Effects of thermal treatments on pectinesterase activity determined in blood oranges juices

The citrus processing industry aims to maintain turbidity and attractive colour of the juice obtained from Sicilian blood oranges. Nevertheless, the presence of pectinesterase (PE, E.C. 3.1.1.11) causes the loss of these peculiar characteristics, due to precipitation of colloids and very fine pieces of pulp in suspension, with negative effects on colour and clarification of the juices. This study compares total PE activity of Sicilian blood oranges (Sanguinello, Moro, Tarocco) with the blonde cultivar Navel, checking enzyme stability with various pasteurisation times and temperatures conditions. Decimal reduction time and temperature (D and z) as well as the kinetic constant (k) were established to optimise and increase the shelf-life of the pasteurised juice. Finally, a heat treatment (85 °C × 3 min) of both microbiological and enzymatic efficacy has been developed that does not compromise anthocyanin stability; this treatment could be used by the citrus fruit processing industry as a valid alternative in the production of blood orange juices.