Inactivation of pectinmethylesterase (PME) and quality parameters of orange juice have been studied after high pressure carbon dioxide (HPCD) treatment. The HPCD treatment conditions covered a wide range of temperature from 2 to 40 °C, far below normal thermal treatment, while operating pressure was varied from 10 to 30 MPa and exposure time from 3 to 60 min. A decrease in PME activity was found, even at the lowest temperature studied in this work, 2 °C. Different inactivation kinetic models were used to correlate the PME residual activity: the two-fraction model, the fractional-conversion model and the Weibull model. The two-fraction model presents the lowest mean relative deviation. Some quality parameters such as colour, pH, ºBrix, turbidity, ascorbic acid, total acidity and particle size distribution (PSD) were also determined right after HPCD treatment and along storage at 4 °C up to 12 days. PSD shows that HPCD treatment results in a volume increase of small particles and a volume decrease of large particles regarding the non-treated orange juice. Calcium content was also determined before and after HPCD treatment to check for insoluble calcium carbonate formation but not significant changes were observed in calcium content after HPCD treatment.MINECO (CTQ2015-64396-R

This work investigates the effect of supercritical carbon dioxide (SC-CO2) treatment on four commer-cial lipases. The influence of experimental conditions: temperature (35–70◦C), pressure (10–25 MPa),exposure time (1–3 h) and depressurization steps (1–3) on the residual activity was studied. Activityenhancement was verified for free enzymes (Palatase 20000 L and Lipozyme CALB L) treated at mildconditions; while the highest temperature and pressure and the longest exposure time assayed led toactivity losses. On the other hand, activity losses or no significative effect of the treatment in the enzymeactivity were observed on immobilized enzymes (Lipozyme RM IM and Lipozyme 435). Qualitative stud-ies were also performed: Fluorescence emission spectra showed changes in the conformational structureof both two free enzymes after SC-CO2treatment. Scanning electron micrographs showed morphologicalalterations in the immobilization supports of the treated enzymes; while infrared spectra did not showchemical modifications.(MINECO) and the EuropeanRegional Development Fund (ERDF) for financial support to theproject CTQ2012-39131-C02-01