Sterilisation

Sterilisation is the elimination or extermination of all micro-organisms as well as the inactivation of viruses that could be found on an object. After sterilisation, such objects must be free of germs capable of reproducing. 

At present, there are no specific guidelines or rules for the sterilisation of freeze-drying systems. However, to ensure a sterilisation compliant with cGMP, sterilisation with saturated steam at a temperature of 121.1 °C corresponding to a saturated vapour pressure of 2.5 bar abs. has become widespread in practice. 

The direct sterilisation of particulafe solid foods in a gas-solid fluidized bed was proposed as long ago as 1968 by Lawrence et al. (1968) who sterilised wheat flour in steam-air mixtures at the pilot scale. However, Jowitt (1977) described an atmospheric pressure process for fhe sferilisation of canned foods in which the cans are immersed in a fluidized bed of inert particles. This has a number of advantages compared to the conventional retorting process using pressurised steam or hot water  

In a retort which uses condensing steam the heat transfer coefficient to the can is of the order of 5000-10 000 and therefore the 

However, this does not necessarily apply to foods which heat by convection. Jowitt quotes both peas in brine and soup as examples where the process time was doubled in a fluidized bed (22 minutes) compared to a steam-heated retort (11 minutes) for the same total process lethality. However, increasing the fluidized bed temperature by 8K resulted in almost equal process times and approximately equal retention of the heat-sensitive vitamin thiamine. Following the heating and holding stages of the sterilisation operation, the cans were cooled in a fluidized bed in which heat was removed by cooling water passed through finned tubes immersed in the bed (Jowitt and Thorne, 1971). 

Based upon the work of Evans et al. (1983), Thorpe (1987) describes a semi-commercial scale continuous-flow fluidized bed disinfestor capable of handling up to 150 th of wheat. He gives a detailed description of the thermodynamic performance of the plant together with a mathematical model of the process which is validated by experimental results obtained from the plant. The plant consists of a single fluidized 

There are a large number of chemicals which are able to kill micro-organisms in addition to antibiotics. Many of these are used on surfaces or skin and go under a variety of names. Chemicals used in the presence of dirt or dense bacterial populations are known as disinfectants. Antiseptics are used on the skin to reduce the bacterial population and thus the risk of infection. Sterilants are compounds used to sterilise enclosed spaces, whilst preservatives are compounds which stop bacteria attacking organic matter. These definitions form a spectrum and compounds frequently overlap from one group to the next. 

Chemicals used against micro-organisms may be divided into two groups, bacteriostatic and bactericidal (biocidal). Bacteriostatic compounds are those which stop bacteria growing, whilst bactericidal compounds are those which kill bacteria. The division is not clear cut as many compounds are bacteriostatic at low concentrations and bactericidal at high concentrations. The extent of the bactericidal effect of any compound is governed by four factors. These are  

The process of sterilisation is required for any product used in a situation where there is a risk of infection. Sterilisation requires the application of a chemical (biocide) to a product, or the physical removal of micro-organisms from the product. The objective is to kill the bacteria, the definition of bacterial death being the irreversible loss of reproductive ability. There are a number of chemical and physical methods available to achieve this objective. The physical methods 

In all cases where a product requires sterilising, there is a risk of damage to the product, and it is necessary to balance the risk of damage against the risk of failing to sterilise the product successfully. It is therefore necessary to choose a method that causes maximum destruction/removal of the bacteria, with minimum damage to the product. 

Although a knowledge of the microbiological origin and history of the product is useful, sterilisation processes can be developed on a worst case scenario. Bacterial spores are more resistant than vegetative cells and can be used as 

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Liquid chlorine dioxide, ClOj, boils at 284 K to give an orange-yellow gas. A very reactive compound, it decomposes readily and violently into its constituents. It is a powerful oxidising agent which has recently found favour as a commercial oxidising agent and as a bleach for wood pulp and flour. In addition, it is used in water sterilisation where, unlike chlorine, it does not produce an unpleasant taste. It is produced when potassium chlorate(V) is treated with concentrated sulphuric acid, the reaction being essentially a disproportionation of chloric(V) acid ... 

Miscellaneous Applications. PEIs and their derivatives ate used as cementation auxihaties in cmde oil exploration (459), and for breaking cmde oil emulsions (460) in cmde oil extraction. Seed coatings of water-soluble copolymers containing polyethyleneimine have been developed (461). Polyethyleneimine derivatives have positive photoresist properties (462) amidated polyethyleneimines improve the flow properties of cement (463) and with few exceptions, A/-acyla2iddines act as chemical sterilisers for insects (464). 

Reports of sterilisation (qv) against bacteria by nonthermal effects have appeared, but it is generally beheved that the effect is only that of heating (164). Because microwave heating often is not uniform, studies in this area can be seriously flawed by simplistic assumptions of uniform sample temperature. 

In addition to these forms of water, several other official aqueous vehicles can be used. These are isotonic injections that can be sterilised, eg, sodium chloride. Ringer s, dextrose, dextrose and sodium chloride, and lactated Ringer s. Addition of water-miscible solvents such as ethanol or propylene glycol increases solubiUty and stabiUty. 

Phthalocyanines are excellent lubricants at temperatures of 149—343°C (191). Combinations with other lubricants, like grease, molybdenum, or tungsten sulfides, have found appHcations in the automotive industry or professional drilling equipment (192—195). Further uses include indicators for iron(Il), molybdenum(V), and uranium(IV) (196) or redox reactions (197), medical appHcations like hemoglobin replacements (198) or sterilisation indicators (199), or uses like in gas filters for the removal of nitrogen oxides from cigarette smoke (200). 

Neomycin [1404-04-1] (33) or neomycin sulfate [1405-10-3], isolated from Streptomjcesfradiae (34—36), is sometimes used for gut sterilisation and other nonsystemic apphcations. Neomycin is a mixture of neomycin B /719-04-0] CggH N Ogg (9)... 

Low humidity ethylene oxide gas sterilisa tion procedures and moisture-proof packaging for polyglycoHc acid products are necessary because of the susceptibihty to degradation resulting from exposure to moisture and gamma sterilisation. 

J. J. Perkins, Principles andMethods of Sterilisation in the Health Sciences 2nd ed., Charles C. Thomas, Springfield, lU., 1969. 

G. B. Phillips and W. Miller, Validation of Steam Sterilisation Technical Monograph 1, Parenteral Dmg Association, 1978. 

Steam Sterilisation and Sterility Assurance Association for Advancement of Medical Instmmentation, Arlington, Va., ANSI/AAMI ST46,1993. 

R. R. Ernst, Industrial Sterilisation Ethylene Oxide Gaseous Sterilisation for Industrial Applications Duke University Press, Durham, N.C., 1973. 

Sterilisation of Health Care Products—Chemical Indicators, Part 1 General Requirements, AAMI 1114001-D, 1995-11-30, Association for the Advancement of Medical Instmmentation, Arlington, Va., 1995, proposed new American National Standard. 

Validation and Foutine Monitoring of Moist Heat Sterilisation Processes, ISO 11134, International Standards Organization, Geneva, Switzerland. 

Fermentative Manufacture. Throughout the years, riboflavin yields obtained by fermentation have been improved to the point of commercial feasibiUty. Most of the riboflavin thus produced is consumed in the form of cmde concentrates for the enrichment of animal feeds. Riboflavin was first produced by fermentation in 1940 from the residue of butanol—acetone fermentation. Several methods were developed for large-scale production (41). A suitable carbohydrate-containing mash is prepared and sterilised, and the pH adjusted to 6—7. The mash is buffered with calcium carbonate, inoculated with Clostridium acetohutylicum and incubated at 37—40°C for 2—3 d. The yield is ca 70 mg riboflavin/L (42) (see Fermentation). 

The converted mash is pumped to a clean sterilised fermentor and the yeast inoculum is added. The set temperature range for whiskey fermentation of 72 hours is usually 17—21°C. At the beginning, the mash converted composition is approximately 80% sugars, mainly maltose and some (<1%) dextrose (primary conversion). The pH is adjusted to reduce initial bacterial growth. Grain neutral spidts are usually set at 27—29°C to expedite fermentation. Temperatures above 35°C inhibit yeast reproduction and promote rapid bacterial growth. Above 40°C actual yeast kill occurs. 

The radioactive isotope Cs is important commercially in process control instmments and for sewage sludge sterilisation. The isotope has along half-life — 30 yi )i however, it must be weU-shielded because of the high biological hasard. 

In the 1970s questions were raised about certain immunological complications as a consequence of male sterilisation or vasectomy. Clinical epidemiological data do not appear to indicate that this actually occurs in clinical practice. No significant long-term side effects of male sterilisation have been demonstrated. 

Voluntary female sterilisation is the world s most widely used family planning method. An estimated 138 million women of reproductive age used the method in 1990, 43 million more than in 1984. Millions more are expected to ask for the method during the 1990s (97). 

Because of the increa sing worldwide interest and demand for simple, effective, and inexpensive female sterilisation, a variety of procedures and methods have been developed. These approaches differ whether they are performed postpartum, postabortum, or in interval situations. The choice of methods also largely depends upon the physician s prior training, knowledge, and experience. Excellent reviews have been written on sterilisation (98). 

Voluntay Female Sterilisation, Population Reports, Series C, no. 10, Population Information Program, The Johns Hopkins University, Baltimore, 1990. 

Decorative eye cosmetic products have been reported to be subject to pathogenic microbial contamination. Regulatory agencies in several countries, therefore, permit the use of mercury-containing preservatives in eye makeups. The infections reported were to a large extent caused by contamination during use, and the introduction of self-sterilising preparations seems warranted. 

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