Application of ultraviolet radiation type C and pretreatments as an emerging and innovative technology for unripe bananas drying: Kinetic and diffusive study, color, and microstructure

Abstract

One problem that plagues fruit production is post-harvest losses. The development of new technologies that promote conservation and improve efficiency, as well as adding value, is necessary. In this sense, drying is an interesting alternative. The objective of this work was to analyze the effect of ionizing radiation (ultraviolet type C, UV-C) during convective drying of unripe banana slices aiming at potential degradation of surface compounds. Pretreatments with acetic acid solution (2 % w/w) and ultrasound (25 kHz) were also performed. The samples were evaluated in terms of drying kinetics, color parameters, and the surface morphology of the unripe banana slices, using Scanning Electron Microscopy (SEM). Results showed that estimating effective diffusivity through a mathematical approach, ignoring the phenomenological conditions, can generate results 100$\times$ lower than those calculated through a phenomenological approach. The drying time to reach equilibrium moisture content was impacted by the treatments studied, reaching a maximum reduction of 12.92 %, with the application of the acetic acid during the pretreatment step, and a maximum increase of 17.08 % for the pretreated with the acetic acid and UV-C radiation-assisted dried banana. The pretreatments reduced sample darkening, while the application of UV-C radiation increased it. SEM analysis showed the photodegradative effect of UV-C radiation on compounds present in banana sap and its effects on the slice surface morphology. Its application with the pretreatments had a synergistic effect on this degradative aspect. With an unprecedented contribution, this work reveals the effect of UV-C radiation on the drying process through the degradation of surface compounds.