Response surface methodology (RSM) and Box-Behnken experiment design (BBD) were employed for optimization of biosurfactant shaking flask fermentation conditions of a Pseudomonas aeruginosa strain. Using Design Expert 8.0.5b software, multiple binomial mathematical models were established to study the influence of carbon sources (waste vegetable oil, WVO), nitrogen source (NaNO3) of and potassium source (KCl) levels in fermentation broth and their interactions on fermentation yield of biosurfactant. Significance tests showed that the model with the oil spreading circle (OSC) as response value was significant while that with rhamnolipid production by colorimetric method was narrowly significant (P=0.0531, R2=0.8218). Ultimately the optimal parameters were reached as WVO 5.04%, NaNO3 2.70 g/L, KCl 1.37 g/L with two index as response values. Under optimized conditions, the expected rhamnolipid yield increased dramatically. OSC measurement with diluted broth acting as the response value, rather as surface tension measurement or colorimetric method showed advantages such as easy and simple to conduct, the requirement for volume of broth, low cost and more precise to construct the optimal model.
Key words: Pseudomonas aeruginosa, response surface methodology, rhamnolipid, aerobic fermentation
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