Physical Pretreatments to Enhance Purple-Fleshed Potatoes Drying: Effects of Blanching, Ohmic Heating and Ultrasound Pretreatments on Quality Attributes


In this study, it was aimed to investigate alternative pretreatment solutions including blanching, ultrasound and ohmic heating to limit the adverse effects of drying conditions on the functional properties of purple-fleshed potato (PFP). In order to investigate how functional properties were saved with pretreatments carried before drying, treatment-specific operational conditions were studied for each method. Control drying (drying of potato slices without any pretreatment) was used for comparison. Thus, whether the pretreatment created any considerable change in the functional properties of potato samples was evaluated. Voltage gradients of 20 and 40 V/cm and application times of 2 and 4 min were the studied operational conditions of ohmic heating, whereas ultrasound amplitude levels of 50% and 100% were used with the same application time values. For the blanching process, potato slices were dipped in the boiling water and kept for 2 min. Results showed that the drying time of PFP was independent of pretreatments. Total phenolic content, antioxidant activity (DPPH and ABTS) and anthocyanin content of potato slices subjected to low amplitude short-term ultrasound pretreatment were found to be higher than the corresponding values of the control group. Also, the total phenolic and anthocyanin contents of potato samples treated before drying by ohmic heating at a high electric field (40 V/cm) for 4 min were better than the control samples. The closest colour values to fresh potato were obtained on the samples pretreated by ultrasound application (US-50/2). Depending on pretreatments, any significant change in the rehydration ratio of dried PFP was observed. Also, FTIR spectroscopy with chemometric analyses was studied and results indicated that ohmic heating and ultrasound treatments revealed high potential as innovative pretreatments applied before drying of PFP slices and they were superior with respect to control one.