## 4 Discussion and Conclusions  
In this research, headspace sampling using SPME, GC-MS and simultaneous olfactometry was used to investigate the key volatile aroma compounds in Frontenac and Marquette wines harvested at two maturity time points. ADA was performed to determine the key compounds present in these wine samples, and detected by human nose. Fifty-eight VOCs were detected in headspace of wines made from Frontenac and Marquette grapes harvested at 22\({}^{\circ}\) and 24\({}^{\circ}\) Brix by GC-MS, excluding ethanol and IS. In this study, the use of an internal standard was used to estimate relative chromatographic retention time and relative concentrations, assuming equal response factor across all analytes. A range of VOCs was detected by mass spectrometry including 9 alcohols, 5 aldehydes, 5 alkanes, 29 esters, 2 each of ketones, nitrogenous compounds, phenolic compounds and others. Yeast metabolism produces important wine volatiles such as higher alcohols, fatty acids, esters, and aldehydes. The reported results correspond to expected VOCs with the exception of diethyl phthalate and dibutyl phthalate. Phalates in the wine could be an issue of contamination from packaging [34]. Marquette wines made from grapes harvested at 22\({}^{\circ}\) Brix had nine more aroma notes than grapes harvested at 24\({}^{\circ}\) Brix. The most impactful compounds as determined by ADA were ethyl hexanoate and ethyl isobutyrate (both from 22\({}^{\circ}\) Brix grapes); and ethyl decanoate and ethyl butyrate, both from 24\({}^{\circ}\) Brix grapes. Published aroma descriptors for ethyl hexanoate are apple peel and fruit, sweet and rubber for ethyl isobutyrate, grape for ethyl decanoate, and apple for ethyl butyrate [35]. Frontenac wines made from both harvest points had six aroma notes each. The most impactful compounds as determined by ADA were ethyl hexanoate and ethyl octanoate (both from 22\({}^{\circ}\) Brix grapes); and ethyl octanoate, ethyl decanoate, 1-pentanol, and ethyl isobutyrate from 24\({}^{\circ}\) Brix grapes. Published aroma descriptors for ethyl octanoate are fruit and fat, balsamic for 1-pentanol [35]. An external calibration was used to quantify ethyl hexanoate, ethyl isobutyrate, and ethyl octanoate, and OAVs were calculated. The most impactful aroma compound with calculated OAV >50,000 was ethyl isobutyrate contributes a fruity aroma. A previous study reported \(\beta\)-damascenone, phenylethyl alcohol, acetic acid, linalool, and ethyl hexanoate quantified in Frontenac and Marquette grapes from veraision to harvest [9]. The compound ethyl hexanoate, responsible for fruity aromas increased in berry juice with increased growing degree days and differed by location in [PERSON] et al., 2013 [9]. In the wines in this study, no difference  
Figure 9: Odor (aroma) activity values of target analytes in headspace of Marquette and Frontenac wines made from berries harvested at 22\({}^{\circ}\) and 24\({}^{\circ}\) Brix. Odor detection thresholds for each analyte in water (and wine when available) from Leffingwell and Associates [33] were used to calculate OAV. OAV is the ratio of analyte concentration to its odor detection threshold. Ethyl octanoate is the dominate aroma compound present in headspace of Marquette and Frontenac wine samples (excluding alcohol), followed by ethyl hexanoate and ethyl octanoate. These compounds impart fruity aromas to the wine samples. was found in ethyl hexanoate; however, these were taken from fruit with a greater level of ripening. However, \(\beta\)-damascenone, phenylethyl alcohol, acetic acid, and linalool are present in the wines from this study. Metabolic action of yeasts an influence wine aroma; specifically, precursors bound to glycosides or by decarboxylation of hydroxycinnamic acids to the equivalent vinylphenols [1]. Another study on Frontenac wine aroma reports 15 VOCs using a stir bar coated with PDMS [36]; 13 of these compounds were also detected in this study using headspace DVB/Carboxen/PDMS SPME.