Valorization of tomato pomace: extraction of value-added components by deep eutectic solvents and their application in the formulation of cosmetic emulsions

Deep eutectic solvents (DESs) have been explored as an alternative to hazardous solvents to extract phenolic compounds. The aim of this work was estimate the performance of choline chloride-based DESs regarding the extraction of phenolic compounds of tomato pomace and determination of their antioxidant activity. Green choline chloride-based DESs coupled with ultrasound-assisted extraction were performed to extract. The solvents were choline chloride:1,2-propanediol (1:2 v/w):water (10% w/w) and choline chloride:lactic acid (1:2 v/w):water (10% w/w).The phytochemical constituents of tomato pomace extracts were verified with a combination of high-performance liquid chromatography coupled to diode-array detection and tandem mass spectrometry (HPLC-DAD-MS). The total antioxidant activity of the extracts was assessed using phosphomolybdenum (PM) method. The redox behavior of tomato pomace extracts was evaluated by means of cyclic voltammetry. The DES-based tomato pomace extracts were used as the antioxidant agent to develop a natural cosmetic formulation (colloidal solutions). The zeta-potential, colloidal stability, and the antioxidant, antimicrobial, and antifungal activity were studied. The antioxidant activity of the cosmetic emulsions has been studied by means of cyclic voltammetry. The tomato pomace extracts contain significant quantity of phenolic acids and flavanols (26-37% of the total compounds). Chlorogenic acid was detected as the main phenolic compound in tomato pomace extracts (ranging from 37.23 to 52.33 mu g/g). The total antioxidant power of the extracts varies in the range at 408 to 511.18 mu g/g extract. Choline chloride-based DESs have low values of oxidation potentials. Zeta-potential of obtained colloidal solutions (cosmetic formulation) varies from - 0.0102 to - 0.0594 mV indicating the moderate stability of obtained cosmetic emulsions. The following ranking of antioxidants was obtained: cosmetic emulsions with extract obtained by choline chloride:lactic acid deep eutectic solvent > cosmetic emulsions with extract obtained by choline chloride:1,2-propanediol deep eutectic solvent. Antibacterial and antifungal activity of the cosmetic emulsions with DES extracts relative to Gram-positive (Bacillus subtilis), Gram-negative (Escherichia coli), and Candida albicans wound pathogens were studied. Thus the DESs could serve as solvents to produce a phenolic-rich tomato extract could be readily applicable to cosmetic formulations.

Automated summary

This study evaluated the application of choline chloride-based deep eutectic solvents (DESs) in the extraction of phenolic compounds and determination of antioxidant activity in tomato pomace. The DES extracts showed significant antioxidant activity and can be used for the development of natural cosmetics.