Process Optimization and Changes in Quality Characteristics of Hot Air Dried Onion Slices (Allium Cepa L.)

Different experimental combinations for onion dehydration process variables i.e. drying temperature, slice thickness and KMS (potassium meta-bisulphate) concentration were tried using BoxBehnken design of experiments. Response surface methodology (RSM) was utilized to research the impact of hot air drying temperature (50, 60 and 70°C), slice thickness (3, 5 and 7 mm), and pretreatment (0.1, 0.3 and 0.5% K2 S2 O5 ) on the responses viz. drying time, color change, pyruvate content, rehydration ratio of the dried onion slices. The drying process was optimized for maximum rehydration ratio, pyruvate content and minimum color change, drying time within experimental range. The optimum operating conditions using selective quality parameters for KMS concentration, slice thickness and drying temperature was 57.31°C, 3 mm and 0.5%, respectively. An analysis of variance exposed that among the process variables, drying temperature followed by thickness of the slice had the most significant effect on all the product responses. Optimum values of the response parameters, in particular the drying time, color change, pyruvate content and rehydration ratio acquired were 671.6 mins, 3.53, 12.93 μmol/g and 4.98, respectively. Organoleptic evaluation was also carried out and it was found that at drying air temperature of 60°C and 3 mm slice thickness, dried onion slices retain maximum color, flavor, and taste and have maximum overall acceptability.