The aim of this work was to address the air-borne application of power ultrasound in the convective drying
of grape skin, a by-product of winemaking. For that purpose, convective drying experiments were carried
out on red grape skin at 40, 50, 60 and 70 C with (21.7 kHz, 45 W) and without power ultrasound
application. The kinetic intensification was evaluated by modeling the drying kinetics using empirical
and diffusion models. Meanwhile, the quality of the dried product was determined by obtaining ethanolic
extracts and assessing the total phenolic content and antioxidant capacity by means of the FRAP method.
Moreover, individual polyphenols were identified by HPLC-DAD-ESI-MS/MS and a Partial Component
Analysis (PCA) was performed in order to elucidate the relationships between the measured variables
that were related to bioactive content.
Both temperature and ultrasound application had a significant (p < 0.05) influence on the drying kinetics,
which were satisfactorily described by both the Peleg and diffusion models. In addition, both factors
significantly (p < 0.05) influenced the total phenolic concentration and antioxidant capacity of the
extracts. Ultrasound application reduced the antioxidant potential, probably due to oxidase activation
and cell degradation. Bioactive potential, on the other hand, was increased as a consequence of hightemperature
drying, leading in particular to a greater release of malvidin 3-O-b-D-galactoside.
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