Recovery of aqueous phase of broccoli obtained by MHG technique for development of hydrogels with antioxidant properties

Natural and blanched broccoli were processed by microwave hydrodiffusion-gravity (MHG) for recovering their bioactive liquid phases. The corresponding phenolic content, antioxidant properties, colour and energy requirements were evaluated. Functional hydrogels characterised mechanically were formulated with selected bioactive liquid phases. Results indicated that liquid phases obtained from natural and from blanched broccoli using MHG at 300 W exhibited the highest bioactive content (about 0.15 and 0.34 mg GAE/g broccoli dry weight, respectively). The blanched treatment promoted the bioactive compounds extraction (around 18 mg extract/g blanched sample dry weight) without notably modifying the colour features. Energy consumption requirements did not exhibit significant differences between both types of samples, close to 370 kJ. Hydrogels formulated using as gelling matrix both alginate or gelatine exhibited typical gel behaviour, independently of the bioactive extract used. It was identified a gel softening (about ten times) in the hydrogels enriched with bioactive compounds. Textural features were consistent with those found from rheological measurements. Frozen storage for long time periods (3 years) did not damage the bioactive and colour properties of broccoli extracts.