Extraction of tomato pomace with "green" solvents and evaluation of antioxidant properties

Most conventional organic solvents are toxic and pose high risks to human health. In this context, green solvents, such as deep eutectic solvents (DES), are promising and environmentally friendly. DES exhibit the advantages of ionic liquids and, in addition to being inexpensive, are low- or non-toxic, renewable and often biodegradable. The most important by-product generated from the vegetable industry is the so-called pomace that still contains a large number of bioactive compounds of great interest, such as phenolic compounds which have antioxidation properties. Antioxidant compounds are known as molecules that are able to stabilize, inhibit, deactivate and scavenge free radicals, thus protecting the human body against oxidative damage. In this study, a choline chloride-based deep eutectic solvent was used in ultrasound-assisted extraction of "green" organic compounds from tomato pomace (Lycopersicon esculentum. Mill.). Characterization HPLC-DAD methods were employed and total phenolic (TPC) and total flavonoid compounds (TFC) were assayed. Various experimental techniques including DPPH and ABTS radical scavenging activity were used to characterize the antioxidant activity of the extract. The phenolic content of the extracts was determined by the Folin–Ciocalteu method. The results also indicated the highest antioxidant activities measured in terms of 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging (40%) and 2,2′-azino-bis-(3-ethylbenzothiazoline)-6-sulfonic acid (ABTS)(50%), as well as highest total phenolic content (TPC) (11.12 ± 0.02 mg gallic acid equivalent/g fresh weight). For this reason, in the future, the use of eutectic solvents may be the best method for the extraction of organic compounds from tomato pomace.