الفهرس 
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Abstract
The aim of the present study was to investigate the effect of the microwave heating compared with other heat treatments such as grilling , frying and boiling on the fate of pathogenic bacteria such as Escherichia coli O157:H7, Salmonella typhimurium , Staphylococcus aureus and Bacillus cereus inoculated onto chicken burger and meat sausage samples . The study also evaluated the efficacy of heat treatments on the chemical composition of samples at the elimination point.
Methods & Results:
Tested bacteria were used for inoculation. Stock cultures of the strain were prepared. A 24 culture of the tested strain was inoculated at 1% (v/v) into TSB, followed by incubation at 37°C for 24 h. Both of chicken burger and sausage were immersed into 200 ml of prepared inoculum for 30 min , and placed in sterile glass Petri dishes. One sample was reserved for estimating bacteria concentration of the tested samples as positive control. The remaining samples were heated individual at different time .
Results generated through the realization of this study could be summarized as follows:
• This study showed that E. coliO157:H7 was more heat resistant than Salmonella typhimurium under the same conditions.
• Microwave heating is the best method of inactivating E .coli O157:H7 and Salmonella typhimurium. Then , boiling followed by frying . Grilling was the latest one ,becuse of the shortest time of exposure.
• Staphylococcus aureus is inactivated by grilling(15min.) for both chicken burger and meat sausage ( at 86ºC and at 89ºC ), respectively,and boiling(5min.) at72ºC for chicken burger and at 89ºC for meat sausage but not by microwave heating and frying .
• Viable count of Staphylococcus aureus could be decreased more than heating before by reheating after standing for some time using microwave heating and frying.
• Bacillus cereus is not inactivated but decreased by the all heat treatments.
• A slightly decrease in the viable count of Bacillus cereus was noted after heating then reheating samples after standing period for some time.
• Bacillus cereus and Staphylococcus aureus were more resistant to microwave heating than E. coli O157:H7and Salmonella typhimurium because the cell wall of gram-positive bacteria is generally much thicker and stronger than that of gram-negative bacteria.
• A changes in the chemical composition of samples were found by all heat treatments at the elimination point after E. coli O157:H7and Salmonella typhimurium except Staphylococcus aureus by microwave heating and frying and Bacillus cereus by all heat treatments.
• A loss in moisture ,fat and ash contents of chicken burger inoculated with E. coli O157:H7 was noticed .While , protein content ,TBA and TVN values were increased. The results indicated that the lowest decrease in moisture and ash contents were noticed by grilling . After frying, the lowest decrease in fat content was observed , whereas the lowest increase protein content was observed. The lowest value of TBA was observed after grilling and the lowest value of TVN was noticed by boiling because of leaching out.
• The chemical composition of samples are slightly changed at the elimination point of microbes by microwave heating compared with other heat treatments because of the short time exposure.
Conclusion:
it could be concluded that microwave heating realized safety and more quality compared with other conventional heat treatments.