الفهرس 
Review of LiteratureOnly 14 pages are availabe for public view
 |  | from | 134 |  |  |
| | | from | 134 | | |
Abstract
Lactic acid bacteria are a huge group of bacteria that consist of both rod and cocci bacteria. Lactic acid bacteria are characterised by being Gram-positive, catalase-negative and oxidase-negative, non-sporulating bacteria. Lactic acid bacteria produce many antimicrobial substances that can be used in many applications in many industries as the food industry. The most important antimicrobial substance produced by lactic acid bacteria is bacteriocins. Bacteriocins have had great interest in recent years due to their unique characteristics so can be used widely in many food industries.
In this study, sixteen bacterial isolates were isolated from different food samples collected from the Egyptian market (raw cow milk, yogurt and traditional fermented sausage). The isolates were differentiated based on the morphological characters and biochemical tests. All isolates were characterized using the Gram test, and catalase test, growth on different concentrations of Nacl and tolerance to acidity. All sixteen isolates were Gram-positive and catalase-negative. Only ten isolates were able to grow on different concentrations of NaCl and have a tolerance to acidity. Based on the biochemical test results, out of sixteen isolates, ten isolates are considered to be lactic acid bacteria.
To determine the most potent isolate, the antimicrobial activity of cell-free supernatants obtained from the ten isolates was tested against indicator pathogens ( S. aureus ATCC 29213, E. coli ATCC 51659, S. mutans ATCC 25175 and P. aeruginosa strain E1 MG847103) using well diffusion method. The antimicrobial activity of the supernatants obtained from the ten selected isolates was variable. The highest antimicrobial activity was against S. aureus ATCC 29213 and the lowest antimicrobial activity was against E. coli ATCC 51659.
The isolate that showed the highest antimicrobial activity against indicator pathogens is selected and identified using molecular techniques as L. plantarum strain N1. The sequence was submitted to GeneBank under accession number OM019104.
The effect of different factors on the antimicrobial activity of supernatant from the most potent isolate strain N1 was studied. To ensure the proteinous nature, the BLIS was treated with proteolytic enzymes (trypsin, proteinase K, and catalase). The treatment resulted in a complete loss of antimicrobial activity of the BLIS. This proves that the material that is responsible for antimicrobial activity in the supernatant is protein in nature. The effect of other enzymes as trypsin was studied. There is no loss of activity after treatment with trypsin, the BLIS maintained 100 % of inhibitory activity.
The effect of pH was also studied. BLIS was treated with different ranges of pH from 2.0 to 12.0. There was no complete loss in antimicrobial activity after treatment in all tested pH ranges. BLIS was stable over a wide range of pH values. It maintained 78.9% of its activity after being kept at pH 12.0 for 2 h. And 73.69% after being kept at pH 2.0 for 2 h. The optimal pH value for the isolated BLIS was pH 6 (100 % residual inhibitory activity).
The isolated BLIS show thermal stability. It maintained antimicrobial activity against tested pathogens after treatment with heat at different values. Different values of temperature for different time intervals were used for the treatment of BLIS. The BLIS retained 95 % of its antimicrobial activity after autoclaving (121℃ for 20 min). Also, it maintained 90 % of its antimicrobial activity at 90 ℃ for 1 h.
The crude BLIS was partially purified by using two methods, acetone precipitation followed by cation exchange chromatography. The acetone precipitation method is only for separating protein from other compounds that may be found in the supernatant and for decreasing the working volume. The BLIS after acetone precipitation showed higher activity than the crude BLIS.
The partially purified BLIS after acetone precipitation was further purified using FPLC-cation exchange on SP-Sepharose column. All the produced fractions are tested for their antimicrobial activity against tested pathogens. The fraction that has antimicrobial activity is located on the tail of the peak, this may be due to the low concentration of BLIS in the isolated extract.
The aim of this study was the development of antimicrobial biodegradable food packaging. Biodegradable films were made from cellulose acetate. Many concentrations were used to determine the best concentration to be used in the study and the most suitable concentration to be used as food packaging. The films that had sufficient flexibility to be used as food packaging were films that had 3% and 6% cellulose acetate. Other concentrations were not suitable to be used as food packaging due to rigidity. The films were coated with partially purified BLIS and tested for antimicrobial activity against indicator pathogen S. aureus ATCC 29213. The films show antimicrobial activity against pathogens.