Improving the Drying of Onion Using the Instant Controlled Pressure Drop Technology

Abstract

In the present article, a new manner to use the instant controlled pressure drop (DIC) was adopted in the drying of onion. Instead of using it as a texturing treatment inserted in the second stage of hot air swell-drying operation and performed when water content is less than 30 g H2O/100 g dry matter, here the DIC was performed as a blanching–steaming pretreatment of fresh cut onion, with a steam pressure of 0.2–0.5 MPa, for 5–15 s, and an instant pressure drop (with a rate > 5 MPa s−1) toward a vacuum of 5 kPa. Afterward, drying was carried out with 40°C, 1 m s−1, and 267 Pa partially pressure humidity hot air. Although this DIC treatment aimed to avoid notable expansion, it could intensify mass transfer, reducing the total drying time, which reached 700 min instead of 3200 min for untreated samples; the effective diffusivity and the initial starting accessibility dramatically increased. Consequently, sensorial and nutritional attributes could be preserved with a perfect decontaminated end product.