Enhancing Quality in Ultrasound-Assisted Puffing Drying of Apples: Optimization of Process Parameters and Phenolic Retention Modeling

Abstract The study was aimed at investigating the quality parameters of apple slices dried using ultrasound-assisted puffing drying (UAPD). Using the Box–Behnken response surface methodology, ultrasonic duration (20–40 min), puffing temperature (40–60 °C), and puffing duration (5–15 min) were optimized. Additionally, the effect of these parameters on physicochemical, microstructural, and bioactive properties was investigated. Moderate ultrasonic and puffing conditions (30 min, 50 °C, and 10 min) provided the best balance between tissue, expansion, and total phenolic compounds. Under optimized conditions, the total phenolic compound content reached 3575 ± 177 mg GAE/kg and yielded a result very close to the model prediction with 94.15% accuracy. Ultrasonic pretreatment improved mass transfer, while puffing drying increased porosity and reduced moisture and water activity. However, excessive ultrasound or high puffing temperatures caused phenolic degradation and color darkening. SEM micrographs confirmed the formation of expanded, porous matrices due to cell rupture and vapor expansion. Overall, ultrasonic-assisted puffing drying, when optimized with the response surface methodology, demonstrated the potential to produce crisp apple snacks that preserve nutritional value.