Food Protection Trends - May 2009 - 274

TABLE 1. Program Times and temperatures during dishwashing Dishware Granules Wash Time (s) Temp. (°C) 65 65 Rinse Time (s) 20 40 Temp. (°C) 8 85 Combi mode Normal Plates, cutlery, etc. Pot wash No Yes 120 210* * 210 s wash cycle: 180 s with granules and 30 s without granules TABLE 2. Type of dishware and soil in the different experiments Experiment Dishware 9 plates 9 plates Dishwasher Two 1/1 65 mm trays One 1/2 200 mm tray One 1/3 200 mm tray One 1/1 20 mm tray Hand dishwashing (A) Hand dishwashing (B) 12 plates 10 plates 10 plates In test B, ten plates with soil 2 (pie filling base) were soaked for five min in the dishwashing bowl and then a manual washing was started, so that the plates were soaked for 5–12 min. Each plate was washed for 30 s, dipped in the water rinse in the bowl, and placed in a basket. Another ten plates with soil 3 (boiled rice) were soaked for five minutes in the dishwashing bowl, and the same washing procedure was used. One person washed the plates with soil 2, and another person washed the plates with soil 3. Two hand dishwashing experiments were performed to evaluate the experimental procedure used; these experiments were performed on two non consecutive days, and the machine dishwashing experiments were performed on a separate day. The types of dishware and soil in the dishwasher and the hand dishwashing experiments are summarized in Table 2. samples were immediately neutralized by addition of 1 ml 0.1 M HCl and cooled in an ice bath. Samples of 20 ml were aseptically withdrawn from the washing bowl and from the rinse water bowl at different time-points during the hand dishwashing tests, and the samples were cooled. The dishwater and rinse water samples were streaked out on Tryptic Soy Agar (Merck 1.05458.0500) and kanamycin esculin azide agar (Merck 1.05222.0500). A volume of 100 µl sample was streaked out in duplicate on each type of medium. The rinse water samples were not diluted before spreading. For dishwater, both undiluted samples and samples diluted 1:10 were spread. The agar plates were incubated for 3–4 days at 36°C. Soil 1 1 1 1 1 2 3 RESULTS Bacterial counts and temperatures of the dishwater during machine dishwashing and hand dishwashing are summarized in Fig. 2. The dishware was soiled with the more complex and adhering soil 1 in both experiments. The bacterial counts in the dishwasher were reduced by more than 3 log units within 5 min. The water in the wash tank in the dishwasher had a temperature of 65°C. Bacterial reduction was much slower during hand dishwashing, in which a reduction of 0.7 log units was observed after 43 min. The temperature, approximately 50°C at the start of the hand dishwashing experiment, decreased over time (43°C after 43 minutes). Figure 3 displays the bacterial counts and temperatures in the two hand dishwashing experiments. Plates with soil 1 were cleaned in Experiment A, whereas plates with soils 2 and 3 were cleaned in experiment B. Bacterial reductions and temperatures were similar in the two hand dishwashing experiments. After 14–15 minutes, a bacterial reduction of 0.7 log units and a temperature decrease of 4°C Analyses of dishware Kanamycin esculin azide agar (~50°C) was poured onto the bottom inner areas of the washed trays and on the washed plates. Only the inner circle (~14 cm in diameter) of the plates was covered with agar. All washed dishware was included, as well as non-soiled dishware. The trays and plates were incubated for 3 days at 36°C. Analyses of wash and rinse water Samples of 20 ml were aseptically withdrawn from the wash tank of the dishwasher at different time points. The 274 FOOD PROTECTION TRENDS | MAY 2009

Food Protection Trends - May 2009

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