Antimicrobial Activity Of The Chitooligosaccharides Prepared By Enzymolysis

Penicillium sp.ZD-Z1 screened out from the soil was applied to submerged fermentation to produce chitosanase. After fermented for 65-70 hours, fermentation broth was harvested by follow steps: ultrafiltration, precipitation with 95% cold ethanol (3:1 V/V) and freezing centrifugation. At last, Endo-chitosanase ChA and exo-chitosanase ChB were isolated by IEC method. 2% (W/V) solution of chitosan degraded by ChA or ChB respectively was ultrafiltered by membrane with MWCo 2kDa. Ultrafiltrate was processed further by spray drying to get the powder product S1 and S2.After fermented for 65 hours, fermentation broth was harvested and ultrafiltered by ultrafiltration membrane with MWCo 10 kDa, 5 kDa and 2kDa saparately. Ultrafiltrate was processed by spray drying to get the powder product S3(0-2kDa), S4(2k-5kDa) and S5(5k-10kDa).Dryness product S1, S2, S3, S4 and S5 were determined by using the acetylacetone's method and the number average molecular weight of chitooligosaccharide were 3726, 475, 2133, 5170 and 8952.Antimicrobial activity of chitooligosaccharides S1, S2, S3, S4 and S5 with different molecular weights were examined against Escherichia coli and Bacillus subtilis. It was observed that the bactericidal effect to Escherichia coli decreased with the increase of average molecular weight.However,the bactericidal effect to Bacillus subtilis increased with the Increase of average molecular weight and concentration. To Bacillus subtilis 0.5% chitooligosaccharide of S3 represented only an inhibition rate of 85.5% but S4 and S3- could exceed the inhibition of 90%. Whereas S2 had no antimicrobial activity nearly and the number of Bacillus subtilis increased with the augment of concentrati.on.In concentration 0.25% , 0.5% and 1% of chitooligosaccharide S2 ,the colony number were about 480%, 300% and 130% of the colony number in the blank:.The chitooligosaccharides S1, S2 and S3 were prepared respectively by endo-chitosanase , exo-chitosanase and chitosanase. Antimicrobial activity of three chitooligosaccharides with different molecular weights were examined against seven pohytopatho genie fungi by determining the inhibitory growth curves. It was observed that S1 showed higher antimicrobial activity than S3 and S2 had no antimicrobial activity nearly .To some extent,it can even promote the growth of some pohytopathogenic fungi.