Development of Crispy, Antioxidant-Rich Sultana Grape Chips via Hybrid Pre-Drying and Explosion Puff Drying

This study aimed to develop high-quality, crispy, and nutritionally enriched chips from frozen Sultana grapes by optimizing pre-drying strategies and explosion puff drying (EPD) parameters. Due to the challenges of drying high-sugar fruits, pre-drying methods, including hot air drying (HAD), microwave drying (MD), and hybrid combinations, were employed to reach specific moisture targets prior to EPD. A hybrid approach, consisting of MD at 360 W to 70% moisture followed by HAD at 60°C to 65%, proved most effective in preserving structural integrity, texture, and antioxidant potential. Subsequent optimization of EPD using a Box-Behnken design demonstrated that puffing temperature and time significantly affected expansion ratio (ER), crispness, adhesiveness, browning index (BI), and antioxidant activity (DPPH). The optimal conditions (104°C puffing temperature, 5 min puffing time, and 76°C system temperature) yielded grape chips with high expansion, enhanced crispness, reduced adhesiveness, and minimal browning (desirability: 0.814). Comprehensive analyses confirmed the superiority of the hybrid pre-drying approach, resulting in lower water activity, improved color preservation (higher L* and lower BI), higher phenolic content and antioxidant activity, and enhanced energy efficiency (higher specific moisture extraction rate [SMER]) compared to single drying methods. Scanning electron microscopy (SEM) observations further revealed a more uniform and porous microstructure, supporting improved puffing behavior and textural quality. In conclusion, this study provides a scalable and energy-efficient drying strategy for producing value-added functional grape snacks and offers a practical framework for applying EPD technology to other high-moisture fruits. PRACTICAL APPLICATIONS: This study presents a scalable strategy for producing high-quality, crispy grape chips from high-moisture fruits using hybrid pre-drying and explosion puff drying. The approach effectively improves texture, color, and antioxidant retention while enhancing energy efficiency. It can be readily integrated into existing industrial drying systems and applied to other sugar-rich fruits. Additionally, it supports the valorization of surplus grapes, contributing to sustainable and value-added food production.