Acetic Acid Vapor

Acetic acid is known for its preservative properties [122] and has been used extensively in foods such as pickles, salad dressing, tomato products, and mustards. Vaporized acetic acid has also shown biocidal effects for decontamination of fruits and vegetables. Researchers have demonstrated that fumigation with acetic acid vapor or vinegar vapor could control postharvest decay of fruits and vegetables such as apples, grapes, stonefruit (peaches, nectarines, and apricots), strawberries, oranges, kiwifruit, tomatoes, and coleslaw made from cabbage [123-127]. They also demonstrated that fumigation treatments with 242 ppm (v/v) gaseous acetic acid in air for 24 hours at 22°C or for 12 hours at 45°C could reduce 3 to 5 log CFU/g Salmonella Typhimurium, E. coli O157:H7, and Listeria monocytogenes on mung bean seed without significant reduction of seed germination rates [128]. Recently, Sapers et al. [43] evaluated the use of pressurized acetic acid vapor to decontaminate apples inoculated with E. coli. In their vacuum-pressure cycle system, a vacuum (508 to 686 mmHg) was applied to a 6 l stainless steel treatment, where inoculated apples were placed, and then acetic acid vapor generated from glacial acetic acid at 60°C was applied to the vessel to achieve a pressure of 34.5, 68.9, or 103.4 kPa. The treatment time was 5 to 30 minutes, and temperatures ranged from 40 to 60° C. After the treatment, the apples were immediately rinsed with tap water for 30 seconds, observed for treatment-induced injury, and prepared for microbiological analysis. They found that the vapor treatment with three vacuum-pressure cycles at 60°C provided population reductions exceeding 3.5 log CFU/g. However, these conditions induced discoloration. When a total treatment time of 5 minutes was used, log reductions increased with increasing treatment temperature and the number of vacuum-pressure cycles applied. Treatment pressure did not appear to affect the bacterial log reduction. During storage for several hours, the treated Golden Delicious apples developed dark lesions surrounding the lenticels which penetrated several millimeters into the flesh beneath the skin, indicating that acetic acid vapor treatment may not be useful for apples under these conditions.

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