Growth Enhancement of Bifidobacterium lactis Bo and Lactobacillus acidophilus Ki by Milk Hydrolyzates

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Abstract
The determination of the best conditions of preparation of a (tentatively) probiotic starter culture that might be suitable for cheese making composed solely of Bifidobacterium lactis Bo and Lactobacillus acidophilus Ki is critical if a consistently reliable acid production is to be achieved, especially because bifidobacteria have stringent requirements for growth. Therefore, we determined whether B. lactis Bo and L. acidophilus Ki required or benefitted from the addition of milk hydrolyzates (brought about by proteinase or neutrase as the nitrogen source). The growth and acid production of B. lactis in milk were affected by the addition of proteinase-mediated hydrolyzate and, to a lesser extent, by neutrase-mediated hydrolyzate; a higher degree of hydrolysis of either hydrolyzate resulted in greater biomass increase and greater acid production. This result suggests that the poor growth of bifidobacteria in milk is due partially to the lack of small peptides and free amino acids. The rates of growth and acidification by B. lactis were enhanced when cocultured with L. acidophilus (1:1 inoculum ratio). Conversely, the growth rates and acid production of L. acidophilus were not positively affected by the addition of either milk hydrolyzate. Although L. acidophilus grew slowly, its proteolytic system was apparently able to generate its own nitrogen source. Nevertheless, coculture with B. lactis (1:1 inoculum ratio) led to enhanced rates of growth and acidification when compared with that of the single strain, suggesting some degree of symbiosis between the strains.