1. Knowledge about agar
Agar, also known as agar or frozen powder, is also known as "seaweed" because it was originally extracted from Japanese seaweed. The finished agar is white or light yellow powder or thin strips, mainly composed of complex macromolecular polysaccharides. Its hydrolysate is composed of 40% D-galactose, 3% sulfate and 2% pyruvate, in fact, it is a mixture of two components, agar gum and agarose. Agarose is the sulfate ester of agarose, which relies primarily on the gravitational pull of hydrogen bonds to form a network structure. As a result, agarose gels are somewhat less stable than coagulants that form a network structure by cross-linking chemical bonds.
Agar is soluble in hot water but not in cold water, so it is necessary to boil agar when preparing the medium. As the temperature increases, the agar gradually dissolves and begins to solidify when the temperature drops to 40. When preparing the medium, it should be noted that due to the different quality of agar produced in different places, the hardness, transparency and color of the aqueous agar solution of the same concentration will be different after solidification. Inferior quality agar not only has poor coagulation, but also carries a lot of impurities.
2. Knowledge about agar coagulability
As a coagulant of the medium, the coagulation of agar is not only related to the quality of the agar itself, but also affected by the sterilization temperature, sterilization time, agar amount and pH value.
1）0.7%～0.The 8% aqueous agar solution will solidify well after cooling, and the dosage of agar tends to be basically stable for commonly used microbial media, usually about 2% for strip agar and 1% for powdered agar5%。
2) The pH of the medium has a great influence on the coagulation of agar, which is a key factor in whether the agar can coagulate within the normal concentration range30
3) In 430 (4) When the prepared solid medium pH is below 3At 44, its coagulation will be affected by the sterilization temperature, sterilization time, agar amount and pH value. Among them, the sterilization temperature and sterilization time were negatively correlated with the agar coagulation, and the amount and pH value of agar were positively correlated with the agar coagulation. However, among these factors, the influence of agar amount is not very large, so the sterilization temperature, sterilization time and pH value should be focused on during the sterilization process of this type of medium. Using a lower sterilization temperature, a shorter sterilization time, and an appropriate increase in the pH of the medium can significantly improve the coagulation of agar. The pH is low (40), pH is the main factor affecting the solidification grade.
Stratification of the sterilized medium.