Structure and antimicrobial comparison between N-(benzyl) chitosan derivatives and N-(benzyl) chitosan tripolyphosphate nanoparticles against bacteria, fungi, and yeast

Chitosan (Ch) was reacted with seven benzaldehyde analogs separately through reductive amination in which the corresponding imines were formed and followed by reduction to produce N-(benzyl) chitosan (NBCh) derivatives. ¹H NMR spectroscopy was used to characterize the products. The nanoparticles (NPs) of Ch and NBCh derivatives were prepared according to the ionotropic gelation mechanism between Ch products and sodium tripolyphosphate, followed by high-energy ultrasonication. Scanning electron microscopy, particle size, polydispersity index, and zeta potential were applied for the NPs examination. The particle size was ranged from 235.17 to 686.90 nm and narrow size distribution (PDI <1). The zeta potential of NPs was varied between -1.26 and -27.50 mV. The antimicrobial activity was evaluated against bacteria (Erwinia carotovora subsp. atroseptica, Erwinia carotovora subsp. carotovora, and Ralstonia solanacearum), fungi (Aspergillus flavus and Aspergillus niger), and yeast (Candida albicans). The action of NBCh derivatives was significantly higher than Ch. The NPs had considerably higher than the Ch and NBCh derivatives. The activity was directly proportional to the chemical derivatization of Ch and the zeta potential of the NPs. The antimicrobial efficacy of these derivatives formulated in a greener approach could become an alternative to using traditional antimicrobial applications in an environmentally friendly manner.

Silver Nanoparticles and Polyphenol Inclusion Compounds Composites for Phytophthora cinnamomi Mycelial Growth Inhibition

Phytophthora cinnamomi, responsible for "root rot" or "dieback" plant disease, causes a significant amount of economic and environmental impact. In this work, the fungicide action of nanocomposites based on silver nanoparticles and polyphenol inclusion compounds, which feature enhanced bioavailability and water solubility, was assayed for the control of this soil-borne water mold. Inclusion compounds were prepared by an aqueous two-phase system separation method through extraction, either in an hydroalcoholic solution with chitosan oligomers (COS) or in a choline chloride:urea:glycerol deep eutectic solvent (DES). The new inclusion compounds were synthesized from stevioside and various polyphenols (gallic acid, silymarin, ferulic acid and curcumin), in a [6:1] ratio in the COS medium and in a [3:1] ratio in the DES medium, respectively. Their in vitro response against Phytophthora cinnamomi isolate MYC43 (at concentrations of 125, 250 and 500 µg·mL^-1) was tested, which found a significant mycelial growth inhibition, particularly high for the composites prepared using DES. Therefore, these nanocomposites hold promise as an alternative to fosetyl-Al and metalaxyl conventional systemic fungicides.

Valorisation of chitinous biomass for antimicrobial applications

The chitin and chitosan market worldwide has shown tremendous growth, propelled by the expansion in the application domain. The market volume is projected to be more than 155 thousand metric tons by the year 2022. The global market for chitin and chitosan derivatives is expected to reach $4.2 billion by 2021 up from $2.0 billion in 2016 at a compound annual growth rate (CAGR) of 15.4%, from 2016 to 2021. Among chitin derivatives, chitosan is projected to offer the highest growth potential. The demand for a reliable source of high quality chitosan is rapidly increasing as new value added products enter the market. At the same time the growth of value added chitosan based products are limited by the availability of a sustainable supply chain. Antimicrobial properties are of special interest in the packaging, cosmetic, food and biomedical sector. Most of the latter applications warrants high-volume and low cost materials. However, the process chemistry for bulk chitosan manufacturing is currently not very environmentally friendly. Green technologies for chitosan modification have increased in recent years and now face the challenge of economic viability. In this review the status of antimicrobial chitosan derivatives will be reported with a critical review of the chemical technologies that would mitigate the commercialisation of these biopolymers in the antimicrobial biopolymer market sector. The amount of publications per annum has increased exponentially and the lack of global standardised antimicrobial test protocols make it rather challenging to properly evaluate the relative efficacy of these polymers.