Pre-treatments with ethanol and/or ultrasound can be used to change food structure and improve mass transfer. However, each treatment affects differently each vegetable matrix, with specific impact on drying. Therefore, the objective of this work was to study the effect of pre-treatments with ethanol and/or ultrasound on the macro and microstructure of the different regions of carrots (cortex and core), focused on future drying. The following treatments were evaluated: Ethanol (E), Ethanol+Ultrasound (E+US), Water+Ultrasound (W+US) and control (C). The carrot slices were submerged in ethanol (99.8% v/v) for 30 min. Ultrasound was applied in an ultrasonic bath (25 kHz, 20°C, nominal power of 135 W and volumetric power of 23.9 for water and 25.7 W/L for ethanol). The quantity of water or ethanol was fixed in 1.4 L for each treatment, and the proportion to sample 7:1(v/m). Macrostructure changes were evaluated by texture analysis, considering a penetration assay and shrinkage. Microstructure was evaluated by optical microscopy. After pre-treatments, no structural changes were observed in the xylem and phloem vessels of carrot core. However, the parenchymal cells present into both cortex and core were withered due to water outlet in pre-treatments E and E+US, due to osmotic dehydration, also causing shrinkage of carrot slices. Furthermore, their cell wall became thinner and disorganized, losing their polyhedral shape. On the other hand, the W+US treatment resulted in cellular swelling in both carrot regions, due to water absorption, increasing the slice’s projected area. The pre-treatments E and E+US made the initial layers of tissue more resistant to penetration, in both core and cortex, when compared with control. On the other hand, the W+US treatment was more resistant to penetration only in core, due more absorption of water in this region; in cortex, the resistance to penetration had same behaviour of control. In conclusion, the treatments affected parenchymal cells making them wilted (E and E+US) or swell (W+US) and these changes also influenced the product macrostructure in both the cortex and core regions. In fact, those changes can affect the subsequent drying process.
Acknowledgments: FAPESP-2019/05043-6; CNPq-131235/2020-6; CNPq-306557/2017-7; CAPES-001; FONDECYT-409-2019.