X-axis: time (min); Y-axis: pH; log cfu are shown in colour (scale on the right of the graphs). Numbers in the bacterial names are the strain numbers in the FAM-database of ALP. Figure 3 Acid resistance of Bifidobacterium dentium, B. longum subsp. infantis and B. adolescentis. X-axis: time (min); Y-axis: pH; log cfu are shown in colour (scale on the right of the graphs). Numbers in the bacterial names are the strain numbers in the FAM-database of ALP. Figure 4 Acid resistance of Bifidobacterium breve and B. animalis subsp. lactis. X-axis: time (min); Y-axis:

pH; log cfu are shown in colour (scale on the right PRIMA-1MET in vivo of the graphs). Numbers in the bacterial names are the strain numbers in the FAM-database of ALP. All the other tested Bifidobacterium strains (B. longum, B. breve, B. longum subsp. infantis and B. adolescentis) showed a similar but different pattern from B. animalis subsp. lactis (Figures 2, 3 and 4). They had a short survival time below pH 2.5 and survived in higher numbers above pH 3.5. With the aim of developing a method to simulate the GI in the bioreactor, a further test was done with one strain. To observe the influence of a food matrix, concentrated B. longum subsp. infantis was resuspended in skim milk IWR-1 cell line before inoculating into acidic solutions.

As shown in the right-hand column of Figure 5, milk had a direct effect on the survival of the strain. Between pH 3.0 and 3.5 the bacteria survived for 120 min with a reduction of log 2. Below pH 3.0 the survival rate decreased to about log 5. The decrease in survival below pH 3.0 was rapid but regular over time. At pH 3.5 and above, the strain was resistant for at least 120 minutes. Figure 5 Comparison of acid resistance of Bifidobacterium longum subsp. infantis 14390 suspended in NaCl or skim milk. Left: Bifidobacteria resuspended in NaCl, right: Bifidobacteria resuspended in milk. X-axis: time (min); Y-axis: pH; log cfu

are shown in colour (scale on the right of the graphs). Numbers in the bacterial names are the strain numbers in the FAM-database of ALP. The left-hand column of Etofibrate Figure 5 shows the same strain without added skim milk. At a pH above 3.5, there was no influence on the survival of the bacteria. However, below pH 3.5 the survival decreased depending on the duration of incubation. Between pH 3.0 and 3.5 the strain had already decreased by about log 5. After 30 min incubation, there was almost a linear decrease in survival with decreasing pH from 3.0 to 2.5. Simulation in the bioreactor Most systems described in the literature consist of several reaction vessels, e.g. the SHIME [6]. Other studies used immobilized cells with three reactors [25] or a dialysis system [8]. Based on the work of Sumeri et al. [9] and the collected data of the conditions in the intestinal passage we were able to limit the simulation to one vessel.