Rheology of Sol-Gel Thermal Transition in Cowpea Flour and Starch Slurry

A thermal scanning rigidity monitor was used to follow rheological changes during heating of cowpea flour and starch slurries. The gelantinization temperature of cowpea starch was in the range 67–78°C. For cowpea flour, in addition to starch gelatinization, a shallow plateau was observed. The starch gelatinization onset temperature shifted from 67°C for starch to 72C for 25% cowpea flour that contained 12–15% starch. The modulus (G′) of cowpea gels increased with flour concentration according to a power relationship. Rigidity of the cowpea starch and flour gels decreased at temperatures higher than 78 and 87°C, respectively.     

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.     

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.     

Firmness of Cowpea Gels as a Function of Moisture and Oil Content, and Storage

Cowpea gels produced using cold-mixed cowpea flour slurry showed large firmness gradients; the gradients were small when the slurries were hot-mixed at 70°C and held for 30–60 min. Firmness of the gels decreased exponentially with fat and moisture contents, and linearly with salt content. Firmness increase during storage could be described by an apparent first-order rate equation; the apparent rate constants followed an Arrhenius-type relationship with an apparent activation energy of about 5 kcal/mol over the range 20–41°C.     

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 Pretreatment on Functional and Nutritional Properties of Cowpea Meal

The efficiency of decorticating cowpeas was improved by hydrating to 25%, then drying to ?10% moisture. Effects of drying temperature (50°, 70°, 90°, 110°, and 130°C) on functional and nutritional properties of cowpea meal were assessed. Extraction rate (yield) was unaffected by heating. Average particle size and water absorption of meal were greatest for intermediate temperatures. Starch was not gelatinized at any temperature. Reduction in protein solubility, which occurred at temperature 90°C., was associated with changes in gel electrophoresis patterns. Protein solubility was negatively correlated with previously reported values for specific gravity and apparent viscosity of cowpea pastes. Increases in drying temperature reduced thiamin content and increased browning of the meal.     

Development And Characterization of Extruded Fura From Mixtures of Pearl Millet and Grain Legumes Flours

Dehulled pearl millet flour (100%) and blends of pearl millet, cowpea, groundnut and soybean flours at 80:20, 70:30 were extruded at 30 g moisture/100 g sample using a Brabender Laboratory single screw extruder to develop extruded fura products. The fura extrudates and fura produced in the traditional way were analyzed for their physical and chemical and sensory properties. There were significant differences (p < 0.05) in the puff ratio of the extruded fura products. Pearl millet: cowpea (80:20) fura had the highest puff ratio (4.71) while the pearl millet: groundnut (80:20) fura had the lowest (2.90). The bulk density of the pulverized extruded fura was lower than that of the dried and pulverized traditional fura. The hydration power of the extrudates increased significantly (p < 0.05) at 28°C and 50°C. Extrusion increased the hydration power of products. Fura extrudate containing 100% pearl millet flour had the highest hydration power of 63.9% at 28°C, while the traditional fura had the lowest of 15.8% at 28°C. Protein content of samples increased with supplementation of pearl millet with grain legumes. Sensory evaluation results showed that there were no significant differences among the fura extrudates and the traditional fura with respect to color, texture and overall acceptability except for flavor. Extruded products were still acceptable after 12 weeks storage in polyethylene and cellophane bags at 30 ± 2°C. Extrusion and supplementation processes are therefore one way of producing a convenient shelf stable nutrient rich fura in the areas where fura is commonly consumed.     

Extrusion of Maize–Cowpea Blends in a Modified Oil Expeller

A laboratory oil expeller was modified by using a press cylinder without openings for expelling the oil. Central composite rotatable design for k=3 was used to study the effects of process variables, cowpea level (0–25%), feed moisture (10–25%) and barrel temperature (130–200°C) on product indices (moisture, expansion index, bulk density, water absorption, extractable solids, swell volume and the degree of gelatinisation of flour from the extrudate). Regression models developed to predict product indices were significant and showed no significant lack of fit. The model for moisture content of the extrudate had an R² of 0·98. Product moisture was influenced by the amount of cowpea in the feed, the temperature of extrusion and feed moisture. Furthermore, the product moisture measured at each cowpea level was dependent on the temperature of extrusion. The model for product expansion index showed that this index decreased with feed moisture and the cowpea level. Regression models for bulk density, water absorption, extractable solids and the maximum swell volume of flour from the extrudate were influenced by the process variables. The degree of gelatinisation decreased with cowpea level and increased with extrusion temperature. © 1997 SCI.     

Sensory and Physicochemical Studies of Thermally Micronized Chickpea (Cicer arietinum) and Green Lentil (Lens culinaris) Flours as Binders in Low‐Fat Beef Burgers

Pulses are known to be nutritious foods but are susceptible to oxidation due to the reaction of lipoxygenase (LOX) with linolenic and linoleic acids which can lead to off flavors caused by the formation of volatile organic compounds (VOCs). Infrared micronization at 130 and 150 °C was investigated as a heat treatment to determine its effect on LOX activity and VOCs of chickpea and green lentil flour. The pulse flours were added to low‐fat beef burgers at 6% and measured for consumer acceptability and physicochemical properties. Micronization at 130 °C significantly decreased LOX activity for both flours. The lentil flour micronized at 150 °C showed a further significant decrease in LOX activity similar to that of the chickpea flour at 150 °C. The lowering of VOCs was accomplished more successfully with micronization at 130 °C for chickpea flour while micronization at 150 °C for the green lentil flour was more effective. Micronization minimally affected the characteristic fatty acid content in each flour but significantly increased omega‐3 and n‐6 fatty acids at 150 °C in burgers with lentil and chickpea flours, respectively. Burgers with green lentil flour micronized at 130 and 150 °C, and chickpea flour micronized at 150 °C were positively associated with acceptability. Micronization did not affect the shear force and cooking losses of the burgers made with both flours. Formulation of low‐fat beef burgers containing 6% micronized gluten‐free binder made from lentil and chickpea flour is possible based on favorable results for physicochemical properties and consumer acceptability.     

Nutritional Quality of Hard-to-cook and Processed Cowpea

Hard-to-cook (HTC) defect was induced in cowpea seeds by storing at 37°C and 85% relative humidity (RH) for 6 wk. HTC and control (stored at 7°C, 60% RH) seeds were boiled for 45 and 90 min or ground to flour. Flour was cooked as paste or extruded (20% H₂O, 150°C). Overall dietary quality was estimated as Feed Efficiency and Relative Response Ratio. Protein quality was determined as Nitrogen Efficiency and Relative Nutritive Value. Overall and protein nutritional quality were generally higher for control than for HTC cowpea diets. Processing affected control and HTC seeds differently. Boiling either control or HTC whole seeds improved both overall and protein quality compared to raw seeds, while extrusion substantially increased the quality of control seeds but reduced the quality of HTC seeds. Cooking as paste improved protein and overall quality of control seeds but not protein quality of HTC seeds.     

Survival of Aspergillus flavus conidiospores and other fungi on cowpeas during long-term storage under various environmental conditions

The survival of fungi naturally present on cowpeas (Vigna unguiculata L. Walp. ssp. unguiculata) as well as Aspergillus flavus (Link ex Fries) inoculated on cowpeas and cowpea flour was monitored over a long-term storage period. The combined effects of water activity (a_w), temperature and atmospheric gas content were evaluated. The a_w (0.66 and 0.44) did not influence survival of A. flavus at 4 and 21°C, where remarkably high viability was observed after 20 months of storage. At 37°C, loss of viability was greater than at 4 or 21°C. A more rapid reduction in the viability of conidiospores was noted at a_w 0.66 than at a_w 0.44, both on whole cowpeas and cowpea flour, when storage was at 37°C under atmospheric gas or vacuum. Total fungi (yeasts and molds) and A. flavus populations maintained highest viability when packaged under an atmosphere of nitrogen. The influence of a_w and temperature on survival of these populations was minimal in cowpeas stored under a nitrogen atmosphere.     

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 pre-heating temperature and formulation on porosity,moisture content,and fat content of fried batters

The effect of pre-heating temperatures on moisture and fat contents, and porosity of fried batters was studied. Batter pre-heated at 60 °C showed higher moisture content, lower fat content and lower porosity than non-pre-heated batter and batters pre-heated at 70 and 80 °C. Moisture content, fat content, and porosity at 4 min frying for batters with different pre-heating treatments ranged from 35.08 to 39.37, 3.92 to 5.16, and 13.14 to 45.31 %, respectively. Because of significant reduction in fat content, 60 °C pre-heating temperature was chosen to study the effect of batter formulations on moisture and fat contents, and porosity. Different wheat to rice flour ratios were prepared, and then each batter was pre-heated at 60 °C. Batters with higher wheat flour content showed higher moisture content, and lower fat content and porosity than batters with higher rice flour.     

The relationship between moisture content and equilibrium relative humidity of five types of wheat flour

There was little difference at 5, 15 and 25°C between the moisture content-equilibrium relative humidity relationships of three types of bread flour and a biscuit flour made from wheat. A flour made from wheat a about 18% moisture content heated to 70°C for about 15 min, had a higher equilibrium relative humidity than the other types.     

Effect of thermal processing on genistein,daidzein and glycitein content in soymilk

Soymilk was subjected to various heat treatments at 95, 121 and 140 °C for various lengths of time. The contents of the aglycones of isoflavone (daidzein, glycitein and genistein) of the soymilk were determined using C₁₈ reversed‐phase high‐performance liquid chromatography. Genistein showed greater stability to heat treatment than daidzein and glycitein. Both the daidzein and glycitein contents decreased rapidly during the early stage of heating, but on continued heating the rates of decrease were much slower. Heating may cause an increase or decrease in the genistein content of soymilk depending on the temperature and time used. Upon heating at 95 and 121 °C, there was an increase in the genistein content in the early stage of heating, possibly due the conversion of genistin to genistein. Heating at 140 °C for more than 15 s and prolonged heating at 95 and 121 °C, however, caused a slow decline in the genistein content. Copyright © 2006 Society of Chemical Industry     

Listeria monocytogenes Inactivation in Turkey Rolls and Battered Chicken Nuggets Subjected to Simulated Commercial Cooking

Cured and uncured turkey rolls inoculted with 10⁷Listeria monocytogenes CFU/g were vacuum packaged and cooked to internal temperatures of 68°C and 74°C, respectively, in a steam-injected chamber. Samples were stored up to 15 wk at 4°C. Battered chicken nuggets were also inoculated internally with about 10⁷L. monocytogenes CFU/ g. Nuggets enclosed in bags were cooked under moist heating conditions in a convection oven to an internal temperature of 71°C. Nuggets were flushed with 30% CO₂, 70% N₂ atmosphere and sealed. Chicken nuggets were stored at 4°C up to 30 days. No Listeria monocytogenes were recovered from the cooked products suggesting that similar commercial processes are adequate to reduce populations of L. monocytogenes below detection limits.     

Functional characterization of flour of selected cowpea (Vigna unguiculata) varieties: canonical discriminant analysis

Characterization of 28 varieties of cowpea flour, based on Brabender pasting properties of flour slurry (12% w/w flour: water), was achieved by canonical discriminant analysis. Pasting viscosities at various points on the amyiogram, pasting temperature and paste viscosity ratios were obtained for each variety of flour. Significant varietal influence on pasting properties was indicated by ANOVA (P<0.01) and MANOVA. The hot paste viscosity at 95 °C (HTPV) and the hot paste capacity index (HPCI) had the highest correlations with the 1st and 2nd canonical variables and together accounted for 78% of total variance in the whole dataset. A plot of the second canonical variable against the 1st canonical variable showed that varieties situated together had HTPV values within close ranges. The hot paste viscosity (HTPV) was the most discriminating paste viscosity and could become an important index of functionality of cowpea flour.     

SPECIFIC HEAT of INDIAN UNLEAVENED FLAT BREAD (CHAPATI) AT VARIOUS STAGES of COOKING

A simple inexpensive calorimeter was built to measure specific heat of foods at various process temperatures. By using vegetable/mineral oil as the heating medium in place of water, specific heat at temperatures beyond 100°C can also be evaluated. Specific heat of whole wheat dough and Chapati (round disc prepared mostly from whole wheat flour dough) at various stages of cooking and puffing were determined. Based on the experimental data a linear equation (C = 2476.56 + 23.56M ? 3.79T_e) is proposed from the experimental data for specific heat of wheat flour, dough, cooked and puffed Chapati and for other food materials at moisture levels ranging from 0.1% to 80% and temperature ranges from 303° to 336° K.     

Kinetics of Protein Quality Change in an Extruded Cowpea-Corn Flour Blend under Varied Steady-State Storage Conditions

The effect of varied steady-state storage conditions on the in vitro protein quality of a 70:30 (w/w %) cowpea and corn flour blend was examined. Losses of FDNB-reactive lysine due to Maillard browning reactions were best described by a first-order model with rate constants ranging from 8.9 × 10^-3 wk^-1 for storage at 25°C and a_w of 0.55 to 25.9 × 10^-3 wk^-1 for storage at 55°C and a_w of 0.65. Browning pigment production was best described by a zero-order model. A linear effect of temperature increase on the rates of lysine loss was observed in the statistical model. Implications for storage of products with similar compositions are discussed.     

Development of weaning food formulations based on malting and roller drying of sorghum and cowpea

Sorghum and cowpea were steeped in water for 16 h, allowed to germinate for 72 and 24 h respectively, then dried to about 14% moisture. Roots and shoots of sorghum sprouts were cleaned off and the devegetated malt was kilned at 70°C, moistened with 3% added water, heaped for about 10 min, milled and sieved to obtain debranned malt flour. Cowpea sprouts were split, dehusked, kilned at 85°C and milled. Malted sorghum and malted cowpea flours were blended in the proportion of 70:30 to prepare the malted weaning food (MWF). A precooked weaning food (RDF) was prepared by roller drying a cold water slurry consisting of 70% pearled sorghum flour and 30% toasted cowpea flour. The cooked paste viscosity of MWF was considerably lower than that of RDF and the blend of raw sorghum (70%) and cowpea (30%), at all comparable slurry concentrations. The protein content of MWF was 13.4% and that of RDF was 13.0%, but the available lysine content of MWF protein was 3.85% and that of RDF protein was 2.95%. The protein efficiency ratio for MWF (2.26) was significantly higher than that for RDF (1.87).