From Waste to Value: Phenolic Content and Antioxidant Potential in Labdanum Residues via Solid–Liquid and Subcritical Water Extraction

Cistus ladanifer L. is a Mediterranean shrub and is widely distributed in the Iberian Peninsula. It has high importance in the perfume industry and is used as a medicinal plant due to its essential oils. Its residues from distilleries, however, are underutilized. These residues are potential sources of phenolic compounds that can be extracted and used in several applications. In this work, extracts from distillery residues were produced using two methods, solid–liquid extraction (SLE) and subcritical water extraction (SWE). Two extracts were produced for each method, under different conditions. For the SLE extraction, the two treatment options were CLL40°C (1g:50 mL 50:50 water:methanol (v/v), 1 h extraction time, 40 °C) and CLL60°C (1g:100 mL 50:50 water:methanol (v/v), 1 h extraction time, 60 °C). For the SWE extraction, the extracts were produced by mixing 2 g of CLL with 200 mL of ultrapure water at 60 bar and 100 or 150 °C. The yield of the extraction was assessed, along with its total phenolic content (TPC) and antioxidant activity being assessed using different assays (DPPH^• and ABTS^•+ scavenging activities and FRAP assay). CLL40°C displayed the highest TPC (175.24 ± 21.82 mg gallic acid equivalents/g dry extract) and the strongest antioxidant activity in the DPPH^• and ABTS^•+ assays (267.81 ± 60.11 and 518.90 ± 50.16 mg Trolox equivalents/g dry extract). CLL60°C displayed the highest results in the FRAP assay (11.64 ± 2.96 mg ascorbic acid equivalents/g dry extract). The analysis of the SWE extracts is currently being performed and will be finished in time for the conference. These results will offer valuable information on the impact and potential of different extraction methods for the valorization of labdanum residues and phenolic extraction.