Infrared heating under optimized conditions enhanced the pasting and swelling behaviour of cowpea starch.

Native starches are not suitable for industrial use and must be modified for improved functionality. In this study, the effect of moisture preconditioning and infrared heating time on physicochemical properties of cowpea starch was investigated using a two-factor central composite rotatable design. Factors (moisture levels:10-40 g/100 g starch and infrared heating time:10-60 min) with their corresponding α mid-point values resulted in 13 experimental runs. Selected functional and pasting properties were determined as response variables. Starch samples produced under optimized conditions were compared with corn starch and their physicochemical properties determined. Except for pasting temperature, cowpea starch prepared using the optimal conditions (moisture: 46.21 g/100 g starch, dry basis and heating time of 32.88 min) had higher functional and pasting properties compared with the native cowpea starch. Infrared heating significantly reduced the gelatinization temperatures of cowpea starch but did not significantly change that of the corn starch. The crystallinity and double-helical order structure of moisture conditioned cowpea starch also reduced after modification. Cowpea starch showed a bigger granule size, higher swelling power but lower water absorption capacities and pasting properties compared with the control. The infrared heating process is a novel and promising modification method for improving the swelling properties of starch.

Physical properties and water absorption kinetics of three varieties of Mucuna beans.

The physical properties and water absorption kinetics of three varieties of Mucuna beans (Mucuna pruriens, Mucuna rajada and Mucuna veracruz) were determined in this study. Physical properties including length, width, thickness, geometric mean diameter, sphericity, porosity, bulk density, area, volume and one thousand seed mass were calculated while hydration kinetics was studied by soaking Mucuna beans in water at 30 °C, 40 °C and 50 °C and measuring water uptake at 9 h interval. Peleg's equation was used to model the hydration characteristics and Arrhenius equation was used to describe the effect of temperature on Peleg's rate constant k1 and to obtain the activation energies for soaking. Significant variations were observed in almost all the physical properties of the different varieties, however, there were no significant differences (p < 0.05) in their thicknesses and bulk densities. The effectiveness of fit of Peleg's model (R2) increased with increase in soaking temperature. Peleg's rate constant k1 decreased with increase in soaking temperature while k2 increased with temperature increase. Activation energies of Mucuna pruriens, Mucuna rajada and Mucuna veracruz were 1613.24 kJ/mol, 747.95 kJ/mol and 2743.64 kJ/mol, respectively. This study provides useful information about the properties of three varieties of Mucuna beans that could be of importance to processors and engineers for process design and optimization.

Structural and functional characteristics of optimised dry-heat-moisture treated cassava flour and starch.

The flexibility of hydrothermal conditions gives rise to an array of effects on the properties of starch-containing systems. This study examined and optimised moisture, temperature and time conditions with regards to functional properties of cassava flour and starch. The derived optimal conditions for cassava flour were 25%, 90 °C and 45 min, respectively, while cassava starch were 27%, 120 °C and 21 min, respectively. Consequently, effect of the optimal conditions on structural, physicochemical, rheological and melting characteristics of cassava flour and starch were studied. Optimal heat-moisture treatments changed both morphology and size distribution of cassava flour and starch granules. Relative crystallinity of cassava flour increased (34 to 40%) and cassava starch decreased (32% to 23%) following optimal-heat-moisture treatment. Both cassava flour and starch upon optimal dry-heat-moisture treatment exhibited enhanced; swelling power (15.57 to 21.62 g/g and 17.24 to 19.64 g/g, respectively), peak viscosity (3555 to 5493 cP and 6377 to 8701 cP, respectively), elasticity (tan δ) (0.31 to 0.24 and 0.58 to 0.47, respectively) and melting onset temperature to conclusion temperature range (14.66 to 15.75 °C and 23.26 to 30.69 °C, respectively). This research presents hydrothermal conditions that can effectively be applied in industry to improve the bakery potentials of cassava flour and starch.

Impact of steam-heat-moisture treatment on structural and functional properties of cassava flour and starch.

In this study, moisture, steam-temperature and time conditions were optimised in relation to functional properties of cassava flour and starch. The optimal conditions for cassava flour were 15% moisture, 120 °C and 1 bar for 10 min and for cassava starch were 19% moisture, 120 °C and 1 bar for 20 min. Structural, physicochemical, viscoelastic and thermal characteristics of cassava flour and starch upon the optimal steam-heat-moisture treatments were examined Volume-based diameter (D(4.3)) of cassava flour granules reduced (107.87 to 42.94 µm) and cassava starch granules increased (17.67 to 50.88 µm) when subjected to optimal steam-heat-moisture treatments. The optimal steam-heat-moisture treatments had no effect on the crystal patterns of cassava flour and starch (A-type), nonetheless, relative crystallinity of cassava flour was increased (34 to 59%) and cassava starch was decreased (32 to 27%). Increments in swelling power (17.24 to 19.07 g/g) and peak viscosity (6377 and 7330 cP) and, reductions in solubility and loss factor (tanδ) were ensued by the optimal steam-heat-moisture treatment of cassava starch. Both optimal steam-heat-moisture treatments of cassava flour and starch had increased thermal stability but reduced breakdown viscosity, setback viscosity (528 to 230 cP and 1259 to 938 cP, respectively) and gelatinisation enthalpy.