Novel enhancement of stability and antimicrobial activity of beetroot pigment nanocomposites via graphene oxide and silver nanoparticles

TL;DR

This study shows how combining beetroot pigments with silver and graphene oxide nanoparticles improves their stability and antimicrobial power, offering a sustainable alternative to chemical methods.

Contribution

A green synthesis method to enhance beetroot pigment stability and antimicrobial activity using silver and graphene oxide nanoparticles.

Findings

Pig-Ag-GO nanocomposite showed the highest inhibition zones, up to 29 mm against S. aureus at 100 mg/mL.

Pig-Ag-GO had the lowest MICs across all tested strains, demonstrating strong antimicrobial efficacy.

The combination of Ag and GO with beetroot pigments significantly improved pigment stability and activity.

Abstract

Natural pigments like betalains have strong antimicrobial properties but degrade quickly under environmental stress, limiting their stability in practical applications. This study presents the green synthesis of silver (Ag) and graphene oxide (GO) nanomaterials using a chitosan assisted method and their incorporation into beta vulgaris pigments to enhance overall performance. Trace amounts of pre-synthesized silver nanoparticles and graphene oxide were added to beta vulgaris ethanolic extract and subsequently embedded within a xanthan-gum polymer matrix to enhance pigments stability in beta vulgaris extract. This bioactive formulation improves the stability of sensitive pigments including anthocyanins and betacyanins by reducing degradation, while also strengthening antimicrobial activity due to the intrinsic properties of Ag and GO. Synthesized metals Ag, GO and different mixture of beta vulgaris extract with metals (pigment-Ag, pigment-Go, pigment-Ag-Go, pigment with xanthan gum and free xanthan gum) were characterized with the UV-Vis spectroscopy, fluorescence spectroscopy FTIR, Raman, SEM and TEM. Antimicrobial activity was evaluated against Gram-negative (Escherichia coli, Salmonella typhi), Gram-positive (Staphylococcus aureus, Streptococcus mutans), and fungal (Candida albicans) strains using both Agar well diffusion and microplate MIC assays. Inhibition zones increased with concentration (25, 50, and 100 mg/mL), with Pig-Ag-GO showing the highest activity at 100 mg/mL, producing zones up to 29 mm, especially against S. aureus. MICs were determined using concentrations ranging from 50 to 1000 µg/mL. The control pigment showed moderate activity, with MICs ranging from 247 to 333 µg/mL for Gram-negative bacteria, 108 µg/mL for S. aureus, and 717 µg/mL for C. albicans. Pig-Ag and Pig-GO exhibited improved efficacy, while the Pig-Ag-GO nanocomposite demonstrated the lowest MICs across all strains 200 µg/mL for E. coli, 217 µg/mL for S. typhi, 68 µg/mL for S. aureus, and 600 µg/mL for C. albicans. These results confirm the synergistic antimicrobial effect of combining silver and graphene oxide with natural pigment, enhancing both activity and stability. This study highlights a sustainable alternative to conventional chemical methods, utilizing green synthesis for metal nanoparticles to enhance pigment stability and maintain long-term antimicrobial properties.

The online version contains supplementary material available at 10.1038/s41598-026-42211-w.

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