From impregnation to drying: Unraveling the complexities of apple processing for enhanced efficiency and product quality

The study’s purpose was to assess ultrasound’s effectiveness in vacuum impregnating apples with ascorbic acid, and to evaluate the effects of drying conditions on ascorbic acid retention. Drying kinetics, water activity, and color of the dried products were also analyzed in relation to drying conditions. Ultrasound (35 kHz, 240 W) was used during individual impregnation phases (30 min) and also throughout the process (70 min). Drying was conducted using free and forced convection (2 m/s) at 40, 50, and 70 °C, and microwave-assisted forced convection (2.45 GHz, 100 W). It was found that ultrasound did not affect impregnation, as a similar content of ascorbic acid was observed in the products regardless of the ultrasound’s phase or duration. Drying conditions significantly influenced drying kinetics and ascorbic acid stability, with higher air temperatures accelerating drying but reducing ascorbic acid content. Excessive ultrasound exposure during impregnation further decreased ascorbic acid content. The most successful method was impregnation under forced convection drying at 50 °C without ultrasound.