Empirical modelling as an experimental approach to optimize lactone production

The biotransformation of ricinoleic acid, carried out by Yarrowia lipolytica, leads to the formation of γ-decalactone, a well-known peach-like aroma compound, interesting to produce and to use in the flavouring industry, reason why it is imperative to define the most appropriate conditions for its production. Thus, the aim of this work is the optimization of operating conditions for this lactone. However, as the accumulation of another compound, namely 3-hydroxy-γ-decalactone (the precursor of two other aromatic compounds, dec-2-enolide and dec-3-enolide), may also occur simultaneously in the biotransformation medium, and since this compound may as well be of interest for the flavouring industry, the operating conditions for its production were also a focus of attention. Therefore, a 32 level full-factorial design was used to determine the effect of pH and dissolved oxygen concentration (DO) on the production of γ-decalactone and 3-hydroxy-γ-decalactone. Since both factors were found to influence the two lactones production, a response surface methodology (RSM) analysis was also applied to identify the optimal conditions for the production of those two compounds. The statistical model pointed out pH = 6.17 and DO = 44.4% as the best conditions optimizing γ-decalactone production. Using these optimal conditions, the maximal γ-decalactone concentration achieved was 680.9 mg L−1, which was quite similar to the predicted value of 718.7 mg γ-decalactone L−1. Among the range of operating conditions tested, no optimization was possible for 3-hydroxy-γ-decalactone production, since all possible solutions corresponded to operating conditions not analyzed.