ARS | Publication request: MICROBIAL QUALITY OF FRESH-CUT ICEBERG LETTUCE WASHED IN WARM OR COLD WATER AND IRRADIATED IN A MODIFIED ATMOSPHERE PACKAGE

Submitted to: Journal of Food Safety
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 30, 2007
Publication Date: May 1, 2008
Citation: Rajkowski, K.T., Fan, X. 2008. Microbial quality of fresh-cut iceberg lettuce washed in warm or cold water and irradiated in a modified atmosphere package. Journal of Food Safety. 28:248-260.

Interpretive Summary: The microbial counts of fresh-cut iceberg lettuce were determined after being washed in either warm or cold water. The background counts were lower after the warm water wash by a hundred fold. The lettuce was given an irradiation treatment of 0.5, 1 or 2 kGy and then refrigerated to determine the microbial counts after being stored. Immediately after irradiation at a 1 or 2 kGy dose, the microbial counts dropped another 1000 fold. Upon refrigerated storage, this reduction in counts was maintained for up to two weeks. The combination of warm water wash and irradiation at 2 kGy can increase the shelf life of fresh cut lettuce while assuring a microbial safe product.

Technical Abstract: The microbial keeping quality of fresh-cut iceberg lettuce was determined after being washed in either 5 or 47 C water for 2 min and packaged in a modified atmosphere film bag. The lettuce samples were treated with gamma-radiation to 0, 0.5, 1, or 2 kGy while maintaining a refrigerated temperature (4 C). Samples were analyzed for total aerobic, coliform and Enterobacteriaceae counts after refrigerated storage up to 14 d. No difference in aerobic counts was observed between the hot and cold washed samples while both the coliform and Enterobacteriaceae counts were reduced by 2 logs after the warm water wash. The irradiation treatment at 1 and 2 kGy reduced the aerobic counts on both washed samples by 2 logs and the coliform and Enterobacteriaceae count by 1 log and 2 log for the hot and cold washed samples, respectively. The observed log reductions were maintained for 14 d. The combination of a warm water wash and irradiation at 2 kGy had the best microbial keeping quality.