Introduction to Microbial Culture Medium Raw Materials - Agar

Agar, also known as agar, is commonly referred to as agar or frozen powder. Its English name is Agar. Agar is a type of alginate extracted from red algae such as cauliflower, river hedge, and seaweed. It is a long-chain polysaccharide complex composed of agarose and agarose gel, and its chemical component is poly (galactose sulfate), which belongs to colloidal substances. Agar is a coagulant widely used in food production as a food additive, in addition to being used in the preparation of solid and semi-solid microbial culture media and biochemical reagents.

Agar is currently an ideal coagulant in solid culture media. Agar, as a coagulant for culture media, is rarely affected by enzymes produced by bacteria and is resistant to pressure sterilization. When agar is mixed with water and heated to 100 ℃ or higher, it can form a translucent or transparent gel. When it is cooled to 40 ℃~45 ℃, it can form a gel. When other nutrients are added, it can be made into a solid culture medium. It is the basic experimental material for microbiology, heritage, cytology, tissue culture and other laboratories.

The strength of agar gel determines the amount of agar used in the culture medium formula. Generally, the amount of powdered agar used in preparing solid culture medium is about 1%~1.5%. There are obvious differences in the strength of agar gel from different manufacturers and different batch numbers. The amount of agar with high gel strength should be reduced when producing culture medium, otherwise the content of agar should be increased. The amount of agar powder with different gel strength used to prepare the culture medium is different. Therefore, we recommend using gel strength to express the hardness of the medium.

The appropriate gel strength of the culture medium is generally 400~700g/cm²Between the ranges, the appropriate gel strength of different culture mediums needs a lot of experiments to determine. Insufficient addition of agar can cause the culture medium to be difficult to solidify, and it is prone to scratching when streaking and inoculating bacteria; Excessive addition of agar not only results in unnecessary waste but also causes the culture medium to become too hard, directly affecting the absorption and utilization of nutrients by microorganisms. Agar is easy to degrade under acidic conditions, and too little agar added in the medium with slightly acidic pH will lead to the decrease of gel strength and affect the product quality.