settling during the initial stages of gelatinisation). The 0.1% guar solution was selected after Rapid Visco Analyser, Modulated DSC and settling studies indicated that it minimised any effect on starch gelatinisation compared to carboxy methyl cellulose and xanthan. The Rheoscope study demonstrated that the viscosity of the starch during gelatinisation is related to changes in starch granules as a result of swelling. There was a two to threefold increase in starch granule size during the gelatinisation for all starches except for high amylose maize starches. Viscosity development during the gelatinisation was affected by the presence of B-type granules, whose presence tended to reduce the overall viscosity increase, indicating the importance of starch granules size and their distribution in determining the rheological responses of starch during gelatinisation.
Influence of lipids on the thermal and mechanical properties of concentrated starch gels
Journal of Agricultural and Food Chemistry, 1991
Interactions between lipids [sodium dodecyl sulfate (SDS); glycerol monostearate; cetyltrimethylammonium bromide; L-a-lysophosphatidylcholine (LPC)] and starches (wheat, rice, pea, and garbanzo bean) were studied in thermoset gel networks of high starch concentrations 120-3576 w/w) by small amplitude oscillatory shear measurements and differential scanning calorimetry. All lipids reduced the apparent gelatinization enthalpies of the granular starches, suggesting complexation with the starch molecules upon heating; granule structure destabilization effects were shown only with SDS. Although rice and wheat starch gels exhibited higher storage modulus (G' ) values when lipids were included, smaller changes in the viscoelastic properties were observed for the legume starches; the higher amylose content of pea and garbanzo bean starches appears to dominate the rheological behavior of their composite gels. Among the lipids examined, LPC exerted the greatest effect in increasing the G' and decreasing the tan 6 (G"/G' ) of rice and wheat starch gels. Kinetic experiments on the evolution of modulus (G' ) and the development of the staling endotherm during storage of gels (35% w/w, 8 "C) indicated that lipids retard both processes. At concentrations between 8 and 40% (w/w) of rice and garbanzo bean starch gels, the dependence of storage modulus on starch concentration (C) followed power law relationships; G' varied as C2.1-2*9.
Cereal Chemistry, 2001
In this study, 3% aqueous high-amylose maize starch (Hylon VII) dispersions were heated to temperatures of 140-165°C. The onset and rate of gel formation was observed using a small-strain oscillation rheometer as a function of temperature from 90 to 25°C. The gel formation clearly began earlier in high-amylose starch paste preheated at lower temperatures, but the rate of gelation was slower and the resulting gel was weaker in comparison with starch pastes preheated at higher temperatures. In addition, the structure of the final gels was studied using large deformation compression measurements. The most rigid gel structure on the basis of small and large deformation tests was obtained for high-amylose starch gel preheated to 150-152°C, depending on the type of measurement. The rate of gelation was also fastest in that temperature range. High-amylose gels heated to higher temperatures lost their rigidity. The molecular weight distribution of starch molecules was measured by size-exclusion chromatography. Heating caused extensive degradation of amylopectin, which had a great effect on amylose gel formation and the final gel properties of high-amylose maize starch. Micrographs of Hylon VII gels showed that phase separation of starch components visible in light microscopy occurred on heating to higher temperatures.