Optimization of minimal thermal treatment conditions for sour cherry (Prunus cerasus L.) juice using ultrasound-ohmic combination treatment

This study aimed to optimize minimal thermal treatment conditions for sour cherry juice using response surface methodology. The effects of ultrasound power (UP; 54, 35, 14 W), ultrasound time (UT; 8, 5, 3 min), ohmic electrical field strength (OE; 40, 30, 20 V/cm) and ohmic time (OT; 8, 5, 3 min) on total phenolic content (TPC), antioxidant activity (AA), color values (L*, a*, b*, $∆E$), total monomeric anthocyanin content (TMAC), polymeric color (PC), color density (CD), polymeric color ratio (PC%), total mesophilic aerobic bacteria (TMAB) and yeast-mold count (YM) were investigated. UP significantly affected TPC, L*, a*, b*, and $∆E$, while OE affected TPC, TMAC, PC, PC%, and TYC. UT affected TPC, L*, AA, CD, PC and PC%, and OT level affected TPC and b* values. The optimum points were determined by considering maximum TPC as 28.7564, maximum AA as 6.7714, maximum TMAC as 4.9616, maximum L* as 21.3839, maximum a* as 5.5396, maximum b* as 3.4260, maximum color density as 27.1412, minimum polymeric color as 17.3148, minimum PC% as 4.9253, minimum TYC as 1.9251 and minimum TMBC as 2.3301. The optimum levels were found to be 54 W, 8 min, 27.06 V/cm and 8 min. Improvements in TPC, TMAC and AA were determined after ultrasound-ohmic combination thermal treatment. Although ohmic (OH) has the effect of maintaining juice quality, its effectiveness is impacted by the electrochemical properties of food. By using ultrasound, the electrical conductivity values of juices were increased; thus, ultrasound improved the electrochemical properties of sour cherry juice. Further studies are needed to evaluate the effects of ultrasound-ohmic combination for juice processing on a large scale.