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Water yam (Dioscorea alata) flour was processed using standard wet milling procedure prior to the extrusion process, which led to the determination of extrudate properties of the flours. A single‐screw extruder (DCE 330, NJ) was used in evaluating the extrudate properties, which included torque, mass flow rate, residence time, specific mechanical energy and expansion ratio of the flours from the water yam samples. The effect of extrusion and process variables: feed moisture content, screw speed and barrel temperature on the extruder torque, residence time, mass flow rate, specific mechanical energy and expansion ratio for the variety were determined and predictive models were also developed using response surface methodology. It was observed that changing the feed moisture content, barrel temperature and screw speed significantly (P < 0.05) affected expansion ratio, torque, mass flow rate, residence time and specific mechanical energy of all the extrudates. Increasing the feed moisture content (18–28% db) and screw speed (80–180 rpm) resulted in a substantial decrease in expansion ratio (46.6%), residence time (27.5%) and specific mechanical energy (83.6%); whereas, increasing the screw speed significantly increased the mass flow rate (64.5%) of extrudates. Regression analysis indicated that screw speed and feed moisture content were the major process variables showing significant (P < 0.05) linear, quadratic and interaction influences on mass flow rate, expansion ratio and specific mechanical energy. PRACTICAL APPLICATIONS This investigation was conducted with a broad intention of enhancing the value of water yam flours and its suitability for incorporation in the production of noodle‐like products. This was accomplished by varying the feed moisture content, screw speed and barrel temperature, and determining their effects on resulting extrudate properties.

The thin layer drying behaviour of tomato slices dried using hybrid drying method as well as solar and open sun drying was investigated. Six thin layer drying models (Page, Logarithmic, Henderson and Pabis, Newton (Lewis), Wang and Singh and Parabolic) were used to optimize the goodness of fit to the experimental data. The models were compared using coefficient of determination (R 2), chi-square ( 2) and root mean square error (RMSE). The tomato slice dried faster when subjected to hybrid drying method compared to other methods. Tomato slices of 4, 6 and 8 mm thicknesses were dried from 94.22 to 10% (wet basis), for 300, 360, 420 minutes respectively in hybrid drying method. However, it took 420, 510, 600 and 510, 630, 840 min in solar and open sun drying respectively. The drying took place only in a falling rate drying period. The Page model was found to fit the experimental data better as compared to other models. The effective moisture diffusivity values were found to be between 2.00 x 10-10 and 5.84 x 10-10 m 2 /s in hybrid dried slices, 1.37 x 10-10 and 4.40 x 10-10 m 2 /s in solar dried slices and 1.33 x 10-10 and 4.01 x 10-10 m 2 /s in open sun dried tomato slices of 4 to 8 mm thicknesses. The results of these measures have confirmed the consistency of the developed model to describe satisfactorily the thin-layer hybrid, solar and open sun drying characteristics of tomato slices.

The effect of fermentation on physicochemical properties and oxalate content of cocoyam (Colocasia esculenta) flour was evaluated. The cocoyam, white flesh was cleaned, washed, peeled, sliced into chips of 2-2.5 cm thickness, soaked in tap water and left to ferment for 24 h and 48 h. The fermented cocoyam was then drained, dried in cabinet dryer at 60• C for 24 h and milled. The flour samples were passed through a 45 µm mesh size sieve. Unfermented cocoyam flour was also produced and served as a control. Calcium oxalate and some physicochemical properties of flours from the fermented cocoyam were compared with the unfermented flour. Results showed that fermentation effected a significant reduction in oxalate level (58 to 65%) depending on the fermentation period. The amylose content was higher in 48 h fermented flour (55.52%) than in 24 h (54.55%). Pasting (gelatinization) temperature decreased, and water absorption capacity increased markedly due to fermentation.

The thin layer drying behaviour of tomato slices dried using microwave power densities of 1.13, 2.08 and 3.11 W/g combined with air ventilation (50°C) and hot air drying at 40, 50, 70 and 80°C was investigated. The tomato slice dried faster when subjected to microwave heating coupled with hot air ventilation. Drying time decreased considerably with increase in microwave power density and with increase in hot air temperature. Drying took place in a constant rate period followed by the falling rate period after a short heating period. The drying data were fitted to Newton (Lewis), Page, Henderson and Pabis, Logarithmic, Wang and Singh and Parabolic equations. The Parabolic model (R2 = 0.9999; χ2 = 0.0085; MBE = 0.0182 and RMSE = 0.0691) gave the best fit to predict the hot air ventilation drying of tomato slices while the Logarithmic model (R2 = 0.9951; χ2 = 0.0024; MBE = −0.0319 and RMSE = 0.0477) gave the best fit for microwave-assisted hot air drying of tomato slices. The values of the effective diffusivity coefficients of the tomato slices varied between 1.68 × 10–9 and 5.22 × 10–8 m2/s while the activation energy was 27.09 kJ/mol. The lower activation energy indicates that drying of tomato slices requires less energy and is hence a cost and energy-saving method. Microwave drying at 1.13 and 2.08 W/g maintained superior colour quality of the tomato slices.

The optimization of processing parameters for hot air drying of tomato slices using the Taguchi technique was investigated. The tomato samples were water blanched, ascorbic acid (ASA), and sodium metabisulfite pretreated. Thereafter sliced into 4, 6, and 8 mm thickness and dried at 40, 50, and 60°C air temperatures following Taguchi's experimental plan. The drying rate, effective moisture diffusivity, lycopene, β‐carotene, and ASA contents were determined using standard methods. The results showed reductions in drying time as drying temperatures increases. The drying rate curves show the absence of a constant‐rate drying rate period in the entire drying process combinations understudied. The Taguchi analysis shows that the optimum processing conditions for the dried qualities varied significantly (p < .05). The drying temperature is the most significant processing parameter controlling the drying time, lycopene, β‐carotene, and ASA while the slice thickness had a considerable influence on moisture diffusivity. Practical Applications The processing conditions for drying tomatoes have a significant effect on the nutrient contents of the dried products. However, the quest for healthy dried tomato products by consumers necessitates the simulation and further optimization of the drying conditions to minimize the detrimental qualities changes that occur during the drying process. Taguchi technique, a powerful and efficient method for designing processes that operate consistently and optimally over varieties of conditions is, thus, adopted to established optimum processing conditions that can guarantee high nutrients retentions. These results will provide information valuable to the pilot or industrial scale processors and also served as an operational guide for the tomato fruit drying process.