Oven sterilization

The two types of processes currently used in dry-heat sterilization include 1) dry-heat batch sterilization/ oven sterilization and 2) dry-heat tunnel sterilization. Process 1 is the type of dry heat unit widely used in the pharmaceutical industry it uses the principle of convective heat transfer to heat the load. Process 2 is only found in large-scale processes, and the main application of this process is in the sterilization and depyrogenation of glass.f ... 

Laboratory equipment such as incubators, refrigerators, laminar flow hoods, depyrogenation ovens, sterilizers, etc., will be qualified using the same approach as that used for process equipment and utility systems. 

There are four stages involved in oven sterilization. They are (a) drying, (b) heat-up, (c) exposure, and (d) cool-down. 

Each stage of oven sterilization has some considerable drawbacks associated with intrinsic low heat transfer rales from air to product. Inevitably this means slow heating up and cooling down, a problem that can extend cycles from a nominal 2 h to more than 3 h for practical puiposes. A second drawback has to do with lack of uniformity of temperature within the oven. Hot air has a tendency to stratify and to penetrate only poorly around masses of cooler materials. 

CompefBadAg for these difficulties often forces the actual operating temperatures of oven sterilization processes to considerably higher levels than the nominal temperature. The potential for heal damage and even charring of the materials being sterilized from a combination of these drawbacks needs no further elaboration. 

Bacteriological sampling is performed by manual techniques because of stringent sterilization requirements. Samples are taken in wide-mouthed, sterile, glass-stoppered bottles that are wrapped in paper prior to sterilization in an autoclave at 138 kPa (20 psi) or in an oven at 170°C. The botde is unwrapped and the lower portion is held in the hand. The sample is taken with the botde mouth in the direction of the flow. The stopper must be protected from contamination, the botde only partially filled, and the sample stored at 4°C after sampling. For bacteriological samples withdrawn from a tap, the water should mn for five minutes and then be shut off the tap should then be sterilized by flaming before a sample is taken. 

Dry-heat sterilization is generally conducted at 160—170°C for >2 h. Specific exposures are dictated by the bioburden concentration and the temperature tolerance of the products under sterilization. At considerably higher temperatures, the required exposure times are much shorter. The effectiveness of any cycle type must be tested. For dry-heat sterilization, forced-air-type ovens are usually specified for better temperature distribution. Temperature-recording devices are recommended. 

Normal laboratory glassware must first be washed and cleaned. It has to be rinsed with deionised water. The clean glassware is sterilised in an oven set at 200 °C for 1 1 hours. It is suitable to cover glassware with aluminum foil to maintain aseptic conditions after removing the glassware from the oven. If aluminum foil is not available, special heat-resistant wrap paper can be used. The sterile glassware must be protected from the air, which has micro-flora, or any contaminants. Avoid the use of any plastic caps and papers. Detach any labelling tape or other flammable materials, as they are fire hazards. 

Dry heat sterilization is usually carried out in a hot air oven which comprises an insulated polished stainless steel chamber, with a usual capacity of up to 250 litres, surrounded by an outer case containing electric heaters located in positions to prevent cool spots developing inside the chamber. A fan is fitted to the rear of the oven to provide circulating air, thus ensuring more rapid equilibration of temperature. Shelves within the chamber are perforated to allow good air flow. Thermocouples can be used to monitor the temperature of both the oven air and articles contained within. A fixed temperature sensor connected to a chart recorder provides a permanent record of the sterilization cycle. Appropriate door-locking controls should be incorporated to prevent interruption of a sterilization cycle once begun. 

In addition to normal compression set test conditions, usually 22 hours at 70 °C in a hot air oven, pharmaceutical elastomeric closures may be subjected to compression set conditions simulating steam sterilization cycles in an autoclave for 30 minutes at 121 °C. Also, sterilizing cycles employing ETO, radiation, or dry heat are used. Comparison data between formulations are used to develop compression set values that will identify potentially acceptable compounds under these conditions. 

Fig. 1.2 Pasteur s apparatus if the oven is not switched on, the microorganisms in the air enter the sterile culture solution and multiply. If the oven is switched on, they are killed by the heat. After Conaut (1953)...

Notably, low water activity only inhibits mould growth. Most bakery products leave the oven in a sterile condition, any mould contamination is subsequent to baking. The effect of a low water activity is that the osmotic pressure is such that no mould spores can reproduce. Thus the product is safe unless the water activity rises locally. 

PDCB was prepared by suspending cut-up unpeeled potatoes (100 g L ) and carrots (10 g L ) in purified water and heated to boiling in a microwave oven for 5-10 min. Dextrose (d-(- -)-glucose) was added (30 g L ). The medium was sterilized by autoclaving for 20 min at 121 °C and then decanting off the broth. The broth is clear to slightly opalescent and yellowish in colour. No pH adjustment was made. 

Sterilize 150 grams of shredded wheat in a oven at 100 C for one hour. Take care to prevent scorching. At the same time, sterilize a one-gallon glass jug or 4 liter boiling flask. The latter is preferred. 

You have just been hired as the chemical engineer for a small soup company. They have just found that their cans of Cream of Spinach soup have become contaminated with a bacteria whose Latin name is retchiosis barfitosum, which fortunately is not lethal but causes serious discomfort. The cans had been sterilized by heating for 1 h in an oven at 200°F, but this procedure apparently was not adequate. We need to sterilize the prepared soup cans to kill the bacteria, which will multiply on the shelf Bacteria concentrations are determined by coating a known amount of the material on a Petri dish and culturing it so that each bacterium forms a colony that can be counted on the dish. 

Dry heat sterilization, carried out in an oven, is defined exposing the product to at least 150°C for 1 hour and is required for the sterilization of surfaces, such as metal... 

Resins are used in electromc/electncal applications (connectors, circuit boards that are vapor and wave solderable, microwave transparent radomes, integrated circuit chip carriers, miniature switches, explosion proof enclosures, lamp reflectors, and high-precision fiber optic components). Polyetherimide is used for medical components (hat require all forms of sterilization. Other uses are found in the transportation field, dual-ovenable cookware, as well as bearings, fasteners, and advanced composites. 

Two types of dry-heat sterilization systems are utilized in the pharmaceutical industry today. They are the conventional hot air oven and the tunnel system. The major difference between the two systems, as far as validation is concerned, is the belt or line speed variable with the tunnel system. 

As with any sterilization process, the first step in dry-heat sterilizer validation involves qualification of all the equipment and instrumentation used. This step includes examination and documentation of all utilities, ductwork, filters, and control valves or switches for the oven or tunnel unit, and the calibration of the instrumentation used in validating and monitoring the process. The instruments used are as follows ... 

Principles as described above for the physical process validation of batch ovens apply also in the validation of tunnel sterilizers however, in addition to the variables affecting batch oven validation, tunnel sterilizers have an extra variable-belt speed. This variable can be held constant by maintaining the same belt speed throughout the validation process and not changing it after validation has been completed. 

Tunnel sterilizers must demonstrate mechanical repeatability in the same manner as batch ovens. Air velocity, air particulates, temperature consistency, and reliability of all the tunnel controls (heat zone temperatures, belt speed, and blower functions) must be proved during the physical validation studies. 

A suggested step-by-step sequence in the microbial validation of a dry-heat process for sterilizing and depyrogenating large-volume glass containers by a convection batch oven is presented. Procedures for the validation of a tunnel sterilization process have been reported by Wegel [25] and Akers et al. [26],... 

The reactor was composed of a 312-mL total volume jacketed polyacrylic (192 x 46 mm) vessel. The reactor was sterilized using 30% (v/v) ethanol solution for 48-72 h, after which it was drained and washed thoroughly with sterilized deionized water. Brick pieces (4 to 5 mm, total weight of 220 g) were washed with deionized water several times followed by sterilization in an oven at 250°C for 2 h. The particles were then cooled in an anaerobic chamber to room temperature. The void volume inside the reactor was 186 mL. The reactor was packed aseptically with the sterilized brick particles. After the reactor was packed, oxygen-free N2 was passed through the column overnight. This was done to ensure that anaerobic conditions were attained inside the column and inside the particles. 

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