GREEN ULTRASOUND-ASSISTED EXTRACTION OF AÇAÍ ANTHOCYANINS OPTIMIZED BY BOX-BEHNKEN DESIGN: A FOUNDATION FOR NATURAL HALOCHROMIC INDICATORS IN ETHYLENE-RESPONSIVE SMART PACKAGING

Synthetic colorimetric indicators commonly used in intelligent food packaging raise safety and sustainability concerns, driving the search for natural halochromic alternatives. Anthocyanins exhibit pH-responsive color changes suitable for this function, and açaí (Euterpe oleracea) is a Brazilian Amazonian matrix exceptionally rich in these pigments, yet underexplored for technological applications beyond its nutritional value. Efficient, fast, and environmentally friendly extraction is a prerequisite for translating this potential into packaging technology. Thus, this study aimed to optimize the ultrasound-assisted extraction (UAE) of anthocyanins from açaí pulp using a Box-Behnken design and to characterize the resulting extract (anthocyanin content, total phenolics, antioxidant activity, and post-extraction stability) as a technological foundation for natural halochromic indicators in ethylene-responsive smart packaging. A Box-Behnken design (15 runs, including three center-point replicates) evaluated extraction time (1–8 min), temperature (30–60 °C), and ultrasonic amplitude (20–70%), using a sample-to-solvent ratio of 1:3 with acidified ethanol 70% (HCl 0.1 N, pH 2). Extracts were centrifuged (10,000 rpm, 10 min) and compared with a conventional refrigerated extraction (48 h). Total anthocyanins were quantified spectrophotometrically at 535 nm, total phenolics by the Folin-Ciocalteu method (700 nm), and antioxidant activity by the ABTS•+ assay (734 nm). The central point (4.5 min, 45 °C, 45% amplitude) yielded the highest anthocyanin content (13.93 mg/100 g), with replicates confirming process reproducibility (13.02 and 13.05 mg/100 g). Severe conditions (8 min, 60 °C) reduced anthocyanins to 8.81 mg/100 g, indicating thermal degradation and defining the optimal operating window. Total phenolics ranged from 159.09 to 173.56 mg GAE/100 g, with the central point (172.94 mg GAE/100 g) statistically equivalent to the maximum (Tukey, p < 0.05). Central-point extracts showed high antioxidant activity (4,358.9 ± 252.5 µM Trolox/g), retaining approximately 98% after 48 h of storage (4,272.5 ± 67.3 µM Trolox/g), evidencing extract stability. UAE delivered in 4.5 min the extractive performance that required 48 h in the conventional refrigerated process, using a green solvent and mild conditions that preserved anthocyanins. The combination of high pigment content, strong antioxidant capacity, and post-extraction stability meets the key functional prerequisites of a natural halochromic indicator. The optimized green UAE process establishes a validated technological foundation for incorporating açaí anthocyanins into ethylene-responsive smart packaging, contributing to intelligent monitoring of food freshness with natural, sustainable inputs.

Acknowledgments: The authors thank the Federal University of Ceará (UFC) for the PIBIC scholarship granted to L.S.C. and the National Council for Scientific and Technological Development (CNPq).