Research noteEffect of pH, temperature and maturity on pectinmethylesterase inactivation of citrus juices treated by high-pressure homogenization

- Pectinmethylesterase inactivation of homogenized citrus juices was studied.
- Inactivation was a function of pH, maturity and homogenization temperatures.
- Acidification at pH 3.1 greatly decreased enzyme activity of processed juices.
- Homogenization temperature had an intermediate importance to inactivation.
- Maturity had a minimum contribution to placate enzyme activity.

The effects of high-pressure homogenization (HPH) at 150 MPa combined with heating at 58, 63 and 68 °C on inactivation of pectinmethylesterase (PME) were studied in orange and Clementine juices. Juices covering a range of total soluble solids (°Bx) to acid ratios (10.2-15.0 in oranges and 9.2-19.4 in Clementines) were adjusted to pH 3.1, 3.5 and 3.9 before homogenization. Results indicated how the residual PME activity of homogenized samples was greatly attenuated by lowering the pH and in a lesser extent by increasing the homogenization temperature (finding orange enzymes more HPH sensitive than their Clementine counterparts). Generally, ripeness of fruits had little influence on PME inactivation (especially in Clementine juices). In any case, orange and Clementine samples with pH 3.1 and homogenized at 68 °C showed residual PME activities below 10% of the initial value from their respective fresh juices.