What are the physical methods for disinfection and sterilization of Ganoderma lucidum

Disinfection and sterilization are two different concepts. Disinfection is the killing or removal of some microorganisms by physical or chemical means, such as pathogenic microorganisms and vegetative forms of microorganisms, but it has no effect on spores, so it is partial and superficial; sterilization, however, is the killing or removal of all microorganisms by physical or chemical means, so it is complete and thorough.

I. Physical methods

1. Dry heat sterilization is generally used for items that are to remain in a dry state after sterilization.

(1) Flaming sterilization directly burns microorganisms to death with a flame. It is simple, thorough, rapid and reliable, but its scope of use is limited. It is often used for inoculation tools, test tube mouths, bottle mouths, cotton plugs, etc. For glass and porcelain items, they should be thoroughly dried before flaming to avoid cracking.

(2) Dry hot air sterilization uses hot air in an oven for baking sterilization. During operation, the temperature is gradually raised to 140-160°C and held for 2-3 hours to achieve the purpose of sterilization. It is fast and convenient, but it is only suitable for metal and glassware, not for culture media.

2. Moist heat sterilization has high sterilization effectiveness because moist heat steam has strong penetrating power.

(1) High-pressure steam sterilization is also called pressure sterilization. It is based on the principle that steam temperature is proportional to steam pressure, that is, as pressure rises, the boiling point also rises. For example, using a pressure of 0.103 MPa at a temperature of 121°C and holding for 30 minutes can kill all vegetative cells and spores in liquid culture medium. Therefore, it can greatly shorten sterilization time and is the most effective and most widely used sterilization method. In Ganoderma lucidum scientific research and production, a pressure of 0.103 MPa held for 30 minutes is often used to sterilize slant culture media, sterile water, utensils, inoculation tools, etc.; while media with large volume and poor heat conductivity, such as sawdust, bran and cottonseed hulls, require 0.137 MPa held for 1.5-2 hours for sterilization.

Before using a pressure cooker, in addition to carefully reading the instruction manual, the following issues should also be noted.

① Add water before use. Before each use, first add water to the pot, with the amount added reaching the water level mark. Never heat it empty or with insufficient water, as drying out midway may cause an explosion accident.

② Stack materials correctly. Culture media, materials, etc. placed in the pot for sterilization should be stacked with gaps left between them so that steam can flow freely. If stacked tightly, it will hinder steam penetration, causing uneven temperatures inside and outside the materials and creating “dead corners”, resulting in incomplete sterilization.

③ Exhaust all cold air. When heating for sterilization, open the exhaust valve to let the cold air in the pot escape, and close the exhaust valve only when the water boils and a large amount of steam rushes out. If cold air remains in the sterilization pot, it will expand rapidly after being heated and the pressure will rise, causing a difference between pressure and temperature, that is, high pressure and low temperature, forming false steam pressure and resulting in incomplete sterilization.

④ Allow natural pressure reduction after sterilization. After sterilization, let it slowly cool and reduce pressure naturally. If pressure is released too quickly, negative pressure will form in the pot while the pressure inside bottles and bags is momentarily greater than the pressure in the pot, causing the material bags to swell with air, stretch thin, and burst, or causing cotton plugs to become contaminated or fall off. ⑤ Prevent cotton plugs from getting wet. If cotton plugs become wet with condensed water during sterilization, they lose the purpose of filtering bacteria and also lead to mold growth. To prevent moisture, the cotton plugs should face outward or upward, avoiding contact with the pot wall so they are not wetted by condensed water flowing down the surrounding wall. Film can also be wrapped around the bottle mouth or small plastic bags can be placed over it.

(2) Atmospheric pressure steam sterilization is a widely used sterilization method in production, such as steam baskets, iron drums, earthen steaming stoves, steam furnaces, etc. During sterilization, bottles and bags are arranged in an orderly manner with a certain gap on the grid inside the pot, and kept at 100°C for 8 hours or longer for sterilization. After sterilization, wait until the temperature drops below 70°C before opening, otherwise the material bags are prone to swelling with air and stretching thin, becoming unusable. The shortcomings of atmospheric pressure sterilization are long sterilization time, high energy consumption, and the water easily drying out or requiring frequent addition of water.

(3) Intermittent sterilization. Each time, heat until steam is produced and reaches 100°C, hold for 1 hour, then maintain a certain temperature (30-37°C) for 24 hours of culture to promote spore germination into vegetative cells, then carry out a second steaming. A total of 3 times in this way can kill all microorganisms and spores.

(4) Boiling disinfection. Place utensils and items in water and boil for 15 minutes to kill vegetative forms of microorganisms. If 2%-5% carbolic acid is added to the water, spores can also be killed. If 1% baking soda is added, it can raise the boiling point of water, accelerate the death of spores, and prevent metal instruments from rusting due to boiling.

(5) Pasteurization, also called the Pasteur effect or low-temperature disinfection. That is, 60-70°C for a certain period of time kills pathogenic microorganisms and vegetative forms of bacteria. The composting and fermentation of culture material uses this principle to kill harmful microorganisms in it, but the time required is longer.

3. Filtration sterilization is a method of removing microorganisms by using the retention effect of filter materials. It is often used for air filtration and for removing bacteria from certain liquids that are volatile or change properties when heated. Air purifiers in edible mushroom machinery and equipment, and air filtration in fermentation tanks; cotton plugs and masks in spawn production are also simple forms of air filtration.

4. Ultraviolet sterilization. Its bactericidal effect lies in causing cytoplasmic denaturation, leading to death of the bacterial cells. Second, under ultraviolet irradiation, air produces ozone (O3), which also has a bactericidal effect. The strongest bactericidal effect is at a wavelength of 250-260 nanometers, and commercially available ultraviolet lamp tubes mostly have a wavelength of 253.7 nanometers. Different microorganisms differ in their tolerance to ultraviolet light. For example, fungal spores have the strongest tolerance to ultraviolet light, bacterial spores are next, and vegetative forms of microorganisms are the weakest. Ultraviolet light belongs to low-energy electromagnetic radiation and has very poor penetrating power, so it is generally limited to sterilizing object surfaces and air.