Use of pitaya (Selenicereus megalanthus) peel flour as a functional ingredient in pirarucu (arapaima gigas) fish burgers from the Brazilian Amazon

The pirarucu (Arapaima gigas), an Amazonian fish with high protein content, is a promising raw material for burger production, although it presents low levels of fiber and bioactive compounds. In contrast, the peel of yellow pitaya (Selenicereus megalanthus), rich in fiber and antioxidants, is often discarded, despite its potential as a functional ingredient. This study aimed to produce pitaya peel flour (PPF) and evaluate its potential application in the formulation of pirarucu burgers. PPF was obtained through ethanolic extraction (60%, 1:1 m/v), followed by pressing, freezing (-80 °C), and freeze-drying (0.998 mbar at -40 °C for 48 hours). The flour was characterized in terms of its functional properties and incorporated into burgers at levels of 0% (control), 2.5%, and 5%. The samples were evaluated for proximate composition, color, texture, and technological properties. PPF showed low moisture, lipid content, and water activity, along with high levels of fiber, protein, and bioactive compounds, significant antioxidant activity, and high solvent retention capacity. The addition of PPF to the burgers resulted in nutritional improvements (increased protein, fiber, lipid, and ash content) and technological enhancements (reduced shrinkage, higher post-cooking yield, and better moisture retention). Additionally, the flour imparted a yellowish color due to the presence of betaxanthins from the pitaya peel and influenced texture by increasing hardness and adhesiveness. It can be concluded that PPF is a promising functional ingredient for the development of value-added, sustainable fish burgers.