###### Abstract  
The production of gamma-decalactone (GDL) by _Yarrowia lipolytica_ is mainly based on the biotransformation of ribonucleic acid, derived from castor oil triglycerides. The main difficulty in this process is the multitude of factors that determine the growth rate of microorganisms, and thus affect the efficiency of lactose synthesis. In order to improve the technological aspects of GDL biosynthesis in batch culture, the influence of three factors was determined: substrate concentration, medium mixing intensity, and its pH, using the Taguchi solid design method (based on orthogonal array design). On the basis of four bioreactor batch cultures, the most favorable culture conditions in terms of GDL synthesis were selected using the statistical Taguchi method. The statistical method of experimental planning has shown that the optimal parameters of lactone biosynthesis are a constant pH at the level of 7, a variable mixing speed in the range of 200-500 rpm, and a substrate concentration at the level of 75 g/L. Using these parameters, about 2.93 \(\pm\) 0.33 g/L of aroma was obtained. The intensity of mixing turned out to be the most important factor influencing the increase in GDL concentration in the medium. gamma-decalactone; _Yarrowia lipolytica_; batch cultures; bioreactor; Taguchi method 2022120231103390/app122010231  
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are still a matter of investigation by the scientific community: the efficiency of the bioprocess [11; 12; 13; 14] as well as the optimization of conditions for the separation of the compound from the biotransformation medium [15; 16; 17]. Previous studies on the parameters of GDL biosynthesis indicated many factors affecting the biotransformation yield. The selection of appropriate species and strains of microorganisms as well as environmental conditions, including, e.g., temperature, acidity of medium, its composition (including concentration and type of carbon source used), and oxygenation level, seem to have a significant impact. The presence of surfactants, the oxidation-reduction potential of the medium, and the applied technology of biotransformation (step-wise fed-batch cultures, immobilization of cells) could be also crucial for obtaining the maximum lactone concentration [18; 19; 20; 21; 22; 23; 24]. Cultivation in a medium with non-optimized pH reduces access to the carbon substrate and limits cell growth and lactone production [18]. Improper acidity of the medium may affect the intracellular pH of yeast and thus its metabolism. The concentration of GDL also depends on the NAD\({}^{+}\)/NADH ratio, because NAD\({}^{+}\) is a cofactor of 3-hydroxyacyl-CoA dehydrogenase, the activity of which shifts the reaction towards the formation of 3-hydroxy-\(\gamma\)-decalactone. The level of FAD and NAD\({}^{+}\) regeneration depends on the proper aeration of the medium [21]. Oxygen plays an important role in the activity of enzymes acyl-CoA oxidase and 3-hydroxyacyl-CoA dehydrogenase, participating in the regeneration of the above-mentioned cofactors. Moreover, it determines the course of the metabolism of hydrophobic substrates by contributing to the production and reconsumption reactions of GDL [25]. In aerobic cultivation processes, the oxygen transfer conditions depend on several factors such as temperature, pressure, composition of the culture medium, air flow rate, medium viscosity, aeration, stirring speed, and configuration of the medium. The studies show that the increase in the oxygen mass transfer rate (kLa) increases the rate of GDL production; however, the final concentration of aroma decreases [26]. Therefore, the mixing rate should also be properly selected to ensure not only the appropriate oxygen concentration in the medium, but also the proper dispersion of hydrophobic substrates [23; 27].