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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.