Optimization of bacteriocin production by batch fermentation of Lactobacillus plantarum LPCO10

Abstract

Optimization of bacteriocin production by Lactobacillus plantarum LPCO10 was explored by an integral statistical approach. In a prospective series of experiments, glucose and NaCl concentrations in the culture medium, inoculum size, aeration of the culture, and growth temperature were statistically combined using an experimental 2(3)(5-2) fractional factorial two-level design and tested for their influence on maximal bacteriocin production by L. plantarum LPCO10. After the values for the less-influential variables were fixed, NaCl concentration, inoculum size, and temperature were selected to study their optimal relationship for maximal bacteriocin production. This was achieved by a new experimental 3(2)(3-1) fractional factorial three-level design which was subsequently used to build response surfaces and analyzed for both linear and quadratic effects. Results obtained indicated that the best conditions for bacteriocin production were shown with temperatures ranging from 22 to 27 degrees C, salt concentration from 2.3 to 2.5%, and L. plantarum LPCO10 inoculum size ranging from 10(7.3) to 10(7.4) CFU/ml, fixing the initial glucose concentration at 2%, with no aeration of the culture. Under these optimal conditions, about 3.2 x 10(4) times more bacteriocin per liter of culture medium was obtained than that used to initially purify plantaricin S from L. plantarum LPCO10 to homogeneity. These results indicated the importance of this study in obtaining maximal production of bacteriocins from L. plantarum LPCO10 so that bacteriocins can be used as preservatives in canned foods.

FIG. 1.

Bar graph of standardized estimated effects of the different variables tested in the prospective experiment on bacteriocin production by L. plantarum LPCO10. L. fermentum ATCC 14933 was used as the indicator strain. The variables tested were temperature (T), NaCl concentration (S), initial glucose concentration (G), initial inoculum size (IS), and aeration (A). The point at which the effect estimates were statistically significant (at P = 0.05) is indicated by the vertical solid line.

FIG. 2.

Response surface of bacteriocin production by L. plantarum LPCO10, estimated as the log₁₀ of maximal AU per milliliter, and contour lines showing the optimal region as a function of NaCl concentration and the L. plantarum LPCO10 inoculum size. L. plantarum 128/2 was used as the indicator strain.

FIG. 3.

Response surface of bacteriocin production by L. plantarum LPCO10, estimated as the log₁₀ of maximal AU per milliliter, as a function of temperature and NaCl concentration. L. fermentum ATCC 14933 was used as the indicator strain.

FIG. 4.

Contour plot showing the optimal region of bacteriocin production by L. plantarum LPCO10, estimated as the log₁₀ of maximal AU per milliliter, as a function of the inoculum size and NaCl concentration. L. fermentum ATCC 14933 was used as the indicator strain.

FIG. 5.

Response surface of bacteriocin production by L. plantarum LPCO10, estimated as the log₁₀ of maximal AU per milliliter, and contour lines showing the optimal region as a function of temperature and initial inoculum size. L. fermentum ATCC 14933 was used as the indicator strain.

FIG. 6.

Response surface of L. plantarum LPCO10 cell density (log₁₀) as a function of NaCl concentration and temperature.