# Chemical and Sensory Evaluation of Silicone and
## 2 Results and Discussion
### Chemical Analyses Results
#### 2.1.2 Other Volatile Aroma Compounds  
Concentrations of volatile compounds measured in silicone and polylactic acid treated and control spiked wines are presented in Figures 2 and 3, respectively. Overall, the treatments had relatively little impact on VOCs, with the exception of silicone at 600 cm\({}^{2}\)/L, where a trend of lower concentrations was observed, reaching significance in the case of ethyl hexanoate, isoamyl acetate, hexanoic acid and octanoic acid. For PLA, ethyl hexanoate increased significantly for the 50 cm\({}^{2}\)/L and 200 cm\({}^{2}\)/L treatments (Figure 3b), and trended in the same direction for ethyl isovalerate and ethyl-2-methylbutyrate (Figure 3a). This may be attributable to the wine's ethanol and acid matrix  
Figure 1: Change in _iso_-propylmethoxypyrazine (IPMP), _iso_-butylmethoxypyrazine (IBMP), and _sec_-butylmethoxypyrazine (SBMP) concentrations after application of silicone or polylactic acid polymers of varying surface areas. Data represent mean values \(\pm\) standard deviations. Wines with different letters have significantly different concentrations (Tukey’s HSD\({}_{0.05}\)).  
that may have contributed to the release of esters [21]. Several reactions have been proposed in the degradation process of PLA polymers, including hydrolysis, depolymerisation, oxidative degradation, and both inter- and intra-molecular transesterification to monomeric and oligomeric esters [22; 23].  
Several esters increased after silicone treatment in the 50 cm\({}^{2}\)/L application, but the trend was not retained at higher surface areas. The negligible change observed for most other volatiles in the silicone treatment was unexpected, as we expected some scalping would occur.  
The scalping of aroma compounds by non-polar polymers used in highly non-polar silicone-based packaging is primarily governed by log \(p\) values (typically determined at 20 \({}^{\circ}\)C) [24]. It is possible that an absorptive phenomenon under kinetic control was the reason for the limited impact of silicone on VOCs (e.g., rigid pyrazines may have migrated faster than the less rigid compounds). Silicone (PDMS) coatings are used to adsorb VOCs in some analytical methods (e.g., Stir Bar Sportive Extraction and Solid Phase Micro-Extraction), but these applications typically employ higher temperatures and shorter contact time with the silicone than in our study. It is also possible that other aroma compounds not measured in our study had a preferential affinity towards silicone. Finally, the reason for the relative selectivity of silicone for isoamyl acetate compared with its structural isomer ethyl isovalerate remains unclear.  
Figure 2: Concentrations of (**a**) ethyl isovalerate, ethyl 2 methylbutyrate; (**b**) ethyl butyrate, hexanol, ethyl hexanoate, isoamyl acetate, ethyl octanoate; (**c**) phenylethanol and (**d**) hexanoic acid and octanoic acid in untreated (‘control spiked’) wine and wine treated with silicone of varying surface areas (50 cm\({}^{2}\)/L, 200 cm\({}^{2}\)/L and 600 cm\({}^{2}\)/L). Data represent mean values \(\pm\) standard deviations. Wines with different letters have significantly different concentrations for each compound (Tukey’s HSD\({}_{0,05}\)).