Use of a D-optimal mixture design to estimate the effects of diverse chloride salts on the growth parameters of Lactobacillus pentosus

The effects of NaCl, KCl, CaCl2, and MgCl2 and their mixtures on the ionic strength (IS) of the medium and the growth parameters of Lactobacillus pentosus were studied by means of a D-optimal mixture experimental design with constrains (total salt concentration ≤ 9.0%, wt/vol) and the generalized z-value. The IS was linearly related to the concentrations of the diverse salts and its increase, for similar concentrations of salts, followed the order MgCl2 > CaCl2 > NaCl > KCl. Within the experimental region, the lag phase duration (λ) was mainly affected by NaCl and CaCl2 and the interaction KCl with MgCl2. The maximum specific growth rate (μmax) decreased as NaCl (the highest effect), CaCl2, and MgCl2 increased (regardless of the presence or not of previous NaCl); low KCl concentrations had a stimulating effect on μmax, but its overall effect showed a similar trend to the other salts. The maximum population reached (Nmax) was the least affected parameter and decreased as NaCl and CaCl2 concentrations increased regardless of the presence of the other salts. The equations that expressed the growth parameters as a function of the diverse chloride salts, within the limits assayed, were developed and the corresponding z- and harmonic Z-values were estimated.