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

Abstract The effects of NaCl, KCl, CaCl 2 , and MgCl 2 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 MgCl 2  > CaCl 2  > NaCl > KCl. Within the experimental region, the lag phase duration ( λ ) was mainly affected by NaCl and CaCl 2 and the interaction KCl with MgCl 2 . The maximum specific growth rate ( μ max ) decreased as NaCl (the highest effect), CaCl 2 , and MgCl 2 increased (regardless of the presence or not of previous NaCl); low KCl concentrations had a stimulating effect on μ max , but its overall effect showed a similar trend to the other salts. The maximum population reached ( N max ) was the least affected parameter and decreased as NaCl and CaCl 2 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.