Enhancement of Phenolic Recovery by Probe-Type Ultrasound-Assisted Extraction of Acerola By-Product and Evaluation of Antioxidant and Antibacterial Activities

This study aimed to optimize the total phenolic content (TPC) and antioxidant activity (AA) of acerola (Malpighia emarginata) by-product extracts obtained by probe-type ultrasound-assisted extraction and assess the composition and antibacterial activity of the extract obtained under optimized conditions. A Box–Behnken experimental design was applied to evaluate the effects of ultrasonic power (350 to 650 W), ethanol concentration (20% to 80% v v−1), and extraction time (20 to 60 min) on TPC and AA. The optimal extraction conditions were 650 W, 50% (v v−1) ethanol, and 20 min, which yielded the highest values of TPC (3.36 g gallic acid equivalent 100 g−1) and AA through the DPPH radical scavenging method (4.97 mM Trolox equivalents 100 g−1) and a ferric reducing antioxidant power assay (11.35 mM Trolox equivalents 100 g−1). Organic acids, phenolic acids, flavonoids, and alkaloids were identified in the optimized extract, including malic acid, protocatechuic acid, resorcylic acid, and rutin. The optimized extract (2.89–11.32 mg mL−1) inhibited the growth of Listeria monocytogenes, Shigella sonnei, Salmonella enterica subsp. enterica Typhi, Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli. Acerola by-products represent a promising source of extracts with the potential to replace synthetic additives, contributing to the circular economy of agroindustries.