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We investigated the combined antimicrobial effect of nisin and chitosan hydrolysates (CHs) by regulating the antimicrobial reaction order of substances due to differential releasing rate from hydroxypropylmethylcellulose-modified bacterial cellulose (HBC). The minimum inhibitory concentration of nisin against Staphylococcus aureus and that of CHs against Escherichia coli were 6 IU and 200 μg/mL, respectively. Hurdle and additive effects in antimicrobial tests were observed when nisin was used 6 h before CH treatment against S. aureus; similar effects were observed when CH was used before nisin treatment against E. coli. Simultaneously combined treatment of nisin and CHs exhibited the low antimicrobial effect. HBC was then selected as the carrier for the controlled release of nisin and CHs. A 90% inhibition in the growth of S. aureus and E. coli was achieved when 30 IU-nisin-containing HBC and 62.5 μg/mL-CH-containing HBC were used simultaneously. The controlled release of nisin and CHs by using HBC minimized the interaction between nisin and CHs as well as increased the number of microbial targets., (© 2016 Institute of Food Technologists®)

Addition of microcapsules with a high dielectric constant and low specific heat capacity to a battered layer was designed to create a higher temperature in the crust than in the prefried fish nuggets to prevent the water vapor in the fish nuggets from migrating to the crust during microwave heating. Therefore, chitosan-silica hybrids and soybean oil were utilized to prepare the shell and core of the thermally stable microcapsules (MC(CS)), respectively. The MC(CS) were prepared by sol-gel coacervation from an oil-in-water emulsion. The sodium silicate was hydrolyzed and coacervated through polymerization for 24 h at pH 5. The zeta potential analysis indicated that chitosan with a positive charge and silica with a negative charge interacted through electrostatic attraction to form a hybrid shell. The volume mean particle size and encapsulation efficiency of the MC(CS) were 9.6 ± 0.2 μm and 75.6% ± 1.3%, respectively, when oil/chitosan = 0.2 and chitosan/silica = 0.5 (w/w). In addition to H-bonding and electrostatic attraction, Si-O-N bonds were formed between chitosan and silica. Dehydration of the bound water in the MC(CS) was observed in the range of 25 to 250 °C in the differential scanning calorimetry thermal analysis, with the lack of apparent thermal peaks indicating its high thermal stability. The decrease of force to cut the crust observed by texture analysis as well as the increase of hedonic score by consumer acceptance test revealed the addition of 1% MC(CS) significantly improved the crispness of the crust in the microwave-reheated nuggets., (© 2014 Institute of Food Technologists®)

Low molecular weight chitosan (LMWC) and nisin, recognized as cationic antibacterial agents (CAAs), inhibit bacterial growth by interacting with the anionically charged cell wall. In this study, alanine uptake significantly reduced the anionic cell surface charge, as determined by the zeta potential (ZP) measurements, of Staphylococcus aureus, resulting from the incorporation of d-alanine into the cell wall. Minimum inhibitory concentration (MIC) tests and growth inhibition curves revealed that LMWC and nisin possessed inverse antibacterial activity against three strains of S. aureus, depending on the strains' net charge. A twofold reduction in the MIC value of nisin was obtained against S. aureus, inoculated in a 1.0% d- or l-alanine-augmented trypticase soy broth medium. A flocculation test demonstrated that neutralizing the anionic surface charge using d-alanine reduced the adsorption of S. aureus onto LMWC. Furthermore, the reduced surface net charge could enhance the colonization capacity of S. aureus on glass., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

To test various formulas and techniques for manufacturing dry-fabricated bio-film (DFBF) that exhibits physical properties advantageous to the use of the DFBF in wound dressings, a DFBF was fabricated by adding chitosan (Chi) and alginate (Alg) to homogenized bacterial cellulose (BC) obtained from vinegar pellicles in vinegar brewing byproducts in this study. The results revealed that the degree of oxidation in DFBF manufactured using hydrogen peroxide oxidized BC (HOBC), with 0.092% carboxyl group content, was lower than that in DFBF manufactured using periodic acid oxidized BC (POBC), but DFBF made using HOBC exhibited higher elongation, rehydration, swelling ratios, and water vapor transmission than that fabricated using POBC. A DFBF composite gel with 98.5% water content possessed appropriate fluidity for molding. After 10 min of rinsing cross-linked HOBC, 72 ppm of calcium remained in the final DFBF, which not only prevented cell toxicity but also demonstrated desirable mechanical and rehydration properties. Overall, the modified DFBF possessed a high rehydration ratio of 51.69% and could absorb and gradually release naringin by up to 80% within 24 h. This modified DFBF has the potential for exudate absorption and the controlled release of medicinal substances at the initial stage of healing when used in wound dressings. [ABSTRACT FROM AUTHOR]

In this study, thermostable microcapsules prepared with a hybrid of chitosan and silica (MC CS ) as the shell material and soybean oil with a low specific heat capacity as the nucleus were applied to maintaining the crispness of microwave-reheated battered and breaded fish nuggets. The MC CS added batter at 1 g/100 mL concentration exhibited desirable rheological properties and a 40% pick-up rate, as well as a high cutting force, low deformation and desirable number of peaks in the cutting force profile of the fish nuggets reheated in a microwave oven. After microwave reheating, the moisture content of the crust was lower, and moisture content of the fish meat was higher, in the MC CS -containing nuggets than in the MC CS -free nuggets. This phenomenon suggested that the MC CS facilitated the formation of a water barrier by high temperature and high pressure during microwave reheating, which prevented moisture molecules from migrating from the fish meat to the crust. [ABSTRACT FROM AUTHOR]

Abstract: A set of low molecular weight chitosan (LMWC) products with an intrinsic viscosity-molecular weight (M V) spectrum from 6.9kDa to 22.4kDa, with average nanoparticle sizes from 117nm to 965nm, were characterized by their zeta potentials and antibacterial activities. The three strains of Staphylococcus aureus and two strains of Escherichia coli exhibited differential sensitivities to LMWCs. Both LMWC adsorption test and antibacterial test results indicated that antibacterial activity was mainly contributed by the difference in zeta potential between the surface of LMWC particles and the bacteria. Scanning electron microscopy (SEM) revealed that LMWC with an M V of 14.8kDa exerted its antibacterial function by both surface and permeation effects. Once the adsorbed LMWC was washed from the cell wall with an acetate buffer, obvious damages to, and disturbances on, the cell surfaces were observed through SEM. [ABSTRACT FROM AUTHOR]

Abstract: A continuous set of low molecular weight chitosan (LMWC) products was successfully made for this study by coordinating three enzymes (chitinase, lysozyme and cellulase) and two different deacetylated chitosan substrates (80% and 92%). It was observed that the intrinsic viscosity molecular weight (M V) and SEC-HPLC-determined M W distribution of LMWC were directed by both the used enzyme and the degree of chitosan substrate acetylation. LMWC prepared using lysozyme and 92%-deacetylated chitosan had larger M W and, therefore, possessed higher antibacterial activity, as compared to other combinations. LMWC enzyme-directed properties suggest chitinase is more predictable and flexible to produce the specified M V of LMWC. LMWC’s solubility and antibacterial activity, determined as minimum inhibitory concentration (MIC), against Escherichia coli exhibited a negative linear relationship with log M V. E. coli strains showed much higher susceptibility to LMWCs than Staphylococcus aureus strains did. Both species also showed intra-species sensitivity diversity toward LMWC. [Copyright &y& Elsevier]

Laccase was immobilized on the electrospun chitosan/poly(vinyl alcohol) fiber (ceCPL) with specific area of 17.05 m2/g to reinforce the stability of enzymatic time–temperature indicator (TTI). The ceCPL exhibited a high relative activity within 4 °C–40 °C and the activation energy (Ea) of coloration with guaiacol approached 40.9 ± 2.8 kJ/mol for 80 μg/cm2 of ceCPL-immobilized laccase. In dynamic temperature response experiments of ceCPL using intermittent temperature changes between 4 °C and 25 °C, irreversible inactivation did not occur, indicating the desirable tolerance and sensitivity of ceCPL to temperature alterations. Approximately 1 or 38 days was required to reach the endpoint of coloration at 4 °C when 80 or 8 μg/cm2 of laccase were immobilized on ceCPL, respectively. The regression equation derived from kinetic model analysis was conducted and could be further utilized to design a suitable time–temperature indicator (TTI) to monitor food quality according to the color change of ceCPL coloration. • Laccase was immobilized on electrospun chitosan fiber with high surface area. • Immobilized laccase exhibited a high relative activity within 4 °C–40 °C. • Adjusting the laccase amount on chitosan fiber expands active energy range of TTI. • Desirable coloration of TTI was observed in the dynamic temperature response test. • Laccase TTI provides quality information based on time-temperature history. [ABSTRACT FROM AUTHOR]