Hydrothermal treatments of two cowpea (Vigna unguiculata L. Walp) varieties: effect of micronisation on physicochemical and structural characteristics

The effects of a hydrothermal treatment consisting of tempering (to 41% moisture) and heating to 153 °C (micronisation) on the structural and physicochemical characteristics of two cowpea varieties were studied. The untreated varieties had similar cooking times, although cooked Bechuana white cowpeas were significantly (P ≤ 0.05) softer and had a higher incidence of splitting than Var. 462 cowpeas. This may be due in part to differences in cotyledon structure affecting water uptake during cooking. The hydrothermal treatment changed the physical structure and chemical properties of the cowpea seeds. This led to significant (P ≤ 0.05) reductions in the cooking time of micronised Bechuana white and Var. 462 cowpeas, by 47 and 36% respectively, as compared with control samples. Micronisation caused physical fissuring of the seed coat and cotyledon and significantly (P ≤ 0.05) reduced the bulk density of treated seeds. These changes in the physical structure significantly (P ≤ 0.05) improved the initial water uptake during soaking and cooking, increased the enzyme‐susceptible starch and reduced the protein solubility and hydration capacity of the cowpea seeds. Cooked (60 min) micronised cowpeas also had significantly (P ≤ 0.05) more splits and a significantly (P ≤ 0.05) softer texture than control samples. Copyright © 2005 Society of Chemical Industry     

Gamma irradiation of cowpea (Vigna unguiculata L. Walp) seeds: effect on colour,cooking quality and pasting characteristics

Cowpea seeds were treated to various gamma irradiation doses, and their colour, cooking quality and pasting properties studied. Irradiation at 50 kGy resulted in significant browning (indicated by decreases in L colour value) of cowpea seeds. At 2 and 10 (but not at 50) kGy, irradiation led to significant reduction in cooking time of cowpea seeds possibly through irradiation‐induced degradation of starch and pectic substances (indicated by decreases in peak and final viscosities) leading possibly to enhanced heat and mass transfer within the seed cotyledon and cell wall, respectively. At 50 kGy, the cooking time of cowpea seeds was prolonged significantly owing possibly to extensive polymer cross‐linking occurring within the seeds at this high dose. Splitting of cowpea cotyledons during cooking decreased significantly at 50 kGy, but was unaffected at 2 and 10 kGy. Irradiation resulted in significant leaching of nutrients from cowpea seeds during cooking in a dose‐dependent manner.     

Effect of micronisation temperature (130 and 170 °C) on functional properties of cowpea flour

Functional properties of cowpea flour from seeds micronised at two different surface temperatures (130 and 170 °C) were studied. Micronisation (130 and 170 °C) significantly (P ? 0.05) increased the water absorption capacity and least gelation concentration of the flour. The treatment significantly (P ? 0.05) reduced the water solubility and swelling indices, gel strength and foaming capacity of the flour. The changes in cowpea flour functional properties, such as the loss of foaming capacity in flours from micronised (130 and 170 °C) seeds, were associated with significant (P ? 0.05) increase in the surface hydrophobicity and cross-linking of the cowpea protein. SDS–PAGE of the protein-rich fractions revealed changes in the protein subunit profile which included the formation of disulphide bonds and possibly Maillard cross-links. The flour from M-170 °C seeds was significantly (P ? 0.05) darker than was the flour from unmicronised and M-130 °C seeds.     

Effect of Dry Heat Pre-Treatment (Toasting) on the Cooking Time of Cowpeas (Vigna unguiculata L. Walp)

Four cowpea varieties (Brown beans, Oloka beans, IAR48 and IT89KD-288) were toasted at 105 °C, and used to study the effect of dry heat treatment on the cooking time and nutrient composition of cowpea seeds and also its effect on the functional properties of resultant flour of the cowpea seed varieties. Toasting reduced the cooking time for brown and oloka cowpea varieties from 55.00–31.00 and 70.67–51.67 min, respectively. The cooking time for IAR48 and IT89KD-288 cowpea varieties increased from 104.67 to 106.00 and 88.00 to 88.67 min, respectively. The results indicate that the cooking time of cowpea seeds can be reduced significantly on toasting, while maintaining their potential as functional agents in the food industry for nutrition and utilisation. Correlation between the amount of water imbibed by cowpea seeds and their cooking time was -0.74, but was not significant at p ≤ 0.05, suggesting that there is no significant relationship between the amount of water imbibed by cowpea seeds and their cooking time.     

Changes of Selected Physical and Chemical Components in the Development of the Hard-to-Cook Bean Defect

The effects of storage temperature and humidity were monitored on several physical and chemical components of cowpeas and beans. Seeds stored at 29°C, 65% RH required prolonged cooking times; however, seeds stored in other conditions (5°C, 30% RH; 29°C 30% RH; and 5°C, 65% RH) maintained short, stable cooking times throughout storage. As cooking time increased, phytate, phytase activity, amylose solubility, high methoxyl pectin and protein solubility decreased. Solids leached during soaking and low methoxyl pectin increased as cooking time increased. These results were consistent with the proposed theory that the hard-to-cook defect involves interactions between phytate, minerals, and pectin. However, they did not eliminate possible roles of starch and protein solubility.     

Reduction in Lentil Cooking Time Using Micronization: Comparison of 2 Micronization Temperatures

Laird No. 1 lentils micronized (high‐intensity infrared heat) to give internal temperatures of 138 and 170 °C were compared to unprocessed lentils stored at room temperature. Micronized lentils, which had been tempered to 33% moisture for 16 h, required less force to compress after cooking and contained increased levels of gelatinized starch and pectic substances but decreased levels of soluble protein, phytic acid, and neutral detergent fiber compared to the unprocessed lentils. Cell walls in the micronized lentil were less susceptible to fracture, and the microstructure was more open. Properties of the micronized lentils were better when the internal temperature reached 138 °C. When micronized to an internal temperature of 170 °C, cooked lentils were harder, possibly due to greater moisture losses and a change in the neutral detergent fiber. Micronization resulted in a slight darkening of the lentils, and this was accentuated at 170 °C.     

Physico‐Chemical and Structural Characteristics of Vegetables Cooked Under Sous‐Vide,Cook‐Vide,and Conventional Boiling

In this paper, physico‐chemical and structural properties of cut and cooked purple‐flesh potato, green bean pods, and carrots have been studied. Three different cooking methods have been applied: traditional cooking (boiling water at 100 °C), cook‐vide (at 80 and 90 °C) and sous‐vide (at 80 °C and 90 °C). Similar firmness was obtained in potato applying the same cooking time using traditional cooking (100 °C), and cook‐vide and sous‐vide at 90 °C, while in green beans and carrots the application of the sous‐vide (90 °C) required longer cooking times than cook‐vide (90 °C) and traditional cooking (100 °C). Losses in anthocyanins (for purple‐flesh potatoes) and ascorbic acid (for green beans) were higher applying traditional cooking. β‐Carotene extraction increased in carrots with traditional cooking and cook‐vide (P < 0.05). Cryo‐SEM micrographs suggested higher swelling pressure of starch in potatoes cells cooked in contact with water, such as traditional cooking and cook‐vide. Traditional cooking was the most aggressive treatment in green beans because the secondary walls were reduced compared with sous‐vide and cook‐vide. Sous‐vide preserved organelles in the carrot cells, which could explain the lower extraction of β‐carotene compared with cook‐vide and traditional cooking. Sous‐vide cooking of purple‐flesh potato is recommended to maintain its high anthocyanin content. Traditional boiling could be recommended for carrots because increase β‐carotenes availability. For green beans, cook‐vide, and sous‐vide provided products with higher ascorbic acid content.     

Effects of Pre-decortication Drying Treatment on the Microstructure of Cowpea Products

A pretreatment process developed to prepare cowpeas for mechanical decortication by dry abrasion involves wetting, equilibrating, and drying. Drying temperatures of 50°C, 70°C, 90°C, 110°C, and 130^°C affected the microstructure of cowpea seeds, meal and akara (fried cowpea paste). Severe heat treatment damaged the middle lamella of cotyledon cells, changed the birefringence property of starch granules, reduced the amount of air incorporated in whipped paste and produced akara with a nonuniform, dense structure.     

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.     

Effect of cooking time and ingredients on the performance of different starches in white sauces

The effect of white sauce ingredients and increased cooking time at 90 °C on the degree of gelatinization of corn, waxy corn, rice, potato and modified waxy corn starches was studied. The changes in pasting properties, linear viscoelastic properties, and microstructure were determined. In all the native starches in water, a longer cooking time at 90 °C caused greater starch granule swelling and more leaching of solubilized starch polymers into the intergranular space. These effects were more noticeable in the waxy corn and potato starches. The potato starch was the most affected, with complete disruption of the starch granules after 300 s at 90 °C. The microstructural changes which transformed a system characterized by starch granules dispersed in a continuous phase (amylose/amylopectin matrix) into a system with an increase in the continuous phase and a decrease in starch granules were associated with a decrease in system viscoelasticity. The elastic moduli were higher in the sauce than in the starch in water system. However, with the exception of potato starch, the white sauce showed lower viscoelasticity than the starch in water system. The white sauce ingredients decreased the effect of cooking time on the starch gelatinization process, particularly in potato starch.     

Effect of hydrothermal treatment of runner bean (Phaseolus coccineus) seeds and starch isolation on starch digestibility

The study investigated the effect of traditional soaking and cooking, storage after cooking and freezing (? 18 °C, 21 days) and autoclaving of two varieties of runner bean on starch digestibility. Results achieved were compared with digestibility of isolated starch subjected to similar treatments. The digestibility of native starch from Nata var. seeds was lower after isolation than in raw flour. This starch was characterized by a higher content of fat and lower values of swelling power (SP) and amylose leaching (AML). After the thermal treatment, a significantly higher content of rapidly digestible starch (RDS) was observed both in seeds and starch. It was accompanied by reduced contents of resistant starch (RS) and slowly digestible starch (SDS). In flours from cooked seeds, the content of RDS was observed to be higher than in flours from autoclaved seeds, despite similar changes in contents of other constituents (ash and protein). It was probably due to better starch gelatinization owing to the long-lasting soaking of seeds. This resulted in a greater decrease of amylose content of starch compared to the other flours. Differences in SP, AML and thermal properties between starches isolated from two bean varieties had no influence on their digestibility after cooking. The storage of starch pastes at a temperature of ? 18 °C, unlike that of seeds, resulted in a significant increase in RS content, which shows the importance of other flour components in the process of starch retrogradation.     

Effect of Pre-decortication Drying Treatment on the Textural Quality of Cowpea Products: Seeds and Akara

This study describes the influence of a pre-decortication drying treatment on the textural quality of cowpea seeds and akara (fried cowpea paste). Heat-treated seeds were more brittle than the unheated control, but there were no significant differences in seed brittleness among drying temperatures. Akara from the 110°C treatment was less cohesive and required more energy per unit mass to shear and compress than the other samples. Overall, the 50°. 70° and 90°C treatments produced akara that compared favorably in textural quality to the control. Objective textural parameters obtained from either TPA or the Kramer cell method correlated well with sensory measures of texture.     

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.     

Effect of ageing-induced changes in rice physicochemical properties on digestion behaviour following storage

The changes in rice grains structure and digestion behaviours were investigated following storage at 4 °C and 37 °C, respectively. Pasting study indicated that rice samples stored at 37 °C demonstrated a consistent increase in the time to peak viscosity of the Rapid ViscoAnalysis parameters, implying a quick ageing progress. Compared to the rice stored at 4 °C, aged rice (stored at 37 °C) showed a coarser morphology after cooking by SEM, suggesting a limited starch gelatinization. Consistently, ageing process led to a decrease in the leaching of starch molecules in cooking residual water, which further confirmed that starch granules in aged rice grain caused less hydration and swelling. The analysis of the amount of cell wall remnants showed that rice stored at 37 °C caused a significant increase in the amount of cell wall remnants along the storage at 37 °C, which might suggest that the cell wall structure of the rice grains became more lignified because of the ageing. Furthermore, the ageing process significantly reduced rice digestion kinetics both in rate and extent. Thus, it is assumed that ageing process leads to the cell walls becoming more strengthened and lignified, which makes the rice grain more organized in its structure, and subsequently reduces starch granules disruption and molecules leaching during the cooking. Therefore, this study suggests that the changes in digestion behaviours of rice are highly associated with the changes in rice physical and chemical properties occurred during storage and the ageing process might be another option for manipulating rice digestion properties.     

Influence of Extrusion Cooking on In Vitro Digestibility,Physical and Sensory Properties of Brazilian Pine Seeds Flour (Araucaria Angustifolia)

Brazilian pine seeds (pinhão) are gluten‐free products derived from Araucaria angustifolia. The commercialization of these seeds is essentially associated with a low level of industrialization. In this context, extrusion cooking is a potential alternative for preparing extrudates of pinhão as a food product, which can be easily digested and is ready for human consumption. Brazilian pine seeds flour was processed in a single‐screw extruder following a central composite rotatable design. Three factors (independent parameters) were considered: moisture content (14 to 22 g/100 g), screw speed (100 to 250 rpm), and temperature in the 3rd heating zone (120 to 200 °C). The structural characteristics, in vitro digestibility and sensory acceptance were also evaluated. The resistant starch contents is almost reduced to zero after extrusion cooking while the slowly digestible starch content is increased. An increase in moisture positively affected the hardness and the luminosity (L^*), although it negatively affected the volumetric expansion index, crispness, and color parameters (a^*, b^*, and ΔE). The experimental conditions of this study allowed the production of expanded extrudates from Brazilian pine seeds with good expansion, texture properties, and acceptance qualities. Thus, extrusion cooking was found to be a potential method for the industrialization of Brazilian pine seeds as a food product.     

Cell wall modifications during cooking of potatoes and sweet potatoes

Sweet potato (Ipomoea batatas L) tissue, when cooked at 70 °C to activate β‐amylase and break down starch, takes on a distinctive firm, brittle texture and does not show the cell separation that occurs in, for example, cooked potato (Solanum tuberosum L). Similar cooking conditions increase firmness in other plants by activating pectin methyl esterase which de‐esterifies pectic polysaccharides and protects them from thermal depolymerisation. We therefore isolated cell walls from both potatoes and sweet potatoes cooked at 70 °C and 100 °C and determined the remaining degree of methyl esterification of their pectins. Pectins from both species were demethylated to a similar extent at 70 °C and 100 °C. Since cooking sweet potato at 100 °C induced cell separation and softening, it is concluded that β‐amylase is rapidly inactivated at that temperature and swollen starch distends and separates the cells, whereas the firm texture obtained by cooking that species at 70 °C is not the result of pectin demethylation but is caused by the breakdown of starch to oligomers that can escape from the cell. © 2000 Society of Chemical Industry     

Changes in the biochemical and functional properties of the extruded hard‐to‐cook cowpea (Vigna unguiculata L. Walp)

Changes in the biochemical and functional properties of the hard‐to‐cook cowpea bean after treatment by the extrusion process are reported. The extrusion was carried out at 150 °C, with a compression ratio screw of 3:1, a 5‐mm die, and a screw speed of 150 r.p.m. The extrusion caused the complete inactivation of the α‐amylase and lectin and it also reduced the trypsin inhibitor activity (38.2%) and phytic acid content (33.2%). The functional properties were also modified by the process, an increase of 2.5 times in the water absorption index and 3.1% in the water solubility were observed. The digestibility of the hard‐to‐cook flour of the cowpea bean was improved after the extrusion, with a 55.9% increase in protein digestibility and a 5.9% increase in starch digestibility.     

The effects of post-harvest handling on physical,chemical and functional properties of cowpea (Vigna unguiculata) seed

Damage by insects and mould, proximate composition, cooking rate and functional properties of sun-dried and stored cowpea (Vigna unguiculata) seeds were evaluated. Cowpea samples spread between black polythene films were placed on cement (CS), Wooden (WS) and corrugated iron sheet (CIS) surfaces, respectively, and sun-dried for 5 h. Storage lasted 6 months in jute and polythene bags. Results show that sun-drying and storage in polythene bags significantly (p < 0.05) lowered the extent of insect and mould damage, moisture-loss at drying, emulsion activity and stability, foaming capacity and foam stability. Treated cowpea seeds could be stored safely for about 5 months. In contrast, storage in jute bags significantly (p < 0.05) lowered only foam stability. Moisture loss during sun-drying principally lengthened cooking time as storage duration progressed. Therefore, assessment of moisture content before and during storage is a preferred quality index of cowpea seeds stored in polythene bags. © 1999 Society of Chemical Industry     

Effects of time/temperature treatments on potato (Solanum tuberosum) starch: a comparison of isolated starch and starch in situ

Previously, time/temperature treatments of starch have been performed mainly on starch/water systems. In this study the same time/temperature treatments were applied to starch/water systems and to potato starch in situ. Two potato varieties (Solanum tuberosum cultivars Asterix and Bintje) were used. The effect of time/temperature treatments on gelatinisation behaviour was evaluated using differential scanning calorimetry (DSC). A blanching process was simulated by heating samples to 74 °C and then cooling them to 6 °C. A DSC scan showed that starch was completely gelatinised after this treatment. Retrogradation of amylopectin increased during storage at 6 °C from 0 to 24 h after blanching. Annealing of starch, with the aim of altering cooking properties, was performed by heating samples to temperatures below the gelatinisation onset temperature. Treating samples at 50 °C for 24 h caused a shift in gelatinisation onset temperature of 11–12 °C for isolated starch and 7–11 °C for in situ samples. The extent of the annealing effect depended on the difference between onset and annealing temperatures, and prolonged treatment time increased the effect. Starch/water systems and tissue samples behaved similarly when exposed to time/temperature treatments. The most apparent difference was the shift of gelatinisation to higher temperatures in tissue samples. Copyright © 2003 Society of Chemical Industry