Effect of Freeze-Drying Conditions on Antioxidant Compounds of Broccoli

Abstract

The effect freeze-drying conditions, i.e. particle size, use of infrared radiation, and drying air temperature in Atmospheric Freeze-Drying (AFD) or freezing rate in vacuum Freeze-Drying (VFD) on the total selenium content, total polyphenols content and anti-radical power of broccoli was investigated. Two factorial designs were used, with three factors in two levels each one, for each type of freeze-drying. In AFD, the experimental factors were drying air temperature (5°C or 15°C), particle size (1.0 or 1.5 cm equivalent diameter), and use of infrared radiation (IR; yes or no). In VFD, the factors were freezing rate (high: by immersion in liquid nitrogen, low: in a household freezer at -30°C during 24 h), particle size and IR use, in the same levels as for AFD. In AFD, all experimental factors significantly affected the antioxidant properties of broccoli, while in VFD only the total polyphenols content was affected by freezing rate. Both AFD and VFD impaired antioxidant properties of the processed vegetable to different extents; however the content of total polyphenols and Se were considerably higher in broccoli subjected to AFD. Then AFD is an attractive alternative for broccoli preservation since it allows keeping some healthy properties of the vegetable. Finally, this technology seems promising in the functional food industry considering broccoli as raw material for this use.