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Shelf Temperature and Depressurisation Strategy Affect Bioactive Retention and Functionality of Freeze-Dried Pumpkin
Daniela Sumczynski1, Libor Červenka2, Helena Velichová1
1Department of Food Analysis and Chemistry, Faculty of Technology, Tomas Bata University in Zlín, Vavrečkova 5669, 760 01 Zlín, Czech Republic.
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.
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