Broccoli (Brasica oleracea) treated under pressure-shift freezing process

摘要

The experiment was carried out on broccoli to study the freezing effects under pressure using the pressure shift freezing treatment (PSF). The treatment was applied to samples that were in polyethylene bags, sealed under a vacuum at 180 MPa, -16°C and 210 MPa, -20°C and in samples blanched for 2 and 3 min. Protein content, peroxidase (POD), polyphenoloxidase (PPO) activity and structure were analysed. The final results showed that the proteins decreased after the treatments. Five heat-cold-pressure shock proteins of 50, 43, 39, 36 and 20 KDa were found. The assayed conditions were not enough to inactivate the POD and PPO enzymes. Four POD-iso-zymes of 110, 80, 50 and 39 KDa were detected and the highest activity was for the 80 KDa isoform. The sensorial test revealed that after 30 days of frozen storage at -20°C the flavour of broccoli was not acceptable to consumers, but the texture remained quite firm. Cryo-Sem revealed that the vacuole membrane was destroyed and an internal disorganised cell was observed after the PSF treatment.