Bacterial cellulose films with ZnO nanoparticles and propolis extracts: Synergistic antimicrobial effect

Alexandra Mocanu,Oana-Maria Popa,Cristina Busuioc,Liana Socaciu-Siebert,Paul Dietrich,Gabriela Isopencu

doi:10.1038/s41598-019-54118-w

Alexandra Mocanu, Oana-Maria Popa + Show 4 more

Open Access

https://doi.org/10.1038/s41598-019-54118-w

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Abstract

This study aimed to obtain possible materials for future antimicrobial food packaging applications based on biodegradable bacterial cellulose (BC). BC is a fermentation product obtained by Gluconacetobacter xylinum using food or agricultural wastes as substrate. In this work we investigated the synergistic effect of zinc oxide nanoparticles (ZnO NPs) and propolis extracts deposited on BC. ZnO NPs were generated in the presence of ultrasounds directly on the surface of BC films. The BC-ZnO composites were further impregnated with ethanolic propolis extracts (EEP) with different concentrations.The composition of raw propolis and EEP were previously determined by gas-chromatography mass-spectrometry (GC-MS), while the antioxidant activity was evaluated by TEAC (Trolox equivalent antioxidant capacity). The analysis methods performed on BC-ZnO composites such as scanning electron microscopy (SEM), thermo-gravimetrically analysis (TGA), and energy-dispersive X-ray spectroscopy (EDX) proved that ZnO NPs were formed and embedded in the whole structure of BC films. The BC-ZnO-propolis films were characterized by SEM and X-ray photon spectroscopy (XPS) in order to investigate the surface modifications. The antimicrobial synergistic effect of the BC-ZnO-propolis films were evaluated against Escherichia coli, Bacillus subtilis, and Candida albicans. The experimental results revealed that BC-ZnO had no influence on Gram-negative and eukaryotic cells.

Highlights

This study aimed to obtain possible materials for future antimicrobial food packaging applications based on biodegradable bacterial cellulose (BC)
The first step in our research study was to investigate the morphology of unmodified Bacterial cellulose (BC) films (Fig. 1a), respectively zinc oxide nanoparticles (ZnO NPs) obtained in the absence of BC and ultrasounds (Fig. 1b)
The presence of ultrasounds allows a better control of the obtaining process of relatively monodisperse inorganic nanoparticles[50] and the application of ultrasounds determined the entrapment of ZnO NPs on the surface of the BC films, and in the porous parts of the membranes forming agglomerated structures between the irregular fibers (Fig. 1c)

Summary

Introduction

This study aimed to obtain possible materials for future antimicrobial food packaging applications based on biodegradable bacterial cellulose (BC). The design of antibacterial or antimicrobial materials implies several important aspects, such as: (i) the use of cheap raw materials and agricultural or food wastes; (ii) facile synthesis and processing method; (iii) biocompatible properties in the case of medical or food applications; (iv) reduced impact on the environment at the end of the life span; (v) manufacturing of biodegradable products. Bacterial cellulose (BC) results from the fermentation processes of different biomass residues in the presence of Gluconacetobacter xylinum assigned as Acetobacter xylinum bacteria[4]. Its remarkable properties such as high retention of water, high mechanical and thermal resistance, and crystalline structure due to the 3D irregular disposal of BC nanofibers[5] made it suitable for different industrial fields. BC and BC composite materials have gained a lot of attention in water splitting or waste treatment applications[6,7], proton conducting membranes[8], supercapacitors, solar cells and transparent displays[9,10] and in the field of wound dressings[11,12], food packaging[13,14,15,16], tissue engineering[17,18] and superabsorbent in agriculture applications to improve the pedoclimate conditions for arid soils[19]

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