Drying kinetics, powder properties, and bioactive components of bitter orange (Citrus aurantium L.) dried by microwave-assisted foam-mat approach

Abstract

Microwave-assisted foam-mat drying is a hybrid process which shares the advantages of microwaves (faster dehydration) and foam-mat drying (high efficiency and developed product quality). In this work, the microwave drying of bitter orange fruit (at 90, 180, and 360 W) was studied by determining the drying and color kinetics, powder properties, total phenolic content (TPC), and antioxidant behavior. A foam-mat approach was also utilized, measuring foam density, stability, and expansion values. Egg albumen (EA) was used as a foaming agent at a concentration of 40%, 50%, and 60% of the fruit paste. The results showed that, the foam expansion and foam density ranged from 9 to 16% and 0.899 to 0.948 g/cm(3), respectively, and the stability of the foam after 3 h remained the same as at the beginning (100%). The drying process was best described by the models of Sigmoid and Hii et al., while the quadratic equation proved to be the most appropriate for measuring the total color change (Delta E). The lowest final Delta E (13.042) was found in dehydrated bitter oranges at 90 W with an EA of 60%. The Carr index and Hausner ratio of the powders ranged from 16.565 to 25.714 and 1.227 to 1.346, respectively. No statistically significant differences were observed in the TPC values of the samples with EA (7.869-8.771 mg GAE/g DM), except for the sample dehydrated at 90 W (10.057 mg GAE/g DM) (p > 0.05). The antioxidant data of the dried specimens were very close, and about 79% of the antioxidant molecules were destroyed by the thermal treatment (regarding ABTS technique), compared to fresh fruits.