Application of response surface methodology in the optimisation of a growth medium for enhanced natural preservative bacteriocin production by a probiotic bacterium.

In this study, a statistics-based experimental design was utilised for the optimisation of a growth medium which possibly enhanced bacteriocin production by Streptococcus phocae PI80. Carbon, nitrogen sources and a bio-surfactant were first screened using a one variable at a time technique and scored for increasing yield production. The selected variables were further statistically optimised using response surface methodology with a central composite design. The high- and low-level limits of the selected variables were determined, and a set of 34 experimental runs were performed. The concentration of each medium ingredient influenced the bacteriocin activity to about 22,500 AU mL⁻¹. The carbon and nitrogen sources were identified as significant factors in restraining the bacteriocin activity produced by S. phocae PI80. The statistics-based experimental design was found to be very efficient in optimising the media components in a number of experimental runs, with a three-fold increase in bacteriocin activity compared to the un-optimised medium. The optimum medium composition was found to be sodium succinate (10.0 g L⁻¹), yeast extract (4.0 g L⁻¹), glucose (9.0 g L⁻¹), NaCl (10.0 g L⁻¹), Tween 80 (6.0 g L⁻¹) and K₂HPO₄ (1.0 g L⁻¹). This optimised medium is two-fold more cost effective than the commercial Lactobacillus MRS medium.