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

Abstract

Cut iceberg lettuce (Lactuca sativa L.) was washed in chlorinated water (0–100 mg l−1 total chlorine) at temperatures up to 54 °C 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 °C yielded acceptable quality. Comparison with cut lettuce washed at 4 °C 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 50 °C, 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 50 °C for 1 min were not significantly different (P>0.05) after 1 or 7 days of storage at 1 °C. Addition of chlorine (100 mg l−1 total) significantly reduced (P<0.05) aroma development during storage for 1 or 7 days following a wash at 50 °C, but not at 4 °C. Sensory comparison of lettuce washed at 50 °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.