Microwave and Ultrasound Pre-Treatments for Drying of the Rocha Pear: Impact on Phytochemical Parameters, Color Changes and Drying Kinetics

The objective of this research was to evaluate the effect of drying temperature and innovative pre-treatments (i.e., microwave and ultrasound) on Rocha pear drying behavior and quality characteristics, such as color, total phenolic content and antioxidant activity. Experiments were carried out with pear slabs subjected to microwaves (2450 MHz, 539 W, 4 min, microwave oven) and ultrasounds (35 kHz, 10 min, in an ultrasonic bath) as well as control samples. The drying process was conducted in a tray dryer at three different temperatures (50, 55 and 60 degrees C) and a fixed air velocity of 0.75 m/s. Microwave technology resulted in a higher quality deterioration in dried pear samples compared to those of controls and ultrasound pre-treated samples. The combined application of ultrasound pre-treatment and the higher drying temperature of 60 degrees C was characterized by the lowest color changes (Delta E = 3.86 +/- 0.23) and higher preservation of nutritional parameters (total phenolic content, TPC = 345.60 +/- 8.99; and antioxidant activity, EC50 = 8.80 +/- 0.34). The drying characteristics of pear fruits were also analyzed by taking into account empirical models, with the Page model presenting the best prediction of the drying behavior. In conclusion, ultrasound application is a promising technology to obtain healthy/nutritious dried Rocha pear snacks as dietary sources for consumers.

Automated summary

The combined application of ultrasound pre-treatment and higher drying temperature showed significant improvement in drying quality of Rocha pears, maintaining color stability and nutritional content. The use of the Page model provided the best prediction of drying behavior.