What are casamino acids?
Casamino acids (also written casamino acid, or acid-hydrolysed casein) are made by hydrolysing milk casein completely with hydrochloric acid at high temperature. Enzymatic hydrolysis leaves many peptides; acid hydrolysis cuts all the way down, so the product is almost entirely free amino acids and has the highest amino nitrogen to total nitrogen ratio of any peptone.
Two properties follow from the process:
- No tryptophan: acid hydrolysis destroys tryptophan, so casamino acids lack this one amino acid. Organisms or experiments that need it require supplementation, or tryptone instead.
- Salt content: the acid is neutralised with sodium hydroxide, which leaves sodium chloride in the product. Standard grades carry more salt; low-salt and vitamin-assay grades have salt and vitamins removed.
Casamino acids, tryptone and casein peptone compared
All three start from casein. The difference is how it is cut.
| Casamino acids | Tryptone | Casein peptone (enzymatic) | |
|---|---|---|---|
| Hydrolysis | Hydrochloric acid, complete | Pancreatic (tryptic) enzymes | Pancreatic or other enzymes |
| Main constituents | Free amino acids | Short and medium peptides plus amino acids | Peptides plus amino acids |
| AN/TN | Highest (around 50 % and above) | Medium | Medium |
| Tryptophan | None | Present, high | Present |
| Salt | High (grade dependent) | Low | Low |
| Typical use | Defined media, Salmonella and diphtheria toxin culture, M9 in molecular biology | LB, TSB, general bacteriology | General bacteriology, fermentation |
In short: choose casamino acids when you need to know exactly which amino acids are in the medium, and tryptone when you need the organism to grow well.
Where casamino acids are used
- Defined and minimal media: M9 plus casamino acids is a standard combination in molecular biology; the free amino acids spare the cells from synthesising them without introducing peptides.
- Toxin and antigen production: traditional diphtheria, tetanus and pertussis processes use acid-hydrolysed casein because the composition is simple and consistent from batch to batch.
- Vitamin assays: the vitamin-assay grade has vitamins removed, so the only vitamins in the medium come from the sample under test.
- Fermentation: as a starter nitrogen source where fast initial growth is wanted, paired with a slower-releasing peptone.
When not to use casamino acids
- The strain is a tryptophan auxotroph, or the product requires tryptophan.
- The process is salt-sensitive, for example selection with salt-sensitive antibiotics.
- A Halal or animal-origin-free claim is required: casein is a milk protein and therefore of animal origin; use soy or yeast peptone instead.
- The fermentation needs peptides as inducers, as in some protease production, where free amino acids can repress the product.
Frequently asked questions
Are casamino acids the same as casein hydrolysate? Casein hydrolysate is the general term and covers both enzymatic and acid hydrolysis. Casamino acids refers specifically to the acid-hydrolysed product. Check the hydrolysis method on the specification sheet.
How should casamino acids be stored? They are more hygroscopic than most peptones. Close tightly after opening and keep dry. Caking from moisture affects weighing but not composition.
Does STBIO MEDIA supply them? Yes. Casamino Acids, Tryptone and Casein Peptone are all in the product list, with amino nitrogen, total nitrogen, salt and tryptophan data on the specification sheets for direct comparison.