Optimizing the Enzymatic-Assisted Extraction of Aromatic Compounds from Red Wine Lees ^†

In this research, we aimed to optimize the enzymatic-assisted extraction of volatile oily compounds from red wine lees, which give cognac flavor to the wine. By recovering the wine lees byproducts, the following can be obtained [1]: wastewater, ethanol, antioxidants, tartrate (as calcium tartrate and tartaric acid) and yeast cells. The chemical analysis showed that the volatile composition of wine lees [2,3] consists of esters, acids, alcohols, aldehydes, furanic compounds, terpenes and C13-norisoprenoids, whilst the phenolic composition [4] contains flavonoids and non-flavonoids. In the first stage, an enzymatic treatment was performed before the extraction of light oils using different concentrations of β-glucanase/pectinase from Novozymes (2500 PGNU/g Polygalacturonase and 75 BGXU/g β-glucanase (exo-1,3-), Novozymes, Bagsværd, Denmark), at different reaction temperatures and times. The treatment was performed to a mixture of 1.5/1 w/w wine lees aqueous sediment (from Ișalnița, Dolj county) and double-distilled water, under agitation. In the second stage, hydrodistillation of the mixture was performed using a Clevenger installation, but with prior removal of the first distillation head from the collecting tube, followed by recirculation of the azeotrope in the system at reflux until the substrate was depleted, at 141 °C in the heated bath for 4 h 20 min as previously reported [5]. The final concentrated distillate, rich in light volatile oils, was collected from the collecting tube, and the concentration of the main esters was determined using Gas Chromatography–Mass Spectrometry from calibration curves of a standard purchased from Sigma Aldrich (Merck Group, Darmstadt, Germany). In order to maximize the concentration of esters in the volatile oils extracted from wine lees, the optimization of the necessary enzymatic-assisted extraction conditions (concentration, temperature and time) was performed using Response Surface Methodology with the Design Expert v11 application (Stat-Ease, Minneapolis, MN, USA). The main esters present in the sample are ethyl octanoate, ethyl decanoate, ethyl dodecanoate and ethyl hexadecanoate. The concentrations of these major esters ranged from 0.158% to 0.481% in hydrodistillate. The final polynomial equation of the estimated coefficients was calculated using Analysis of Variance for the selected factorial model. The experimental values of ester concentrations of the volatile oily compounds are similar to the predicted values obtained using Response Surface Methodology. The extraction temperature and time had higher significance than the β-glucanase/pectinase concentration on the aromatic composition extracted from red wine lees. However, the enzymatic extraction treatment applied to the wine lees before the hydrodistillation process, increasing the concentrations by more than 30% according to the data analysis. We optimized the enzymatic-assisted extraction of volatile oily compounds from red wine lees. Applying an enzymatic pre-treatment with β-glucanase/pectinase before the hydrodistillation process, the wine lees releases higher ethyl ester concentrations, which are responsible for the aromatic smell and taste, than without the enzymatic pre-treatment, which represents an encouraging process.