Flow Sterilization

CONTINUOUS FLOW STERILIZATION Heat Transfer to Shear-Thinning Fluids 

Physical Model of Non-lsothermal Laminar Flow Tube Sterilizer 

This dimensionless length is valid within 2% for 0.3 1.0 and —4 4, and the strength of coupling of the momentum and energy transport equations was characterized by the equation  

Results similar to those of Simpson and Williams were obtained by Kumar and Bhattacharaya (1991). 

Continuous Sterilization of a Fluid Food Containing Starch 

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Laminar flow sterilization tunnels are widely used in high-speed aseptic manufacturing. Typically, laminar flow tunnels contain three sections (1) preheating, (2) heating, and (3) cooling. 

Figure 10.1. Electron micrograph of flow-sterilized coffee cream f homogenized fat globules.

When performing experiments with cells for a long-time period, following exposure one is required to perform electroendocytosis under sterile conditions. Thus, the electrodes are sterilized with 70% ethanol for 30 min, with subsequent washing with sterile water and drying under laminar flow. Sterile cuvettes (e.g., from Elkay Products, Inc., Shrewsbury, MA, USA) should be used, and the whole procedure of electric treatment and incubation should be performed in a laminar hood. 

Chapter 8. Heat transfer in continuous flow sterilization and to canned foods under intermittent agitation. 

The concerns for sterility can he addressed by installation of laminar flow sterile air filters that provide a constant source of clean air to the work area. Mechanically, room air is channeled through a prefilter and then a sterile high-efficiency particulate air (HEPA) filter prior to flowing across the work surface at uniform velocity (Fig. 18.2). Fully equipped laminar flow safety cabinets are very expensive (> 8000) and may not be justified in the winery microbiology laboratory. However, tabletop workstations that incorporate HEPA-filtered air are available at considerably less cost ( 3000) and serve as good alternatives. 

Eactors that could potentiaHy affect microbial retention include filter type, eg, stmcture, base polymer, surface modification chemistry, pore size distribution, and thickness fluid components, eg, formulation, surfactants, and additives sterilization conditions, eg, temperature, pressure, and time fluid properties, eg, pH, viscosity, osmolarity, and ionic strength and process conditions, eg, temperature, pressure differential, flow rate, and time. 

Bacteriological sampling is performed by manual techniques because of stringent sterilization requirements. Samples are taken in wide-mouthed, sterile, glass-stoppered bottles that are wrapped in paper prior to sterilization in an autoclave at 138 kPa (20 psi) or in an oven at 170°C. The botde is unwrapped and the lower portion is held in the hand. The sample is taken with the botde mouth in the direction of the flow. The stopper must be protected from contamination, the botde only partially filled, and the sample stored at 4°C after sampling. For bacteriological samples withdrawn from a tap, the water should mn for five minutes and then be shut off the tap should then be sterilized by flaming before a sample is taken. 

In the holding section of a continuous sterilizer, correct exposure time and temperature must be maintained. Because of the distribution of residence times, the actual reduction of microbial contaminants in the holding section is significantly lower than that predicted from plug flow assumption. The difference between actual and predicted reduction in viable microorganisms can be several orders of magnitude therefore, a design based on ideal flow conditions may fail. 

Horizontal laminar flow clean air benches are not BSCs (Section 10.3.4). They discharge HEPA-filtered air across the work surface and toward the user. These devices only provide product protection. They can be used for certain dean activirie.s, such as the dust-free assembly of sterile equipment or electronic devices. These benches should never be used when handling potentially infectious materials. The worker can be exposed to materials on the clean bench. Horizontal clean air benches should never be used as a substitute for, i biological safety cabinet. 

Dilution rate is defined as the number of tank volume pass through per unit time, D = F/V. The residence time is defined as the tune required for one unit volume of reactor to be replaced by the flow rate, t = VIv. When feed is sterile, there is no cell entering the bioreactor, which means x0 = 0, the rate may be simplified and reduced to ... 

A 2 IB. Braun airlift fermenter with a working volume of about 2000 ml was used. Sterile air is sparged through a sintered plate located near the bottom of the central concentric tube. There was no mechanical stirring only the air nozzle was forced through the centred tube and the flow directed to the annulus tube side. Aeration causes circulation of media the flow is gentle without serious shear forces. The temperature is maintained at 26 °C. 

Radioisotopes have important commercial applications. For example, americium-241 is used in smoke detectors. Its role is to ionize any smoke particles, which then allow a current to flow and set off the alarm. Exposure to radiation is also used to sterilize food and inhibit the sprouting of potatoes. Radioisotopes that give off a lot of energy as heat are also used to provide power in remote locations, where refueling of generators is not possible. Unmanned spacecraft, such as Voyager 2, are powered by radiation from plutonium. 

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