Synergistic Effect of Ultrasound and Osmotic Pretreatment on the Drying Kinetics and Antioxidant Properties of Satkara (Citrus macroptera): A Novel Preservation Strategy

This study aimed to investigate the effects of combined ultrasound and osmotic pretreatment conditions on the drying kinetics and antioxidant properties, such as total phenolic content (TPC), total flavonoid content (TFC), vitamin C content, and DPPH radical scavenging activity, of dried Citrus macroptera (Satkara) fruits. The fruit slices were immersed in 10% aqueous solutions of sucrose (S), glucose (G), and fructose (F) followed by an ultrasound treatment (40 kHz) for 10, 20, or 30 min. The samples were then dried in a convective oven at 50, 60, or 70 °C and 30% relative humidity with a constant air velocity of 3 m s−1. Four thin-layer kinetic models, namely Page, Newton, Henderson and Pabis, and Logarithmic, were evaluated. Among these, Page was found to be the most suitable model for predicting the drying kinetics. The pretreatment process accelerated the drying process significantly, reducing the drying time up to 6 h. Additionally, the pretreated samples exhibited improved retention of quality attributes, with vitamin C being best preserved in S solutions, TPC in both S and F solutions, TFC in F solutions, and DPPH in all three sugar solutions (S, F, and G). The application of ultrasound during osmotic treatment also had a positive impact on TPC and TFC retention, whereas it presented a negative effect on vitamin C when used for a prolonged duration and a negligible one on the antioxidant capacity. Overall, this study provides a new perspective on the drying kinetics of Satkara fruits, and their respective properties after drying, and being subjected to combined ultrasound and osmotic pretreatment. These findings will contribute to the development of effective and efficient drying methods suitable for industrial applications to produce dried Satkara products with a minimum quality degradation.