Activity, localisation and thermal inactivation of deteriorative enzymes in Australian carrot (Daucus carota L) varieties

Four Australian carrot varieties have been selected for a study of deteriorative enzymes. The varieties included those commonly used for table and also for processing purposes (Red Hot Original, Red Count, Top Pak and Red Hot Carotene 100). The activities of three deteriorative enzymes (peroxidase, catechol oxidase and pectinesterase) have been assayed in juices prepared from whole carrot as well as superficial tissues, core, root tip and stem end. The levels and relative distribution vary for the different enzymes and varieties studied. Thermal inactivation was assessed over a range of temperatures. Catechol oxidase was found to be the least stable and pectinesterase the most stable in each of the varieties. In most cases, effective inactivation was achieved within 2 min at 85 °C. The enzymes of Top Pak variety showed greater thermal stability. In this variety, pectinesterase required treatment at 90 °C to ensure rapid inactivation. It is concluded that pectinesterase should be used as the indicator enzyme in the assessment of blanching sufficiency for processing of carrots.