Enhancing drying efficiency and quality of seed-used pumpkin using ultrasound, freeze-thawing and blanching pretreatments

•Three pretreatments of seed-used pumpkin before far-infrared drying were established.•Freeze-thawing pretreatment can significantly enhance the drying efficiency.•Blanching pretreatment improved the quality characteristics of seed-used pumpkin.•Ultrasound pretreatment effectively maintained original appearance of samples. Effects of blanching (BL), ultrasound (US) and freeze-thawing (FT) pretreatments prior to far-infrared drying (FIRD) on drying characteristics, water distribution, and quality parameters of seed-used pumpkin (SUP) slices were investigated in this study. US, BL and FT pretreatments significantly accelerated drying rate due to the destruction of cell structure. Modified Page model was the fittest model for predicting the FIRD process. Low field nuclear magnetic resonance (LF-NMR) results revealed that T2 distribution curves of all pretreated samples moved rapidly to the positive x-axis direction, indicating an increase in the rate of water migration. The color of US-FIRD was closer to fresh SUP. BL-FIRD exhibited the highest free polyphenols content (241.28 ± 1.11 mg GAE/100 g DW) and total carotenoids content (129.69 ± 2.49 μg/ g DW), increasing by 45% and 34% respectively compared to the untreated sample.