Encapsulated purple sweet potato peel extract as antioxidant and sustainable colourant to preserve the quality of beef burgers during the shelf life

Ultrasound-assisted extraction was used to obtain an anthocyanin-rich extract from purple sweet potato peels. The resulting extract exhibited strong antioxidant activity (243.6 μmol Fe⁺²/g FRAP, 93.23 mg Trolox/g ORAC, 26.63 mg Trolox/g DPPH, and 20.89 mg ascorbic acid/g ABTS) and a high anthocyanin content (2433.6 μg/g dry weight), making it suitable for use as an additive in meat products. Four batches of beef burgers were prepared: a control (CON, no antioxidant), ERI (500 ppm sodium erythorbate), E2500 (2500 ppm extract), and E5000 (5000 ppm extract). The effect of the encapsulated extract on colour parameters, oxidative stability, microbial quality, and sensory attributes was evaluated during refrigerated storage. The extract positively influenced colour parameters. E5000 provided similar protection against discoloration as ERI, exhibiting the smallest decrease in a* values (40.6 % vs. 32.6 % for E5000 and ERI, respectively) and limiting metmyoglobin formation (28.8 % vs. 57.5 % for E5000 and ERI, respectively). A dose-dependent effect was observed, with significantly lower TBARS values at higher extract concentrations (2.53 vs. 1.90 MDA/kg for E2500 and E5000, respectively, at the end of storage). These findings confirm the extract's effectiveness as an antioxidant without detrimental sensory effects.