Natural colorants have gained increased popularity among consumers and food producers due to their
reputation as safer and healthier alternatives to commonly used artificial analogues. These natural
pigments can be obtained from by-products resulting from food processing, such as the fruit peels of
the Brazilian species Eugenia brasiliensis and Eugenia involucrata, thus contributing to the valorisation
and circularity of these undervalued raw materials. Therefore, since these fruit peels present anthocyanin
concentrations that justify their exploitation, this study aimed to optimize and compare the recovery of
these pigments from these plant by-products using heat- and ultrasound-assisted extraction (HAE and
UAE, respectively) methods. For process optimization, a central composite rotatable design coupled with
response surface methodology was implemented, considering time, ethanol/water ratio, and
temperature (for HAE) or ultrasonic power (for UAE) as relevant independent variables. While UAE
resulted in higher extraction yields (40–42%, w/w), HAE led to higher anthocyanin contents (18 mg g−1
from E. involucrata and 323 mg g−1 from E. brasiliensis). Furthermore, the HAE global optimum involved
only 2 min of processing. Both theoretical models were experimentally validated by applying the modelpredicted
extraction conditions, and the obtained anthocyanin-rich extracts were analysed for colour
and in vitro bioactive properties. In general, the extraction method did not greatly affect the colour or
the antimicrobial and cytotoxic activities of the extracts. However, only E. brasiliensis extracts showed
cytotoxicity on human tumour cell lines, which also stood out for their antioxidant activity, possibly due
to the higher anthocyanin content. Thus, Eugenia spp. fruit peels could be an alternative renewable
source of natural food colourants with bioactive properties. Nonetheless, since E. brasiliensis extracts
displayed moderate toxicity towards normal cells, the toxicity threshold should be further investigated to
ensure the safe exploitation of this raw material as a possible source of natural food colourants.
The authors are grateful to the Foundation for Science and
Technology (FCT, Portugal) for financial support through
national funds FCT/MCTES (PIDDAC) to CIMO (UIDB/00690/
2020 and UIDP/00690/2020) and SusTEC (LA/P/0007/2020).
National funding by FCT, P. I., through the scientific employment
program-contract for the contracts of J. Pinela (CEECIND/
01011/2018), C. Pereira (CEEC Institutional), S. Heleno (CEEC
Institutional), and L. Barros (CEEC Institutional), and the
research grants of B. R. Albuquerque (SFRH/BD/136370/2018
and COVID/BD/152908/2022) and F. Mandim (SFRH/BD/
146614/2019) are acknowledged.
