EN 17735: 2022. Food hygiene - Commercial dishwashing - Hygiene requirements, testing.
Test not accredited yet in our laboratory.
The standard EN 17735 (previously DIN SPEC 10534 standard) specifies the hygiene requirements related to the design, construction and operation of commercial dishwashing equipment used for cleaning wash ware that is used in contact with food, such as, crockery, glassware, cutlery, reusable boxes and similar items, used in professional kitchens, such as restaurants, canteens and hospitals, and in commercial companies as bakeries, butchers, etc. Domestic dishwashing machines, washer disinfectors for the treatment of medical devices and machines for industrial use are excluded from the scope of this standard.
The standard EN 17735 provides information on the requirements for commercial dishwashing equipment and describes methods for testing the hygienic performance of dishwashing equipment. The requirements to test the hygienic performance of a washing process are: a) The wash ware must be visually clean; b) The wash ware must be dry upon removal from the wash ware carriers, tolerating the remaining drops on the support points and the residual humidity inside the hollow items; c) The machine must achieve a level of disinfection performance in accordance with microbiological requirements; d) treating agents used in the cleaning process shall be removed from the wash ware to a level that is not harmful to health.
Depending on the scope of application and the intended use there are different tests to evaluate the hygienic performance of a washing process: type test and post-installation tests. In our laboratory, only type tests are performed, the tests that must be carried out by manufacturers to verify that the dishwasher works in a hygienic way. For this, the client must send the dishwasher equipment to our laboratory and the test would be carried out with the detergent described by the standard. The different types of tests indicated by the standard are described below.
1.-The type tests, which aim is to check the cleanliness and dryness by means of a visual inspection, to carry out the temperature control of the equipment and to analyze the reduction obtained after the process in the Enterococcus faecium bacteria on the test supports.
For batch-type dishwashing machines and rack conveyor dishwashing machines includes the evaluation of the cleaning and disinfection performance with stainless steel bioindicators contaminated with a specific inoculum of Enterococcus faecium in a medium of bovine albumin soil, mucin and starch, which are placed in 24 cm diameter plates or cutlery trays. To perform the assay with the bioindicators on the dishes, the rack for the dishes is filled according to the manufacturer's instructions and the bioindicators are fixed to the dishes using supports (one bioindicator per dish will be used). The number of dishes will depend on the load of the test dishwasher: 10 to dishwasher with a rack size of 400 mm x 400 mm and 18 plates for a rack size of 500 mmx 500 mm. 50% of the plates shall be fitted with a bioindicator. To test with the bioindicators on the cutlery trays, load the cutlery tray of the commercial test dishwasher with three spoons, three forks and three knives in each compartment and placing a bioindicator between the cutlery in each container. If there is no cutlery tray one with at least 8 compartments shall be used. The test is carried out using the shortest cycle program and using a reference detergent and rinse aid indicated by the standard. At the end of the cycle, new test bioindicators are placed up to perform 2 test cycles. Prior to microbiological examination of bioindicators, they should be visually inspected for cleanliness. The degree of dryness of the dishes and cutlery should also be recorded. In the plates, 90% of the bioindicators should show a ≥ 5 log reduction and none should show a reduction below 4 log reduction in E. faecium titre. In the cutlery tray, 7 out of 8 bioindicators should show a ≥ 5 log reduction and none bioindicator should show a reduction below 4 log in E. faecium titre. If the test requirements are met, it can be concluded that other laundry items will also be cleaned and disinfected if properly placed.
The type test for flight dishwashing machines a test rack is used to hold 10 bioindicators of stainless steel contaminated with a certain inoculum of E. faecium in a soil containing bovine albumin, mucin and starch in two levels. Prior to microbiological evaluation, bioindicators should be visually inspected for cleanliness. To demonstrate the hygienic performance of the washing process, all 10 bioindicators should show a minimum reduction of 5 log in E. faecium titre.
As previously, the test with bioindicators in the cutlery tray must also be performed. In the cutlery tray, 7 of 8 bioindicators should show a reduction of ≥ 5 log and none of the bioindicators should show a reduction below 4 log in the E. faecium titre.
2.-Post-installation tests are organized by the operating company and are intended to verify that commercial dishwashers meet hygiene requirements, if they are operated in accordance with the instructions. The post-installation test consists of: the aerobic colony count of the wash ware surface and the aerobic colony count of the detergent solution. All the wash ware tested shall be given a visual inspection for cleanliness and dryness.
Of these tests in IVAMI, only the TYPE TESTS (#1.-) could be carried out, including the elimination of Enterococcus faecium, since the rest of the tests must be done after the installation of the equipment in its place of use.
Simulated-use test for PT4 products intended for disinfection in dishwashing machines
(EN 17735: 2022 standard and BPR Guidance:2023)
The EN 17735 standard describes a test to evaluate commercial warewashes equipment, using a reference detergent. Nevertheless, the BPR Guidance states that for testing a PT4 product intended for disinfection in a dishwashing machine, the procedure described in the DIN SPEC 10534 Standard (currently replaced by the EN 17735 Standard) might be helpful for designing a simulated-use test. In our laboratory, we perform a simulated-use test based on the EN 17735 Standard to evaluate the efficacy of PT4 disinfectants used in dishwashing machines.
The BPR guidance indicates that for tests with PT4 products (for disinfection in the food area) intended for disinfection in dishwashing equipment, the following tests are required for these disinfectants:
- A quantitative suspension test (phase 2, step 1); and
- A quantitative surface test (phase 2, step 2); and
- A simulated use or field test (phase 3) for disinfectants used in (dish) washing machines;
All tests must simulate practical conditions appropriate to their intended use (temperature, dirt, different surfaces, contact time, etc.). The BPR guidance indicates that dishwashing products are normally used at 40ºC and that therefore tests should be carried out at this temperature. If they are used at lower temperatures, for example if they are used in the rinse step after washing, the tests can be carried out at 20°C.
The laboratory tests should be performed under these conditions. If the exact conditions cannot be met, for example, in household machines, reasonable worst-case conditions must be tested (e.g. lowest temperature, shortest time…).
According to the BPR Guidance, equipment and dish washing disinfectants should be at least sufficiently effective against bacteria and yeasts. Nevertheless, for uses in industrial dish washers for specific purposes, an exception can be made when sound justification is provided. For all other groups of organisms, data only have to be provided when activity against those organisms is claimed. Relevant groups of test organisms, next to bacteria and yeasts, can be fungi (fungal spores), viruses, bacteriophages, and bacterial spores. Bacteriophages are mainly of importance in the dairy industry.
The test organisms used in efficacy tests are normally stated in the applicable standard test methods. For dish washing disinfectants Salmonella spp., Listeria spp. and Campylobacter jejuni are relevant target organisms. For products which claim general efficacy against bacteria, the standard test bacteria should be tested. For these products, efficacy against Salmonella spp., Listeria spp. and Campylobacter jejuni is assumed, because they are more susceptible than the standard test bacteria. When the product is intended to be used at high temperatures (>40 ºC) relevant test organisms for these temperatures should be used (Enterococcus faecium, for bacteria).
The test according to the EN 17735 standard under the specific conditions of the BPR guidance is usually performed with E. faecium, with bovine albumin, mucin and starch as interference substance and using bioindicators located in plates and cutlery, with 2 series, according to EN 17735 instructions. Nevertheless, since the BPR Guidance states other possibilities, the client must specify the test conditions requested (test microorganisms, and interference substance) and the program intended to be use (time and temperature of the disinfection cycle) according to the product instructions. Since the criteria for considering bactericidal activity is not stated by the BPR Guidance, the criteria indicated by the EN 17735 is followed: In the plates, 90% of the bioindicators should show a ≥ 5 log reduction and none should show a reduction below 4 log reduction in bacterial titre. In the cutlery tray, 7 out of 8 bioindicators should show a ≥ 5 log reduction and none bioindicator should show a reduction below 4 log in bacterial titre. For yeasticidal activity, such as the EN standards and what is indicated for PT4 products used in dishwashers by the BPR Guide for phase 2 tests, it will be considered to present activity when a reduction of one logarithm less than those previously indicated occurs. That is to say: In the plates, 90% of the bioindicators should show a ≥ 4 log reduction and none should show a reduction below 3 log reduction in yeast titre. In the cutlery tray, 7 out of 8 bioindicators should show a ≥ 4 log reduction and none bioindicator should show a reduction below 3 log in yeast titre.