The drying curves and the degradation kinetics of three different quality attributes (total carotenoids (TC) and total polyphenols (TP) contents and antioxidant activity (AA)) of carrots during drying at different temperatures (from 40 to 90°C) have been experimentally evaluated and modeled. A diffusional model taking into account the solid shrinkage and both the external and internal water transfer resistances was used to accurately represent the water transfer in carrot during drying (average mean relative error (MRE) of 3.3 ± 0.6%). The effective moisture diffusivity was found to follow the Arrhenius relationship (E_a = 76.0 kJ/mol) and the mass transfer coefficient a linear dependence with air temperature. The Weibull model was used to satisfactorily simulate the degradation kinetics of the three quality attributes considered (average MRE of 2.8 ± 1.2% for TC content, 5.7 ± 1.0% for TP content, and 3.6 ± 1.8% for AA); these were the E_a of 52.7 kJ/mol for TC; 22.1 kJ/mol for TP; and 27.5 kJ/mol for AA kinetics. By using the proposed models, the estimated optimum drying temperature to best retain the total carotenoids content ranged between ca. 42–46°C; meanwhile, in order to maintain the TP content and the antioxidant activity at the highest levels, the drying needed to be carried out at temperatures of ca. 60–75°C. These results indicate that the TC retention is more influenced by the drying temperature, while the TP and AA retentions are more sensitive to drying time exposure. However, it was possible to establish a global optimum air temperature which ranged between 52.6 and 57.7°C, decreasing the TC, TP, and AA retentions by less than 2.2% from their respective optimal values.

Orange byproduct (flavedo and albedo) from juice extraction, was used as raw material for this study. Kinetics of total phenolic and total flavonoid contents and antioxidant activity was experimentally determined during both conventional (agitation at 80 rpm) and ultrasound assisted (at 520 and 790 W/L) aqueous extraction from orange byproduct at 5, 15, and 25 °C. An extraction mathematical model was also developed. Significant increase of biocompounds extraction yields was observed as temperature and acoustic power density increased. Ultrasound assistance allowed higher yields at lower temperatures and shorter times. Yields of total phenolic and total flavonoid contents and antioxidant activity obtained with ultrasound extraction (790 W/L, 25 °C, 3 min) were 29%, 39%, and 197% higher, respectively, than those obtained by conventional extraction. The extraction kinetics curves were properly represented by the Weibull model for both conventional and acoustic extraction (mean relative error lower than 5%). Naringin, neohesperidin, and hesperidin were the main phenolic compounds found in the extracts, followed by ferulic, sinapic, and cuomaric acids. Neohesperidin, hesperidin, coumaric acid, and sinapic acid presented the highest yields, especially when extraction was assisted by ultrasound. Meanwhile, naringin and ferulic acid were extracted in a lesser extent, most likely due to their lipophilic character.