Abstract
Recently, ultrasonic assistance during pretreatments has
been found to accelerate the removal of water from food-
stuffs during convective drying. The effect of power ultra-
sound application on polyphenoloxidase (PPO) activity
and drying kinetics were evaluated by applying acoustic
assistance in a soaking treatment before convective drying.
Treatments were carried out using three different soaking
media, distilled water, apple juice, and citric acid, at 25
◦C during 5 min, without acoustic assistance (0 W/cm2),
and then with two acoustic densities: 2.1 and 12.9 W/cm2.
Treated samples exhibited a decrease in the PPO activity
by 13 to 58% in comparison with that in the fresh sample.
The highest inactivation was observed when treatment was
carried out with 12.9 W/cm
2
using apple juice (40%) and
1% citric acid (58%), whereas samples soaked in water
showed the lowest decrease (19%). Convective drying of
soaked samples was carried out at 50 ◦C and an air velocity
of 1.0 m/s. Drying curves were studied until a nal mois-
ture content of 0.20 kg water/kg dm was achieved. Com-
pared with the fresh sample, the drying time of the treated
one decreased by 13.3% when it was treated with water
without acoustic assistance( ..the smallest reduction), and by 42.4% when the sample
was soaked in 1% citric acid and 12.9 W/cm2 (treatment
which promoted the highest reduction).
