Cooperative optimization of sea buckthorn (Hippophae rhamnoides L.) drying via pulsed vacuum variable-temperature technique: Balancing energy consumption and product quality

This study proposes a three-stage variable temperature strategy for pulsed vacuum drying (PVD) of sea buckthorn to investigate the effects of different stage parameters on drying kinetics, microstructure, and quality attributes, thereby addressing the challenges of high specific energy consumption (SEC) and significant degradation of thermosensitive components associated with conventional constant-temperature drying of sea buckthorn. In the early stage, the high temperature of 80°C rapidly removed free water and established an inward-high and outward-low moisture gradient. The resulting micro-channels, together with the elevated temperature, collectively accelerated the drying rate. Compared to constant-temperature drying at 70°C, this strategy resulted in a notable reduction in drying time and SEC, alongside a significant improvement in vitamin C (VC) retention. During the middle stage at temperatures of 65 to 75°C, it is conducive to inhibiting the decomposition of heat-sensitive components under the condition of reduced internal moisture. The highest VC retention during the middle stage was observed at 70°C. During the last stage, temperatures of 60 to 70°C effectively mitigated structural collapse. Although this temperature range resulted in increased SEC compared to drying at 80°C, it produced marked improvements in the retention of VC, total flavonoid content (TFC), and total phenolic content (TPC). Extending the vacuum holding time from 5 min to 15 min significantly reduced browning degree (BD), markedly increased TFC, TPC, VC, and substantially decreased SEC. Meanwhile, prolonging the atmospheric pressure holding time from 3 min to 9 min notably reduced SEC but exacerbated oxidative nutrient loss due to prolonged air exposure. Principal component analysis (PCA) determined the optimal parameters, with the highest comprehensive score (10.67) achieved when the early stage was set to 80°C. Model calculations recommended the following optimized parameters: Early stage drying temperature: 80°C; middle stage: 70–75°C; last stage: 65–70°C; vacuum holding time: 15 min; atmospheric pressure holding time: 3 min. This variable temperature strategy in PVD stage-controlled drying effectively balances energy consumption and product quality, providing a valuable framework for future sea buckthorn drying research. • Proposes a novel three-stage variable-parameter PVD model for sea buckthorn. • Variable-temperature PVD lowers energy use and boosts sea buckthorn quality. • Greater pulsation ratio improve sea buckthorn drying efficiency and quality. • Achieved the coordinated optimization of drying energy consumption and quality. • Lab-scale findings lack key industrial translation data such as detailed energy cost.