Pomegranate by-products can be an asset to the food industry due to the richness in
bioactive and antimicrobial compounds. This work studied the influence of conventional solvent
and sonication-assisted extraction methods on the bioactive profile, antimicrobial properties, and
phytotoxicity effect of the peels and seeds extracts from Acco, Big Full, and Wonderful pomegranate
cultivars. The bioactive composition of the extracts was evaluated for the content of total phenolics,
total flavonoids, and antioxidant activity (expressed as the half-maximal inhibitory concentration—
IC50) by spectrophotometric methods, while the tannins were determined by titration and the
anthocyanins were estimated by the pH-differential method. For the evaluation of the antimicrobial
activity, the disk diffusion method of Kirby-Bauer was adapted through inhibition halos against
Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Bacillus cereus, and Yarrowia lipolytica.
The extracts’ phytotoxicity was evaluated in vitro on garden-cress seeds. Extracts from conventional
extraction were richer in total phenolics, expressed as gallic acid equivalents (0.16–0.73 mg
GAE/mg extract), while those from sonication-assisted extraction had higher contents of total
flavonoids, expressed as catechin equivalents (0.019–0.068 mg CATE/mg extract); anthocyanins,
expressed as cyanidin-3-glucoside (0.06–0.60 g C3G/mg, dry basis); and antioxidant activity (IC50,
0.01–0.20 mg/mL). All extracts were more effective against Gram-positive bacteria and yeasts than
Gram-negative bacteria. In general, the sonication-assisted extracts led to higher inhibition halos
(8.7 to 11.4 mm). All extracts presented phytotoxicity against garden-cress seeds in the tested concentrations.
Only the lowest concentration (0.003 mg/mL) enabled the germination of seeds and root
growth, and the sonication-assisted extracts showed the highest Munoo-Liisa vitality index (51.3%).
Overall, sonication-assisted extraction obtained extracts with greater bioactive and antimicrobial
potential and less phytotoxicity.
This work was supported by the Portuguese Foundation for Science and Technology (FCT)
under the scope of the strategic funding of CEB (UIDB/04469/2020), CERNAS (UIDB/00681/2020),
CIMO (UIDB/00690/2020), and the Associate Laboratory SusTEC (LA/P/0007/2020). The European
Regional Development Fund funded MobFood operation (LISBOA-01-0247-FEDER-024524). L.C.
acknowledges research grants CEB-BI-14-2019 and FCT-IPC-i2A-CERNAS/Escola de Verão/BI-01-08,
and L.S. acknowledges the research grant FCT-IPC-i2A-CERNAS/Escola de Verão/BII-01-07, all
provided by FCT. The Article Processing Charge (APC) was funded by the Polytechnic Institute
of Coimbra.
