FIGURE 4.

The stress tolerance of Propionibacterium freudenreichii is different during growth in cow’s milk ultrafiltrate (MUF) or soymilk ultrafiltrate (SUF). P. freudenreichii CIRM-BIA129 was cultivated in MUF or SUF. The cultures were then subjected to a heat challenge (A, 55°C for 30 min), oxidative challenge (B, 1.15 mM H₂O₂ for 1 h), acid challenge (C, pH = 2 for 1 h), and bile salts challenge (D, 1 gL^–1 for 1 h), as described in section “Materials and Methods.” P. freudenreichii viability was determined by CFU counting before and after the challenges. The results are expressed as percentage survival. Error bars represent the standard deviations for triplicate experiments. Significant differences are reported using different letters above the columns (p ≤ 0.05).