The contribution of ß-damascenone to the berry-like aroma of red wines

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The contribution of ß-damascenone to the berry-like aroma of red wines

Johann Marais, ARC Infruitec-Nietvoorbij, Stellenbosch
Key words: ß-damascenone, red wine, SPME
Abstract
Forty wines each of Pinotage, Shiraz and Cabernet Sauvignon were analysed for ß-damascenone by headspace solid-phase micro extraction (SPME). This component occurred in all the wines at levels well above its sensory threshold value. Wines of these three varieties were also spiked with ß-damascenone and sweet-associated, fruity, berry-like aromas were observed. It is suggested that ß-damascenone plays an important role in the berry-like aromas of red wine varieties, especially that of the locally developed Pinotage.
Introduction
ß-damascenone is considered to be an important impact aroma component in grape juice and wine (Naiker & Allen, 1996; Kotseridis et al., 1999; Kotseridis & Baumes, 2000; Waldner & Marais, 2002). It has a complex aroma which has been described as reminiscent of exotic flowers with fruit and berry undertones (Ohloff, 1978; Naiker & Allen, 1996), and also as sweet, raisin-like (Simpson & Millar, 1984), honey-like, ionone-like and cooked quince-like (Kotseridis et al., 1999). ß-damascenone has a sensory threshold of 0.002 µg/L in water (Buttery et al., 1988). For wine, different threshold values have been reported, namely 50 µg/L (Simpson & Millar, 1984) and 4 µg/L (Kotseridis et al., 1998). Recently, a threshold value of 0.05 µg/L was reported in a 10% alcohol solution (Guth, 1997). Although these large differences in reported threshold values are confusing, the impact of ß-damascenone should not be underestimated.
ß-damascenone was first identified in grapes and wine by Schreier & Drawert (1974). Mechanisms for its formation from the carotenoid neoxanthin were proposed by Skouroumounis & Sefton (2001). It appears that ß-damascenone concentration varies considerably between wines. Values of approximately 0.2 to 1.3 µg/L were reported in Merlot wines (Kotseridis et al., 1998). Particularly high ß-damascenone concentrations, ranging from 66 to 170 µg/L, were found in Chardonnay wines (Simpson & Millar, 1984) and as high as 980 µg/L in Scheurebe wines (Guth, 1997).
In SPME/sniffing studies on Pinotage headspace aroma, previously conducted at Nietvoorbij, ß-damascenone was identified as one of the most potent impact components involved. Concurrently, iso-amyl acetate was found to exhibit a strong banana-like aroma, which is in agreement with the identification thereof as an impact aroma component of Pinotage (Van Wyk et al., 1979). The aim of the present study was to determine ß-damascenone concentrations by headspace SPME in a spectrum of South African red wines, and also to determine the impact of this component on the berry-like aroma of specific wines.
Materials and methods

SPME and GC analysis

A SPME fibre, coated with 100æm PDMS (Polydimethylsiloxane), was used. The extraction and analysis conditions applied, were decided on after thorough evaluation of conditions used in similar studies (Whiton & Zoecklein, 2000; Rocha et al., 2001; Vianna & Ebeler, 2001; Hartmann et al., 2002). Wine (100 mL) was poured into a 250 mL glass bottle and 10 g sodium chloride was added. The fibre was exposed for 60min to the headspace of the wine, while the wine was kept at 30oC and stirred continuously. Immediately after the headspace sampling, the adsorbed aroma was analysed by gas chromatography by keeping the fibre in the injection port for 5min.

Quantification

Eight model wines were prepared, extracted by SPME and analysed by gas chromatography. Peak areas of ß-damascenone were plotted against actual added concentrations to obtain a standard curve and a linear regression equation. The reproducibility of the method was determined by analysing six individual samples of a Pinotage wine (2003 vintage).

Wines

Wines of Pinotage, Shiraz and Cabernet Sauvignon (40 of each variety) used in this study, were collected from the entries in the 2002 National Young Wine Show and analysed for ß-damascenone. All wines were from the 2002 vintage and were 100% of the specific variety. The number of wines of each variety represented as far as possible the cultivation distribution (%) thereof in each of the main South African regions (Table 1). These regions were classified into seven climatic groups, where Region III represented 1667 to 1943 degree days, Region IV from 1944 to 2220 degree days and Region V above 2220 degree days (Le Roux, 1974). Where not enough wines were available from a region, wines from neighbouring, climatically-comparable regions were collected.

Spiking of wines

Three wines from the 2003 vintage, i.e. Pinotage, Shiraz and Cabernet Sauvignon, were obtained from Nietvoorbij and analysed for ß-damascenone. This component was then added to each wine at the following concentrations: 5, 15, 30 and 60 µg/L, respectively.

Sensory evaluation

A panel of six experienced judges evaluated the spiked wines. The wines of each cultivar were presented to the judges in sequence of increasing concentration of the added ß-damascenone. In each case, wines were compared to the control, which had no additions. Descriptions, such as exotic flowers and berries were mentioned as a guide-line. Each judge was allowed to express his/her own opinion on the aroma nuances of each wine perceived, but afterwards a uniform description was agreed upon.

Results and discussion
The SPME method showed good accuracy (standard calibration curve with a correlation coefficient of R2 = 0.9911). The regression equation was y = 0.0062x + 0.0338 (y = concentration in µg/L, x = peak area). Reproducibility of the determination of ß-damascenone was found to be excellent with a standard deviation of 2.06%.
The ß-damascenone concentrations in the red wines are shown in Figure 1. Average concentrations for each variety varied between regions, but a clear pattern could not be identified. When all values per variety were averaged, that of Cabernet Sauvignon was slightly higher than that of Shiraz, and both were higher than that of Pinotage. When the standard deviations are considered, the highest values were again associated with Cabernet Sauvignon and the lowest with Pinotage. This pattern confirmed results obtained in a previous, preliminary investigation where ß-damascenone was determined by liquid/liquid extraction (Waldner & Marais, 2002). Values were, however, higher in the present investigation, which may be ascribed to the fact that a wider, more representative spectrum of wines was analysed. The fact that ß-damascenone was determined by headspace analysis could of course also have played a role. The complex wine/headspace equilibrium could result in different concentrations of this volatile between the two phases. In all cases, the concentrations of ß-damascenone were well above its sensory threshold value of 4 µg/L in wine (Kotseridis et al., 1998), but not above 50 µg/L as reported by Simpson & Millar (1984).
The original ß-damascenone concentrations for the three spiked Pinotage, Shiraz and Cabernet Sauvignon wines, were 14.2, 26.5 and 20.5 µg/L, respectively. Aroma descriptions for these wines, before and after addition of ß-damascenone, are presented in Table 2. An aroma reminiscent of "sweetness" was continually perceived in the wines to which ß-damascenone was added. This was already obvious at the 5 µg/L added level. Nuances of purple/black fruit (plum, cherry) were perceived at the lower ß-damascenone levels and those of red fruit at the higher levels. At the two highest levels it became overpowering. The sweet-associated aromas eventually masked the vegetative and spicy aromas of Cabernet Sauvignon and Shiraz, respectively. It was, however, interesting to observe that the aroma nuances of ß-damascenone apparently complemented the typical Pinotage varietal aroma more than in the case of the other two varieties. This is probably due to the fact that the typical aroma of Pinotage wine also gives the impression of "sweetness".
Wine aroma and quality are the culmination of the effects of various components, and synergism among components probably plays an important role. Varietal characters are therefore normally the result of a number of contributing components. Nevertheless, impact components do exist and it is suggested that ß-damascenone was one that contributed to the sweet-associated, berry-like aromas of the wines in this study. It is reasonable to deduce that it played a more important role in Pinotage wine aroma than in that of the other two varietal wines, even if it occurred in lower concentrations in the former.
(View Table 2)
Conclusions
ß-damascenone occurs in Pinotage, Shiraz and Cabernet Sauvignon wines well above the threshold values reported by most researchers. It is suggested that this component is an important contributor to the berry-like aromas of red varietal wines. It appears that especially Pinotage wine aroma benefits from the presence of ß-damascenone.
Literature cited
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Acknowledgements
The donation of wines by the South African National Wine Show Association is appreciated.
For further information contact Dr Johann Marais at (021) 809-3096 or johannm@infruit.agric.za.

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