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

Abstract

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 °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 °C was characterized by the lowest color changes (ΔE = 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.

Clean Label “Rocha” Pear (Pyrus communis L.) Snack Containing Juice By-Products and Euglena gracilis Microalgae

“…In terms of total phenolic compounds, no significant (p > 0.05) differences were detected between pomace, turbid juice, clarified juice, and retained fraction. The obtained value for the puree (33.82 ± 1.824 mg 100 g −1 ) is lower than the value reported by Önal et al (65) to "Rocha" pear. About the remaining fractions, there is a significant (p < 0.05) loss in total phenols, in the centrifugation.…”

Physicochemical, Sensory and Nutritional Properties of Foods Affected by Processing and Storage

“…Therefore, more research is needed to stablish the optimal conditions for the application of the pre-treatments. In this context, Önal et al [ 9 ] evaluated the effect of drying temperature and innovative pre-treatments (microwave and ultrasound) on drying behavior and quality characteristics, such as color, total phenolic content and antioxidant activity of “Rocha” pear, a traditional Portuguese cultivar. The authors concluded that ultrasound application is a promising technology to obtain healthy/nutritious dried “Rocha” pear snacks.…”

Influence of three drying methods on physicochemical properties of okra (Abelmoschus esculentusL.) powder

“…The moisture diffusion channel from the interior layers to the product surface is obstructed if case‐hardening occurs. As a result, diffusion will slow down, and the drying period will be extended (Nascimento et al, 2016; Önal et al, 2021; Tao et al, 2018).…”

“…One of the most prominent reasons for phenolic compound losses might be the thermal instability of microwave heating. In addition, the heat instability of phenolic chemicals in the food matrix might influence the separation process (Önal et al, 2021).…”