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Leakage of ammonia in food facilities has been known to occur in the past. Ammonia leaks often lead to food contamination in food plants and can cause illness among consumers who accidentally consume the food products contaminated with high levels of ammonia. Therefore, a rapid, simple yet accurate method has to be established for on-site ammonia level screening in food plants to ensure the food is safe. One of the primary objectives in this study was to verify and optimize an ion selective electrode (ISE) method for its accuracy and reproducibility in determining ammonia in meat. Different extraction procedures (blending and vortexing) and different solvents (nanopure water with/without pH adjustment (control, 3.0, 4.0, 5.0, and 6.0) using either HCl/NaOH or HClO4/NaOH; potassium phosphate buffer (PPB) at different concentrations (0.1M, 0.02M and 0.01M) and pH (5.8, 6.0, 6.2, 6.5, 6.8, 7.0, and 7.2) were tested to improve the performance of the ISE method. Blending spiked meat with pH 6 0.01M potassium phosphate buffer (PPB) as the solvent was shown to give better ammonia recovery and lower coefficients of variation. The recoveries were >90% with coefficients of variation ranging from 3.6 to 14.2% for ammonia concentrations ranging from 10 to 200ppm in spiked meat samples.
This study further investigated the rate of ammonia uptake in fresh and frozen meat samples (2.5x2.5x1 inch) exposed to 200ppm ammonia in N2 gas at three different temperatures - ambient (20-25oC), refrigeration (3-5oC), and freezing temperatures (-13oC), for times of 1 to 12 hours. A selected packaging film (2.4 mil Cryovac type B6620) was also tested for its permeability to ammonia gas during 12 hours exposure at 3-5oC. The rate of ammonia uptake in fresh meat was 58.4±7.1ppm per hour for 20-25oC during 6hours time exposure and 56.4±5.8 ppm per hour for 3-5oC during 9hours time exposure. A sign of saturation was observed after exposing fresh meat for more than 9 hours at 3-5oC. Frozen meat had a slower ammonia uptake rate which resulted in an ammonia concentration approximately 6 times lower than the ammonia level in fresh meat samples after 12hours exposure. Moreover, the 2.4mil Cryovac type B6620 packaging film provided a good barrier to ammonia gas. The ammonia concentrations (ppm) between both non-exposed (control) and vacuum-packed meat samples exposed to 200ppm NH3 gas at 3-5oC showed no significant differences (P<0.05).
Selected removal methods (1 to 2 hours air flushing, 2hours vacuum treatment, and 2%acetic acid rinsing) for lowering ammonia levels in contaminated meats were also investigated in this study. All of the removal methods showed minimal ammonia reduction (<10%) in contaminated meat samples exposed to 200ppm NH3 gas for 4 hours at 3-5oC.
Advisor: Randy L. Wehling