Unravelling the migration of bioactive and volatile compounds coupled with water sublimation from grapes to recovered water during dynamic freeze-drying

The production of raisins by freeze-drying (FD) generates large volumes of water removed from fresh grapes, which contains antioxidant-active substances and volatile aromatic compounds. The migration pattern of those compounds and their interaction with water during dynamic FD was investigated, and results revealed that the free and weakly bound water in grape tissues gradually reduced as internal pores formed. Through high-performance liquid chromatography characterization, the concentration of total phenolic compounds in the recovered water peaked around 3 mg/L at 60 h, alongside the identification of key volatile compounds such as linalool and ethyl butyrate. The migration of these compounds was closely linked to the moisture decrease in the grapes, suggesting that the water sublimation facilitated the transfer of beneficial compounds to the recovered water. This study provides theoretical foundation for utilizing recovered water as value-added resource in food industry.