Sterilisation resistance

One result of this development work is an instrument for accurately measuring a key property of can coatings, the sterilisation resistance. First, however, a brief description of can coatings and some of their properties is in order. The discussion will be limited to coatings to be applied to the interior of food-or beverage-containing cans since this application requires the highest chemical resistance. Most of the work described has been carried out with can lacquers of the solid epoxy resin/phenolic-formaldehyde (E/PF) type as these are the predominant type used in Western Europe. 

Biological Indicator Microorganism Micro-organism of a known sterilisation resistance, that is used to develop and/or validate a sterilisation process. The micro-organisms are frequently used on a carrier, which is supporting material on which test organisms are deposited. 

All feed streams are sterilised before being metered into the fermentation vessel. Contaminants resistant to the antibiotic rarely find their way into the fermenter. When they find a way to contaminate media, their effects are so catastrophic that prevention is of paramount importance. A resistant, (3-lactamase producing, fast-growing bacterial contaminant can destroy the penicillin.5 The contaminants not only consume nutrients intended for the fungus, but also cause loss of pH control and interference with the subsequent extraction process. 

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. 

Stickler D.J. King J.B. (1998) Intrinsic resistance to non-antibiotic antibacterial agents. In Principles and Practice of Disinfection, Preservation and Sterilisation (eds A.D. Russell, W.B. Hugo G. A J. Ayliffe), 3rd edn. Oxford Blackwell Science. 

Refrigerator parts, packaging, structural housing panels, pipe, defroster and heater ducts, sterilisable household items and hospital equipment, hoops, battery parts, blow moulded containers, including automotive petrol tanks, film wrapping materials, wire cable and insulation and chemical-resistant pipe. 

It is, however, impossible to make a general statement as to the minimum amount of ozone required to sterilise air, because so many factors are involved. Some organisms are more resistant than others, whilst time, temperature, and the presence of moisture have an important influence upon the results. It is interesting to note, however, that Duplul6 has drawn attention to the paucity of bacteria in the air of Bordeaux—an ail that is characterised by its high percentage of ozone. 

Polyethylene naphthalate (PEN) polyesters are made from 2,6-naphthalene dicarboxylic acid or 2,6-naphthalene dicarboxylic acid, dimethyl ester. They have higher temperature resistance than amorphous PET and are increasingly used in applications requiring heat sterilisation of the food/drink, although PEN at the moment is significantly more expensive. Table 10.5 lists commonly used substances in polyesters. 

The organism is sensitive to physical agents such as heat sterilisation, radiation and cold shock [6,7], and it is therefore its resistance to antimicrobial agents which poses the major problem. The continued use of antibacterial agents will no doubt exacerbate the situation unless more effective agents are discovered. 

Any plastic constituent in addition to the function it serves must have heat stability, UV light stability, weather resistance, low solubility in terms of extraction, compatibility with other constituents and good dispensability. Where plastics have to be sterilised by irradiation, certain constituents may be degraded, or even continue to degrade after irradiation. Certain antioxidants are degraded by gamma irradiation. 

Resistance to sterilisation process (dry heat, moist heat, irradiation, UV, etc.). 

Cast polypropylene (PP) is extensible, moisture-resistant, clear and seals at temperatures above those used in steam sterilisation. Oriented PP is strong and can be used in thin gauges. Unless coated or coextruded the film cannot be heat sealed without distortion. OPP is very clear, but can also make an opalescent film. Has a similar degree of inertness to HDPE. 

Another tough, clear film. Withstands steam sterilisation. Rather expensive. Only fair moisture resistance but good scuff resistance. Used in some laminations. 

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