Sterilization treatment

Pesticides are susceptible to a variety of transformations in the environment, including both chemical degradation and microbial metaboHsm. Microbial transformations are catalyzed exclusively by enzymes, whereas chemical transformations are mediated by a variety of organic and inorganic compounds. Many pesticide transformations can occur either chemically or biologically. Consequentiy, most pesticide dissipation studies include sterile treatments to... 

Microbiological fouling may develop from time to time, and periodic sterilizing treatment with steam or hot water may be required. 

Paekaging material has a dual role and aets both to eontain the produet and to prevent the entry of microot nisms or moisture wMeh may resrrlt in spoilage, and it is therefore important that the sotrrce of contamination is not the packaging itself. The microflora of packaging materials is dependent upon both its eomposition and storage eonditions. This, and a consideration of the type of pharmaeeutioal product to be packed, determine whether a sterilization treatment is required. 

In the case of injectables and ophthalmic preparations which are manufactured aseptically but do not receive a sterilization treatment in their final container the packaging has to be sterilized. Dry heat at 170°C is often used for vials and ampoules. Containers and closures may also be sterilized by moist heat, chemicals and irradiation, but consideration for the destruction or removal of bacterial pyrogens may be necessary. 

Heat treatment of milk has little effect on surface tension except that sterilizing treatments cause an increase of a few dynes cm-1 coinciding with grain formation (Nelson 1949). This effect undoubtedly results from denaturation and coagulation of the proteins so that they are no longer effective surface-active agents. 

It is necessary to forewarm milk to impart adequate heat stability to the concentrate to permit it to withstand subsequent sterilization treatments. The heat-induced casein micelle-whey protein complexes in forewarmed milk are less sensitive to heat than native whey proteins and thus provide the required stability to the concentrate. The forewarming treatment also stabilizes the milk mineral system by com-plexing Ca and Mg ions with casein micelles and by converting ionic forms to the less reactive form of colloidal phosphate (Morr 1975). 

The micro-organisms must have high resistance to the sterilization treatment which they are being used to validate. This does not mean that they must be the most resistant micro-organism known to man. B. stearothermophilus has D i-values of l min according to conditions of culture and the substrate upon which they are mounted. This is higher than most spores of Bacillus spp., which tend to have Di2i-values below 0.5 min. 

The micro-organisms must have stable resistances to the sterilization treatment which they are being used to validate. There are data from commercial suppliers of Bis to show that spores of B. stearothermophilus survive and retain stable resistances over long periods of crudely controlled storage. The micro-organisms must be easily culturable and preferably be easily identifiable in culture. Very few micro-organisms share with B. stearothermophilus the ability to grow in simple culture media at 55-60°C. 

Use Urea and melamine resins, polyacetal resins, phenolic resins, ethylene glycol, pentaerythritol, hexamethylenetetramine, fertilizer, disinfectant, biocide, embalming fluids, preservative, reducing agent as in recovery of gold and silver, corrosion inhibitor in oil wells, durable-press treatment of textile fabrics, industrial sterilant, treatment of grain smut, foam insulation, particle board, plywood, a versatile chemical intermediate. 

In summary, there is always a finite probability of a survivor occurring, no matter the strength or duration of a sterilization process. In other words, absolute sterility, in the sense of total freedom from all viable life forms, can never be achieved in practice. The acceptance of exponential inactivation lunetics has led to two different approaches to the establishment of standards of satisfactory sterilization treatment, the inactivation factor approach and the sterility assurance level (SAL) approach. 

In the first instance, the intensity or durtUion of the sterilization treatment may be very high, possibly loo high to be tolerated by some products. This begs the practical question of why such an intense process must be used. It might be argued that the actual contaminants on the product are far less resistant to the sterilization treatment than the reference microorganisms. 

In the limiting case there are two phases associated with application of a sterilization treatment to a population of items with an initial mean number of contaminants greater than one. In the first phase the effect of increasing treatment is to decrease the total number of microorganisms without effecting any change in the propoition Pic) of nonsterile items in the population ... 

If it is assumed that the technology of the sterilization treatment in question can be controlled sufficiently well to deliver reasonably precise incremental treatment levels, then the procedures and precautions required to derive reproducible survival curves are quite similar. 

Probably the most widely known method of calculating D-values from quantal response experiments is the Stumbo 19 method. Each sample should con.sist of at least ten (and rarely more) replicate items carrying the same number of contaminants Nq), Samples should be exposed to increments of sterilization treatment, and then each replicate should be tested for viable microorganisms separately in suitable recovery conditions. The number of sterile replicate.s q is scored after incubation. The Z>-value may be calculated from... 

A separate )-value is usually calculated for each increment of sub<process sterilization treatment and an overall D-value taken from the arithmetic mean. 

The same type of experimental design, allowing that each increment of sub-process sterilization treatment d is equal, may be used to calculate O-values by the Spearman Karber method [20]. The total duration of sterilization treatment should be chosen to cover the whole of the quantal region from /]. which is defined as the longest lime at which every replicate is still found to be nonsterile, to time tfi, which is the shoitest exposure at which every replicate is found to be sterile as tested. The Speannan Karber equation allows estimation of a factor u as... 

Tailed Survival Curves Tailed survival curves cannot be extrapolated. They are characterized by a slope that diminishes with increasing exposure to the sterilization treatment. They are often described as concave. ... 

Tails have not been seen throughout the whole range of sterilization treatments. For instance, no genuine case of tailing has been attributed to inactivation by ionizing radiation. This may be because of the nature of biochemical mechanisms of inactivation specific for nucleic acids. On the other hand, it may be... 

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