A paper in the Journal of Chemical Technology and Biotechnology (“Response Surface Optimization of the Critical Media Components for the Production of Surfactin,” 1997, Vol. 68, pp. 263–270) describes the use of a designed experiment to maximize surfactin production. A portion of the data from this experiment is shown in Table P6.13. Surfactin was assayed by an indirect method, which involves measurement of surface tensions of the diluted broth samples.

Relative surfactin concentrations were determined by serially diluting the broth until the critical micelle concentration

(CMC) was reached. The dilution at which the surface tension starts rising abruptly was denoted by CMC−1 and was considered proportional to the amount of surfactant present in the original sample.

(a) Analyze the data from this experiment. Identify the significant factors and interactions.

(b) Analyze the residuals from this experiment. Are there any indications of model inadequacy or violations of the assumptions?

(c) What conditions would optimize the surfactin production?