Extraction of betalaine from red pitaya peel using deep eutectic solvent and its research in films

Perishable food poses significant food safety hazards and threatens public health. Consequently, pH indicator films have garnered considerable interest due to their potential for early detection of food spoilage. This research used red-fleshed pitaya peel powder as raw material, and betalaines were extracted using DES composed of choline chloride and citric acid as hydrogen bond donors and acceptors, respectively. The extraction conditions were optimized by response surface experiment, and the content of betalaine (BT) extracted in the verification experiment was 4.39 mg/g. The film was prepared using the solvent casting technique. The above DES/BT solution (DES/BT) was added into sodium alginate (SA) and sodium carboxymethyl cellulose (CMC) pH indicator films, and the effects of DES/BT on the physicochemical, optical and surface properties of the films were studied. The results showed that the film with 0.7 mL (1.4 %, v/v) DES/BT had the best tensile strength(23.14 MPa), water solubility(16.02 %), and water vapor permeability (7.64×10⁻⁵g*m*m⁻²*Pa*h⁻¹). The addition of DES and DES/BT made the film surface texture uniform and wrinkle-free and the UV transmittance decreased from 73.27 % to 61.83 %. Experiments on the film in different pH solutions showed that the film had a colorimetric response. Overall, the incorporation of DES/BT into the films presents significant potential for monitoring food freshness.