Production of flavoured volatile organic compounds (VOCs) by Candida oleophila GK10: Optimisation using factorial design and response surface analysis

Response surface analysis was applied in optimising volatile organic compound (VOC) production by shaken-flask cultures of a selected Candida oleophila strain. A fractional factorial experiment (2n−k) was designed by setting four parameters at two levels: pH (3–7), concentration of yeast extract (YE=5–15 g l−1), glucose (C=10–30 g l−1) and (NH4)2HPO4 (N=5–15 g l−1). VOCs produced were sampled by means of headspace solid-phase microextraction (SPME), separated and identified by gas chromatography–mass spectroscopy (GC–MS). On the basis of the results of factorial design, YE and C were optimised by performing a central composite design. Second order polynomial models and response diagrams were obtained for total VOCs (VOC1), esters (EST) and isoamyl acetate (IAA) production. A range of variation of YE and C able to maximise simultaneously all three responses has been found. Average final values of responses (VOC1=125.3 mg l−1; EST=18.1 mg l−1; IAA=16.80 mg l−1) were in good agreement with calculated values, thus confirming the reliability of our empirical model in describing VOC production.