**6. Conclusion**

304 Lactic Acid Bacteria – R & D for Food, Health and Livestock Purposes

*D***(acid)-value (min)**

*B. bifidum B. infantis B. longum B. adolescentis* 

*z***(acid)-value (in pH units)**

*z***(bile)-value (% ox-bile concentration)**

4.5 23.80 14.10 12.00 7.60

4.0 8.40 6.00 5.70 3.98

3.5 3.00 2.70 2.60 2.05

3.0 1.10 1.10 1.20 1.10

1.11 1.55 1.35 1.55

0.15% 17.40 10.50 9.60 6.80

0.30% 7.40 5.20 4.70 3.20

0.45% 3.20 2.55 2.30 1.58

0.60% 1.40 1.30 1.10 0.75

0.40 0.48 0.49 0.46

**Table 5.** Selected *Bifidobacterium* strains and their calculated *D*(acid)-, *D*(bile)-, *z*(acid)- and *z*(bile)-values.

**Bile Salts** *D***(bile)-value (min)**

**pH** 

Apart from the isolation, enumeration, unequivocal taxonomical characterization, screening and selection of tolerant strains of bifidobacteria to gastric acid and bile salts studies, the assessment of the tolerant bifidobacteria to bile salts and low pH has been made possible by use of *D*- and *z*-value concept. After log-conversion, inactivation followed first-order kinetic law whereby validating the kinetic assumptions of the latter concept. The projected *z*(acid) and *z*(bile)-values were all fairly similar for the bifidobacteria strains and suggested the effect of increasing the bile salt concentration or decreasing the pH on the *D*(acid)- and *D*(bile)-values. This approach is useful for measuring the resistance and sensitivity of lactic acid bacteria or bifidobacteria to these two hostile gastrointestinal conditions. The approach pursued in this chapter would be extremely useful for predicting the suitability of bifidobacteria and/or other LAB as probiotics for use in real life situations. While the mechanisms of probiotic survival in the GI tract could be more complex, the practical utility of the *D*(acid)- and/or *D*(bile)- and their *z*(acid)- and *z*(bile)-values is significant.
