Side-stream lignins: Potential antioxidant and antimicrobial agents in milk.

In recent years, lignin has drawn increasing attention due to its intrinsic antibacterial and antioxidant activities, biodegradability, and biocompatibility. Yet, like several other biogenic structures, its compositional heterogeneity represents a challenge to overcome. In addition, there are few studies regarding food applications of lignin. Herein, we evaluate the antimicrobial and antioxidant effects of lignin from two different sources. These lignins were characterized by attenuated total reflectance Fourier-transform infrared (ATR-FTIR) and hydrogen nuclear magnetic resonance (1H NMR) spectroscopies. Their antibacterial and antioxidant capacities (DPPH and Folin-Ciocalteu methods) were also investigated. Susceptibility tests were performed with the minimal inhibitory (MIC) and bactericidal (MBC) concentrations using the micro-broth dilution technique. Kraft lignin presented higher radical-scavenging and antibacterial activities than alkali lignin, indicating the dependence of antioxidant and antibacterial activities on the precursor biomass. Scanning electron microscopy shows morphologic changes in the bacteria after exposure to lignin, while confocal microscopy suggests that kraft lignin has affinity towards bacterial surfaces and the ability to cause cell membrane destabilization. Lignin inhibited the growth of Staphylococcus aureus and Salmonella Enteritidis in skimmed milk, herein taken as food model. Our results suggest that lignins are promising candidates for green additives to improve quality and safety within the food chain.

Chitosan/gelatin films with jatobá resin: Control of properties by vegetal resin inclusion and degree of acetylation modification.

Blending chitosan and gelatin, two biodegradable and non-toxic polymers, is a recurrent choice in food coating or biomaterials development. The incorporation of vegetal extracts into chitosan/gelatin films can improve or introduce some properties to these materials. Jatobá resin is a product of Hymenaea genus trees with antimicrobial and anti-inflammatory activities, interesting properties for films applied in several areas. The chitosan degree of acetylation (DA) influences the inter and intramolecular interactions of this polymer and, therefore, also implicates in changes of its properties. This research aims to study the influence of jatobá resin inclusion and chitosan DA modification on chitosan/gelatin films properties. Both jatobá resin and chitosan DA affected physicochemical, antimicrobial and barrier properties of the films, allowing the control of these properties by changes in these parameters. Jatobá resin incorporation and the decrease in chitosan DA significantly improved antimicrobial activity and water vapor permeability of films with the reduction of water solubility and swelling.

Combination of Rhamnolipid and Chitosan in Nanoparticles Boosts Their Antimicrobial Efficacy.

Nanomaterials have emerged as antimicrobial agents due to their unique physical and chemical properties. The development of nanoparticles (NPs) composed of natural biopolymers and biosurfactants have sparked interest, as they can be obtained without the use of complex chemical synthesis and toxic materials. In this study, we develop antimicrobial nanoparticles combining the biopolymer chitosan with the biosurfactant rhamnolipid. Addition of rhamnolipid reduced the size and polydispersity index of chitosan nanoparticles showing a more positive surface charge with improved stability, suggesting that chitosan-free amino groups are predominantly present on the surface of nanoparticles. Antimicrobial activity of chitosan/rhamnolipid nanoparticles (C/RL-NPs) against Staphylococcus strains surpassed that of either single rhamnolipid or chitosan, both in planktonic bacteria and biofilms. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of C/RL-NPs were determined considering the concentration of each individual molecule in NPs. MIC values of 14/19 µg mL-1 and MBC of 29/37 µg mL-1 were observed for S. aureus DSM 1104 and MIC and MBC of 29/37 and 58/75 µg mL-1 were observed against S. aureus ATCC 29213, respectively. For S. epidermidis, MIC and MBC of 7/9 and 14/19 µg mL-1 were noticed. Chitosan and chitosan nanoparticles eliminate the bacteria present in the upper parts of biofilms, while C/RL-NPs were more effective, eradicating most sessile bacteria and reducing the number of viable cells below the detection limit, when NPs concentration of 58/75 µg mL-1 was applied for both S. aureus DSM 1104 and S. epidermidis biofilms. The improved antibacterial efficacy of C/RL-NPs was linked to the increased local delivery of chitosan and rhamnolipid at the cell surface and, consequently, to their targets in Gram-positive bacteria. The combination of chitosan and rhamnolipid offers a promising strategy to the design of novel nanoparticles with low cytotoxicity, which can be exploited in pharmaceutical and food industries.