Optimization of different pretreatments including blanching, soaking in different concentration of sodium chloride solution and vacuum drying on oil uptake and quality features of deep-fried eggplant

Understanding the relation between different variables affecting deep-fat frying before and during the frying process through the modelling, could be used to set up the optimal conditions for controlling the process that results in improvement of the quality of final fried product. In the present study, the Response Surface Methodology (RSM) and Central Composite Design (CCD) was employed in order to investigate the effects of independent variables including blanching and soaking in different concentration (3, 5 and 7%) of sodium chloride solution as well as vacuum drying (1, 2 and 3 hours) prior to deep-fat-frying and also the effect of frying duration (40, 80 and 120 s) on oil uptake and quality features of deep-fried eggplant. The equations achieved through the examinations revealed that independent variables had significant effect (P < 0.05) on the parameters. Among the studied parameters, vacuum drying was found as the most efficient variable. Moreover, blanching had a significant effect (P < 0.05) on all of the treatments. Although it reduced the oil uptake, caused adverse effects on the quality of the final product such as increasing of shrinkage and colour changes. In conclusion, the optimization of variables showed that samples soaked in 3% sodium chloride solution, dried for 2 hours, and fried for 40 s had the least oil content (1.70 g/1 g of dry matter without oil), moisture content (5.70 g/1 g of dry matter without oil), percentage of shrinkage (32%) and colour changes (ΔE = 25) in comparison with the control sample.