Opuntia cactus fruit (prickly pear flesh and agricultural residues such as peels and stalks) is an important source of bioactive compounds, including betalains and phenolic compounds. In this work, two double emulsion W1/O/W2 formulations (A and B) were designed to encapsulate green extracts rich in betalains and phenolic compounds obtained from Opuntia stricta var. dillenii (OPD) fruits with the aim of improving their stability and protecting them during the in vitro gastrointestinal digestion process. In addition, the characterization of the double emulsions was studied by microscopy and the evaluation of their physical and physico-chemical parameters. Formulation A, based on Tween 20, showed smaller droplets (1.75 µm) and a higher physical stability than Formulation B, which was achieved with sodium caseinate (29.03 µm). Regarding the encapsulation efficiency of the individual bioactives, betalains showed the highest values (73.7 ± 6.7 to 96.9 ± 3.3%), followed by flavonoids (68.2 ± 5.9 to 95.9 ± 7.7%) and piscidic acid (71 ± 1.3 to 70.2 ± 5.7%) depending on the formulation and the bioactive compound. In vitro digestive stability and bioaccessibility of the individual bioactives increased when extracts were encapsulated for both formulations (67.1 to 253.1%) in comparison with the non-encapsulated ones (30.1 to 64.3%), except for neobetanin. Both formulations could be considered as appropriate microcarrier systems for green OPD extracts, especially formulation A. Further studies need to be conducted about the incorporation of these formulations to develop healthier foods.
Keywords: Opuntia stricta var. dillenii fruits; betalin and phenolic green extracts; bioactive bioaccessibility; double emulsions; in vitro gastro-intestinal digestion; microscopic studies.