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 gamma-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 mu g/mL for Delta t 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.

Automated summary

The peel of Hylocereus costaricensis fruit contains a large amount of betacyanins, which can be used as natural colorants and show no toxicity. Through optimizing the ultrasound-assisted extraction method, the maximum content of betacyanins was successfully extracted. The peel extract exhibited bioactive properties such as antioxidant hemolysis inhibition and inhibition of pathogenic bacteria growth.