Most of the bifidobacteria break down lactose in to lactic acid and acetic acid in the proportion of 2:3. This high concentration of acetic acid gives the product flat vinegar like taste and flavour, which will not go very well with the consumer. In order to obtain desired growth rate and flavour production in the bifidus milk, it is better to culture them along with other lactic acid bacteria. When cultured along with Lactobacillus acidophilus, the growth characteristics of bifidobacteria are not adversely affected.
Fortification of condensed whey solid and whey protein concentrate further boosted the growth of bifidobacteria. Symbiotic relationship exists between bifidobacteria and Streptococcus thermophilus when they are co-cultured. S.thermophilus releases carbon dioxide during fermentation of lactose, which provides the required anaerobic condition for the bifidobacteria, boosting its growth. A similar relationship also exists between the Lactobacillus bulgaricus and bifidobacteria; the former is highly proteolytic and breaks down casein in to peptides and amino acids, which favours the growth of the latter. In this way, the milk containing bifidobacterium or bifidus milk can indeed be manufactured with the available resources sans breast or human milk.