Microbiological state of precut mixed salad: shelf life, hygienic state and characteristics of some pathogens

A high total bacterial load (10(7)-10(8) cfu/g) was reached at 6 degrees C already after 2-3 days of storing commercially manufactured mixed salads. I n freshly shredded iceberg salad the initial bacterial contamination was lo wer, so that when stored at 6 degrees C 10(7) cfu/g were reached after 5 da ys. When the cooling of the samples was interrupted for a certain period (3 , 6, 12, 24 hours respectively), the growth of the natural microflora incre ased significantly within 6 hours when the temperature was heightened to 25 degrees C. At 15 degrees C the cooling interruption had to last at least 1 2 hours to reach higher amounts of microorganisms compared with the continu ously cooled samples. In some experiments with artificially contaminated iceberg salad the interr uption of the cooling process by transferring the sample to a temperature o f 25 degrees C resulted in an increase of S. lexington, E. coil, and L. mon ocytogenes, provided that the interruption lasted longer than 6 hours. On t he other hand interruption of cooling with 15 degrees C initiated propagati on of E. coli and S. lexington only if the stop lasted 12 hours and more. T he number of L. monocyotgenes did not increase during a cooling stop of:15 degrees C/24 hours. Accordingly, high E. coli and Listeria numbers in salad may result either from unhygienic manufacturing methods or from a longer i nterruption of cooling. As such potentially harmful circumstances cannot be excluded, Salmonella should not be present in salad products. The study investigates the suitability of lactate concentration as a hygien ic parameter in salad products. It was concluded, that a lactate concentrat ion of more than 200 mg/kg indicates that storage temperatures are too high and/or storage times too long.