【Sterile Technical Instructions】

Micro-giant BioEngineering  2009.06.19

  In the basic pre-processing of the (purebred) microbial culture and fermentation process, the first priority is to create and maintain a sterile environment. To avoid the interference of bacteria in the cultivation process and affect the yield rate, or even cause failure or variation (especially the metabolism of secondary products). To make a provision of sterile technical instructions for equipment concerns as follows:

1. No dead-angle design

All wetted parts inside the fermentation vessels must not have a right-angle arc design, and the length (neck) of the stop valve or blind cover with the nearest pipe port must be less than 2d (inner pipe diameter). All parts with a secondary online sterilization pipeline must have the concept of a sterilization buffer room, ex. sampling valve (tube), dosing feed tube, transfer tube, shaft seal... All wetted parts use diaphragm valves or at least food & pharmaceutical sanitary valves (but need to take care of the sterilization methods).

2. Complete sterilization

In principle, the sterilization method adopts the high temperature and high pressure (SIP) sterilization method, which mainly uses the enthalpy in the superheated steam to achieve the sterilization effect. If it is SIP, pay more attention to the concept of air and automatic sterilization. Whether sterilization is complete is related to the following four elements:

2.1 Temperature:

In principle, the temperature in the high temperature and high pressure (SIP) sterilization method should be 121 °C (if it is intended for Thermophile spores, it must be higher and accompanied by three times of air sterilization and cooling). Although the higher temperature is easier to sterilize, it may cause the nutrients in the culture medium to be destroyed.

2.2 Pressure:

The sterilization pressure is generally set between 1.2~1.5kg/cm2, but the place where the pressure SENSOR is placed must be considered (there will be a slight difference between the top of the vessels and the exhaust gas). The concept of "pressure" here still attaches importance to the sterilization and heating process. The sterilization temperature must rise symmetrically with the sterilization pressure. If there is an abnormality, it may be that cold air remains, which will affect the sterilization effect.

2.3 Time:

This refers to the time during sterilization after reaching the sterilization temperature. Generally, it is set between 20 and 40 minutes (liquid fermentation). Note that if the temperature drops below the sterilization temperature in the middle, the timing must be recalculated, and the reasons should be reviewed to avoid it.

2.4 Flow:

It would be a futile effort without flow even with temperature, pressure, and time. The steam for sterilization must be introduced from the upper part, and an exhaust valve (to remove condensed water) is made at the lowest position to ensure the sterilization effect of the steam. Therefore, all pipelines that need to be sterilized must be equipped with a small exhaust valve (or even a sanitary trap), especially the T-type valve is the best.

3. Maintain positive pressure

To ensure that the sterilization effect can be maintained continuously, it is very important to maintain the positive pressure of the system from sterilization to harvest. It is generally maintained with sterile air filtered to at least 0.2 μm. Therefore, in the event of a power outage, the system must be able to keep the positive pressure for at least 12 hours, so the selection of all automatic valves should consider the state of the power outage (use the N.C. type). When the sterilization process enters the cooling section, too fast pressure relief can easily cause a bumping phenomenon, so the cooling method must be adopted in stages. If the cooling is too fast, there will be concerns about local negative pressure, especially at the exhaust, an exhaust filter can be installed to prevent reverse pressure pollution. However, it should be noted that the exhaust filter is easily blocked by moisture. Therefore, it is necessary to install an electric heater to heat the filter housing to avoid it.

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