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The objective of this paper is to emphasize the fact that while consistent interest has been paid to the industrial use of chitosan, minor attention has been devoted to spread the knowledge of a good characterization of its physico-chemical properties. Therefore, the paper attempts to critically comment on the conflicting experimental results, highlighting the facts, the myths and the controversies. The goal is to indicate how to take advantage of chitosan versatility, to learn how to manage its variability and show how to properly tackle some unexpected undesirable features. In the sections of the paper various issues that relate chitosan properties to some basic features and to advanced solutions and applications are presented. The introduction outlines some historical pioneering works, where the chemistry of chitosan was originally explored. Thereafter, particular reference is made to analytical purity, characterization and chain modifications. The macromolecular characterization is mostly related to molecular weight and to degree of acetylation, but also refers to the conformational and rheological properties and solution stability. Then, the antimicrobial activity of chitosan in relation with its solubility is reviewed. A section is dedicated to the formulation of chitosan biomaterials, from gel to nanobeads, exploring their innovative application as active carrier nanoparticles. Finally, the toxicity issue of chitosan as a polymer and as a constructed nanomaterial is briefly commented in the conclusions. [ABSTRACT FROM AUTHOR]

Chitosan is a linear aminopolysaccharide that has been widely used for the formation of chitosan-based nanoparticles by ionic gelation with sodium tripolyphosphate (TPP). Often, the experimental design used to obtain these systems does not take into consideration important variables, such as the degree of acetylation (DA) and the molecular weight ( M w ) of chitosan. In this work, we studied the formation of chitosan-TPP nanoparticles with chitosan samples of varying DA and M w (DA0 ∼ 0–47% and M w ∼ 2.5–282 kDa). We addressed the influence the degree of space occupancy and the degree of crosslinking on the physical properties of chitosan-TPP nanoparticles. Nanoparticles that comprised chitosan of DA ∼ 0–21.7% behaved differently than those made of chitosan of DA ∼ 34.7–47%. We attributed these differences to the polymer conformation and chain flexibility of the distinct chitosans in solution. Moreover, chitosan of high M w were found to have a stronger preference for incorporating into the formed nanoparticles than do low- M w ones, as determined by SEC-HPLC. These results open new perspectives to understand the formation of chitosan nanoparticles by the ionic gelation technique. [ABSTRACT FROM AUTHOR]

The objective of this paper is to emphasize the fact that while consistent interest has been paid to the industrial use of chitosan, minor attention has been devoted to spread the knowledge of a good characterization of its physico-chemical properties. Therefore, the paper attempts to critically comment on the conflicting experimental results, highlighting the facts, the myths and the controversies. The goal is to indicate how to take advantage of chitosan versatility, to learn how to manage its variability and show how to properly tackle some unexpected undesirable features. In the sections of the paper various issues that relate chitosan properties to some basic features and to advanced solutions and applications are presented. The introduction outlines some historical pioneering works, where the chemistry of chitosan was originally explored. Thereafter, particular reference is made to analytical purity, characterization and chain modifications. The macromolecular characterization is mostly related to molecular weight and to degree of acetylation, but also refers to the conformational and rheological properties and solution stability. Then, the antimicrobial activity of chitosan in relation with its solubility is reviewed. A section is dedicated to the formulation of chitosan biomaterials, from gel to nanobeads, exploring their innovative application as active carrier nanoparticles. Finally, the toxicity issue of chitosan as a polymer and as a constructed nanomaterial is briefly commented in the conclusions.

Abstract: Bacillus cereus is an endospore-forming bacterium able to cause food-associated illness. Different treatment processes are used in the food industry to reduce the number of spores and thereby the potential of foodborne disease. Chitosan is a polysaccharide with well-documented antibacterial activity towards vegetative cells. The activity against bacterial spores, spore germination and subsequent outgrowth and growth (the latter two events hereafter denoted (out)growth), however, is poorly documented. By using six different chitosans with defined macromolecular properties, we evaluated the effect of chitosan on Bacillus cereus spore germination and (out)growth using optical density assays and a dipicolinic acid release assay. (Out)growth was inhibited by chitosan, but germination was not. The action of chitosan was found to be concentration-dependent and also closely related to weight average molecular weight (Mw) and fraction of acetylation (FA) of the biopolymer. Chitosans of low acetylation (FA =0.01 or 0.16) inhibited (out)growth more effectively than higher acetylated chitosans (FA =0.48). For the FA =0.16 chitosans with medium (56.8kDa) and higher Mw (98.3kDa), a better (out)growth inhibition was observed compared to low Mw (10.6kDa) chitosan. The same trend was not evident with chitosans of 0.48 acetylation, where the difference in activity between the low (19.6kDa) and high Mw (163.0kDa) chitosans was only minor. In a spore test concentration corresponding to 102–103 CFU/ml (spore numbers relevant to food), less chitosan was needed to suppress (out)growth compared to higher spore numbers (equivalent to 108 CFU/ml), as expected. No major differences in chitosan susceptibility between three different strains of B. cereus were detected. Our results contribute to a better understanding of chitosan activity towards bacterial spore germination and (out)growth. [Copyright &y& Elsevier]

Abstract: Chitosans, polysaccharides obtained from the exoskeleton of crustaceans, have been shown to exert antibacterial activity in vitro and their use as a food preservative is of growing interest. However, beyond a consensus that chitosan appears to disrupt the bacterial cell membrane, published data are inconsistent on the chemical characteristics that confer the antibacterial activity of chitosan. While most authors agree that the net charge density of the polymer (reflected in the fraction of positively charged amino groups at the C-2 position of the glucosamine unit) is an important factor in antibacterial activity, conflicting data have been reported on the effect of molecular weight and on the susceptibility among different bacterial species to chitosan. Therefore, we prepared batches of water-soluble hydrochloride salts of chitosans with weight average molecular weights (Mw) of 2–224kDa and degree of acetylation of 0.16 and 0.48. Their antibacterial activity was evaluated using tube inhibition assays and membrane integrity assays (N-Phenyl-1-naphthylamine fluorescence and potassium release) against Bacillus cereus, Escherichia coli, Salmonella Typhimurium and three lipopolysaccharide mutants of E. coli and S. Typhimurium. Chitosans with lower degree of acetylation (FA =0.16) were more active than the more acetylated chitosans (FA =0.48). No trends in antibacterial action related to increasing or decreasing Mw were observed although one of the chitosans (Mw 28.4kDa, FA =0.16) was more active than the other chitosans, inhibiting growth and permeabilizing the membrane of all the test strains included. The test strains varied in their susceptibility to the different chitosans with wild type S. Typhimurium more resistant than the wild type E. coli. Salmonellae lipopolysaccharide mutants were more susceptible than the matched wild type strain. Our results show that the chitosan preparation details are critically important in identifying the antibacterial features that target different test organisms. [Copyright &y& Elsevier]

Abstract: Enzymatic defense responses and protection against Phytophthora nicotianae were studied in tobacco plants treated with chitosan of different molecular weights (MW) and degrees of acetylation (DA). The concentration and mode of chitosan application affected enzymatic induction in tobacco leaves. β-1,3-Glucanase (EC 3.2.1.6) activity required 10 times the polymer concentration relative to the oligochitosan mixture to induce the highest activity above control when treated by foliar spray, indicating the influence of molecular weight in this response. PAL (EC 4.3.1.5) and POD (EC 1.11.1.6) activities increased above control as a result of the influence of polymer degree of acetylation when treatments were applied by foliar spray. A higher DA favored PAL activity, whereas a lower DA induced higher POD activity. Using an in vitro bioassay, it was found that the three chitosan compounds caused a reduction of the infection index of P. nicotianae in tobacco plants that was dependent on elicitor concentrations. There was a significant relationship between the reduction of the infection index and an increase in PAL activity when chitosan was applied by foliar spray and by substrate drench to the plant rhizosphere. These results demonstrate the influence of chitosan physico–chemical properties in plant-induced resistance and the relevance of particular responses in plant protection against pathogens. [Copyright &y& Elsevier]

The dissolution behavior of chitin in a series of ionic liquids containing alkylimidazolium chloride, alkylimidazolium dimethyl phosphate, and 1-allyl-3-methyl-imidazolium acetate has been studied. Chitin with a low degree of acetylation and low molecular weight can be readily dissolved in ionic liquids, while those with a high degree of acetylation can also be dissolved in ionic liquids with various critical solution temperatures (CST) mainly depending on the structure of the chitin and the ionic liquids. The results indicated that the dissolution behavior of chitin in ionic liquids was affected by the degree of acetylation (DA), the crystallinity, and the molecular weights of chitin, as well as the nature of the anion of the ionic liquid. [ABSTRACT FROM AUTHOR]

Abstract: The influence of high-intensity ultrasonication on the molecular weight and degree of acetylation of chitosan was investigated. High-molecular weight shrimp chitosan was purified by alkaline precipitation and dialysis from aqueous solution. A 1% (w/v) chitosan in 1% (v/v) aqueous acetic acid was sonicated for 0, 0.5, 1, 5, 15, and 30min at 25°C at power levels of 16.5, 28.0 and 35.2Wcm−2. Degree of acetylation was determined by high-pressure liquid chromatography with photodiode array at 210nm, monitoring acetyl groups released after complete hydrolysis and deacetylation of samples. Average molecular weight of ultrasonicated chitosan was determined by measurements of intrinsic viscosity of samples. The degree of acetylation of purified chitosan was 21.5%. Results indicated that neither power level nor sonication time altered the degree of deacetylation of chitosan molecules. Intrinsic viscosity of samples decreased exponentially with increasing sonication time. Rates of intrinsic viscosity decrease increased linearly with ultrasonic intensity. Results were analyzed in terms of molecular weight decreases. The Schmid polymer degradation model was used to analyze the molecular weight decay as a function of sonication time. A first order relationship for the dependence of the reaction rate on the ultrasonic intensity was suggested. Results of this study indicate that high-intensity ultrasonication can be utilized to reduce molecular weight of chitosan while maintaining the degree of acetylation. [Copyright &y& Elsevier]