Natural pigments as eco-friendly staining agents: evaluation of β-carotene-rich carrot and betanin-rich beetroot extracts for bacterial biofilm visualisation

This study aimed to obtain a β-carotene-rich extract from carrot (CEC) and a betanin-rich extract from beetroot (BEB) and to assess their staining capacity on bacterial biofilms. The extracts were analysed using UV-Vis spectroscopy and HPLC. Strains of Gram-positive and Gram-negative bacteria were cultured to form biofilms, which were subsequently stained with the extracts. Photographs were taken after biofilm staining via optical microscopy. The UV-Vis spectrum of CEC revealed bands at 477 nm and 450 nm, whereas BEB exhibited at 534 nm and 482 nm. The HPLC chromatogram of CEC showed peaks at retention times (RT) of 14.13 and 15.07 min. In contrast, BEB displayed a relatively simple profile at an RT of 21.09 min. Images indicated that CEC had a more effective staining capacity than BEB, particularly in Gram-negative strains. These findings suggest that CEC could be further explored in microbial identification protocols.