Extraction, chemical characterization, and antioxidant activity of bioactive plant extracts

Bio-preservation methods based on the use of natural extracts have been proposed as hurdles to increase the safety of many food products. The objective of this work was to study the phytochemical profile, biological activity, and antioxidant potential of six plant extracts, and their ability to be used as food preservatives.

In this sense, rosemary, lemon balm, basil, tarragon, sage, and spearmint dry aerial parts were mechanically grinded. The extractions were performed using a sample/solvent ratio of 1:20, in a shaking water bath (at 150 rpm) at 60 °C for 90 min, and a Soxhlet apparatus (7 recycles), with ethanol 70% (v/v) (Et70%) and distilled water (dH₂O) as solvents in both methods. The influence of the distinct extraction methods and solvents on the total phenolic content (TPC, determined by Folin-Ciocalteu method), total flavonoid content (TFC), and antioxidant activity (determined by FRAP, ABTS•+ and DPPH assays) of the natural extracts was evaluated. Identification and quantification of phenolic compounds was achieved by Ultra-High Performance Liquid Chromatography.

The results show that both methodologies and solvents are adequate to obtain bioactive extracts. The TPC of water bath extracts was similar regardless of the solvent, apart from spearmint and sage extracts (higher TPC in ethanolic extracts). Alternatively, higher differences were observed in the TPC of Soxhlet extracts depending on the solvent, as aqueous extracts revealed greater TPC values. The TFC revealed differences due to the solvent for both methods: for water bath extracts, Et70% lead to higher TFC; while for Soxhlet extracts, dH₂O delivered extracts with greater TFC. Regarding antioxidant activity, all extracts showed promising results.

These outcomes provide insight on the phytochemical profile and biological activity of plant extracts and their value as bio-preservatives to be included in foods, thus encouraging the food industry to replace chemical preservatives with others that are plant-based.