The influences of drying method and metabisulfite pre-treatment on the color, functional properties and phenolic acids contents and bioaccessibility of pumpkin flour

Pumpkin flours were produced by hot-air oven drying or freeze-drying, with or without a pre-treatment with metabisulfite. Freeze-dried pumpkin flour had deep orange color while metabisulfite caused loss of fresh pumpkin color. Freeze-drying let to better functional properties: higher water holding capacity (92 mL 100 g−1), oil binding capacity (314 mL 100 g−1) and synergy with BSA for emulsification. Oven drying and metabisulfite pre-treatment both increased phenolic contents and bioaccessible phenolics (1237, 457 mg of GAE 100 g−1 DW, respectively). The most abundant phenolic acids were p-hydroxybenzoic (0.83-1.68 mg g−1), followed by caffeic acid (0.68-1.28 mg g−1) and chlorogenic acid (0.35-0.92 mg g−1) in all pumpkin flours. Oven-drying and metabisulfite pre-treatment led to higher phenolic acid levels. Oven-dried pumpkin flour without metabisulfite pre-treatment may be more appropriate as a functional and nutritional ingredient.