Operations sterilisation

Raw materials Containers Human resources Occupational safety and health Premises Equipment Basic operations Sterilisation methods Aseptic handling Quality requirements and analysis... 

Typical units for productivity are kg m 3 h 1. Factors that influence productivity include the production time of the fermentation, the time required to dean and set up the reactor, the sterilisation time and the length of the lag phase of growth. Figure 2.2 shows how total productivity and maximal productivity can be calculated for a batch fermentation. The dedsion as to when the fermentation is terminated (maximum or total productivity) depends on the operating costs, which include the capacity of the fermentation vessel, energy costs and labour costs. 

True. Batch cultures give lower overall outputs than continuous cultures, as they suffer from non-productive down-time (the time taken to empty, clean, re-sterilise and re-fill the fermentor). After inoculation, considerable time can be taken for biomass to build up to a level where substrates are effectively utilised. Continuous cultures do not suffer such drawbacks once they are in operation. 

Aseptic harvesting is necessary to overcome the need for medium re-sterilisation before recycling. Sterilisation costs are high. If biomass can be recovered by an aseptic process, the medium can be recycled without re-sterilisation. This excludes centrifugation, which cannot be operated under aseptic conditions. 

The production-scale fermentation unit, with a projected annual capacity of over50,000 tonnes was fully commissioned in 1980. The bioreactor (Figure 4.8) is 60 m high, with a 7 m base diameter and working volume 1,500 m3. There are two downcomers and cooling bundles at the base. Initial sterilisation is with saturated steam at 140°C followed by displacement with heat sterilised water. Air and ammonia are filter sterilised as a mixture, methanol filter sterilised and other nutrients heat sterilised. Methanol is added through many nozzles, placed two per square metre. For start-up, 20 litres of inoculum is used and the system is operated as a batch culture for about 30 h. After this time the system is operated as a chemostat continuous culture, with methanol limitation, at 37°C and pH 6.7. Run lengths are normally 100 days, with contamination the usual cause of failure. 

Both fungi will grow at pH 2.5, at which non-aseptic processes can be operated (that is without sterilisation). However, the SCP grown in non-aseptic systems is suitable only as feed. The SCP from both organisms can be used as a high-protein food additive, but Fusarium sp. must be ground up (powdered) for this. In addition, the filamentous fungus can be used to make meat substitutes. For this the SCP must be prepared deep-frozen and not dried. 

To produce Candida sp. as food additive the above process could be operated, except that fermentation would have to be aseptic (with sterilisation costs). The cost would be 0.647 + 0.04 = 0,687 per kg biomass or 1.145 per kg protein. 

Dry heat sterilisation is used for equipment that can withstand high temperature and dry heat but cannot withstand wet or steam autoclave. This method is often used for glassware as it dries and sterilises in one operation. The pipets must be wrapped in dustproof aluminum foil or placed in metal pipette cans. The can lids are removed during heating and replaced after sterilisation, that is before any dust can get in the can. Disposable items are not recommended for dry heat sterilisation. This method may only be good for permanent reusable glass pipettes. 

Electron beam sterilisation is a high-voltage potential established between a cathode and an anode in an evacuated tube. The cathode emits electrons, as a cathodic ray or electron beam. A high intensity of electrons is produced. These electrons are accelerated to extremely high velocities. These accelerated electron intensities have great potential as a bacteriocide. Most electron beams operate in a vacuum. As a result the unwanted organisms in the media vanish and the media is sterilised. 

Pharmaceutical manufacture may involve the contracting out of certain operations in the process, such as packaging and labelling, terminal sterilisation of products. 

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). 

Bottle systems are more varied, whether for glass, polyethylene terephtha-late (PET) or other plastic. Bottles are rinsed with oxonia solution and then sterile water prior to filling. The filler is generally of a non-contact type (it does not touch the bottles) and product is either weighed in or measured volumetrically. Caps are also chemically sterilised (unless a foil closure is used) and applied on a capper monoblocked with the filler, enclosed in a high efficiency pure air (HEPA) filtered enclosure. The filler and final rinser are in a class 100 room and file operator wears full protective clothing to prevent infection of the product. 

Figure 9.1 Aseptically operated filling and closing lines for bottles and wide-mouth containers made of glass and plastics. (1) one-lane feed transfer (2) in-feed into bottle sterilisation unit (3) bottle sterilisation unit (4) discharge (5) two-lane transport of bottles to filler (6) aseptic 10-up inline filler (7) closing machine (8) discharge for closed bottles (9) fid punch and in-feed (10) aseptic module.

Hazards attendant on use of ethylene oxide in steriliser chambers arise from difficulties in its subsequent removal by evacuation procedures, owing to its ready absorption or adsorption by the treated material. Even after 2 evacuation cycles the oxide may still be present. Safety is ensured by using the oxide diluted with up to 90% of Freon or carbon dioxide. If high concentrations of oxide are used, an inert gas purge between cycles is essential [7]. The main factors in safe handling and use on laboratory or small pilot plant scales have been identified [8]. Safe operation of ethoxylation processes on industrial scale is discussed, with case histories [15],... 

In most of the above-mentioned processes, high operation temperatures are necessary while the reaction atmospheres usually contain considerable amounts of steam because water is one of the reactants, or because water is added to reduce coke formation. Also in food processing and medical applications, steam is often used for sterilisation. Thus, in many applications the membranes must be sufficiently stable in environments of both increased temperature and containing steam. In this work, this is called hydrothermal stability. 

Desired properties. Innumerable compounds have local anaesthetic properties, but few are suitable for clinical use. Useful substances must be water-soluble, sterilisable by heat, have a rapid onset of effect, a duration of action appropriate to the operation to be performed, be nontoxic, both locally... 

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