Intensification of convective drying of Apple by means of acoustically assisted pretreatments: Effects of PPO activity and drying kinetics

Autores UPV
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CONGRESO Intensification of convective drying of Apple by means of acoustically assisted pretreatments: Effects of PPO activity and drying kinetics

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).