Characterization and modeling of thin layer drying of cocoyam slices

Convective hot air drying of cocoyam slices was investigated at different drying temperature (40 to 90) and slice thickness (2, 4, 6 mm) at an air velocity of. The effect of drying temperature and slice thickness on the drying characteristics and drying time were determined to study the effects of heat on processed cocoyam. Mathematical modeling of the thin layer drying process was performed using eight thin layer drying models. The models were tested for validity using coefficient of determination (), chi square () and root mean square error (RMSE). The effect of the drying temperature on the colour of dried cocoyam was also investigated. The colour was measured using CIE L* a* b* method. The results showed that, increasing the drying air temperature and decreasing slice thickness reduces the drying time of cocoyam. The effective moisture diffusivity increased with increase in drying temperature and the biot number () of cocoyam at temperature of 40 to 70 were less than 0.1 while that of 80 to 90 were in the range of 0.1 <  100. The activation energy obtained at 40 to 90 was 37.92 kJ. The Page model was found to be best fit for the drying kinetics of cocoyam. The largest colour difference was observed at 90 compared to the fresh sample. Increase in temperature reduced the brightness and yellowness of cocoyam

Development and preliminary testing of a bambara groundnut sheller

A centrifugal bambara groundnut pod shelling machine was designed and constructed to crack various sizes and varieties of bambara groundnut. The sheller was fabricated with locally available materials from the formation of a new idea which aimed at easing the pain, stress, intensive labour, time consumption, undue cost and the cumbersome operation encountered in the traditional method of shelling. The machine consists of three main units, namely the hopper, shelling unit and power transmission unit. The sheller uses impact technique and was designed to shell bambara groundnuts effectively and also to eliminate drudgery associated with the traditional methods of shelling legumes. Five hundred (500) samples of sundried bambara groundnuts at 6% (wet basis) which were randomly selected were shelled at an impeller rotation speed of 1636 rpm. The results of the test showed that the shelling efficiency, seed damage, partially shelled pods, unshelled pods and the machine capacity were 83.2%, 17.4%, 7.8%, 9% and 75000 seeds/hr respectively

Physical Properties of African Kidney Bean (Phaseolus vulgaris) Relevant to its Processing

Physical properties of food and bio-materials are required to design systems appropriate for their processing. For this purpose, some physical properties of African kidney bean (Phaseolus vulgaris (L.)), were investigated. Various techniques including the micrometer screw gauge; water displacement; correlation; inclined plane and cone methods, were adopted. Results obtained revealed the sample had a major diameter of 0.982 ± 0.66cm; intermediate diameter of 0.724 ± 0.32cm; minor diameter of 0.716 ± 0.28cm; sphericity of 0.082 ± 0.05cm; roundness of 0.0742 ± 0.07cm; bulk volume of 57.237 ± 0.00cm3; solid volume of 32.0 ± 0.71cm3; bulk density of 0.708 ± 0.00g/cm3; solid density of 1.2659 ± 0.64g/cm3; specific gravity of 1.2659 ± 0.64; porosity of 44.1 ± 1.24%; estimated surface area of 48.750 ± 0.05cm2. Its coefficients of sliding friction on different surfaces were: plastic, 0.13 ± 0.02; plywood, 0.13 ± 0.01; galvanized metal, 0.10 ± 0.01. The sample had a low an angle of repose of 29.43 ± 0.76º from the cone it formed in its natural rest position which indicated that its processing equipments need not be designed to have steep angles in order to have free flow during operations

Effect of moisture content on some mechanical properties of mucuna bean

Some mechanical properties of mucuna bean seed were studied at different moisture levels to provide relevant data for development of cracking machine for the seed. The frictional coefficient of the seed on five structural surfaces (plywood, aluminum, glass, steel, and wood) was determined using the incline plane method. The mechanical properties were determined using a Universal Testing Machine. The coefficients of friction of the seed on the respective structural surfaces were observed to have increased with increasing moisture levels. The force to crack the seed on its major axis decreased from 1595.1 to 244.9N as moisture level increased from 4.79 to 18.53% (dry basis), with a similar trend also observed on the minor axis. The deformation on both axes decreased as moisture level increased. The stress on the major and minor axes respectively increased from 2.79 to 21.61 N/mm2 and 5.12 to 21.01 N/mm2, as moisture level decreased. The force required to crack the seed and energy to break on both axes decreased as moisture level increased. The stress on the major and minor axes increased with moisture level. Regression equations were used to establish relationships between the properties measured and the moisture level of the seed

Influence of ultrasound-pretreated convective drying of Roselle (Hibiscus sabdariffa L) leaves on its drying kinetics and nutritional quality

The drying kinetics and the nutritional qualities of Roselle (Hibiscus sabdariffa L) leaves as affected by ultrasound pretreatment during hot air drying were investigated in this work. Ultrasound frequency and power at 20 kHz and 600 W, respectively, were used for the experiment. Roselle leaves were subjected to ultrasound pretreatment in distilled water for 0 min (untreated), 5 min (UD5), 10 min (UD10) and 15 min (UD15) before hot air drying. The result showed that UD15 samples had about 47% reduction in drying time compared with the untreated samples. The effective moisture diffusivity of the treated and untreated samples ranged from 1.21 to 3.29 × 10−1m2/s. The Page and Logarithmic models best described the drying behavior for the untreated and treated samples respectively. The values of the mass transfer Biot number (ratio of internal mass transfer resistance to external mass transfer resistance) for all the samples ranged from 0.9032 to 1.2391. The samples of UD10 and UD5 had the highest amount of carotenoid and vitamin C contents, respectively, amongst the untreated and treated samples. The total color change of the treated samples were significantly lower than the untreated samples after drying. Drying of Roselle leaves is usually done using convective drying method with its attendant's effects such as long drying time, loss of nutrients and high energy usage. But this work showed that application of ultrasound pretreatment during drying of Roselle leaves can significantly reduce the drying time and at the same time retain the nutritional quality of the dried treated samples