Dry Sterilisation Process

The term Dry sterilization process (DSP ) refers to a specific trockenaseptisches sterilization process, for example, in the food industry in cold aseptic filling of beverages ( juices, water, UHT milk, ...) in plastic bottles made ​​from PET or HDPE as well as in the pharmaceutical industry applies.

In kaltaseptischer filling a sterile or bacteria-reduced product is bottled without being subsequently heated for preservation again. The bottles must therefore be sterilized before filling to prevent recontamination of the sterile product in this way. Due to the temperature sensitivity of the plastic materials the sterilization process may not heat the cylinder and therefore are chemical sterilization are used. Dry the sterilization process using an aqueous hydrogen peroxide solution having a concentration of 30 to 35 percent to achieve the killing of germs.

The bottles to be sterilized are first placed in a sterilization chamber. The sterilization chamber is designed as a vacuum vessel and is evacuated by vacuum pumps up in the rough vacuum range into it. Then a measured amount of hydrogen peroxide solution is vaporized in a vaporizing device. With a compound of the evaporation device with the evacuated sterilization chamber of the steam flow due to the pressure difference between the evaporation means and the evacuated sterilization chamber into the latter. The steam expands greatly as it flows into the evacuated sterilization chamber under cools and condenses instantaneously. The resulting condensate film covering all surfaces within the sterilization chamber, all bottles surfaces, inside and out, as well as all interior surfaces of the sterilization chamber.

The energy released in the condensation heat of vaporization heats the resulting condensate surface such that the hydrogen peroxide contained therein largely dissociated. This produces radicals, in particular, atomic oxygen, which still kill the microorganisms adhering to the surfaces in a split second during the condensation process. In comparison to other methods, the sterilization is carried out instantaneously killing bacteria and it is not necessary to exposure or hold time.

Immediately after the completion of the condensation process, steam and condensate are removed by pressure reduction to below 1 hPa by vacuum pumps from the sterilization chamber. In this case, the resting on the surface when the vaporized condensate film falling pressure in the sterilization chamber falls below the vapor pressure of the condensate. The re-evaporation of the condensate causes a drying of the surfaces and complete removal of hydrogen peroxide.

For removal of the sterilized bottles the evacuated sterilization chamber must be vented to atmospheric pressure. For this purpose, sterile air is used to prevent recontamination of the sterile bottles now by sterile air.

The method requires a process time of 6 seconds. Compared to the reference germs, endospores of different strains of Bacillus subtilis and Bacillus stearothermophilus commonly used in hydrogen peroxide process, both in Count Reduction Tests as well as in end -point test reached the Dry sterilization process kill rates of 106 .. 108 ( " log6 " ... " log8 ") or germ reductions to below 10-6 ... 10-8 of the initial germ count.

Leave the sterilized articles in the sterilization chamber completely dry. Only the outermost surface layer of the articles during the sterilization process, warmed slightly ( by about 10 to 15K ). The method is well suited for all applications where thermolabile items must be sterilized, in which very high kill rates are required and need the short lead times.

NB 1: To describe the performance of a sterilization process are unfortunately in common parlance tantamount, the phrases " the germ reduction is log6 ", " the germ killing is log6 " or " the kill rate is log6 " used. This is not only imprecise but mathematically strictly speaking, even nonsensical. These common expressions resulting from the incorrect use of the mathematical expression log 106 = 6

NB 2: The concepts of rate of kill, bacteria reduction and survival probability is probability statements in a statistical sense. It can be illustrated by the following two examples that are statistically equivalent:

Example 1: In a trial fraught with a 107 germs object is sterilized by a method that achieves a germ reduction of 6 orders of magnitude ( 106 or " log6 "), ie in which the survival probability of microorganisms is 10-6. Averaged over a statistically significant number of such experiments survive 107/106 = 10 or 107 * 10-6 = 10 germs per object.

Example 2 In an attempt afflicted with 10 seeds objects to be sterilized by a process that achieves a microbial reduction of 6 orders of magnitude ( 106 or " log6 "), ie in which the survival probability of microorganisms is 10-6. If a statistically significant number of such objects being sterilized, the number of surviving bacteria on the objects 10/106 = 10 * 10-6 = 10-5 or 10-5, which means that each time a survivor germ per 105 = 100,000 objects is encountered.

NB 3: Strictly speaking it is incorrect to speak of " surviving nuclei ". The main problem is not necessarily the presence of some microorganisms, but their ability to Zellteilungsyklen short, resulting in a time- exponential growth of the germ count. With a large number of existing germs then the amount generated by these to metabolic products, some of which are highly toxic, lead to poisoning of all kinds. The real problem are therefore " reproducible germs ". To determine the number of the surfaces of the sterilized article to be washed with a buffer solution and cultured for any germs present in this solution, for example, after a sterilization process. Did the buffer solution " reproducible germs " so they form macroscopic by their exponential increase after a few days, colonies on the nutrient medium. Each of these colonies comes now expressed incorrectly, by a replicable from seed. Expressed Exact dates each of these colonies from a " colony forming unit ", KBE, from (English: colony forming unit, cfu).

• Filling Technology
• Hygiene