Chlorophyllase inactivation as a measure of blanching efficacy and colour retention of artichokes (Cynara scolymus L.)

Abstract

The response of the enzyme chlorophyllase of Maipo-ecotype artichokes (Cynara scolymus L.) to three thermal inactivation treatments (microwave, steam or boiling water) were evaluated. The temperature - activity profile of the enzyme, between 25 and 45 °C, shows maximum activity at 30 °C. Curves of thermal inactivation of chlorophyllase vs. time were plotted for the three treatments, resulting in complete inactivation of the enzyme after a blanching time of 2, 6 and 8 min for microwave, steam and boiling water processes, respectively. Measurement of peroxidase activity was performed as an indicator of blanching process adequacy. Colour changes during the blanching time needed to inactivate the enzyme chlorophyllase were seen with the three treatments, but more in steam treated artichokes than with the others. Steam blanched artichokes during the time needed to inactivate chlorophyllase also showed lower values for lightness index, hue and chroma than water and microwave oven treatments. Microwave and boiling water blanched artichokes best preserved the original perceptual colour. A total peroxidase inactivation without detectable loss of ascorbic acid for microwave blanching, compared with a 16.7% loss of ascorbic acid with boiling water blanching, indicates better quality for microwave blanched artichokes. © 1998 Academic Press Limited.