The growing demand for natural products benefits the development of bioprocesses to obtain value-added compounds using residues such as sweet whey, which is rich in lactose. The yeast Kluyveromyces marxianus can ferment sweet whey to obtain 2-phenylethanol (2-PhEtOH), which is a superior alcohol with a rose aroma. Such fermentation only requires the addition of L-phenylalanine (precursor) and (NH₄)₂SO₄ (salt). Therefore, it was sought to improve the fermentation conditions to produce 2-PhEtOH, which, in turn, would achieve the maximum decrease in the Chemical Oxygen Demand (COD) of the fermentation medium. With the use of the Response Surface Methodology and the application of a Central Composite Design for optimization, two parameters were evaluated as a function of time: salt concentration and precursor. The experimental data were adjusted to a second order polynomial, identifying that the precursor concentration presents a statistically significant effect. The best conditions were: 4.50 g/L of precursor and 0.76 g/L of salt, with a maximum production of 1.2 g/L (2-PhEtOH) at 48 h and achieving a maximum percentage of COD removal of 76% at 96 h. Finally, the optimal conditions were experimentally validated, recommending the use of the model.

In some fermentation systems, whey components (lactose, proteins and minerals) can produce isopentyl acetate (IA). An analysis of the best conditions for IA production with Kluyveromyces marxianus was developed in this work. The experiment design was two-factor and three-level design based on a response surface methodology (RSM) using Design-Expert^® software. The analysis of anomeric protons by nuclear magnetic resonance (1H-NMR) showed 81.25% of β lactose content. This characteristic favored the production of IA. The maximum output (Mp) of IA, determined by gas chromatography, was 9.52 g/L (p < 0.05). The central composite design (CCD) was used to perform the factor analysis. Results showed that concentrations of 0.03 (g/L) ammonium sulphate and 0.3 (v/v) of isoamyl alcohol are the best conditions for a maximum rate of IA production. The production of IA can reduce the discharge of whey, allowing its reuse and revaluation.

In many countries, whey from the dairy industry is an abundant waste that generates an important environmental impact. Alternative processes to use the whey and minimize the environmental impact are needed. This work considered six formulations with different ammonium sulfate and L-phenylalanine (L-Phe) concentrations to produce bioethanol in sweet whey fermentation by Kluyveromyces marxianus. The results showed a maximum bioethanol concentration equal to 25.13 ± 0.37 g L⁻¹ (p < 0.05) for formulation F6, with 1 g L⁻¹ of L-Phe and 1.350 g L⁻¹ of ammonium sulfate (96 h). For these conditions, the chemical oxygen demand removal percentage (CODR%) was 67%. The maximum CODR% obtained was 97.5% for formulation F3 (1 g L⁻¹ of L-Phe) at 96 h; however, a significant decrease in bioethanol concentration (14.33 ± 2.58 g L⁻¹) was observed. On the other hand, for formulation, F3, at 48 h of fermentation time, a bioethanol concentration of 23.71 ± 1.26 g L⁻¹ was observed, with 76.5% CODR%. Based on these results, we suggest that the best conditions to obtain a significant bioethanol concentration and CODR% value are those used on the configuration F3 at 48 h.