From Fig. 4a, the application of frequency at 80 Hz with a specific
energy input of 166 kJ/kg impacted a rapid reduction of the maximal
cutting force to 72 N and to 49 N for vertical and parallel positioned
carrots respectively. The cutting force peak, observed when cutting
the xylem region (+15 to 0 mm) had decreased from 49% to 65%;
emphasising the importance to take into consideration the carrot arrangement
during PEF processing. For example, in the case of a carrot
piece with fibre direction parallel to the electrode was more preferable
for reduced cutting force. Initially, in order to penetrate the outer region
of carrot, i.e. epidermis, the cutting force was reduced almost 50% to
that of the force required on reference (untreated) carrots. Following
the penetration through the cortex region, PEF-treated carrot at 80 Hz
and parallel positioned led to a more pronounced tissue flexibility
whereby it resulted in decreased cutting force but increased again
when reaching the endodermis region and then xylem at 15 mm
measured from the epidermis. Overall, the application of high pulse
frequency of 80 Hz and specific energy of 166 kJ/kg achieved an even
cutting surface through the entire carrot cylinder as depicted in Fig. 4d
(left). In fact, PEF treatment with parallel positioned carrots was more
effective with regards to reducing cutting force to that of vertical adjustment,
due to the larger surface area exposed to the electrodes for effective
cell disintegration in addition to cell membrane components
disruption