Optimization of a Bifidobacterium longum production process

Bifidobacteria are used as probiotics mainly in the dairy industry as cell suspensions or as freeze-dried additives. So far there have been no reports on a thorough investigation on factors influencing the production process or a statistical approach to the optimization thereof. A 28-4 fractional factorial design was used in determining the critical parameters influencing bioreactor cultivations of Bifidobacterium longum ATCC 15707. Glucose, yeast extract and l-cysteine concentrations were found critical for the cultivation of this strain. Glucose and yeast extract concentrations were further studied together with temperature in a three factor central composite design. The optimized cultivation conditions were temperature 40 °C, yeast extract concentration 35 g l−1 and glucose concentration 20 g l−1. Freeze-drying of frozen cell suspensions of B. longum was studied first in controlled temperatures and thereafter with temperature programming experiments. The results were statistically evaluated. A temperature program with a 2 h temperature gradient from −10 to 0 °C, a 10 h temperature gradient from 0 to +10 °C and a 12 h temperature hold at +10 °C was found best for the freeze-drying process. Temperature programming reduced drying times by over 50% and improved the product activity by over 160%.