The effect of brine temperature (20, 30, 40 and 50°C) on the osmotic drying behaviour of shark slabs (10 · 5 · 1 cm) in saturated (100°) brine was investigated. The parameters investigated were weight reduction, water loss, salt gain and water activity. Salt uptake and moisture data were analysed using various mathematical solutions based on Fick's Law of Diffusion and the effective diffusion coefficients were predicted after considering the process variables. The expressions presented by Azuara et al. (1992), based on the model presented by Crank (1975), were successfully used to predict the equilibrium point and to calculate diffusion coefficients at not only the initial stages of dehydration, but also at different times during the osmotic process.

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The objectives of this study were to investigate the effect of temperature (40, 50, 60, and 70°C), and air velocity (0.5, 1, and 2 m/s) on the drying behavior of West Indian lemongrass (Cymbopogan citratus) leaves. Drying was carried out in a computer‐controlled tray dryer. Overall, the effect of temperature was seen to be more important than that of air velocity, but the air velocity did have an effect on drying rates at the start of the drying process at 50–70°C. Drying rate constants, diffusivity values, and activation energy were determined. Twenty‐two empirical and semiempirical thin‐layer models were tested, and although model fit varied, the Midilli model could be applied to all data with reasonable prediction of MR values.

Pumpkin seeds are a major agricultural waste from the fresh-cut produce industry. The objective of this study was to investigate the drying behavior of untreated, whole pumpkin seeds in a fluidized bed dryer at 50–80 °C (2.87 m/s), with a view to producing a high-quality pumpkin powder from dried seeds. Seeds were dried at 50–80 °C to an average equilibrium moisture value of 0.035 to 0.006 g H2O/g DM (3.4 to 0.6% wb). Drying occurred in the falling rate period only and drying rate constants ranged from 0.0226 to 0.0900 1/min with corresponding diffusivity values for the first falling-rate period ranging from 4.68 to 18.63 × 10−10 m2/s. The activation energy (Ea)—for the first falling rate period was determined to be 43.9 kJ/mol. Of the nineteen thin layer models tested, the Alibas model could be successfully used as a general model to predict the Moisture Ratio (MR) data for all temperatures investigated. After drying, seeds were blended to produce powders, which were found to be high in fat, crude protein and fiber.

The effect of temperature (35, 50, and 60°C) on the rehydration behavior of microwave‐dried amaranth (Amaranthus dubius) leaves was investigated. Leaves were dried at 700 W power level before rehydrating in water. The higher the rehydration temperature, the higher the equilibrium moisture content of the leaves, although the effect was not statistically significant. The increase in rehydration ratio was significant only as temperature increased from 50 to 60°C. The process was adequately described by the Peleg sorption model, with the Peleg rate constant (K 1) and the Peleg capacity constant (K 2), both decreasing as rehydration temperature increased. While the color difference (ΔE) between fresh leaves and leaves rehydrated at 35°C was significantly higher than for the leaves rehydrated at 50 and 60°C, this difference was not visible. Cooking of leaves occurred beyond 120 min at the higher rehydration temperatures . Based on the results, rehydration of microwave‐dried leaves was successfully carried out at 35°C, however, rehydrated leaves were darker than the fresh leaves. Increasing the temperature to 50°C improved the rehydration capacity and the color of the leaves, however, cooking of leaves occurred by the second hour of the process.

The effect of air temperature on the drying behavior of unsalted and salted catfish (Arius sp.) slabs (10 × 5 × 1 cm) was investigated. Drying at 30 and 40C occurred in both the constant rate and falling rate periods, while drying at 50 and 60C occurred in the falling rate period only. Drying rate constants increased from 0.0474 to 0.2352 1/h for unsalted slabs and from 0.0819 to 0.3038 1/h for salted slabs as drying temperature increased from 30 to 60C. Diffusion coefficients increased from 1.61 to 5.79 × 10 -10 m 2 /s in unsalted slabs and from 2.31 to 8.55 × 10 -10 m 2 /s in salted slabs. Six mathematical thin layer drying models were applied to the moisture ratio data and the two-term model gave the best prediction. The rehydration ratio averaged 1.20 and 1.22 for unsalted and salted slabs, respectively. A drying temperature of 50C for 8 h is recommended. PRACTICAL APPLICATIONSDrying of both fresh and salted fish continues to be of importance in many developing countries as a preservation method. In the Caribbean region, dried, salted fish remains a very popular part of the cuisine due to the flavor, and many imported brands dominate the supermarket shelves due to the poor inferior sensory characteristics and keeping quality of locally produced salted fish. Improvement in the drying methods for local and regional fish types requires a better understanding of the drying mechanisms and how drying is affected by various controllable factors. The present work seeks to investigate the drying of locally available catfish (Arius sp.). It focuses on the interaction between process conditions, drying kinetics and product quality to arrive at clear conclusions which can facilitate the improved production of dried, salted catfish fillets and which can be beneficial to the industry.for animal feeding (Waterman 1976;Fellows and Hampton 1992). In order to prevent spoilage, the moisture content of fish needs to be reduced to 25% or lower depending upon the oiliness of the fish (Fellows and Hampton 1992). Salting of fish before drying has been traditionally used to improve the shelf life and impart flavor. Salted dried fish having moisture contents in the range of 35-40% (wb) and salt contents in the range of 15-20% (wb) will have a minimum good quality storage life of 3 weeks to 2 months (FAO 1981).The main considerations in any drying process are to produce a dried product in the shortest possible time, with the lowest negative impact on product quality, using the

The effect of microwave power level (200, 500, 700 and 1000W) on the drying behaviour of amaranth (Amaranthus dubius) leaves was investigated. Higher microwave power levels effected faster drying and there was an increase in drying rate constant (k) as microwave power level increased from 200 to 1000W and an increase in diffusivity (D eff ) values from 3.04 x 10 -10 to 2.82 x 10 -9 m 2 /s. Leaves dried at 1000W power level however showed noticeable scorching after 540s of drying. Drying at the lower microwave power levels occurred in the constant and falling rate period, while at the higher power levels drying occurred in the falling rate period after an initial warm-up phase. Amaranth leaves could be dried at 700W power from an initial moisture content of 6.00 g H 2 O/g DM (85.7% wb) to 0.08 g H 2 O/g DM (7.6% wb) in 11.5 min. Overall, of the twenty-two thin layer models applied to the MR data, the Alibas model gave the best fit in terms of both the root mean square error (RMSE) and the chi-square statistic ( 2 ).

This work investigated the technique of vacuum freeze drying of avocado pulp (Persea americana var. Pollock) to produce a dried cake which could be blended into a powder to be used in various food applications. Frozen, mashed avocado pulp samples were dried in a Benhay SB-4 vacuum freeze dryer. For comparison, fresh pulp samples were also oven-dried in a Unitemp drying cabinet at 60°C. Samples were dried until constant weight was achieved after which they were blended into powders and analysed. Analyses included determination of moisture content, water activity, pH and total soluble solids content, colour assessment, proximate analyses, physical properties, rehydration behaviour and a preliminary storage assessment. Drying data was used to generate rate and Moisture Ratio (MR) curves and thin layer models applied to the MR data. The moisture content and water activity values of the fresh pulp averaged 3.16 g H2O/g dry matter (76.0% wet basis) and 0.889, respectively. Samples were successfully dried in the freeze dryer to an average moisture content of 0.02 g H2O/g dry matter (2.1% wet basis) after 72h, and a final average water activity of 0.356. Drying occurred in the falling rate period and the drying rate constant (k1) averaged 0.2496 1/h. The Verma model was found to best fit the Moisture Ratio (MR) data. Compared with oven-dried samples, the freezedried samples dried to lower equilibrium moisture values, did not show any signs of browning and was higher in protein and fat content. The freeze-dried 'cake' was easier to blend to a light, free-flowing powder which easily rehydrated to a form which closely resembled fresh avocado puree. Freeze drying is therefore an attractive option to produce a high-quality Pollock avocado powder, without the use of heat or the application of chemical preservatives to preserve colour.