Red pitaya (Hylocereus costaricensis) peel as a source of valuable molecules: extraction optimization to recover natural colouring agents

Hylocereus costaricensis peel contains large amounts of betacyanins and can be exploited as a source of natural colorants. This work aimed the chemical characterization and evaluation of bioactive properties of this byproduct and the optimization of the ultrasound-assisted extraction (UAE) of betacyanins using the response surface methodology (RSM). Oxalic and malic acids and traces of fumaric acid were detected, as well as the four tocopherol isoforms, predominantly γ-tocopherol. Four betacyanins were identified and used as response criteria for UAE optimization, namely phyllocactin, isobetanin, isophyllocactin, and betanin. Sample processing at 487 W for 38 min result in the maximum betacyanin content (36 ± 1 mg/g dw). The peel extract inhibit the oxidative haemolysis, with IC50 values of 255 and 381 μg/mL for Δt of 60 and 120 min, respectively, and the growth of pathogenic bacteria, with minimum inhibitory concentrations ranging from 5 to 20 mg/mL. Furthermore, no toxicity was observed for normal cells.The authors are grateful to the Foundation for Science and Technology (FCT, Portugal) for financial support by national funds FCT/ MCTES to CIMO (UIDB/00690/2020); C. L. Roriz PhD’s grant (SFRH/ BD/117995/2016), L. Barros and C. Calhelha also thank the national funding by FCT, P.I., through the institutional scientific employment program-contract for their contracts, and S.A. Heleno (CEECIND/ 03040/2017) and J. Pinela (CEECIND/01011/2018) through the individual scientific employment program-contract. The authors are also grateful to the European Regional Development Fund (ERDF) through the Regional Operational Program North 2020, within the scope of project Mobilizador Norte-01-0247-FEDER-024479: ValorNatural® and GreenHealth (Norte-01-0145-FEDER-000042. Finally, P. Morales is also grateful to UCM ALIMNOVA Research Group (GR105/18).