Process of Modeling and Optimizing the Osmotic Dehydration Pre-treatment of Okra Drying
Keywords:drying rate; duration; hot-air dryer; model equations; temperature; quality parameters
Okra [Abelmoschuscaillei (A. Chev.) Stevels] drying was studied by a factorial experiment under randomized complete block design using a laboratory-scale hot-air dryer. Two osmotic solution concentrations (40 and 60 oBrix of sucrose), three osmotic process durations (60, 120 and 180 min) and four drying temperatures (50, 60, 70 and 80 oC) were considered with each trial conducted in triplicates. Drying rate was determined as the ratio of change in mass of okra to the change in drying time as drying progresses. The ash content, crude fibre, crude fat, crude protein, bulk density, least gelation concentration and water absorption capacity were investigated as quality parameters. Model equations were developed using Essential Regression (ESSREG) analysis and Statistical Package for Social Sciences (SPSS) to relate output parameters to process variables. The results showed that an optimum drying rate of 16.69 g/h could be achieved by subjecting okra to osmotic dehydration pretreatment using a solution of 40 oBrix sucrose for 149.10 min and dried with a temperature of 80 oC. The ash content of 3.76% could be obtained at 40 oBrix, 180 min and 50 oC. An optimum value of 29.65% was obtained for crude fibre at an osmotic solution concentration of 60 °Brix, osmotic process duration of 180 min and drying temperature of 80 oC. Crude fat content of okra has 4.03% as its optimum value and this corresponds to a combination of 60 oBrix osmotic solution concentration, 180 min osmotic process duration and 74.60 oC drying temperature. An osmotic solution concentration of 60 °Brix, osmotic process duration of 60 min and drying temperature of 80 oC should be selected to give the optimum crude protein of 14.12%. Predicted values of drying rate, ash content, crude fibre, crude fat, crude protein and water absorption capacity (WAC) compared favourably with the observed values. This implies the models reliably predicted the drying characteristics of okra very well in terms of these output parameters. It could be inferred from this study that the drying process of okra can be optimized under different drying conditions. Further studies should be carried out on the factors that affect the storability of dried okra for long-time storage and preservation. An investigation into the use of sodium chloride for osmotic dehydration pretreatment as a means of improving the post-drying palatability of okra should be considered for further study.
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