GREEN EXTRACTION OF ANTHOCYANINS FROM RED CABBAGE WASTE USING PRESSURIZED ACID WHEY AS SOLVENT: AN UPCYCLING APPROACH

The sustainable development products and processes is a challenge faced by industries. In this sense, the use of agro-industrial residues via sustainable technologies and ecologically correct solvents for the recovery of bioactive compounds of industrial interest figures out as an economically viable alternative. Red cabbage leaves (Brassica oleracea L.) are post-harvest residues that have high concentrations of anthocyanins, a natural colorant. The substantial increase in the residual production of acid whey by dairy companies reveals an imperative need for the recovery of this effluent, which can be a promising alternative to conventional solvents for the extraction of biocompounds from plant matrices. In this context, the main objective of this study was to evaluate the potential use of acid whey as an alternative solvent for the extraction of anthocyanins from red cabbage leaves (wastes). The Pressurized Liquid Extraction (PLE) method was studied (T = 80 °C; t = 15 min; P = 100 bar; flow rate = 3mL/min) in comparison with a conventional method of Heating-Stirring Extraction (HSE) (T = 80°C and t = 15 min). Furthermore, performances of the acid whey against the ethanol acidified with citric acid (0.1% v/v C₆H₈O₇ in ethanol 70% v/v) was evaluated. The extracts were chemically characterized by total monomeric anthocyanins (TMA), total phenolic content (TPC), polymeric color density, individual anthocyanins (LC-DAD-ESI/MSn) and antioxidant activity determined based on chemical and cellular assays. The anti-inflammatory activity and cytotoxic properties (in four tumor cell lines) of the extracts were tested. The antibacterial activity was evaluated against four gram-negative bacteria and two gram-positive bacteria and antifungal activity against two Aspergillus sp. The extracts obtained by PLE showed the highest levels of TPC and antioxidant activities determined by chemical methods. In addition, the acid whey extracts showed higher anthocyanin extraction yields (293.37 and 183.98 mg C3G/100g) in relation to obtained by ethanol (202.81 and 159.15 mg C3G/100g), values referring to PLE and HSE, respectively. The main anthocyanin determined in red cabbage residue extracts was cyanidin-3-O-(feruloyl)-sophoroside-5-O-glycoside (949 m/z) (3.68 mg/g for PLE). The cell-based antioxidant activity assays indicated a weak activity (100 < IC50 < 200 μg/mL), for both extracts (obtained using PLE with acid whey and ethanol). The same was observed for the extracts against microbial activities. No anti-inflammatory activity and cytotoxic effects on monkey kidney cells (GI50 > 400 μg/ mL) were determined for the extracts. The absence of toxicity in anthocyanin-rich extracts, is crucial for industrial applications in the food and pharmacological fields. Overall, this is the first report of the application of pressurized acid whey as a sustainable alternative for the recovery of anthocyanins from red cabbage leaves. Taken together, the results indicated not only a great extraction efficiency but also that the obtained product has promissory potential as a natural colorant with biological potential.