Antimicrobial Activity of a Low-Molecular-Weight Chitosan Obtained from Cellulase Digestion of Chitosan

A water-soluble chitosan hydrolysate with high activity against Escherichia coli was obtained during cellulase digestion of chitosan for 18 h. This 18-h hydrolysate is composed of low-molecular-weight chitosan (LMWC), with a molecular weight of 12.0 kDa, and chitooligosaccharides, which are composed of sugars with a degree of polymerization of 1 to 8. LMWC has a strong activity at 100 ppm against many pathogens and yeast species, including Bacillus cereus, E. coli, Staphylococcus aureus, Pseudomonas aeruginosa, Salmonella enterica serovar Typhi, and Saccharomyces cerevisiae, while the chitooligosaccharides have much weaker antimicrobial activity than does LMWC. Accordingly, the antimicrobial activity against E. coli in the 18-h hydrolysate proved to come mainly from the presence of LMWC.

Antibacterial Activity of a Chitooligosaccharide Mixture Prepared by Cellulase Digestion of Shrimp Chitosan and Its Application to Milk Preservation

The antibacterial activity of a chitooligosaccharide mixture prepared by digestion of shrimp chitosan with cellulase at 50°C for 14 h was evaluated. Sugars with 1 to 8 degrees of polymer (DP) were found in this chitooligosaccharide mixture, and the weight percentage of sugars with DP ≧ 6 was 44.3%. Minimal lethal concentrations of this mixture against Aeromonas hydrophila, Escherichia coli, Listeria monocytogenes, Pseudomonas aeruginosa, Salmonella Typhimurium, Shigella dysenteriae, Staphylococcus aureus, Vibrio cholerae, and Vibrio parahaemolyticus in nutrient broth were 5 to 29 ppm, which were much lower than those of the chitosan reactant (50 to 1,000 ppm). The antibacterial activity of this mixture in the sterilized milk against E. coli O157, L. monocytogenes, Salmonella Typhimurium, and S. aureus was much stronger at 4°C than at 37°C. When raw milk was supplemented with either 0.24% or 0.48% (wt/vol) of this oligosaccharide mixture and stored at 4°C for 12 days, its mesophilic and psychrotrophic counts were reduced by at least 3 log cycles, and there was very little change in pH. In addition, this mixture retarded the growth of Salmonella species and caused quicker reduction of Staphylococcus species in raw milk. Accordingly, the shelf life of raw milk at 4°C was extended by at least 4 days.

Ultrastructural localization of β-1,4-glucan-containing molecules in the cell walls of some fungi: a comparative study between spore and mycelium

An exoglucanase, purified from a cellulase produced by the fungus Trichoderma harzianum was complexed to colloidal gold and used for localizing β-1,4-glucan-containing molecules in the cell walls of some fungi. With the exception of Aspergillus niger, β-1,4-glucan-rich molecules were found to be associated with conidial walls of Trichoderma viride, Fusarium oxysporum f.sp. radicis-lycopersici, Verticillium albo-atrum, Penicillium thomii, and Ophiostoma ulmi. The abolition of wall labeling following previous cellulase digestion suggested that the compunds detected by the exoglucanase–gold complex were likely of cellulosic nature. Differences in cell wall composition between conidia and mycelium were reflected by the absence of β-1,4-glucan-containing molecules in the vegetative walls of most fungi tested. This raises the question as to what extent the chemical composition of spore walls should be considered as an important criterion in the taxonomy and phylogeny of fungi. The disappearance of these molecules upon conidial germination (with the exception of O. ulmi) suggests that lytic enzymes are produced to cause wall breakdown. The presence of molecules with β-1,4-linkages in conidia probably contribute to reinforcement of the wall architecture. Key words: fungi, spores, β-1,4-glucan, gold cytochemistry.