Thermosonication as pretreatment for improving drying kinetics of black grape: An optimization study

Abstract

In the present study, the thermosonication pre-treatment conditions were optimized using response surface methodology to improve the drying kinetics of the black grapes. The drying performance outputs of the optimum thermosonication conditions and potash solution were also compared for the first time. The quadratic model is the best mathematical model to predict the effect of thermosonication conditions on the drying rate, total monomeric anthocyanin-(TMAC), and total phenolic-(TPC) contents of the grape samples. Based on the goals and limitations of the studied variables (ultrasound energy density-UED, temperature, TPC, TMAC, and drying rate), the optimum thermosonication conditions were calculated as 743.1 J/g UED and 16.6 °C. The validation study findings indicated that the mathematical model of drying rate, TMAC, and TPC can be used in the prediction due to low relative error values (5.6–7.0 %). The optimum ultrasound pre-treatment reduced 32 % the drying time compared to the untreated samples. The water diffusion coefficient-(D_eff) was calculated as 0.589 × 10⁻¹⁰, 0.891 × 10⁻¹⁰, and 1.404 × 10⁻¹⁰ m²/s for the untreated, pre-treated with the optimum ultrasound conditions and potash solution, respectively. These results highlighted that thermosonication can reduce drying time of grapes, operational cost, and environmental pollution, which reveals the potential application of ultrasound technology instead of the chemical potash treatment.