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The effect of some physical and chemical treatments on the functional and pasting characteristics of native tigernut starch (TNNS), native sweet potato starch (SPNS) and blends of tigernut-sweet potato starch were studied. Native tigernut and sweet potato starches were subjected to physical (annealing and heat-moisture) and chemical (acetylation) modifications and compared to tigernut (T)-sweet potato (S) starches blends (T75:S25, T50:S50, T25:S75). Only heat-moisture treatment (THMT) significantly (p ≤ 0.05) increased water absorption capacity of the TNNS while only acetylation significantly (p ≤ 0.05) increased the oil absorption capacity of the native tigernut starch. The bulk density was significantly (p ≤ 0.05) reduced by annealing and acetylation. In addition, TNAS, mixture of blends and SPNS had higher swelling capacity than TNNS. The final and peak viscosities of TNNS, SPNS and all the starch blends were between (217–280 RVU) and (214–395.3 RVU) respectively with SPNS having the highest values, followed by T75:S25 (75% tigernut starch: 25% sweet potato starch) and TNNS in that order. TNNS also had the highest setback viscosity. Samples THMT, TANN and TNAS significantly (p ≤ 0.05) reduced the breakdown viscosity and the pasting temperature. The scanning electron micrograph showed that the native and modified starches of tigernut were similar to those of other starches. Overall, the results showed that many of the pasting characteristics of TNNS were comparable to SPNS, while SPNS had with better functional characteristics.

The influence of stabilizing agent and the drying temperature on the drying characteristics of watermelon puree was carried out in this study. The drying of the foamed watermelon was done in a mechanical dryer at constant temperature ranging from 65 oC - 80 oC and stabilizing agent (carboxyl methylcellulose, CMC) from 0.5 - 2.5%. The drying behaviour of the foam-dried watermelon was expressed based on moisture content, drying rate and drying time while the non-dimensional moisture ratio was fitted into ten (10) existing mathematical thin layer drying models. Also, the effective moisture diffusivity and activation energy were determined using Fick's law of diffusion and Arrhenius type equation respectively. The result shows that the moisture content reduces progressively with time and the time taken to foam dry the watermelon to a specific moisture content increases with decrease in the stabilizing agent and increase in the temperature of the system. The Hii et al model was selected as the best model with averagely high degree of predictability compared to other selected models for the prediction of the drying behaviour of the foam dried watermelon. The value of the effective moisture diffusivity (Deff) of the foam-dried watermelon increased with increase in the drying temperature and decrease in the stabilizing agent from 0.5 - 2.5% while the activation energy ranges between 10 and 14 kJ/mol. [ABSTRACT FROM AUTHOR]

Milling operation is one of the most used size reduction techniques in several household and food processing industries. Optimization of the milling process of a hammer mill that consists of a shaft fitted with 18 swinging hammers and a screen situated below the chamber was carried out using response surface methodology (RSM) with three factors (Moisture content, machine speed, and feed rate) and three responses (Milling efficiency, milling capacity, and particle mean diameter) for two varieties of maize (DMRSTWM and DMRSTYM). Maize sample of known weight was introduced through the hopper to the hammer mill operated at constant machine speed and responses were determined using gravimetric methods. The result shows that the optimum machine performance values for DMRSTWM variety were 92.98%, 94.77 g/s, and 0.28 mm for the milling efficiency, milling capacity and particle mean diameter respectively with 0.966 desirability value while the obtained optimum machine performance values for DMRSTYM variety were 94.85%, 100.96g/s, and 0.29 mm for the milling efficiency, milling capacity and particle mean diameter of the milled product respectively with 0.950 desirability value. To obtain amaximized milling efficiency and milling capacity with a finely milled product the milling machine should be operated at the machine speed of 2964.21 rpm, a feed rate of 180 kg/h and 4.00% moisture content for DMRSTWM varieties and machine speed of 2795.76 rpm, a feed rate of 177.99 kg/h and 4.00% moisture content for DMRSTYM varieties, this findings could be applied in both small and large scale feed and food processing industries. [ABSTRACT FROM AUTHOR]

The effect of drying temperature and microwave power was carried out on the drying characteristics of milled carrot. The milled carrots were dried in laboratory oven (40 - 80 OC) and microwave drying system (180-900W) at constant sample thickness and air velocity of the system. Moisture content, moisture ratio, drying rate and drying time were used to examine the drying characteristics of the milled carrot and the dimensionless moisture ratio was fitted into the ten (10) thin-layer empirical model to properly predict the drying behaviour of milled carrot. In addition, the temperature and power dependence of the effective diffusivity (Deff) coefficient was expressed by an Arrhenius type relationship and the activation energy (Ea) was determined. The initial moisture content of milled carrot was approximately 87.78% ± 0.35 (wet basis) and the result shows that the microwave drying system reduces the drying time of the milled carrot as its drying rate is higher than that of the oven dried sample. The Hii et al model was selected as the best thin layer mathematical model for predicting the drying characteristics of the milled carrot. The effective moisture diffusivity (Deff) of milled carrot increased progressively from 100.49×10-10(m2/s) to 250.16×10-10 (m2/s) as the power increased from 180W to 900W in the microwave drying system and this result is higher than that of the oven dried sample which decreases progressively from 69.01×10-10 (m2/s) to 20.32×10-10 (m2/s) as the temperature decreases. The activation energy ranges between 13.22 - 38.65 kJ/mol for microwave oven and 22.00 to 39.89 kJ/mol for laboratory oven. [ABSTRACT FROM AUTHOR]