Continuous Sterilization

Sterilization can be carried out in a continuous mode rather than in batches. Continuous sterilization offers several advantages  

It simplifies production planning, thus allowing maximum plant utilization and minimum delays. 

It can be operated at a high temperature (140°C instead of 121 °C in batch sterilization) therefore, the sterilization time can be shortened (holding time of 1 to 2 minutes). 

It requires less steam by recovering heat from the sterilized medium. As a result, it also requires less cooling water. 

It is easier to automate the process thus, it is less labor intensive. 

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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. 

Not all the nutrients required during fermentation are initially provided in the culture medium. Some are sterilized separately by batch or continuous sterilization and then added whilst the fermentation is in progress, usually via automatic systems that allow a preset programme of continuous or discrete aseptic additions. 

Continuous SO3 single-pass sulfonation processes, 23 543-552, 550 Continuous solution polymerization, reactors used for, 23 394-395 Continuous steel casting, 23 266-270 difficulties of, 23 266-267 universality of, 23 269-270 Continuous sterilization, in fermentation, 11 35-36... 

High temperature short time (HTST) continuous sterilization, in fermentation, 11 35-36, 45 High temperature steam electrolysis, 13 784... 

Traveling temperature sensors for continuous sterilizer shall be located throughout the conveyor system per plan and traceable placement diagram. The temperature sensors shall be placed in various locations within each distribution run. 

Sterilizer engineering drawings Sterilizer operation procedure Sterilizer sanitization procedure Sterilizer maintenance procedures Sterilizer specification utilization list Distribution thermocouple location diagrams Temperature sensing unit location diagram (continuous sterilizers) Sterilizer process log sheets... 

Figure 10.2 Continuous sterilizing systems, (a) Heat exchanger and continuous steam injection and (b) heat exchanger and indirect heater.

Figure 10.4 [1] shows the results for theoretical calculations [4] for the ratio n, the number of viable cells leaving the holding section of a continuous sterilizer, to Hq, the number of viable cells entering the section, as a function of the Peclet number (Pe), as defined by Equation 10.7, and the dimensionless Damkohler number (Da), as defined by Equation 10.8 ... 

A medium is to be continuously sterilized at a flow rate of 2 in a ster-... 

A medium, which flows through an 80 mm i.d. stainless tube at a flow rate of 1.0 m h , is to be continuously sterilized by indirect heating with steam. The temperature ofthe holding section is maintained at 120 °C. The number of bacterial spores of 10 rn in the entering medium must be reduced to 0.01 m . The specific death rate of the bacterial spores in the medium, medium density, and medium viscosity at 120 °C are 180 h , 950 kgm , and 1.0kgm h , respectively. 

Fig. 1.4-8. Quasi-continuous sterilization of fruit juice (adopted from Mitsubishi Heavy Ind., Japan 1992)...

A continuous sterilizer consists of three main sections heating, holding, and cooling. 

A continuous sterilizer with a steam injector and a flash cooler will be employed to sterilize medium continuously with the flow rate of 2 m3/hr. The time for heating and cooling is negligible with this type of sterilizer. The typical bacterial count of the medium is about... 

The manufacturer s test is to ensure beyond a reasonable doubt that the product remains in a sterile condition at the point of use. The validation of sterilization processes guarantees initial sterility, and package integrity testing verifies the continued sterility of the product device after processing, storage, and handling. 

Matsunaga, T., Tomoda, T., Nakajima, T., Nakamura, N. and Komine, T. (1988) Continuous-sterilization system that uses photosemiconductor powders. Appl. Environ. Microbiol. 54, 1330-1333. 

Interest in continuous methods for sterilizing media is increasing, but for the successful operation of a continuous sterilizer, foaming of the media must be carefully controlled and the viscosity of the media must be relatively low. The advantages of continuous sterilization of media are as follows. 

Fed batch processes have a higher production per volume and often also a higher product concentration in the final fermentation broth. They need, however, continuous sterilization and an automatic feeding system. A fed batch process starts with the inoculum and a small part of the medium. More medium is added after the fermentation has reached a certain rate. The cells continue to grow until the reactor is full. The broth is removed from the reactor and the products are harvested. A small part of the fermentation broth is left in the reactor as the inoculum for the next batch. 

Liao, H.-J. 1998. Simulation of continuous sterilization of fluid food products the role of thermorheological behavior of starch dispersion and process, Ph.D. thesis, Cornell University, Ithaca, NY. 

It is known that plug flow conditions are approached in laminar helical flow and for this reason Rao and Loncin (1974a) suggested that this type of flow could be used advantageously in continuous sterilization of foods. It is interesting to note that one continuous thermal processing system in which plug flow conditions are claimed to exist is based on helical flow (Anonymous, undated). 

Continuous Sterilization of a Fluid Food Containing Starch... 

Liao, H.-J., Rao, M. A., and Datta, A. K. 2000. Role of thermorheological behavior in simulation of continuous sterilization of a starch dispersion. iChemE Trans. Part C—Food and Bioproducts Process. 78(C1) 48-56. 

Lin, S. H. 1979. Residence time distribution in continuous sterilization process. Process Biochem. 14(7) 23-25. 

Continuous sterilization has been used since the 1960s as part of integrated filling lines for glass containers and is becoming increasingly important, especially in the area of contract sterilization. 

Sims M, Estigarribia E. Continuous sterilization of aqueous pumpable food using high pressure carbon dioxide. 4th International Symposium on High Pressure Process Technology and Chemical Engineering, Venice, 2002. 

The size and niunber of batching tanks depend upon whether the plant uses continuous sterilizers or batch sterilization. The difference is that in the latter case, the tanks can be large (5 0 to 80% of the size of the fermenter), and usually all the materials are mixed together. For continuous sterilizers, there is usually a minimum of four smaller tanks so that proteins, carbohydrates and salts can be batched and sterilized separately. In this case, the tanks are considerably smaller than the fermenter. 

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