Novel pretreatments for vacuum freeze-drying: Effects on the drying process and quality of dried mango cubes

Abstract

Vacuum freeze-drying is one of the primary technologies for producing high-quality fruit and vegetable products. As a critical step, pretreatment significantly affects both the drying process and product quality. This study employed ultrasound (US), electric field (EF), osmotic dehydration (OD), and freeze–thaw (FT) as pretreatments for mangoes before vacuum freeze-drying to systematically explore the differences in their performance. Moisture distribution analysis indicated that FT led to overall water loss, whereas US and OD specifically reduced free water content. Regarding drying rate, US exhibited the most pronounced enhancement. In terms of physicochemical properties, all pretreatments reduced the ΔE between dried and fresh mangoes and caused vitamin C degradation. Notably, the US and FT pretreated dried mangoes exhibited higher contents of both polyphenols and β-carotene, contributing to enhanced antioxidant activity. Microstructural analysis revealed that US maintained intact cell structures with uniform and dense pores; FT caused the most severe cell damage; and OD resulted in the fewest pores. GC-MS analysis demonstrated that all pretreatments reduced volatile flavor compounds, with US and FT achieving better retention. Notably, EF retained the highest levels of terpenoid flavor compounds. An OPLS-DA model (Ry2 = 0.997, Q2 = 0.994) was established and effectively discriminated among pretreatment methods based on volatile flavor profiles. In summary, US demonstrates the best overall performance in drying efficiency, structural preservation, and antioxidant activity, whereas EF shows potential for flavor regulation. In contrast, OD and FT have certain limitations as pretreatments for vacuum freeze-drying.