Abstract: Okras were dried in a vacuum dryer to a moisture content about (5 ± 0.5)% (mf). The drying and quality characteristics of okras were evaluated in terms of moisture content, rehydration ratio, hue angle, total color difference (ΔE) and VC content. In order to achieve faster drying rate along with a high-quality product, the drying conditions, including drying temperature (30 to 70 ℃), system pressure (10 to 50 kPa) and slice thickness (5 to 30 mm) were optimized by response surface methodology based on average drying rate (A-DR) and VC content. Drying models were obtained by the nonlinear fitting of drying curves. In addition, the optimization experiments were carried out based on a second-order central composite rotatable design, and the fuzzy reasoning method was used for sensory evaluation of okra quality under the optimized drying conditions. As a result, moisture content curves of okra during vacuum drying conformed to the Logarithmic model best. Analysis of variance showed that a second-order polynomial model predicted well the experimental data. The drying conditions of 60 ℃ temperature, 18 kPa pressure and 10 mm slice thickness were found optimum for okra vacuum, which resulted in relatively high levels of comprehensive score (0.911), A-DR (1.059 kg/(kg·h)) and VC content (8.315 mg/100 g, md). At the same time, the product dried under the optimum conditions could be accepted by consumers.

Key words: okra, vacuum drying, model, response surface methodology