Temperature heat sterilization

A. High temperature, heat sterilized or retorted above 100 °C (212 °F). 

For high temperature, heat sterilized or retorted products. 

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. 

Superheated steam results when steam is heated to a temperature higher than that which would produce saturated steam. The equiUbrium between hquid and vapor is destroyed, and the steam behaves as a gas. It loses its abiUty to condense into moisture when in contact with the cooler surface of the article to be sterilized. This process resembles dry-heat sterilization more than steam sterilization and, under ordinary time—temperature conditions for steam sterilization, does not produce stetihty. 

The lethal effects of dry heat on microorganisms are due largely to oxidative processes which are less effective than the hydrolytic damage which results firm exposure to steam. Thus, dry heat sterilization usually employs higher temperatures in the range 160-180°C and requires exposure times of up to 2 horns depending upon the temperatrrre employed (section 10). 

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. 

Recent sterilizer developments have led to the use of dry-heat sterilizing tunnels where heat transfer is achieved by infra-red irradiation or by forced convection in filtered laminar airflow tunnels. Items to be sterilized are placed on a conveyer belt and pass through a high-temperature zone (250 - 300 + °C) over a period of several minutes. 

Other heating equipment. Autoclave used for sterilization can be used to achieve superheating condition at 120°C. For higher temperature heating, a domestic pressure cooker, or a plastic steamer may be used. Some commercial laboratory pressure cookers have been designed for AR-IHC with controlled temperature. A water bath can be used to achieve lower temperature heating condition. 

Aseptic BPS machines are subject to steam-in-place sterilization following standard CIP cycles. The SIP cycles are routinely measured by thermocouples located in fixed positions along the product pathway. Validation of SIP cycles should be carried out to demonstrate that consistent sterilization temperatures are achieved throughout the equipment to prove that the system can be effectively sterilized. Validation should also identify suitable positions for routine use, or justify the fixed probe positions already in place. The SIP validation is generally carried out with the help of additional thermocouples and should include the use of biological indicators (appropriate for moist heat sterilization). Test locations should include areas which may be prone to air or condensate entrapment. An accurate engineering line drawing of the system to aid identification of suitable test locations and document test locations selected should be available. 

The purpose of this process is the production of foodstuffs that are shelf stable at ambient temperatures and that have better quality characteristics than the corresponding heat-sterilized products. Radappertization dose of low-acid foods must ensure elimination of the spores of the most resistant bacterial pathogen, C. botulinum. The dose selected for the purpose is around 50 kGy, 12 times of the Z>io value. As the product is intended to be shelf-stable at ambient temperature, while autolytic enzymes have high radiation resist-... 

There is another, nonkinetic parameter widely used when evaluating a heat sterilization process. This is the F0 value, defined as the number of minutes required to kill all endospores present in a system held at a temperature of 250°F or 121°C. It should be noted that, in principle, the kinetic approach implies that sterilization cannot be achieved (because there is no zero on a logarithmic plot) so the nonkinetic offers more hope. The F0 can be measured and there is an interconnection between F0 and D if F0 is slightly redefined as the number, n, of D values required to sterilize a system, i.e., F0 = nD. 

Knowledge of the D value at different temperatures in heat sterilization is necessary for the calculation of the Z value. (See p. 87.)... 

These terms heretofore have been applied exclusively in the validation of heat-sterilization processes. The Z value is the reciprocal of the slope resulting from the plot of the logarithm of the D value versus the temperature at which the D value was obtained. The Z value may be simplified as the temperature required for a one-log reduction in the D value ... 

Figure 2 presents thermal resistance plot for a Z value of 10°C, the accepted standard for steam sterilization of B. stearothermophilus spores, and for a Z value of 20°C, the proposed standard [13] for dry-heat sterilization of B. subtilis spores. These plots are important because one can determine the I) value of the indicator micro-organism at any temperature of interest. In addition, the magnitude of the slope indicates the relative degree of lethality as temperature is increased or decreased. 

Validation studies conducted on dry-heat sterilizers can be divided into two basic components. One component envelops all the physical elements that must be qualified, such as temperature control, air particulate levels, and belt speeds. The other component is the biological constituent, which involves studies that prove that the process destroys both microbial and pyrogenic contaminants. 

It is necessary to examine and treat femily members or sexual contacts due to the high risk of reinfestation. Clothing, linens, and grooming instruments should be laundered or sterilized by exposing to dry heat at 140°F (50°C) for 20 to 30 minutes. This heat sterilization can usually be accomplished at the highest temperature settings of most household dryers. Contaminated cosmetics should be discarded. 

The culture media used in fermentation processes contains a variety of unwanted cells and spores which need to be inactivated or removed before fermentation. The most commonly used inactivation method is heat sterilization. Most cells and some spores can be destroyed at60°C-80°C, while some heat-resistant spores such as bacterial spores require more than 120°C. Heat-based methods, however, cannot be used when the product molecules, such as vitamins and antibiotics, are heat sensitive, because the application of high temperatures changes their properties. In these cases, sterile filtration with membrane filters or depth filters is used. 

Stability is an essential condition for PFC emulsions to be of practical use. The principal mechanism for irreversible droplet growth in submicronic PFC emulsions during storage is molecular diffusion (also known as Ostwald ripening or isothermal distillationj.P Coalescence may contribute to instability when mechanical stress is applied and at higher temperatures, as during heat sterilization. Sedimentation and flocculation are fully reversible and pose no problem. 

The aqueous solubility of these derivatives is adversely affected by temperature, however, and precipitation occurs during heat sterilization. The mixture of randomly methylated p-CD (M14-p-CD), however, exhibits a favorable water solubility (>50g/ 100ml) that increases as temperature increases. ... 

Compression set is commonly used as a measure of the dimensional recovery of a rubber compound after compression at a defined level, usually 25%, at a specified time and temperature, usually 24 h at 70°C. High compression set values are associated with rubber that takes a set or loses its ability to spring back after compression. Low compression set is important for rubber closures and syringe plungers that are heat sterilized while under compression and remain under compression for long periods of time before use but must remain elastic and resilient to maintain seal integrity. Compression Set is measured on dimensionally defined test specimens. 

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