Abstract: The antimicrobial effect of five compositions and two components of the compositions against five kinds of indicated microorganisms were studied according to the sanitizing technique criterion under pH5.0 and pH6.0. The indicated microorganisms were Escherichia coli 8099, Staphylococcus aureus ATCC6538, Bacillus subtilis ATCC9372, Candida albicans ATCC10231 and Aspergillus niger ATCC16404 respectively. This seven compositions included five compositions base on chitosan and chitosan- Zn complex, the sole chitosan-Zn complex and ethyl p-Hydroxybenzoate (NJ).The remained live cell numbers were counted by plate counting number method. A series of rudimental microorganism numbers were gained after culture at 0, 4, 24, 48, 72 h and 96 h in the tubes. The logarithm curves of plate count numbers changed with cultured time represented the disinfecting effect of the compositions against the five kinds of indicated microorganisms. The results indicated that the composition A, B, D and E could effectively inhibit the five kinds of indicated microorganisms under pH 6.0, the composition A, B, C, D, E and the sole chitosan-Zn complex had higher inhibition to Escherichia coli 8099 and Staphylococcus aureus ATCC6538 than to the other three kinds of microorganisms, and the antimicrobial effect of NJ was more efficient to Aspergillus niger ATCC16404 and Bacillus subtilis ATCC9372. However, the antimicrobial effect of all the seven compositions was not efficient to Candida albicans ATCC10231 when compared with that of the other four microorganisms, the reason was relative with the high control number of microorgan- isms in the tube, the inhibition of the same composition was more efficient under the low pH and lesser control microorganism number in the tube.

Key words: chitosan, chitosan-Zn complex, biological preservative, composition, evaluation of antimicrobial effect