Optimisation of the extraction process of anthocyanins from roselle and study of their properties

ObjectiveThis study aimed to optimize the extraction process of anthocyanins from Roselle, a medicinal and food plant, and investigate the discolouration mechanism, stability and antioxidant properties of the extracted anthocyanins.MethodsThe extraction process of was optimized using single-factor approach and response surface methodology, the pH of anthocyanin solution was adjusted to observe color changes and to determine the visible spectra. Stability was assessed in terms of pH, light exposure, and temperature. In vitro antioxidant activity was measured through various antioxidant assays.ResultsThe optimal extraction conditions for anthocyanins from roselle: liquid to material ratio of 10∶1 （mL/g）, 0.1% hydrochloric acid as 40%, ultrasonication time of 30 min, and ultrasonication temperature of 60 ℃, at which time the anthocyanin extraction was 2.982 mg/g. Anthocyanin discolouration experiments showed different colour changes of anthocyanins at different pH levels. Anthocyanin stability experiments showed that the preservation rate remained above 85% in a strong acid environment, decreased to about 43% under UV irradiation, and decreased to about 50% in a 70 ℃ environment. In vitro antioxidant assays demonstrated that anthocyanins from roselle exhibited significant scavenging activity, with DPPH radicals, ABTS radicals, and hydroxyl radicals reached 77.33%, 74.27%, and 91.20%, respectively, at a concentration of 2.25 mg/mL.ConclusionUltrasound-assisted acidification method extraction of anthocyanins from roselle improves the anthocyanin extraction rate. Anthocyanins from Roselle have strong antioxidant activity and are suitable for storage and use under acidic conditions at low temperatures and protected from light.