Molecular weight of chitosan influences antimicrobial activity in oil-in-water emulsions

A comprehensive characterization of Hermetia illucens derived chitosan produced through homogeneous deacetylation

The increasing demand for chitin and chitosan is driving research to explore alternative sources to crustaceans. Insects, particularly bioconverters as Hermetia illucens, are promising substitutes as they process food industry waste into valuable molecules, including chitin. Chitosan can be produced by chitin deacetylation: hot deacetylation to obtain a heterogeneous chitosan, the commonly produced, and cold deacetylation to obtain a homogeneous chitosan, not widely available. The two different treatments lead to a different arrangement of the amine and acetyl groups in the chitosan structure, affecting its molecular weight, deacetylation degree, and biological activity. This is the first report on the production and chemical-physical and biological characterization of homogenous chitosan derived from H. illucens larvae, pupal exuviae, and adults. This work, in addition to the report on heterogeneous chitosan by our research group, completes the overview of H. illucens chitosan. The yield values obtained for homogeneous chitosan from pupal exuviae (3 and 7 %) are in the range of insect (2-8 %) and crustaceans (4-15 %) chitosan. The evaluation of the antioxidant activity and antimicrobial properties against Gram-negative (Escherichia coli) and Gram-positive (Micrococcus flavus) bacteria confirmed the great versatility of H. illucens chitosan for biomedical and industrial applications and its suitability as an alternative source to crustaceans.

The Durable Chitosan Functionalization of Cellulosic Fabrics

In this work, the durability of chitosan functionalization of cellulosic textile substrates, cotton and cotton/polyester blended fabrics, was studied. Chitosan is a naturally occurring biopolymer that can be produced inexpensively. It should be dissolved in an acidic solution to activate its antimicrobial and other properties, i.e., good biocompatibility, bioabsorbability, wound healing, hemostatic, anti-infective, antibacterial, non-toxic, and adsorptive properties. The application of chitosan to textile products has been researched to achieve antimicrobial properties, but the durability, after several maintenance cycles, has not. Chitosan functionalization was carried out using maleic acid (MA) and 1,2,3,4-butanetetracarboxylic acid (BTCA) as crosslinking and chitosan-activating agents and sodium hypophosphite monohydrate as a catalyst. To determine durability, the fabrics were subjected to 10 maintenance cycles according to ISO 6330:2012 using Reference detergent 3 and drying according to Procedure F. The properties were monitored after the 3rd and 10th cycles. The crosslinking ability of chitosan with cellulosic fabrics was monitored by Fourier infrared spectrometry using the ATR technique (FTIR-ATR). Changes in mechanical properties, whiteness and yellowing, and antimicrobial properties were determined using standard methods. Compared to maleic acid, BTCA proved to be a better crosslinking agent for chitosan.

Grafted chitosan thin films of various degrees of acetylation as a reusable platform for the investigation of biological interactions

Surface treatment by adhesive polymers is a promising solution to immobilize and study bacteria cells through microscopic assays and, for example, control their growth or determine their susceptibility to antibiotic treatment. The stability of such functional films in wet conditions is crucial, as the film degradation would compromise a persistent use of the coated devices. In this work, low roughness chitosan thin films of degrees of acetylation (DA) ranging from 0.5 % to 49 % were chemically grafted onto silicon and glass substrates and we have demonstrated how the physicochemical properties of the surfaces and the bacterial response were DA-dependent. A fully deacetylated chitosan film presented an anhydrous crystalline structure while the hydrated crystalline allomorph was the preferred structure at higher DA. Moreover, their hydrophilicity increased at higher DA, leading to higher film swelling. Low DA chitosan-grafted substrate favored bacterial growth away from the surface and could be envisioned as bacteriostatic surfaces. Contrarily, an optimum of Escherichia coli adhesion was found for substrates modified with chitosan of DA = 35 %: these surfaces are adapted for the study of bacterial growth and antibiotic testing, with the possibility of reusing the substrates without affecting the grafted film - ideal for limiting single-use devices.

Synthesis and antibacterial analysis of C-6 amino-functionalised chitosan derivatives

Synthesis of 6-O-(3-alkylamino-2-hydroxypropyl) derivatives of chitosan was achieved using a four-step strategy of N-protection, O-epoxide addition, epoxide ring opening using an amine and N-deprotection. Benzaldehyde and phthalic anhydride were used for the N-protection step, producing N-benzylidene and N-phthaloyl protected derivatives, respectively, resulting in two corresponding final 6-O-(3-alkylamino-2-hydroxypropyl) derivative series, BD1-BD6 and PD1-PD14. All the compounds were characterized using FTIR, XPS and PXRD studies and tested for antibacterial efficacy. The phthalimide protection strategy was found to be easier to apply and effective in terms of the synthetic process and improvement in antibacterial activity. Amongst the newly synthesized compounds, PD13 (6-O-(3-(2-(N,N-dimethylamino)ethylamino)-2-hydroxypropyl)chitosan) was the most active with eight times greater activity compared to the unmodified chitosan and, PD7 6-O-(3-(3-(N-(3-aminopropyl)propane-1,3-diamino)propylamino)-2-hydroxypropyl)chitosan) having a four-fold activity than chitosan, was found to be the second most potent derivative. This work has produced new chitosan derivatives those are more potent than chitosan itself and show promise in antimicrobial applications.

The Antibacterial Activity of Egyptian Wasp Chitosan-Based Nanoparticles against Important Antibiotic-Resistant Pathogens

The current work discusses the production and characterization of new biodegradable nanoparticles for biomedical applications based on insect chitosan. Chitosan has numerous features due to the presence of primary amine groups in repeating units, such as antibacterial and anticancer activities. When polyanion tripolyphosphate is added to chitosan, it creates nanoparticles with higher antibacterial activity than the original chitosan. In this study, the ionic gelation technique was used to make wasp chitosan nanoparticles (WCSNPs) in which TEM and FTIR were used to investigate the physicochemical properties of the nanoparticles. In addition, the antibacterial activities of chitosan nanoparticles against extended-spectrum beta-lactamase (ESBL)- and carbapenemase-producing Klebsiella pneumoniae, Escherichia coli, and Pseudomonas aeruginosa were evaluated. The extracted wasp chitosan exhibited high solubility in acetic acid and met all standard criteria of all characterization testes for nanoparticles; the zeta potential indicated stable WCSNPs capable of binding to cellular membrane and increasing the cellular uptake. The produced WCSNPs showed growth inhibition activity against all tested strains, and the bacterial count was lower than the initial count. The inhibition percent of WCSNPs showed that the lowest concentration of WCSNPs was found to be effective against tested strains. WCSNPs’ antibacterial activity implies that they could be used as novel, highly effective antibacterial agents in a variety of biological applications requiring antibacterial characteristics.

Discussions on the Properties of Emulsion Prepared by Using an Amphoteric Chitosan as an Emulsifier

A typical emulsion contains oil and water phases, and these two phases can be combined by an emulsifier with both lipophilic and hydrophilic groups to form a mixture. If the component of water is more than oil, the mixture is termed as o/w emulsion. The water is called the continuous phase and the oil is called the dispersed phase. Oppositely, if the component of oil is more than water, the mixture is termed as w/o emulsion. The oil is called the continuous phase and the water is called the dispersed phase. Chitosan, which is biocompatible and non-toxic, was modified as an amphoteric emulsifier to replace sodium acrylates copolymer in the preparation of emulsions. Both sodium acrylates copolymer and the modified chitosan were used as emulsifiers, respectively, and the properties of moisturizing, transmittance, the number of bacteria, and emulsion stability were measured. The experimental results showed that the amount of amphoteric chitosan is less than that of sodium acrylate copolymer by 20% under a similar degree of emulsification. The measurement of spatial moisture showed the difference in equilibrium humidity was in the range of 2.05 to 2.20 gH2O/kg dry air, indicating that the moisture retention of the modified chitosan is better. In addition, the calculation of bacterial growth confirmed that the number of bacteria in the amphoteric chitosan emulsion and the sodium acrylate copolymer emulsion were 80 and 560, respectively. The emulsion stability was tested by the separation of oil and water phases in the diluted emulsion and by centrifugal accelerated sedimentation. The results showed that, for both emulsifiers, no separation of the oil and water phases occurred within one hour, and the stability of the modified chitosan emulsion was better. Therefore, the modified chitosan successfully substitutes sodium acrylates copolymer as an emulsifier in the preparation of emulsion.

Characterization of chitin and chitosan derived from Hermetia illucens, a further step in a circular economy process

Due to their properties and applications, the growing demand for chitin and chitosan has stimulated the market to find more sustainable alternatives to the current commercial source (crustaceans). Bioconverter insects, such as Hermetia illucens, are the appropriate candidates, as chitin is a side stream of insect farms for feed applications. This is the first report on production and characterization of chitin and chitosan from different biomasses derived from H. illucens, valorizing the overproduced larvae in feed applications, the pupal exuviae and the dead adults. Pupal exuviae are the best biomass, both for chitin and chitosan yields and for their abundance and easy supply from insect farms. Fourier-transform infrared spectroscopy, X-ray diffraction and scanning electron microscope analysis revealed the similarity of insect-derived polymers to commercial ones in terms of purity and structural morphology, and therefore their suitability for industrial and biomedical applications. Its fibrillary nature makes H. illucens chitin suitable for producing fibrous manufacts after conversion to chitin nanofibrils, particularly adults-derived chitin, because of its high crystallinity. A great versatility emerged from the evaluation of the physicochemical properties of chitosan obtained from H. illucens, which presented a lower viscosity-average molecular weight and a high deacetylation degree, fostering its putative antimicrobial properties.

Insect Chitin-Based Nanomaterials for Innovative Cosmetics and Cosmeceuticals

Chitin and its derivatives are attracting great interest in cosmetic and cosmeceutical fields, thanks to their antioxidant and antimicrobial properties, as well as their biocompatibility and biodegradability. The classical source of chitin, crustacean waste, is no longer sustainable and fungi, a possible alternative, have not been exploited at an industrial scale yet. On the contrary, the breeding of bioconverting insects, especially of the Diptera Hermetia illucens, is becoming increasingly popular worldwide. Therefore, their exoskeletons, consisting of chitin as a major component, represent a waste stream of facilities that could be exploited for many applications. Insect chitin, indeed, suggests its application in the same fields as the crustacean biopolymer, because of its comparable commercial characteristics. This review reports several cosmetic and cosmeceutical applications based on chitin and its derivatives. In this context, chitin nanofibers and nanofibrils, produced from crustacean waste, have proved to be excellent cosmeceutical active compounds and carriers of active ingredients in personal care. Consequently, the insect-based chitin, its derivatives and their complexes with hyaluronic acid and lignin, as well as with other chitin-derived compounds, may be considered a new appropriate potential polymer to be used in cosmetic and cosmeceutical fields.

Effect of carbon dots in combination with aqueous chitosan solution on shelf life and stability of soy milk

Use of carbon dots (CDs) in combination with aqueous chitosan solution to extend shelf life and improve stability of soy milk was investigated. Soy milk samples with chitosan solution (0.00%, 0.08%, 0.12%, 0.16% and 0.20%) and banana-based CDs (4%, 6% and 8%) were prepared and stored at room temperature (25-30 °C) for shelf life evaluation. Soy milk with 0.16% chitosan solution exhibited improved stability as evident by increased viscosity, stability coefficient, zeta potential and decreased centrifugation rate compared with soy milk without chitosan. The suitable amount of carbon dots could effectively inhibit the growth of Escherichia coli, Staphylococcus aureus and Bacillus subtilis. Soy milk with 0.16% chitosan and 8% CDs exhibited longer shelf life and significantly lower total bacterial count after storage at room temperature for up to 4 days. Electronic nose-based flavor characteristics of all treated soy milk samples were not far from that of the control sample.

Food Safety through Natural Antimicrobials

Microbial pathogens are the cause of many foodborne diseases after the ingestion of contaminated food. Several preservation methods have been developed to assure microbial food safety, as well as nutritional values and sensory characteristics of food. However, the demand for natural antimicrobial agents is increasing due to consumers' concern on health issues. Moreover, the use of antibiotics is leading to multidrug resistant microorganisms reinforcing the focus of researchers and the food industry on natural antimicrobials. Natural antimicrobial compounds from plants, animals, bacteria, viruses, algae and mushrooms are covered. Finally, new perspectives from researchers in the field and the interest of the food industry in innovations are reviewed. These new approaches should be useful for controlling foodborne bacterial pathogens; furthermore, the shelf-life of food would be extended.

Clarithromycin-Loaded Poly (Lactic-co-glycolic Acid) (PLGA) Nanoparticles for Oral Administration: Effect of Polymer Molecular Weight and Surface Modification with Chitosan on Formulation, Nanoparticle Characterization and Antibacterial Effects

Clarithromycin (CLR) is a member of the macrolide antibiotic group. CLR has low systemic oral bioavailability and is a drug of class II of the Biopharmaceutical Classification System. In many studies, using nanoparticles (NPs) as a drug delivery system has been shown to increase the effectiveness and bioavailability of active drug substances. This study describes the development and evaluation of poly (lactic-co-glycolic acid) (PLGA) NPs and chitosan (CS)-coated PLGA NPs for oral delivery of CLR. NPs were obtained by nanoprecipitation technique and characterized in detail, and the effect of three molecular weights (Mw1: 7.000-17.000, Mw2: 38.000-54.000, Mw3: 50.000-190.000) of PLGA and CS coating on particle size (PS), zeta potential (ZP), entrapment efficiency (EE%), and release properties etc. were elucidated. Gastrointestinal stability and cryoprotectant effect tests were performed on the NPs. The PS of the prepared NPs were in the range of 178 to 578 nm and they were affected by the Mw and CS coating. In surface-modified formulations with CS, the ZP of the NPs increased significantly to positive values. EE% varied from 62% to 85%, depending upon the Mw and CS coating. In vitro release studies of CLR-loaded NPs showed an extended release up to 144 h. Peppas-Sahlin and Weibull kinetic model was found to fit best for CLR release from NPs. By the broth microdilution test method, the antibacterial activity of the formulations was determined on Staphylococcus aureus (ATCC 25923), Listeria monocytogenes (ATCC 1911), and Klebsiella pneumoniae (ATCC 700603). The structures of the formulations were clarified by thermal (DSC), FT-IR, and 1H-NMR analysis. The results showed that PS, ZP, EE%, and dissolution rates of NPs were directly related to the Mw of PLGA and CS coating.

An assessment of antibacterial mode of action of chitosan on Listeria innocua cells using real-time HATR-FTIR spectroscopy

The antibacterial mode of action of chitosan using real-time, horizontal attenuated total reflectance, Fourier-transform infrared (HATR-FTIR) spectroscopy and transmission electron microscopy (TEM) was investigated. Listeria innocua was treated with chitosan solution. HATR-FTIR revealed an increased lethality and substantially metabolomics response on cell components. The main changes in FTIR and their 2nd derivative spectra were at 1045 cm^-1 (carbohydrates in cell wall). Principal component analysis clearly segregated untreated and treated cells. Loadings plot revealed the functional groups in cell wall, cell membrane, phospholipid and protein regions of spectrum that are responsible for the classification of treated and control spectra. Kinetic traces of the metabolomics change suggested that cell wall and cell membrane seemed to be the initial target of the antimicrobial mechanism of chitosan. In agreement with the TEM images, which showed breakage of cell wall integrity. The cell wall, cell membrane, phospholipids, proteins and nucleic acids of FTIR spectral data recorded during the cell inactivation were shown to be linked to the metabolomics cell response in the lethality rate and structure of the cells. This work clearly showed, using HATR-FTIR spectroscopy, how bacteria can change their metabolomics response substantially during the first 45 min of contact time.

Investigation of the Internal Chemical Composition of Chitosan-Based LbL Films by Depth-Profiling X-ray Photoelectron Spectroscopy (XPS) Analysis

Chitosan-based thin films were assembled using the layer-by-layer technique, and the axial composition was accessed using X-ray photoelectron spectroscopy with depth profiling. Chitosan (CHI) samples possessing different degrees of acetylation ([Formula: see text]) and molecular weight ([Formula: see text]) produced via the ultrasound-assisted deacetylation reaction were used in this study along with two different polyanions, namely, sodium polystyrenesulfonate (PSS) and carboxymethylcellulose (CMC). When chitosan, a positively charged polymer in aqueous acid medium, was combined with a strong polyanion (PSS), the total positive charge of chitosan, directly related to its [Formula: see text], was the key factor affecting the film formation. However, for CMC/CHI films, the pH of the medium and [Formula: see text] of chitosan strongly affected the film structure and composition. Consequently, the structure and the axial composition of chitosan-based films can be finely adjusted by choosing the polyanion and defining the chitosan to be used according to its DA and [Formula: see text] for the desired application, as demonstrated by the antibacterial tests.

Application of Chitosan Films Enriched with Oregano Essential Oil on Bologna – Active Compounds and Sensory Attributes

Chitosan films prepared with oregano essential oil were applied on bologna slices. Release of the essential oil compounds during film preparation and application on the meat product and consumer acceptability of bologna enriched with oregano essential oil were tested. Oregano essential oil compounds were quantified by gas chromatography mass spectroscopy (GCMS) after extraction from the filmforming solution, films before and after application on bologna and from bologna slices before and after application of the films. The results indicated that the concentration of components of the essential oil sharply decreased during film preparation, e.g. from 757.7 ppm carvacrol in film-forming solution to 2.1 ppm in dried films. No carvacrol was detected in the films after application on bologna for 5 days at 4°C, mainly due to its diffusion into bologna. It seemed that the moisture and high lipid content of bologna helped the diffusion of the oregano essential oil from the chitosan film matrix into the product. Sensory evaluation suggested that addition of 45 ppm or less of oregano oil to bologna would be acceptable to consumers. Results support the potential use of chitosan–oregano essential oil films as an antimicrobial packaging material for processed meat.

Effect of dual delivery of antibiotics (vancomycin and cefazolin) and BMP-7 from chitosan microparticles on Staphylococcus epidermidis and pre-osteoblasts in vitro

The main aims of this manuscript are to: i) determine the effect of commonly used antibiotics to treat osteoarticular infections on osteoblast viability, ii) study the dual release of the growth factor (BMP-7) and antibiotics (vancomycin and cefazolin) from chitosan microparticles iii) demonstrate the bioactivity of the antibiotics released in vitro on Staphylococcus epidermidis. The novelty of this work is dual delivery of growth factor and antibiotic from the chitosan microparticles in a controlled manner without affecting their bioactivity. Cefazolin and vancomycin have different therapeutic concentrations for their action in vivo and therefore, two different concentrations of the drugs were used. Osteoblast cytotoxicity test concluded that cefazolin concentrations of 50 and 100μg/ml were found to have positive influence on osteoblast proliferation. A significant increase in osteoblast proliferation was observed in the presence of cefazolin and BMP-7 in comparison with BMP-7 alone group; indicating cefazolin might play a role in osteoblast proliferation. On the other hand, vancomycin concentration of 1000μg/ml was found to significantly reduce (p<0.01) osteoblast proliferation in comparison with controls. The microbial study indicated that cefazolin at a minimum concentration of 21.5μg/ml could inhibit ~85% growth of S. epidermidis, whereas vancomycin at a concentration of 30μg/ml was found to inhibit ~80% bacterial growth.

VirR-Mediated Resistance of Listeria monocytogenes against Food Antimicrobials and Cross-Protection Induced by Exposure to Organic Acid Salts

Formulations of ready-to-eat (RTE) foods with antimicrobial compounds constitute an important safety measure against foodborne pathogens such as Listeria monocytogenes. While the efficacy of many commercially available antimicrobial compounds has been demonstrated in a variety of foods, the current understanding of the resistance mechanisms employed by L. monocytogenes to counteract these stresses is limited. In this study, we screened in-frame deletion mutants of two-component system response regulators associated with the cell envelope stress response for increased sensitivity to commercially available antimicrobial compounds (nisin, lauric arginate, ε-polylysine, and chitosan). A virR deletion mutant showed increased sensitivity to all antimicrobials and significantly greater loss of membrane integrity when exposed to nisin, lauric arginate, or ε-polylysine (P < 0.05). The VirR-regulated operon, dltABCD, was shown to be the key contributor to resistance against these antimicrobial compounds, whereas another VirR-regulated gene, mprF, displayed an antimicrobial-specific contribution to resistance. An experiment with a β-glucuronidase (GUS) reporter fusion with the dlt promoter indicated that nisin does not specifically induce VirR-dependent upregulation of dltABCD. Lastly, prior exposure of L. monocytogenes parent strain H7858 and the ΔvirR mutant to 2% potassium lactate enhanced subsequent resistance against nisin and ε-polylysine (P < 0.05). These data demonstrate that VirRS-mediated regulation of dltABCD is the major resistance mechanism used by L. monocytogenes against cell envelope-damaging food antimicrobials. Further, the potential for cross-protection induced by other food-related stresses (e.g., organic acids) needs to be considered when applying these novel food antimicrobials as a hurdle strategy for RTE foods.

Antimicrobial mechanism and activity of dodecyl rosmarinate against Staphylococcus carnosus LTH1502 as influenced by addition of salt and change in pH

Antimicrobial activity and mechanism of action of rosmarinic acid (RA) and dodecyl rosmarinate (RE12) against Staphylococcus carnosus LTH1502 were studied as a function of pH (5.8 to 7.2) and in the presence of salts (KCl and MgCl2, 0 to 500 mM). Microbial cultures were exposed to unesterified RA and to esterified RE12, and cell number was determined by plate counting. Cells exposed to RA and RE12 at the minimum bactericidal concentration (200 and 0.05 mM, respectively) were examined using scanning electron microscopy to observe potential morphological changes. Activity of RA was found to be strongly dependent on pH, salt type, and concentration, whereas RE12 led to the compound's activity becoming independent of pH, salt concentration, and type. Scanning electron microscopy images showed that morphology of cells treated with RE12 after incubation of 1 h was irrevocably altered. Our results suggest that esterification (i) altered the mechanism of action by increasing the compound's affinity for cell membranes and (ii) decreased the compound's susceptibility to changes in environmental conditions that alter its charge. Highly specific changes in structure-activity relationships can be observed when esterifying a naturally active phenol such as RA with an alkyl chain that has a carbon chain length of 12.

Advances in the control of wine spoilage by Zygosaccharomyces and Dekkera/Brettanomyces

Understanding the characteristics of yeast spoilage, as well as the available control technologies, is vital to producing consistent, high-quality wine. Zygosaccharomyces bailii contamination may result in refermentation and CO2 production in sweet wines or grape juice concentrate, whereas Brettanomyces bruxellensis spoilage often contributes off-odors and flavors to red wines. Early detection of these yeasts by selective/differential media or genetic methods is important to minimize potential spoilage. More established methods of microbial control include sulfur dioxide, dimethyl dicarbonate, and filtration. Current research is focused on the use of chitosan, pulsed electric fields, low electric current, and ultrasonics as means to protect wine quality.

Antimicrobial activity of food-compatible plant extracts and chitosan against naturally occurring micro-organisms in tomato juice

BACKGROUND

Chitosan (AC) and five hydroalcoholic extracts from Lithospermum erythrorhizon (SE), Rheum palmatum (RE), Thymus vulgaris (AT), Lippia citriodora (PLX) and a mixture of Rosmarinus officinalis, Salvia lavandulifolia and Thymus mastichina (LA) were tested for antimicrobial activity against bacteria, yeasts and filamentous fungi using two broth dilution methods. The effects of adding single extracts on naturally occurring micro-organisms and sensory qualities of raw tomato juice were also evaluated.

RESULTS

SE extract exhibited the strongest activity, with minimum inhibitory concentrations (MICs) of 100-400 µg mL⁻¹ for Gram-positive and 1600-3200 µg mL⁻¹ for Gram-negative bacteria. Enterobacter aerogenes showed the greatest susceptibility to AC (MIC 1600 µg mL⁻¹). Lethal effects of extracts and AC were achieved at a minimum bactericidal concentration (MBC)/MIC ratio of 2 in 88% of assays. SE and RE extracts and AC also exhibited antifungal effect against yeasts, but they had no activity on filamentous fungi. Control and 100 mg L⁻¹ SE-added tomato juices did not differ in acceptance, but this SE concentration was not effective in the control of microbial load throughout cold storage.

CONCLUSION

Results confirm the antimicrobial potential of the plant extracts, but additional research is needed until the agents responsible for the activities have been determined in order to use them as natural constituents of multiple-barrier food preservation systems.

Effectiveness of chitosan on the inactivation of enteric viral surrogates

Chitosan is known to have bactericidal and antifungal activity. Although human noroviruses are the leading cause of non-bacterial gastroenteritis, information on the efficacy of chitosan against foodborne viruses is very limited. The objective of this work was to determine the effectiveness of different molecular weight chitosans against the cultivable human norovirus and enteric virus surrogates, feline calicivirus, FCV-F9, murine norovirus, MNV-1, and bacteriophages, MS2 and phiX174. Five purified chitosans (53, 222, 307, 421, ~1150 kDa) were dissolved in water, 1% acetic acid, or aqueous HCl pH = 4.3, sterilized by membrane filtration, and mixed with equal volume of virus to obtain a final concentration of 0.7% chitosan and 5 log(10) PFU/ml virus. Virus-chitosan suspensions were incubated for 3 h at 37 °C. Untreated viruses in PBS, in PBS with acetic acid, and in PBS with HCl were tested as controls. Each experiment was run in duplicate and replicated at least twice. Water-soluble chitosan (53 kDa) reduced phiX174, MS2, FCV-F9 and MNV-1 titers by 0.59, 2.44, 3.36, and 0.34 log(10) PFU/ml respectively. Chitosans in acetic acid decreased phiX174 by 1.19-1.29, MS2 by 1.88-5.37, FCV-F9 by 2.27-2.94, and MNV-1 by 0.09-0.28 log(10) PFU/ml, respectively. Increasing the MW of chitosan corresponded with an increasing antiviral effect on MS2, but did not appear to play a role for the other three tested viral surrogates. Overall, chitosan treatments showed the greatest reduction for FCV-F9, and MS2 followed by phiX174, and with no significant effect on MNV-1.

Review of antimicrobial and antioxidative activities of chitosans in food

Interest in chitosan, a biodegradable, nontoxic, non-antigenic, and biocompatible biopolymer isolated from shellfish, arises from the fact that chitosans are reported to exhibit numerous health-related beneficial effects, including strong antimicrobial and antioxidative activities in foods. The extraordinary interest in the chemistry and application in agriculture, horticulture, environmental science, industry, microbiology, and medicine is attested by about 17,000 citations on this subject in the Scopus database. A special need exists to develop a better understanding of the role of chitosans in ameliorating foodborne illness. To contribute to this effort, this overview surveys and interprets our present knowledge of the chemistry and antimicrobial activities of chitosan in solution, as powders, and in edible films and coating against foodborne pathogens, spoilage bacteria, and pathogenic viruses and fungi in several food categories. These include produce, fruit juices, eggs and dairy, cereal, meat, and seafood products. Also covered are antimicrobial activities of chemically modified and nanochitosans, therapeutic properties, and possible mechanisms of the antimicrobial, antioxidative, and metal chelating effects. Further research is suggested in each of these categories. The widely scattered data on the multifaceted aspects of chitosan microbiology, summarized in the text and in 10 tables and 8 representative figures, suggest that low-molecular-weight chitosans at a pH below 6.0 presents optimal conditions for achieving desirable antimicrobial and antioxidative-preservative effects in liquid and solid foods. We are very hopeful that the described findings will be a valuable record and resource for further progress to improve microbial food safety and food quality.

Effect of chitosan on the infectivity of murine norovirus, feline calicivirus, and bacteriophage MS2

Chitosan is known to inhibit microorganisms of concern to plants, animals, and humans. However, the effect of chitosan on human enteric viruses of public health concern has not been extensively investigated. The purpose of this study was to determine the effect of chitosan on three human enteric viral surrogates: murine norovirus 1 (MNV-1), feline calicivirus F-9 (FCV-F9), and (ssRNA) bacteriophage MS2 (MS2). Chitosan oligosaccharide lactate (molecular weight of 5,000) and water-soluble chitosan (molecular weight of 53,000) at concentrations of 1.4, 0.7, and 0.35% were incubated at 37 degrees C for 3 h with equal volumes of each virus at high (approximately 7 log PFU/ml) and low (approximately 5 log PFU/ml) titers. Chitosan effects on each treated virus were evaluated with standardized plaque assays in comparison to untreated virus controls. The water-soluble chitosan at 0.7% decreased the FCV-F9 titer by approximately 2.83 log PFU/ml, with decreasing effects at lower concentrations, and also decreased MS2 at high titers by approximately 1.18 to 1.41 log PFU/ml, regardless of the concentration used. Chitosan treatments at the concentrations studied had no effect on MNV-1 at high titers. Chitosan oligosaccharide showed similar trends against the viruses, but to a lesser extent compared with that of water-soluble chitosan. When lower virus titers (approximately 5 log PFU/ml) were used, plaque reduction was observed for FCV-F9 and MS2, but not MNV-1. The use of higher-molecular-weight chitosan and at higher concentrations with longer incubation may be necessary to inactivate MNV-1. These results in the plaque reduction of human enteric virus surrogates by chitosan treatment show promise for its potential application in the food environment.

Physical, Mechanical, and Antibacterial Properties of Chitosan/PEO Blend Films

Films formed by blending of two polymers usually have modified physical and mechanical properties compared to films made of the individual components. Our preliminary studies indicated that incorporation of chitosan in polyethylene oxide (PEO) films may provide additional functionality to the PEO films and may decrease their tendency to spherulitic crystallization. The objective of this study was to determine the correlation between chitosan/PEO weight ratio and the physical, mechanical, and antibacterial properties of corresponding films. Films with chitosan/PEO weight ratios from 100/0 to 50/50 in 10% increments were characterized by measuring thickness, puncture strength (PS), tensile strength (TS), elongation at break (%E), water vapor permeability (WVP), and water solubility (WS). Additionally, the films were examined by polarized microscopy, wide-angle X-ray diffraction (WAXD), and Fourier transform infrared (FTIR) spectroscopy, and their antibacterial properties were tested against Escherichia coli. The chitosan fraction contributes to antimicrobial effect of the films, decreases tendency to spherulitic crystallization of PEO, and enhances puncture and tensile strength of the films, while addition of the PEO results in thinner films with lower water vapor permeability. Films with 90/10 blend ratio of chitosan/PEO showed the most satisfactory PS, TS, %E, and antibacterial properties of all tested ratios.

Effects of chitosan and a low-molecular-weight chitosan on Bacillus cereus and application in the preservation of cooked rice

Shrimp chitosan with 95% deacetylation and low-molecular-weight chitosan (LMWC) isolated from chitosan hydrolysate were investigated for their effects on the growth of Bacillus cereus and for use in the preservation of cooked rice. Four strains of Bacillus cereus were used: standard strain BCRC 10603 and three isolates (nos. 1 through 3) from cooked rice. The antibacterial activity of chitosan against B. cereus was greatly decreased when the reaction pH was changed from 6.0 to 7.0, but LMWC activity was less affected by this pH change. The susceptibility of B. cereus cells to chitosan decreased with increasing of cell age, in accordance with the relative electronegativity of the cell surface. B. cereus spores were more sensitive to LMWC and chitosan than were vegetative cells. Addition of 80 ppm LMWC and chitosan in sterile saline (pH 7.0) greatly reduced the D-value for the tested four strains at 90 degrees C from 30.77 to 46.51 min to 7.47 to 10.17 min and 4.68 to 7.91 min, respectively, and at 100 degrees C from 1.95 to 2.56 min to 0.89 to 0.93 min and 0.72 to 0.80 min, respectively. Addition of 2,000 ppm LMWC to raw rice water before steam cooking effectively inhibited increases in total aerobic bacteria and B. cereus in cooked rice stored at 37 and 18 degrees C.

Physicochemical properties and bioactivity of fungal chitin and chitosan

Chitinous material was extracted from mycelia of Aspergillus niger and Mucor rouxii grown in yeast peptone dextrose broth for 15 and 21 days, respectively. The extracted material was characterized for purity, degree of acetylation, and crystallinity and tested for antibacterial and eliciting properties. The maximum glucosamine level determined in the mycelium of A. niger was 11.10% dw and in the mycelium of M. rouxii was 20.13% dw. On the basis of the stepwise extraction of freeze-dried mycelia, it appeared that M. rouxii mycelia contained both chitin and chitosan, whereas A. niger contained only chitin. The yields of crude chitin from A. niger and M. rouxii were 24.01 and 13.25%, respectively, and the yield of chitosan from M. rouxii was 12.49%. Significant amounts (7.42-39.81%) of glucan were associated with chitinous compounds from both species and could not be eliminated by the extraction method used. The degrees of acetylation were determined to be 76.53 and 50.07% for chitin from A. niger and M. rouxii, respectively, and 19.5% for M. rouxii chitosan. The crystallinity of fungal chitin and chitosan was estimated to be less intense than in corresponding materials from shrimp shells. The extracted chitin and chitosan in a concentration of 0.1% reduced Salmonella Typhimurium DT104 2576 counts by 0.5-1.5 logs during a 4 day incubation in tryptic soy broth at 25 degrees C. Furthermore, all tested chitinous materials from fungal sources significantly reduced lesions caused by Botrytis cinerea and Penicillium expansum in harvested apples.