Valorisation of tomato pomace: bioactive compounds, antimicrobial activity and photodynamic inactivation

Abstract

Tomato processing generates large amounts of by-products, particularly tomato pomace, which remains an underutilized source of bioactive compounds. The objective of this study was to investigate the potential valorisation of tomato pomace by characterising its polyphenol and carotenoid composition and evaluating its antimicrobial activity, including under photodynamic inactivation (PDI) conditions. Total polyphenol content determined by the Folin–Ciocalteu method was 3.9 ± 0.2 mg g⁻¹ DW for the standard variety (ST) and 3.8 ± 0.3 mg g⁻¹ DW for the high-lycopene variety (HL). HPLC-DAD-ESI-MS/MS analysis tentatively identified 27 polyphenols, with flavonoids representing the dominant class (82%), particularly naringenin chalcone, rutin, quercetin, and naringenin derivatives. Carotenoid levels reached 0.118 ± 0.003 mg g⁻¹ DW in ST and 0.196 ± 0.002 mg g⁻¹ DW in HL, with lycopene accounting for around 93% of the total carotenoid content. Antimicrobial assays revealed only modest activity overall. Polyphenol extracts showed a slight enhancement in antibacterial effect against Staphylococcus aureus when combined with UVA irradiation, while carotenoid extracts displayed little photodynamic response. These findings highlight tomato pomace as a relevant source of bioactive compounds and support its potential valorisation as a sustainable ingredient in food preservation strategies.