Inactivation of pectinmethylesterase in fresh orange juice by cold atmospheric plasma technology: A kinetic study

Preservation of fruit juices requires the inactivation of natural endogenous enzymes, such as pectinmethyles-terase (PME). Within this work, cold atmospheric plasma (CAP), and in particular a dielectric barrier plasma jet fed with helium gas, was demonstrated to effectively inactivate PME of freshly squeezed orange juice in short treatment times (2-30 min). By a combination of temperature measurements and a multidimensional heat transfer model, the temperature profile of the whole sample during plasma treatment was extracted. It was found that the thermal phenomena were not a driving factor for PME inactivation. Plasma treatment of orange juices resulted in inactivation of 55-80% of PME with <5.0% of PME inactivation caused by the temperature increase from 20 to 90 degrees C. The Weibull distribution model compared to the first-order fractional, the sigmoidal logistic and the Hulsheger's kinetic models was found to better describe mathematically (R-2 > 0.99; A(f) = 1.002-1.052) the effect of CAP processing on residual PME activity. Multi-parameter equation fits allowed the prediction of residual PME activity as a function of the applied voltage, helium flow, and treatment time. Generally, higher voltages and lower helium flows applied led to higher PME inactivation rates in fresh orange juice.