Implications of wash water chlorination and temperature for the microbiological and sensory properties of fresh-cut iceberg lettuce

Cut iceberg lettuce (Lactuca sativa L.) was washed in chlorinated water (0-100 mg l(-1) total chlorine) at temperatures up to 54 degreesC to identify a practical commercial process. Based on relative leakage rates and visual assessment of the packaged, stored lettuce. a 1 min treatment at 50 degreesC yielded acceptable quality. Comparison with cut lettuce washed at 4 degreesC revealed that disinfection of the lettuce was improved by heat, although the difference in total microbial populations was only 1 log cfu g(-1). Chlorine addition up to 100 mg l(-1) did not appreciably increase removal of micro-organisms from the lettuce surface at either temperature, although micro-organisms were eliminated from wash water at the lowest concentration applied (25 mg l(-1) total chlorine). Chlorine losses were minimal in wash solutions adjusted to pH 6.1 but exceeded 50% at 50degreesC, and this parameter was not adjusted for experiments on the sensory quality of lettuce washed at both temperatures. The aromas of lettuce washed in tap water at 4 or 50degreesC for 1 min were not significantly different (P > 0.05) after 1 or 7 days of storage at 1 degreesC. Addition of chlorine (100 mg l(-1) total) significantly reduced (P < 0.05) aroma development during storage for I or 7 days following a wash at 50 degrees C, but not at 4 degrees C. Sensory comparison of lettuce washed at 50 degrees C with 0, 10, 25, 50, 75 and 100 mg l(-1) total chlorine by an R-index test procedure indicated that differences in aroma were more apparent at chlorine concentrations >50 mg l(-1). (C) 2003 Published by Elsevier B.V.