Headspace-solid phase microextraction-gas chromatography as a tool to define an index that establishes the retention capacity of the wine polymeric fraction towards ethyl esters

A headspace-solid phase microextraction followed by gas chromatographic analysis (HS-SPME-GC) was developed to be applied in the study of the interactions between the wine polymeric fraction and the ethyl esters: ethyl hexanoate, ethyl octanoate, and ethyl decanoate. Wine models (WM) were prepared with 10% (v/v) aqueous ethanol at pH 3.5 with distinct wine polymeric concentrations prepared from white wine of Vitis vinifera L. var. Fern?o-Pires: 1.0 g L(-1) (PWM1), with a polymeric concentration approaching the real one in wine; 10.0 g L(-1) (PWM10); and 30.0 g L(-1) (PWM30), saturated with polymeric fraction. A reference wine model (RWM) was prepared without polymeric fraction. Each volatile compound (4.0 mg L(-1)) was added separately to the RWM and to the WM with the three levels of polymeric material (PWM). From the retention index (RI) calculated for each compound using the formula: [RI = 1 - (C(RWM) - C(PWM))/C(RWM)], where C(RWM) is the concentration of the compound in the RWM and C(PWM) is the concentration of the compound in the given PWM, the retention capacity of each wine polymeric fraction towards the three esters was established. The higher retention indexes were observed for ethyl decanoate, the more hydrophobic compound, and for the PWM with higher concentration. Furthermore, this study also suggested that the retained compounds are dosed to the headspace, which may promote the perception of their aroma for a longer period of time.