Tyndallization is used at a pharmaceutical factory as one of sterilization methods for thermolabile substances. What is the essence of this method?

Answer options

1. Sterilization with dry heat at 180-200 0C for a lengthy period of time
2. Autoclaving at 119-121 0C with pressure at 1,0-1,1 atm
3. Sterilization with high-frequency and microwave frequency current
4. Triple heating of solution to 40-60 0C with 24-hour-long intervals in between for thermostating
5. Sterilization with flowing steam at 100 0C