الفهرس | Only 14 pages are availabe for public view |
Abstract The main study focused on separation of chitin from crustacean waste (shrimp shell) using some proteolytic bacterial isolates. After that, chitosan was obtained by deactylation and its characteristics were studied using some characterizing tools. The produced chitosan was degraded to different molecular weights and evaluated as an antibacterial agent. Seventy bacterial isolates were obtained from different sources (soil, plant roots and shrimp shell waste) and tested for their ability to produce proteolytic enzymes. One isolate was selected, due its high proteolytic activity and ability to grow using shrimp as carbon and nitrogen source on shrimp shell agar medium and identified as Bacillussubtilis NA12 by 16S-rRNA gene sequences with a high degree of similarity (99 %) as a gene bank database. Factors affecting deproteinization (DP) and demineralization (DM) efficiency of shrimp shell waste (SSW) (carbon source and its optimal concentration, shrimp shell waste concentration, inoculum size and fermentation time) were studied. The most efficient DP (92.40 %) and DM (81.37 %) of SSW by B.subtilis NA12 were sucrose 10 % (w/v) and inoculum size 15 % (v/v 35 x 108 CFU/ml )to ferment shrimp shell waste 5 % (w/v) for 6 days of fermentation time. The effect of γ-irradiation on the performance of selected bacterial strain was studied to maximize chitin yield. Box-Behnken design using response surface methodology was employed to establish the relationship between the previous variables, implied that the model was highly significant. It was found that a sucrose concentration of 5 % (w/v), SSW of 12.5 % (w/v), inoculum size of 10 % (v/v) and fermentation time of 7 days; had a predicted value of DP of 97.65 % whereas the actual experiment gave 96.37 %. The predicted value of DM was 82.94 % whereas the actual experiment gave 82.19 %. Chitosan polymer was successfully prepared by the deacetylation reaction from fermented shrimp shell waste (SSW) by Bacillus subtilis NA12 (crude chitin). Extracted chitin was exposed to different gamma radiation doses ranged from 5 to 35 kGy in equal kGy interval. The degree of deacetylation (DDA %) was determined by potentiometric titration. The structural properties of the two prepared polymers, chitin and chitosan, were characterized by fourier transform infrared spectroscopy (FT-IR), X–ray diffraction analysis (XRD) and thermogravimetric analysis (TGA). The results confirmed that gamma irradiation reduced the time required for deacetylation processes. The data also showed that the prepared chitosan from different irradiated samples have higher solubility and DDA%. The different chitosan samples (CS) obtained from irradiated chitin at 5, 15, 25 and 35 kGy with different MW (from 4.8 x 105 to 3.7 x 104g/mol) with different DDA values (from 84.4 % to 87.9 %)wasevaluated as antibacterial agent against different pathogenic isolates, Pseudomonas aeruginosa was the lowest sensitive to the chitosan samples then Staphylococcus aureus followed by Klebsiella sp. and Escherichia coli. |