Ultrasound assisted immersion freezing of broccoli (Brassica oleracea L. var. botrytis L.)

• The freezing time and quality of broccoli subjected to UAF were studied.
• Ultrasound acoustic intensity within 0.250–0.412 W/cm2 was optimal for broccoli freezing.
• UAF decreased the freezing time within 0.250–0.412 W/cm2 acoustic intensity levels.
• Microstructure, physical and chemical quality of broccoli were better preserved by UAF.
• Outside that acoustic intensity range, the quality of the frozen broccoli was inferior.

Objective: The aim of this study was to research the ultrasound-assisted freezing (UAF) of broccoli.Methods: CaCl2 solution was used as freezing medium. The comparative advantage of using UAF over normal freezing on the freezing time, cell-wall bound calcium to total calcium ratio, textural properties, color, drip loss and l-ascorbic acid contents was evaluated.Results: The application of UAF at selected acoustic intensity with a range of 0.250–0.412 W/cm2 decreased the freezing time and the loss of cell-wall bound calcium content. Compared to normal freezing, the values of textural properties, color, l-ascorbic acid content were better preserved and the drip loss was significantly minimized by the application of UAF. However, when outside that range of acoustic intensity, the quality of the ultrasound-assisted frozen broccoli was inferior compared to that of the normally frozen samples.Conclusions: Selected the appropriate acoustic intensity was very important for the application of UAF.