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- Degradation kinetics of peroxidase enzyme, phenolic content, and physical and sensorial characteristics in broccoli (brassica oleracea L. ssp. Italica) during blanchingPublication . Gonçalves, Elsa M.; Pinheiro, Joaquina; Alegria, C.; Abreu, Marta; Brandão, Teresa R. S.; Silva, Cristina L.M.The effects of water blanching treatment on peroxidase inactivation, total phenolic content, color parameters [-a*/b* and hue (h *)], texture (maximum shear force), and sensory attributes (color and texture, evaluated by a trained panel) of broccoli (Brassica oleracea L. ssp. Italica) were studied at five temperatures (70, 75, 80, 85, and 90 C). Experimental results showed that all studied broccoli quality parameters suffered significative changes due to blanching treatments. The vegetal total phenolic content showed a marked decline. Degradation on objective color and texture measurements and alterations in sensorial attributes were detected. Correlations between sensory and instrumental measurements have been found. Under the conditions 70 C and 6.5 min or 90 C and 0.4 min, 90% of the initial peroxidase activity was reduced. At these conditions, no significant alterations were detected by panelists, and a small amount of phenolic content was lost (ca. 16 and 10%, respectively). The peroxidase inactivation and phenolic content degradation were found to follow first-order reaction models. The zero-order reaction model showed a good fit to the broccoli color (-a*/b* and h *), texture, and sensory parameters changes. The temperature effect was welldescribed by the Arrhenius law.
- Carrot (Daucus carota L.) peroxidase inactivation, phenolic content and physical changes kinetics due to blanchingPublication . Gonçalves, E.M.; Pinheiro, J.; Abreu, M.; Brandão, T.R.S.; Silva, C.L.M.The kinetics of peroxidase thermal inactivation, total phenolic content degradation, and colour (CIE L*a*b*) and texture changes were studied in a temperature range of 70–90 C for carrots (Daucus carota L.). Peroxidase inactivation, total phenolic content degradation and the lightness colour (L* parameter) change were successfully described by a first-order reaction model. The redness and yellowness colour (a* and b* parameters, respectively) and texture (firmness and energy parameters) changes presented a fractional conversion kinetic model behavior. The temperature effect was well described by the Arrhenius law. All the blanching conditions recommended to reduce peroxidase inactivation to an acceptable level (90% loss of its original activity) ensured good quality retention. However, to obtain a high quality carrot product a balance must be made between colour and total phenolic content losses. Therefore, blanching at 80 C for 6 min is suggested as a compromise condition to maximize quality. The overall study indicated that colour is a critical parameter to optimize carrot hot water blanching condition.
- Modelling the kinetics of peroxidase inactivation, colour and texture changes of pumpkin (Cucurbita maxima L.) during blanchingPublication . Gonçalves, E. M.; Pinheiro, J.; Abreu, M.; Brandão, Teresa R. S.; Silva, Cristina L.M.The effects of blanching treatment on peroxidase inactivation, colour and texture of pumpkin (Cucurbita maxima L.) were studied in the temperature range of 75–95 C. Peroxidase inactivation followed a first-order Arrhenius model, where the activation energy and rate of the reaction at a reference temperature of 85 C were 86.20 ± 5.57 kJ mol 1 and 0.27 ± 0.01 min 1, respectively. During blanching, pumpkin became darker and softer with processing time. The degradation of colour (evaluated throughout CIE L*a*b* colour system, with chroma index and total colour difference) and texture parameters (firmness and energy) showed a fractional conversion model kinetics, being the temperature effect on kinetic parameters well described by the Arrhenius law. The results of this work are a good tool to further optimise pumpkin blanching conditions.
- Modelling peroxidase inactivation kinetics in broccoli (Brassica oleracea L.) and pumpkin (Cucurbita maxima L.) using blanching and thermosonicationPublication . Gonçalves, Elsa M.; Pinheiro, Joaquina; Abreu, Marta; Brandão, Teresa R. S.; Silva, Cristina L. M.