Flow Behavior and Gelatinization of Cowpea Flour and Starch Dispersions

The flow behavior of a 25% cowpea slurry with 8% oil held at 70°C showed shear-thinning behavior and an Arrhenius temperature relationship. Cowpea flour (8%) and starch (2.5%) slurries heated for less than 1 min at 70–87°C exhibited shear-thickening while those heated longer times exhibited shear-thinning behavior. Maximum viscosities attained due to heat-induced gelatinization showed a power relationship with temperature of heating. Starch gelatinization kinetics followed a first-order equation and the temperature dependence of the rate constant followed the Arrhenius relationship with an activation energy of about 47.4 kcal/mol. Heating the slurries for >200 min above 80°C resulted in loss of viscosity.     

Thermal Processing of Cowpea Slurries

Isochronal temperature profiles of 20% cowpea flour slurries showed conduction heating while the estimated Rayleigh numbers predicted natural convection heating; apparently, the flour particles suppressed convection. Magnitudes of f_h of cowpea gels increased linearly with fat content, decreased with moisture content, and were independent of the cowpea flour particle size. The heating curve of a 10% cowpea flour slurry at 121°C showed one break due to gelation of protein and starch at about 66°C and another due to loss of rigidity at about 87°C.     

Modeling of Retrogradation of Waxy and Normal Corn Starches

Retrogradation behavior of waxy and normal corn starch gels stored at 5 and 21°C were investigated for 50 days by differential scanning calorimetry. The extend of retrogradation can be expressed as the ratio of retrogradation and gelatinization enthalpy values and these were 70–78% for normal corn starch and 39–68% for amioca stored at two temperatures. Higher retrogradation rates were observed at 5°C for both waxy and normal corn starch. Kinetic data were evaluated by considering retrogradation as consecutive reactions in series and by Avrami Equation. High R² values (0.97–0.98) indicated that both models can be used for prediction. The comparison of rate constants obtained by Avrami Equation indicated that both temperature and amylose content of starch affected the recrystallization rate. By the kinetic model based on consecutive reactions in series, it was proven mathematically that the rate limiting step in recrystallization of starch gels is the nucleation.     

Physicochemical and Functional Properties of Dry and Wet Milling Products of Red Cowpeas

Physicochemical and functional properties of dry- and wet-milled red cowpea flour, protein and starch were evaluated. Bulk density of drymilled red cowpea protein was lower than that of wet-milled protein isolate. Dry-milled starch was darker than wet-milled starch. Gelatinization temperature of starch (64–68–74°C) was quite similar to that of mung bean starch. At water to red cowpea starch ratios of 3:1 and 2:1, DSC thermograms showed a single endotherm with T_o of 68.5–69.0°C, T_p of 73.0–73.5°C, T_m of 79.5–80.0°C, and –ΔH of 4.0–4.6 cal/g starch. Pasting properties of red cowpea starch showed a type C amylogram, similar to mung bean starch. By mixing various quantities of red cowpea starch to tapioca starch pasting properties of the latter could be varied. Water and oil absorptions of cowpea flours increased with the increase in protein contents, as did their emulsifying activity and foaming properties. Emulsion and foam stabilities were quite similar among all the red cowpea products, except for protein isolate which were considerably lower, likely due to a greater degree of protein denaturation during precipitation and drying of the isolate. Composite flours made from mixing wheat and red cowpea flours exhibited dough mixing properties indicative of their potential use in baked products.     

Kinetics of Cowpea Starch Gelatinization Based on Granule Swelling

Granule size measured by laser diffraction was employed to describe the gelatinization kinetics of cowpea starch. During isothermal heating of the starch suspensions over the temperature range 67-86°C, the granule mean diameter increased rapidly initially and gradually leveled off to an equilibrium value that showed both power law and exponential dependency on temperature. Gelatinization of the starch followed pseudo first-order kinetics after an initial time lag that diminished with increased heating temperature. The gelatinization rate constant increased with temperature and could be described by the Arrhenius model with an activation energy of 233.6 kJ/mole.     

DIFFERENTIAL SCANNING CALORIMETRY OF STARCH12

At high water-to-starch (2:1) ratios a single endotherm was obtained for starch gelatinization. As the water-to-starch ratio was decreased the endotherm area decreased and the peak developed a trailing shoulder. At high water-to-starch ratios birefringence is lost over a temperature range of about 7°C. That narrow range increases to about 30°C at a low water-to-starch ratio. Starch and flour gave essentially the same endotherm initiation temperatures. In low-water systems the second DSC peak is much smaller with starch than with flour. It appears that in a starch system, water migrates during gelatinization. In dough, gluten limits that migration. As the level of sucrose was increased in a dough, the transition temperature increased and the gelatinization temperature range decreased. At the levels found in bread doughs both sugar and salt increase starch gelatinization temperatures.     

Freezing and Thawing Conditions Affect the Gel Stability of Different Varieties of Rice Flour

The freeze‐thaw stabilities of three different rice flour gels (amylose rice flour with 28% amylose, Jasmine rice flour with 18% amylose and waxy rice flour with 5% amylose) were studied by first freezing at –18 °C for 22 h and subsequent thawing in a water bath at 30 °C, 60 °C and 90 °C, or by boiling in a microwave oven. The freeze‐thaw stability was determined for five cycles. Starch gels thawed at higher temperature exhibited a lower syneresis value (percent of water separation) than those thawed at lower temperature. Amylose rice flour gels gave the highest syneresis values (especially at the first cycle). The Jasmine rice flour gels gave a higher syneresis value than the waxy rice flour gel. Except for freezing by storage at –18 °C and thawing at 30 °C, there was no separation of water at any cycle when waxy rice flour gel was thawed at any temperature, irrespectively of the freezing methods used. Cryogenic Quick Freezing (CQF) followed by storage at –18 °C and then thawing (by boiling or by incubation at any other temperatures) gave lower syneresis values than all comparable samples frozen by storage at –18 °C. The order of syneresis values for the three types of rice flour was waxy rice flour < Jasmine rice flour < amylose rice flour. The syneresis values and the appearance of starch gels, which had gone through the freeze‐ thaw process, suggested that the order of freeze‐thaw stability of gels for the three types of rice flour was waxy > Jasmine > amylose rice flour.     

Tapioca-Fish and Tapioca-Peanut Snacks by Twin-Screw Extrusion and Deep-Fat Frying

Two half-products were prepared from tapioca starch/catfish fillet-belly flap mince (60:40) and tapioca starch/partially defatted peanut flour (PDPF) (60:40) by twin-screw extrusion. The process variables were temperature in the last two zones of the extruder (90,95,100°C) and screw speeds (100, 250, 400 rpm). Moisture content (40%, wet basis) and feed rate (27 g/min) were held constant. Simultaneously increasing temperature and screw speed resulted in increased expansion, and decreased bulk density and shear strength. Degree of starch gelatinization in half-products ranged from 87 to 95%. Optimum conditions predicted by response surface methodology were: for fish half-products 94–100°C and 220–400 rpm and for peanut half-products, 95–100°C and 230–400 rpm.     

A Comparison between Corn Starch and Dry Milled Corn Products in their Dispersion Properties

Gelatinization of corn starch, flour, meal and grits has been compared. Amylograph curves show differences that can be related to particle size and to constraints on the swelling behavior, presumably due to native protein in the corn milled products. Autoclaving starch and dry milled products at 121 °C in the presence of steam alone merely hardens the particles. However, when the particles are in contact with liquid water, swelling and gelatinization readily occur and gels are formed. Above 10% loading, gels formed by autoclaved grits and meal are significantly more rigid than gels formed from corn starch alone. Flour gives gels of essentially the same properties as the starch up to 30% loading, above which flour gels become more rigid than starch gels and match the gels formed from corn meal and grits.     

Differential Scanning Calorimetry Studies on the Crystallinity of Ageing Wheat Starch Gels

The ageing of wheat starch gels stored at 4°C, 21°C and 30°C was examined by differential scanning calorimetry. Kinetics of the crystallisation process were studied using the Avrami model where it was found that the experimental data fitted the model more satisfactorily when the Avrami exponent was less than unity. At higher storage temperature the starch crystals appeared more symmetrically perfect. Addition of wheat flour pentosans to 50% starch gels did not significantly affect the kinetics of ageing. The extent of crystallisation during the ageing process depends on the moisture content of the starch gel. Crystallinity of the starch gel, measured in the temperature range 306–346°K does not occur if the solids content is below 10% or above 80% and a bell shaped curve is obtained. Reduction of the moisture content of the starch fraction of baked goods either directly or indirectly using materials competing for water, might therefore reduce the staling problem.     

Physico- Chemical Characteristics and Functional Properties of Starch and Dietary Fibre in Grass Pea Seeds

Physico-chemical and functional properties of starch and fibre in raw and processed grass pea seeds were evaluated. Whole grass pea seeds were found to contain 41 % starch and 17% total dietary fibre (2% soluble and 15% insoluble) on dry matter basis. Examination by using scanning electron microscopy revealed oval shaped starch granules with an average width of 17 μm and length of 25 μm. Raw sample had a gelatinization onset temperature of 62°C and two endothermic transition peaks at about 73°C and 94°C, in addition the starch isolated from grass pea flour was shown to have a transition enthalpy (ΔH) of 10 Jg⁻¹. The viscosity of the raw sample (using a Brabender amylograph) reached peak maximum at 80–95°C, decreasing during the 30 min holding time (at 95°C) followed by an increase during cooling to 50°C. Raw whole seed flour was shown to have a water absorption and water solubility index (WSI) of 3 and 16%, respectively. Samples that had been cooked for 60 min had a lower WSI than those cooked for 30 min; this was further reduced in the samples cooked after soaking. The carbohydrate extracted from raw flour was found to be mainly high Mwt carbohydrate (55%), eluted at Kav < 0.2.     

Physico‐chemical and functional properties of starch isolated from ginger spent

Studies were carried out on starch isolated from ginger spent, obtained after the extraction of oleoresin, to explore the possibility of its use as a food ingredient. AM content was found to be 25.5%. SEM showed the granules were disc‐shaped as well as ovoid with a smooth surface. The average granule size was 22.5 ± 3.5 µ in length and 16.9 ± 4.8 µ in width with thickness of ∼3 µ. Ginger spent starch exhibited a high gelatinization temperature (88°C), peak viscosity (678 Brabender units (BU)) and cold paste viscosity (777 BU). It also possessed low paste clarity and higher freeze–thaw stability. Dynamic rheological properties of ginger spent flour, measured using parallel plate geometry showed that the storage modulus (G′) increased and loss modulus (G″) decreased as a function of frequency. Starch from ginger spent flour with high gelatinization temperature and low in vitro starch digestibility (45%) is suitable to use for development of speciality food formulations.     

Thermal Properties of Sorghum Starch

The differential scanning calorimeter (DSC) was used to measure thermal properties of sorghum starch and flour. DSC gelatinization temperatures of 24 nonwaxy sorghum varieties were: T_o (onset temperature): 71.0 ± 1.0°C; T_p (peak temperature): 75.6 ± 0.9°C and T_e (end temperature): 81.1 ± 1.1°C, respectively. The gelatinization energies ranged from 2.51 to 3.96 cal/g. There were no consistent relationships between DSC gelatinization temperatures or gelatinization energies and grain characteristics or physicochemical starch properties. DSC gelatinization temperature for nonwaxy, heterowaxy and waxy sorghum tended to increase as the number of waxy alleles (wx) increased. However, it appeared that at least a difference of two waxy alleles was required before differences in thermal properties of the samples were significant.     

Technological Assessment of Chestnut Flour Doughs Regarding to Doughs from Other Commercial Flours and Formulations

The technological assessment of chestnut flour doughs was studied using Mixolab® apparatus, establishing a comparison with gluten (soft, hard and whole wheat) and gluten-free (rice and yellow corn) flour doughs as well as corn starch pastrymaking and breadmaking formulations. This equipment measures the torque in function of temperature and time, firstly at 30 °C (mixing curve) and secondly the mixing during heating (4 °C/min up to 90 °C) and cooling (4 °C/min up to 50 °C) steps (complete curve). Different hydrations of doughs ranging from 41.4% to 68.5% (flour basis) were necessary to reach the torque of 1.10?±?0.07 Nm. Parameters of mixing such as water absorption, development time, stability and mixing tolerance index were obtained. Parameters of heating and cooling cycle related to weakening of proteins, gelatinization starch, amylase activity and starch retrogradation as well as range of gelatinization temperatures were also determined. Chestnut flour showed suitable parameters in the mixing stage such as arrival time (1.93?±?0.1 min), stability (12.1?±?0.4 min) and departure time (14.0?±?0.3 min). In the heating cycle, chestnut flour exhibited close behaviour to soft wheat flour with cooking stability of 1.12?±?0.01 min and seems to be suitable for pastrymaking products. Finally, in the cooling cycle the behaviour revealed that products of this flour can present problems of staling and crumbs firmness due to high values (2.88 Nm) of C5 parameter.     

Effects of Fatty Acid Addition on the Physicochemical Properties of Corn Starch

The effect of addition of six fatty acids (stearic, palmitic, myristic, oleic, palmitoleic, and myristoleic acid) on the gelatinization, glass transition, and retrogradation properties of corn starch as well as their complexing abilities with amylose were determined. Differential scanning calorimeter studies reflected that addition of fatty acids caused a 73–89% decrease in the gelatinization enthalpy compared to that of the native starch. Besides amylose-lipid formation, exotherm was determined at the same temperature range with the gelatinization endotherm. As a result, it was suggested that fatty acids complexed with amylose during gelatinization. Fatty acid addition significantly increased the glass transition temperature of starch gel. This was attributed to two reasons: the first is due to the physical cross-linking action of amylose–lipid complexes in starch-water system; the second may be due to the effect of uncomplexed fatty acids on water distribution in the gel structure as a result of their amphiphilic character. Thermal properties of amylose-lipid complexes were compared in order to determine the effect of fatty acid properties. It was found that the shorter chain length and unsaturation favored the complex formation but the complexes formed by longer and saturated fatty acids were more heat stable. Addition of fatty acids resulted in 73–90% and 47–71% reduction in the retrogradation enthalpy compared to native starch gels at 5°C and 21°C, respectively. The reduction in the retrogradation enthalpy was inversely related to the amylose-lipid complexing abilities of the fatty acids and it might be explained by the hindrance effect of uncomplexed fatty acids to the water distribution in the starch gel matrix.     

Enzymatic Hydrolysis of Amaranth Flour — Differential Scanning Calorimetry and Scanning Electron Microscopy Studies

High-protein amaranth flour (HPAF) and carbohydrate rich fraction (CRF) were produced from raw flour in a single-step process using a heat-stable α-amylase preparation. Protein content of flour increased from 15 to about 30 or 39% at liquefaction temperatures of 70 or 90°C, respectively, and 30 min hydrolysis time. CRF exhibited 14–22 DE. Enzymatic action at 70°C increased endotherm temperatures and gelatinization enthalpy of HPAF, in relation to gelatinized flour, as assessed by differential scanning calorimetry (DSC). Hydrolysis at 90°C did not affect significantly (P > 0.05) DSC peak temperature. It is suggested that these changes in DSC performance might result from differences in amount and type of low-molecular weight carbohydrates and residual starch. Scanning electron microscopy (SEM) demonstrated that hydrolysis temperature changed substantially the structural appearance of flour particles. HPAF and CRF might find applications as dry milk extender and sweetener, respectively.     

Physicochemical Characterization of Mexican Cowpea (Vigna unguiculata) Tailing Starch

A physicochemical characterization was made of tailing starch isolated from cowpea (Vigna unguiculata), a legume. Proximate composition was 1.6% protein, 3.1% fiber, 0.7%, 0.6% ash and 94.0% carbohydrates as nitrogen‐free extract. Total dietary fiber content was 14.1%, soluble fiber was 12.1%, and insoluble fiber was 2.0% as determined by the Prosky method. Amylose content was 22.9%. Gelatinization temperature ranged from 73.5°C to 86.3°C, the peak temperature being 79.3°C. Gelatinization enthalpy was 12.9 J/g. Swelling power ranged from 6.1 g water per gram starch at 60°C to 26.3 g water per gram starch at 90°C. Solubility, analyzed within the same temperature interval, ranged from 4.3% to 23%. Water absorption capacity was 5.8 g water per gram starch at 60°C and 19.4 g water per gram starch at 90°C. Initial pasting temperature was 78°C, breakdown was ‐68 Brabender Units (BU), consistency was 265 BU, and setback was 197 BU. Clarity, expressed as transmittance, was 13.4%. Syneresis in a 6% gel stored for 24 h at 4°C was 6.6% and 22.5% at −10°C. The physicochemical properties of Mexican cowpea tailing starch indicate that it is a good source of dietary fiber which can be included in food systems that require thermal treatments as bakery products.     

Kinetics of Corn Meal Gelatinization at High Temperature and Low Moisture

The kinetics of corn meal starch gelatinization and melting was investigated. At 25% moisture, in the temperature range 110–140°C. Arrhenius equation parameters were determined by two calculable procedures which agreed well. Activation energy for gelatinization was calculated to be approximately 86.2 kJ/g-mole. Further experiments in the moisture range 13.4–34.4% and temperature range 10–165°C. yielded results for endotherm enthalpies and melt temperature which agreed with literature reports.     

Cowpea cooking characteristics as affected by micronisation temperature: a study of the physicochemical and functional properties of starch

Bechuana white cowpeas were micronised to three temperatures (130, 153 and 170 °C). Cooking properties of the cowpea seeds and the role of starch‐related properties were studied. In all cases, micronisation significantly reduced the cooking time and thus the time required for the cowpea seeds to attain a suitably soft texture. This was attributed in part to the significant improvement in rate of water absorption during cooking and starch pre‐gelatinisation, as evidenced by loss of birefringence and increased susceptibility of the cowpea starch to α‐amylase digestion. However, micronisation to 170 °C resulted in a severe deterioration in pasting properties of the cowpea flour, possibly due to starch depolymerisation and/or amylose‐associated crosslinking. Owing to these changes, cowpea seeds micronised to 170 °C required a longer cooking time than the other two micronised samples. Flour prepared from cowpea seeds micronised to 170 °C may have limited starch functionality. Copyright © 2006 Society of Chemical Industry     

Effects of Gelatinization and Gel Storage Conditions on the Formation of Canna Resistant Starch

The effects of gelatinization and gel storage conditions on the formation of canna resistant starch (RS) were investigated. Starch slurries (10%, dwb) were autoclaved at 121?°C for 30, 60, and 120?min. The gels obtained were subsequently stored at different temperatures (4?°C, 30?°C, and 100?°C) and times (0, 1, 3, 5, and 7?days). Analyses of the RS content in gelatinized starch samples in comparison with that in granular starch showed that the RS fraction in granular starch was very high (97.3% w/w); however, nearly all of the RS was thermally unstable, as indicated by a great reduction in RS content (to 1.9% w/w) after cooking at 100?°C for 20?min. The RS contents in gelatinized starch samples were 12.0?C15.9% w/w, which were reduced to 7.9?C10.8% w/w after cooking. Storage of gels resulted in a significant increase in the amount of the thermally stable RS fraction, e.g., a thermally stable RS content of 16.8% w/w was found in the gel sample gelatinized for 120?min and stored at 4?°C for 3?days. This indicated that the ordered structures of the RS portion were tightened under the storage conditions. The gelatinization temperature of canna starch was 72.2?°C, whereas the RS products exhibited two melting temperature ranges, 51.1?C76.3?°C and 163.1?C165.1?°C, indicating that the newly formed crystals were very strong.