Antibacterial activities of chitosans and chitosan oligomers with different molecular weights on spoilage bacteria isolated from tofu

Seven bacteria were isolated from spoiled tofu and identified as Bacillus sp. (S08), B. megaterium (S10), B. cereus (S17, S27, S28, S32), and Enterobacter sakazakii (S35). In a paper disc test with 6 chitosans and 6 chitosan oligomers of different molecular weights, chitosans showed higher antimicrobial activity than did chitosan oligomers at a 0.1% concentration. Results of inhibitory effects of 6 chitosans on growth of Bacillus sp. (S08) failed to detect viable cells after incubation for 24 hrs at 37 degreesC, even at 0.02% concentration. With B. megaterium (S10) and B. cereus (S27), a 3 to 4 log cycle reduction was found in the chitosan-treated group. The growth of Enterobacter sakazakii (S35) was completely suppressed in the presence of 0.04% chitosan except for 1 chitosan product. The minimum inhibitory concentration of chitosan differed with products and isolates, ranging from 0.005% to above 0.1%.