Effect of microwave power and blanching time in relation to different geometric shapes of vegetables

Microwave (MW) blanching (MWB) of vegetables has been applied in food industry as alternative to conventional treatment. Therefore, this study was aimed to evaluate the efficacy of MWB in terms of peroxidase (POD) inactivation, by applying various process conditions (MW power and process time) to different vegetables (potatoes, savoy and white cabbage), mimicking the most common geometric shapes (cylindrical, cubed, parallelepiped and slabbed). In all 3-D shapes, POD inactivation was initially achieved at the core of sample and gradually extended toward the periphery with the increase of process intensity. However, MWB appeared to be not suitable for reaching the temperature level required for the POD irreversible inactivation on the surface of vegetables, neither in 3-D nor in slabbed shape. The optimal blanching conditions (POD residual activity < 10%), determined by response surface methodology analysis were: 160 W for 120 s for cylinder and large parallelepiped samples; 160 W for 75 s for cube sample; 350 W for 45 s for small parallelepiped sample. Contrariwise, in vegetables mimicking slab geometric shape the POD inactivation did not reach the optimal endpoint of blanching treatment, neither by increasing the MW power nor extending the process time.