## 3 Results
### Adsorption of Gamma-Decalactone on Porous Materials  
The possibility of using adsorption was also analyzed in the research on GDL secretion. For this purpose, one of the selected adsorbents, Amberlite XAD-4, zeolite, or vermiculite, at the concentration of 30 g/L, was introduced into the biotransformation media after the finished reaction and separated from the yeast cells. The GDL adsorption kinetics were analyzed within 6 h of the introduction of the adsorbent by monitoring the decrease in GDL concentration in the solutions (Figure 2). The quantity of the GDL adsorbed corresponded to the difference between the initial concentration (measured immediately after the finished biotransformation reaction) and the final concentration (after the adsorption). The data presented in Figure 2 show that at a concentration of GDL in the biotransformation media of about 3 g/L, the GDL was most effectively adsorbed on Amberlite XAD-4. After 1 h, the amount of the compound adsorbed was over 80%, which was approximately 2.45 g. In the case of vermiculite, after the same time, approximately 43% of the compound was absorbed, i.e., nearly 2 times less. The level of adsorption was the lowest with zeolite; after 1 h, there was still about 80% of the unadsorbed peach lactone in the medium. However, regardless of the type of the adsorbent used, the equilibrium state was reached after approximately 3 h of contact. At equilibrium, the adsorption capacities of zeolite and vermiculite were similar at about 70-80%, while for Amberlite XAD-4 it was over 95%. In order to obtain a more complete picture of the adsorption kinetics from biotransformation media, the initial adsorption rate (based on the first hour of the process) was determined for each of the adsorbents used (Table 4). The data confirm that in the first hour of the process, the highest adsorption rate, at the level of 1.47 \(\times\) 10\({}^{-3}\) g GDL/(adsorbent  
Figure 2: Kinetics of gamma-decalactone adsorption from biotransformation medium on three selected adsorbents: zeolite, vermiculite, and Amberlite XAD-4. (g) \(\times\) minute), is shown by Amberlite XAD-4. This value is twice as high as compared to vermiculite and more than four times as high as compared to zeolite. As the Amberlite XAD-4 resin showed the highest GDL adsorption efficiency, an adsorption isotherm was determined for it, through which the aroma compound separation was fully characterized (Figure 3). The equilibrium concentration of GDL was measured in the range of 0.1--5 g GDL/L (concentration range so far achieved in a microbial culture, depending on the initial concentration of castor oil). The curve shown in Figure 3 is a type 1 isotherm with a visible and achievable level of saturation, characteristic for sorbents in which sorption is limited by the steric effect to one or two molecular layers. Lower lactone concentrations in the medium are up to 4 g/L on average (preadsorption concentration). The adsorption isotherm has a linear relationship R\({}^{2}\) = 0.9814 (points marked with a red line, highlighted in the additional image). Considering the possibility of using adsorption in the separation of GDL from biotransformation media, the effectiveness of removing the adsorbed lactone was also analyzed. The desorption was carried out in 5 cycles with ethyl alcohol, using the ratio of 3 mL of ethanol/g of adsorbent. Each of the adsorbents showed good desorption abilities. Figure 4 shows the amount of the desorbed GDL in 5 extraction cycles, taking into account the efficiency of each stage. The most effective desorption was with the Amberlite XAD-4 resin; about 81% of the lactone was desorbed. In the case of zeolite and vermiculite, the level of desorption was comparable and amounted to 75-76%. It is noteworthy that the tricinoleic acid was extracted from the adsorbents together with the desorbed lactone. Its