W
hite grapefruit pectin met
hylesterase (PME) was successfully purified by affinity c
hromatograp
hy using a kiwi PME in
hibitor as ligand. Electrop
horetic analysis combined wit
h isot
hermal and isobaric-isot
hermal inactivation treatments suggested t
he presence of a labile PME fraction and a stable PME fraction wit
h molecular weig
hts of 31.5 kDa and 23.7 kDa, respectively. Bot
h isot
hermal and isobaric-isot
hermal PME inactivation could be described by fractional conversion models wit
h about 20%of t
he initial activity corresponding to t
he stable fraction. Optimum pH-ionic strengt
h conditions for grapefruit PME t
hermostability were determined. Purified
heat-labile PME (in 20 mM Tris Buffer (pH 7.0)) was submitted to combined t
hermal and
hig
h-pressure inactivation experiments in t
he ranges 10–62 °C and 0.1–800 MPa. T
he combined pressure–temperature dependence of t
he inactivation rate constants could be accurately described by a t
hird degree polynomial model, s
howing a clear antagonistic effect of pressure and temperature on PME inactivation at temperature ≥ 58 °C in a pressure range of 0.1–300 MPa. In t
he context of fruit-juice processing, t
he results obtained suggest t
hat a combined
hig
h-pressure-(low/mild)
heat treatment can eliminate up to 80%of t
he total PME activity t
herefore significantly limiting t
he cloud-loss defect in juices.<
h3>Industrial relevance
h3>
The present works describes the combined thermal and high pressure inactivation of pectinmethylesterase (PME) from white grapefruit. White grapefruit contains two PME fractions with different process stability (both towards temperature and pressure), the stable fraction contributing to about 20%of the total PME activity. The results demonstrate that combined mild heat and high-pressure processing cannot be used to fully inactivate PME in grapefruit juice. However, by eliminating up to 80%of the PME activity (labile fraction), such treatment can probably contribute to a significant decay of the cloud loss defect observed in grapefruit juices, while allowing pasteurisation and good quality retention of the latter. Combining high pressure mild temperature processing with other non-thermal approaches (e.g. use of PME-inhibitor) could be of interest in creating juices with extended shelf-life.