Three questions first
- What does the organism need? Lactic acid bacteria need vitamins and peptides, so yeast extract is almost always included; Bacillus and E. coli are less demanding and grow on tryptone or soy peptone; actinomycetes prefer slowly released nitrogen and starch.
- What does the process need? For biomass and speed, choose a higher amino-nitrogen ratio; for secondary metabolites, a lower degree of hydrolysis with slower release; high-density fed-batch processes must not run short late in the run.
- What does the product need? Plant-based or vegetarian claims exclude animal-derived sources; export to Halal markets needs Halal versions; large vessels are judged on cost per litre of medium.
Where common nitrogen sources fit
- Yeast extract: richest in B vitamins, nucleotides and free amino acids, the most universal growth-factor source, typically 2 to 10 g/L.
- Tryptone (enzymatic casein digest): complete amino-acid profile with high tryptophan, the standard nitrogen source of laboratory media.
- Soy peptone: plant-derived with carbohydrates, suited to lactic acid bacteria and processes that need a plant-based claim, often combined with yeast extract.
- Meat peptone and beef extract: different peptide profile and flavour, common in traditional formulations but with more documentation for animal origin.
- Wheat, pea and rice peptones: plant-based alternatives to animal peptones, each with its own amino-acid profile; trial at small scale when switching.
Practical advice
- Start from the current formulation and change one nitrogen source at a time, comparing cell counts, yield and fermentation time at small scale.
- When changing supplier, compare total and amino nitrogen on the COA before scaling up.
- Share the formulation and target with us for a suggested starting combination and trial range.