Osmotic pretreatment and freeze-drying synergy enhances microbial control and preserves bioactive compounds in blueberries

Drying is a critical postharvest preservation technique that determines the microbial safety, nutritional integrity, and sensory quality of fruits. This study evaluates the influence of osmotic dehydration pretreatment followed by freeze-drying (ODFD) on the physicochemical, microbiological, and functional properties of blueberries (Vaccinium corymbosum). The combined treatment significantly reduced moisture content (from 83.65 ± 0.89% to 19.62 ± 0.78%) and improved microbial control compared to conventional freeze-drying, while maintaining visual and sensory appeal. Although direct freeze-drying retained higher total phenolic and flavonoid levels, ODFD samples exhibited superior anthocyanin retention (7.57 ± 0.15 mg CE/100 g DW) and increased concentrations of key phenolics such as quercetin and malvidin-glucoside. The osmotic pretreatment modulated cell permeability and limited oxidative and enzymatic degradation, contributing to pigment stabilization and enhanced product quality. Moreover, life cycle assessment revealed a 16% lower environmental footprint and 12% cost reduction for the ODFD process compared with freeze-drying alone. These findings demonstrate that osmotic pretreatment prior to freeze-drying is a sustainable and safe dehydration strategy that enhances the functional quality and shelf-life of blueberries while reducing processing energy demand.