2.7. Experimental design
A response surface methodology was used to evaluate the effect of
the different HIPEF treatment variables on the relative contents of carotenoids,
vitamin C, total phenolic compounds and antioxidant capacity. A
central composite design with three faced centered factors was proposed.
Numerical variables were treatment time (500–2000 μs), and
electric field strength (15–35 kV/cm), while polarity (mono- or bipolar)
was a categorical variable, keeping the pulse width (4 μs) and frequency
(100 Hz) constant. The intensity of the current corresponded to 9135,
6525 and 3915 Amperes (A) for 35, 25 and 15 kV/cm, respectively.
The input of electrical energy density supplied to the samples ranged
from 88.7 to 1931.7 MJ/m3 (Table 2).