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 di gestion of shrimp chitosan with cellulase at 50 degrees C for 14 h was eval uated. Sugars with 1 to 8 degrees of polymer (DP) were found in this chitoo ligosaccharide mixture, and the weight percentage of sugars with DP greater than or equal to 6 was 44.3%. Minimal lethal concentrations of this mixtur e against Aeromonas hydrophila, Escherichia coli, Listeria monocytogenes, P seudomonas aeruginosa, Salmonella Typhimurium, Shigella dysenteriae, Staphy lococcus aureus, Vibrio cholerae, and Vibrio parahaemolyticus in nutrient b roth were 5 to 29 ppm, which were much lower than those of the chitosan rea ctant (50 to 1,000 ppm). The antibacterial activity of this mixture in the sterilized milk against E. coli O157, L. monocytogenes, Salmonella Typhimur ium, and S. aureus was much stronger at 4 degrees C than at 37 degrees C. W hen raw milk was supplemented with either 0.24% or 0.48% (wt/vol) of this o ligosaccharide mixture and stored at 4 degrees C for 12 days, its mesophili c and psychrotrophic counts were reduced by at least 3 log cycles, and ther e was very little change in pH. In addition, this mixture retarded the grow th of Salmonella species and caused quicker reduction of Staphylococcus spe cies in raw milk. Accordingly, the shelf life of raw milk at 4 degrees C wa s extended by at least 4 days.