3.1. Effect of carrot matrix and piece position on endogenous enzyme
activity
The initial temperature of carrot samples (carrot mash and carrot
pieces) and treatment medium (phosphate buffer) was standardised
by pre-conditioning at 10 °C to attain an isothermal condition prior to
PEF treatment. In this study, PEF treatmentswere conducted at temperatures
below25 °C to ensure the final temperature of carrots andmedium
after treated with PEF at varying pulse frequencies did not exceed
25 °C. The results have shown that both the semi-solid (carrot mash)
and solid (carrot pieces) food matrices resulted in different effects on
AAO and POD inactivation. It was found that carrot mash (semi-solid
matrix) had higher residual AAO and POD activity (20 to 30% increment)
as compared to intact carrot pieces (solid matrix) when treated
with an electric field strength of 0.8 kV/cm and specific energy input
of less than 50 kJ/kg (Fig. 2). Previous work on PEF-treated apple and
orange juice has also shown increase in polyphenoloxidase and
pectinmethylestease activity, respectively (Van Loey, Verachtert, &
Hendrickx, 2002).