Optimization of the vacuum dehydration of celery (Apium graveolens) using the response surface methodology

The response surface methodology (RSM) was used to optimize the vacuum dehydration conditions of celery. The independent variables were drying temperature (65 to 75 degreesC), vacuum pressure (16 to 20 in Hg) and slice thickness (1 to 3mm). The responses were rehydration ratio, bulk density, final moisture content and over-all acceptability rating. Statistical analysis revealed that temperature, vacuum pressure and slice thickness significantly affected (90% confidence interval) bulk density and final moisture content. Rehydration ratio on the other hand, was affected only by temperature and slice thickness while over-all acceptability rating was not significantly affected by any of the three variables. Contour plots for each of the responses were used to generate an optimum area through superimposition. Model validation was conducted using separate experiments at optimum conditions. Resulting drying curves at optimum conditions showed that vacuum drying of celery occurred in the falling rate period.