Instant controlled pressure-drop as texturing pretreatment for intensifying both final drying stage and extraction of phenolic compounds to valorize orange industry by-products (Citrus sinensis L.)

Abstract This work deals with the economic valorization of orange industry by-products by intensification of both drying kinetics and extraction of phenolic compounds of orange peel using the instant controlled pressure-drop DIC technology. DIC treatment is usually performed on partially dried samples. It starts with a heating/pressurizing stage for a short thermal treatment time to end by an instant depressurization towards a vacuum. In the present case, orange-peel was DIC-textured to be airflow oven dried at 40 °C, 2 m s−1, and 265 Pa of vapor as relative humidity, to reach a final moisture of about 0.05 g H2O/g db. By assuming this operation as shrinkage-free with conditions of Negligible External Resistance (NER), the Coupled Washing/Diffusion (CWD) was applied as phenomenological drying kinetic model, and its effects were perceptively identified through the starting accessibility (δWs) and the effective diffusivity Deff of water within the textured material. DIC-texturing was also recognized as a pretreatment possibly able to improve the solvent extraction of phenolic compounds. Four phenolic compounds were identified by HPLC assessments; namely hesperidin, rutin, flavone, and naringin. DIC allowed growing them from 12.10 to 65.01 (537%); from 11.47 to 27.10 (236%); from 0.006 to 0.007 (117%); and from 0.0002 to 0.00032 (160%) mg/g db, respectively. This highly significant increase of availability of these active molecules should be correlated with the presence of broken-wall cells, which Scanning electron microscopy (SEM) later, revealed and confirmed.