Shelf Temperature and Depressurisation Strategy Affect Bioactive Retention and Functionality of Freeze-Dried Pumpkin Powder

Background: Pumpkin is a source of phenolics and carotenoids, but their retention during freeze-drying may depend on the drying programme. Methods: Pumpkin flesh was freeze-dried using two schedules: a stepwise schedule (SWS; gradual pressure decrease and shelf heating) or a rapid schedule (RS; deep vacuum and direct shelf heating). Final shelf temperatures of 20, 30 and 40 °C were tested. The powders were analysed for phenolic and carotenoid profiles, residual moisture, colour and basic powder functionality. Results: RS produced lower residual moisture (4.7–5.4%) than SWS (6.2–8.8%). Flowability remained poor but improved at higher shelf temperatures. Water-holding capacity increased, while swelling decreased. Higher levels of protocatechuic acid (121–130 μg/g dry weight), (-)-epicatechin (36–39 μg/g dry weight), and ethyl protocatechuate (7.7–8.8 μg/g dry weight) were determined in samples dried at the lowest shelf temperature, regardless of the drying schedule. SWS30 and SWS40 were associated with caffeic acid, syringic acid and trans-2-hydroxycinnamic acid, and all SWS samples had higher quercetin content. RS gave higher carotenoid levels at 20 °C, while responses at 30 and 40 °C depended on the compound. Conclusions: Final shelf temperature and drying schedule affected antioxidant retention and functional properties of pumpkin powder.