This work studies the combined effects of blanching, using either peroxydase (POD) or lipoxygenase (LOX) as indicators, and different freezing conditions on the final quality of green beans. The time-temperature blanching conditions for the freezing experiments were chosen arbitrarily to reach an indicator residual activity of 10%. The blanching temperatures used were 70, 80, 90 and 100°C. After blanching, the samples were submitted to four freezing conditions: a) nitrogen vapor, b) blast freezing, c) natural convection, and d) natural convection inside polystyrene boxes. The freezing rate was measured by means of thermocouples placed in the center of the green beans pods and by fluxmeters adhered to their surfaces. The quality of thawed samples was evaluated by: a) light microscopy of thin cut transversal sections of the pods, b) axial compression tests by application of constant constraint of 2 N and, c) evaluation of color variation using the CIELAB color space. HTST blanching protocols contributed to minimize color and texture deterioration. High freezing rates [＞ -94.2 kJ/(kg.min)] enabled preservation of the internal parenchyma and, consequently the retention of firmness. Color is not significantly affected by the freezing rate.
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