Search

Tamales were produced using a traditional nixtamalization process. The nixtamal was milled into masa, mixed with shortening, and boiled to prepare tamales. Enzymatic methods and DSC enthalpies were used to investigate resistant starch (RS) and starch–lipid complexes (resistant starch 5; RS5). The addition of shortening to masa showed an endotherm of lipid melting with To(m), Tp(m), and Tf(m) of approximately 40, 44, and 50°C, respectively. Processing masa by boiling at >90°C for 2 h to make tamales showed three endotherms: one related to amylopectin retrogradation (RS3), one to starch gelatinization (G), and one to Type I complex (RS5). The retrograded amylopectin presented temperatures of 49, 55, and 60°C for To(RS3), Tp(RS3), and Tf(RS3), respectively. The X-ray diffraction pattern showed that during processing starch Type A complexed with lipids to form a Type V (RS5) amylose–lipid starch complex. The RS5 in tamales estimated by DSC affected blood glucose levels from in vivo tests.

Supramolecular structural changes of maize starch as affected by hydrothermal treatment in excess water were investigated. At a temperature slightly higher than the onset (To) of gelatinization endotherm (G), an increase in the size of the cavity at the granule core and a sharp decrease in the ordering degree of the semi-crystalline lamellae occurred, together with the scattering objects apparently becoming looser. When the temperature approached close to the peak temperature (T-p) of endotherm G (70 degrees C), the semi-crystalline lamellae disappeared, accompanied by the emergence of a dual fractal structure. This suggests that the molecules of swollen maize starch displayed inhomogeneity on nanoscale, with a mass fractal structure at a higher scale level constituted by the scattering objects at a lower scale level. Additionally, it is proposed that a reduction in starch crystallites could enhance the degree of mixing between the crystalline and amorphous materials. The results enable a better understanding of starch supramolecular structural evolutions during the hydrothermal treatment in excess water.

Characteristics of starch obtained at different stages of purification during commercial wet milling of maize were evaluated. L*, whiteness index, swelling power, transmittance and syneresis progressively increased while a*, b*, protein content, lipid content and water binding capacity of the starches decreased after each successive purification stage. Protein and lipids content decreased from 5.2 to 0.3% and from 0.15 to 0.03%, respectively, after each successive purification stage. SDS–PAGE indicated that high MW polypeptides eliminated during early stages of purification than low MW. The starches showed typical A-type XRD pattern along with increasing crystalline region after each successive purification stages. DSC evaluation showed the presence of two endotherms during heating, the first between 69.9 and 81.5°C and second endotherm between 84.1 and 105.3°C being associated with the melting of crystallites and amylose–lipid complexes, respectively. Transition temperatures decreased while gelatinization enthalpy increased with the purification of starch. During cooling, exotherms at peak temperature between 78.8 and 90.3°C was observed. Peak viscosity, final viscosity, breakdown viscosity and setback increased while pasting temperature decreased after each successive purification stage. Storage modulus, syneresis and transmittance of starches revealed increased tendency towards retrogradation with decrease in protein content and lipid content.

Various starches of different AM contents and origins such as wx maize, normal maize, high AM maize, potato, and mungbean starches were hydrolyzed using a H2SO4 solution (3.16 M) at 40°C for 7 days, and the starch particles were isolated from the hydrolysates by centrifugation. The hydrolysis rates varied from 61.4 to 90.9% depending on the starch type. Unexpectedly, A-type starches were more resistant to the acid hydrolysis than B-type starches. XRD results revealed that the starch particles with B-crystalline type exhibited a decrease in peak intensity. In addition, in a DSC analysis, the crystals remaining in the B-type starch particles were readily disrupted in the water dispersion so that no melting endotherm appeared. Electron microscopy confirmed that the starch particles had round or oval shapes with diameters ranging from 40 to 70 nm, which possibly represented the starch blocklets in granules. The acid degraded mainly AM and long AP chains, resulting in increasing the proportion of short chains.

Functional properties of flour from rice variety BG 250 (short-season) and BG 359 (long-season) exposed to soil water stress from flowering to grain maturity were investigated. Protein content was reduced in both varieties but lipid was reduced only in BG 359 in response to soil moisture stress. AAM content decreased in BG 250 but unaffected in BG 359. Water stress increased swelling power, onset of pasting, peak viscosity, granular breakdown, gel hardness, and cohesiveness in both varieties. Gelatinization temperatures in both varieties were unaffected by water stress, while gelatinization enthalpy was increased in BG 359 but unchanged in BG 250. A double endotherm (type I and type II) appeared in AM–lipid complex in all the flour samples. Type I AM–lipid complex was reduced in BG 359 in response to water stress. Only a single endotherm appeared in the re-formed AM–lipid complex in gelatinized starch. The magnitude of the ΔH of re-formed AM–lipid complex was reduced in BG 359 in response to soil moisture stress, but unaffected in BG 250. Water stress decreased AP retrogradation in BG 359 while it was unaffected in BG 250.

The objective of this research was to investigate the effect of heating rate at different moisture contents on starch retrogradation and gelatinization process. Starch retrogradation was not influenced by either moisture content (water/starch ratio of 0.7 or 2.0) or heating rate (5°C/min, 20°C/min, or 40°C/min). In order to further understand the effects of heating rate on starch―water interactions, starch suspensions at a water/starch ratio ranging from 0.7 to 3.0 were heated at 5, 15, or 25°C/min by using a DSC to different final temperatures and rescanned. The deconvoluted G and M1 endotherms and the corresponding additional unfrozen water (AUW) were determined. The results showed that the G and M1 endotherms merged at higher heating rates and at higher moisture contents as expected. A significant interaction was observed between moisture content and heating rate. The results suggest that the gelatinization process is governed by moisture content at the lower heating rate (5°C/ min) and by heating rate at the higher heating rates (15 or 25°C/min). Results from the AUW data suggest that the M1 component of gelatinization dominated at moisture content below water/starch ratio of 1.5 and at 5°C/min heating rate. However, at moisture contents above water/starch ratio 1.0, an interaction was observed between moisture content and heating rate. The data suggest that at higher moisture content (>1.5 water/starch ratio) and at higher heating rate (≥15°C/min), there is still a kinetic limitation to the complete melting of the M1 endotherm.

The retrogradation process of the biphasic endotherms Gr and M1 r for waxy cornstarch was systematically investigated using differential scanning calorimetry (DSC). The high temperature endotherm M1r developed significantly within 2―5 h, while the retrograded endotherm Gr appeared after 5 h storage and increased with time. The single endotherm Gr was separated using an analytical software, and the enthalpy was found to be ∼36% of the total enthalpy of the retrograded starch. Compared to normal cornstarch (∼77% amylopectin content), the final retrogradation ratio of the waxy cornstarch was higher. Both the waxy and normal cornstarches investigated showed a similar pattern of retrogradation process, which developed quickly in the initial stage (up to 1 day) and then gradually came to a near-constant value in the second stage (from 1 to 20 days).

The physicochemical and pasting properties of high amylose rice starches isolated using alkaline steeping method from different Korean rice cultivars, Goamy2 and Goamy, and from imported Thai rice were examined. The protein and lipid contents of the Goamy2 starch were higher than those of the other two starches. The amylose and total dietary fiber contents were ranged from 31.4 to 36.8% and from 6.3 to 8.6%, respectively. Total dietary fiber was positively correlated to amylose content. Water binding capacity was higher in the Goamy2 starch (172.2%) than in the Goamy and Thai rice starches (112.7–115.6%). The swelling power of the Goamy2 starch showed lower values, but its value at 95°C was similar to others because of its rapid increment at 85°C. The granular size of Goamy2 starch was widely distributed compared to those of others. The Goamy2 starch showed a high initial pasting temperature (92.0°C) and low breakdown and setback viscosities. The Goamy and Thai rice starch granules were polygonal-shaped with A-type crystals, whereas the Goamy2 starch granules were round-shaped with B-type crystals. Goamy and Goamy2 starches showed a single endotherm at 60.8 and 76.0°C for peak temperature and 10.0 and 11.5 J/g for gelatinization enthalpies, respectively. The Thai rice starch presented an endotherm with a shoulder peak at 68.3°C (75.3°C for the main peak) and a gelatinization enthalpy of 12.4 J/g.

Some functional and retrogradation properties of native and heat-moisture treated potato and wheat starches were examined in the presence of hydroxypropyl β-cyclodextrin (HPβ-CD). HPβ-CD increased swelling factor, amylose leaching, and solubility of both native and heat-moisture treated wheat starches but it had less impact on corresponding potato starches. Gelatinization enthalpy of native wheat starch was decreased in the presence of HPβ-CD but was increased in potato starch with increasing concentration. Reduction of amylose-lipid complex endotherm in both native and heat-moisture treated wheat starch was observed in the presence of HPβ-CD. Heat-moisture treatment did not change the transition parameters of amylose-lipid complex showing its resistance to hydrothermal treatment. HPβ-CD greatly decreased the pasting temperature of wheat starch. Cold paste viscosity of both native and heat-moisture treated wheat starch was increased by HPβ-CD to a greater extent than corresponding potato starch. Amylopectin retrogradation of all the starches was unaffected in the presence of HPβ-CD but heat-moisture treatment slightly decreased retrogradation of potato starch. These results suggest that HPβ-CD can disrupt the amylose-lipid complex within the starch granule in both native and heat-moisture treated wheat starch but has no influence on amylopectin retrogradation. However, greatly increased wheat starch setback with HPβ-CD indicates its greater effect on wheat starch amylose retrogradation.

The effect of autoclaving temperatures (100-120°C) on yields of enzyme-resistant starch (RS) from normal corn starch and the physicochemical properties of autoclaved-cooled starches were studied. The RS content increased linearly with increasing autoclaving temperature (R 2 = 0.993) and the number of autoclaving-cooling cycles at an autoclaving temperature of 120°C. The effect of the number of autoclaving-cooling cycles was more pronounced than that of temperature. The swollen starch weight measured at 60°C slightly increased as the RS content increased, and then drastically decreased with the continous increase of the RS content (R 2 = -0.969). As the RS content increased, all parameters of Rapid Visco Analyser (RVA) viscosity except breakdown decreased. Log RVA peak viscosity showed a negative correlation with the RS content (R 2 = -0.986). The enthalpy in the differential scanning calorimetry (DSC) endotherm corresponding to the transitions of RS linearly increased as the RS content increased (R 2 = 0.988). The RS content of the heat-treated starch estimated from the relationship between RS content and swollen starch weight at 60°C, log RVA peak viscosity or DSC enthalpy was in good agreement with that determined with the standard method.

Starches from glutinous rice (1.4% amylose), Jasmine rice (15.0% amylose) and Chiang rice (20.2% amylose) were exposed to heat-moisture treatment (HMT) at 100 °C for 16 h and at different moisture levels (18, 21, 24 and 27%). The effect of heat-moisture treatment on structural and thermal properties of these three rice starches was investigated. The HMT did not change the size, shape and surface characteristics of rice starch granules. The A-type crystalline pattern of rice starches remained unchanged after HMT. The relative crystallinity (RC) and the ratio of short-range molecular order to amorphous (RSA) of heat-moisture treated glutinous and Jasmine rice starches decreased with increasing moisture level of the treatments. In contrast, the RC of the treated Chiang rice starch remained practically unchanged. A peak of crystalline V-amylose-lipid complexes was clearly presented in all treated Chiang rice starches. The peak became progressively stronger with increasing moisture level of the treatment. Differential scanning calorimetry (DSC) of all treated rice starches showed a shift of the gelatinization temperature to higher values. Increasing moisture level of the treatments increased the onset gelatinization temperature (To) but decreased the gelatinization enthalpy (AH) of rice starches. A broad gelatinization temperature range (T c -T o ) with a biphasic endotherm was found for all treated Chiang rice starches and Jasmine rice starch after HMT 27 (HMT at 27% moisture level). Additionally the (T c -T o ) of treated Chiang rice starches increased linearly with increasing moisture level of the treatments.

There is considerable debate on the definition and measurement of the amount of amylose in starch and whether hydrophobic ligands can form a complex with amylopectin. One method for amylose determination is through the measurement of amylose-lipid complexation using differential scanning calorimetry (DSC), with the assumption that amylopectin cannot form such a complex. As the sensitivity and methodologies used for DSC improves, the validity of this assumption needs to be tested once again. For the experimental work, α-L-lysophosphatidylcholine (LPC, 10% of starch dry weight) was used as the complexing agent and waxy maize starch. Optimisation of the DSC included changing the heating rate from 10°C/min to 40°C/min, which resulted in a higher sensitivity enabling the recording of an endotherm associated with the dissociation of a starch-LPC complex. The observation of the endothermic formation of such complex could only be achieved when a microcalorimeter, which analyses a much larger sample than a standard calorimeter (190 mg of dry starch compared to 13 mg) was used. There are two possible interpretations for these observations: Either waxy maize starch contains traces of amylose (∼ 0.5-0.7%) and the DSC is sufficiently sensitive to detect these amounts or the α-1,6 glucan long branches of waxy maize starch bind linear aliphatic compounds.

Physical aging of glassy corn starch and its effect on the physical properties of compressed starch bars were investigated by using differential scanning calorimetry (DSC), dynamic mechanical thermal analyzer (DMTA), and Instron texturometer. Amorphous corn starch samples were prepared by drying a starch paste, followed by compressing the dried powders to bar-type specimens under heat (1007C, 1.38610 7 Pa). These bars were then aged at 257C for up to 22 days, after which thermal and mechanical characteristics were determined. There were progressive increases in glass transition temperature and relaxation enthalpy during the aging, which reached limiting values as structural equilibrium of the amorphous matrix was approached. The peak temperature of the relaxation endotherm (DSC thermogram) changed with time in a trend similar to the relaxation enthalpy. The storage modulus (DMTA) increased with aging time, but the peak intensity of tan d decreased. The breaking strength (Instron texturometer) increased gradually with time of aging and reached a maximum. It has been demonstrated the relaxation kinetics for glassy amorphous corn starch can be characterized by both thermal and mechanical properties, such as relaxation enthalpy, storage modulus, and breaking strength.

Tapioca starch was partially hydrolyzed by 6% (w/v) hydrochloric acid at room temperature for various lengths of time. Annealing and freeze-thaw stability of the acid-modified starches were studied using Differential Scanning Calorimetry (DSC). In the annealing study, as the hydrolysis time increased, the effect of annealing on narrowing and shifting the endothermic peak to a higher temperature was decreased. The endothermic transition of annealed 48-h acid-modified tapioca starch showed a narrow peak and a broad shoulder, corresponding to the melting of the amylopectin double helices (crystalline regions) and the retrograded partially hydrolyzed amylose, respectively. This effect of annealing on the sharpening of the endotherm was less pronounced on acid-modified tapioca starches annealed for 192 h and 768 h, respectively. These results indicated that annealing leads to more homogeneous crystallites and this effect is enhanced when the material contains more amorphous and homogeneous domains. In the case of the freeze-thaw stability study, the melting endotherm of recrystallized amylopectin became larger with increasing hydrolysis time. The first detectable endotherm of native tapioca retrograded gel was observed after five cycles, while all acid-modified retrograded gels showed the melting endotherm after only one cycle. Increasing hydrolysis time may increase the proportion of short chain amylose and amylopectin molecules, which are able to form double helices, resulting in an increase in the enthalpy and a higher retrogradation rate of the gel.

Differential 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.

The effect of water on heating wheat starch-water mixtures of water content (between 2.8% and 90%) has been observed by differential scanning calorimetry. Four endothermic transitions were observed for wheat starches heated in the presence of limited water (moisture levels of 40,50%). These transitions appears to be due to melting of amylopectin crystallites, amylose-lipid, and amylose. The heat decomposition temperature range of wheat starch were 253-302°C and the plasticization effect according to the amount of water was small. The melting temperature obtained by extrapolation to zero volunme fraction of water were 234°C for M1 DSC endotherm, 254.3°C for M2 DSC endotherm, 267.8°C for M3 DSC endotherm.

The effects of hydroxypropylation on phase transitions associated with gelatinization of granular rice starch were studied by differential scanning calorimetry. At a 1:1 starch/water ratio, a progressive shift of the biphasic gelatinization endotherms to lower temperatures as well as a broadening and shortening of the G endotherm with increasing molar substitution were observed, indicating increased internal plasticization and destabilization of the amorphous regions of the starch granules. The overall enthalpy of gelatinization was also reduced. Hydroxypropyl groups, which are attached to starch molecules primarily in the amorphous regions of the starch granules, behave as flexible side chains. The motion of these side chains creates a large amount of free volume, thereby lowering the glass transition and crystallite melting temperatures associated with starch gelatinization. The modified starch granules may thus be viewed as internally plasticized polymer resins which are more easily gelatinized than the unmodified starch.

The effect of heating starch-water mixtures of low water content (between 50% and 1.5% water) has been observed by the techniques of both birefringence measurement and differential scanning calorimetry. The temperature at which gelatinization was complete, i. e. at which complete loss of birefringence occurred, increased as the water content was reduced. Complete loss of birefringence occurred over the whole of this range of water content. A correlation was established between the loss of birefringence and passage through the M1 DSC endotherm, assigned to the melting of starch crystallites.

A-type X-ray diffraction spectra of raw rice were weakened upon mild parboiling and completely disappeared in moderately severely parboiled rice. A feeble V pattern of lipid-amylose complex appeared in its place. There was no unambiguous evidence of B-type spectra of retrograded starch, although partial and weak B-like spectra could be seen. Differential scanning calorimetry showed that raw rice flour and starch had a large gelatinization and a small lipid-amylose endotherm, the latter disappearing after defatting. The gelatinization endotherm first decreased and eventually disappeared in samples with moderately severe parboiling, but a small lipid-amylose endotherm was visible in most parboiled rice samples. Results indicate that parboiled rice is largely amorphous with only minor crystallinity, and the peculiar properties of parboiled rice could not be ascribed to altered crystalline form of starch. [Results obtained with maize and potato starches are presented for comparison.]

DSC thermograms from 5–135°C of eight rice starches, pretreated with sodium dodecyl benzenesulfonate (DoBS) to remove milled rice proteins, gave gelatinization endotherms with characteristic temperature ranges. Good positive correlations were found between gelatinization temperatures measured by DSC and photometry, and between gelatinization enthalpies and gelatinization temperatures. The enthalpy of the amylose-lipid endotherm at 90–97°C was less for two DoBS-prepared rice starches than for the same pronase-treated starches. The endotherm was absent in waxy starch, and its enthalpy followed the level of lipids extracted by cold water-saturated butanol (WSB). It was concluded that DoBS treatment removed and replaced some of the starch lipid. Although this DoBS did not form a complex with amylose that was observable by DSC, the adsorbed DoBS was extracted by hot WSB.

The application of Differential Scanning Calorimetry to the gelatinisation of concentrated starch/water suspensions produced a well-defined endotherm under suitable conditions. Measurement of the peak area enabled the heat of gelatinisation to be calculated. The method has been applied to the following aspects of gelatinisation: — 1 Intercomparison of different starches, 2) Effect of granule size, 3 Application to wheat flour, 4 Effect of starch damage, 5 Staling of starch gels, 6 Amylose and amylopectin.

A series of bread samples stored at various temperatures (4°, 25°, and 40°C) were analyzed by differential scanning calorimetry (DSC) to determine if retrogradation (quantified by DSC enthalpy values) and storage temperature were correlated. The increase in enthalpy values during storage time was dependent on storage temperature. However, the rate of recrystallization was not linear at any of the temperatures studied. The net result was that the enthalpy values tended to converge with time, irrespective of storage temperature. Another effect of the increased storage temperature was an increase in the peak temperature (Tp) of the amylopectin endotherm. This indicates either that storage temperature affects the type of crystal being formed as the starch recrystallizes, or that annealing of crystals occurs at the higher storage temperatures. X-ray diffractometry of starch isolated from the crumb gave similar diffraction patterns indicating no difference in crystal type among the treatments. In addition, the DSC endotherm became sharper at the higher temperatures. Thus, the increase in Tp was apparently the result of annealing of the crystals at the higher storage temperatures.

The gelatinization behaviour of hydroxypropyl maize starches of molar substitutions ranging from 0–0.27 was studied using differential scanning calorimetry. Increases in molar substitution up to 0.10 were accompanied by decreases in the enthalpy and in the onset and peak temperatures of the gelatinization endotherm. At higher substitution levels the endotherms obtained were too broad to permit measurement of gelatinization characteristics. The minimum level of moisture required for gelatinization was not significantly affected by substitution with hydroxypropyl groups. Der Einflus der molaren Substitution auf die Gelatinierung von Hydroxypropylmaisstarken. Das Gelatinierungsverhalten von Hydroxypropylmaisstarken mit molaren Substitutionen von 0 bis 0,27 wurde mit Hilfe der Differential-Raster-Kalorimetrie untersucht. Zunehmende molare Substitution bis 0,10 war von einer Abnahme der Enthalpie sowie des Einsetzens und der Peak-Temperaturen der Gelatinierungsendotherme begleitet. Bei hoheren Substitutionsgraden waren die erhaltenen Endothermen zu breit, um die Gelatinierungscharakteristika messen zu konnen. Das Minimum an Feuchtigkeit, das fur die Gelatinierung erforderlich ist, wurde durch die Substitution mit Hydroxypropylgruppen nicht signifikant beeinflust.