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Note 17: Identification of Volatile Organics in Wines Over Time

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by Santford V. Overton and John J. Manura

INTRODUCTION

The flavor/fragrance qualities of liquid commercial products are greatly dependent on the volatile and semi-volatile organic compounds present both in the liquid matrix and the headspace aroma. These compounds are also used in the manufacturing process to obtain the desired physical properties. Off-odors and unusual taste development may occur in alcoholic beverages, as wines and wine coolers, with increased shelf life once opened, or stored at temperatures higher than normal. Problems associated with off-odor/off-taste development are thought to be related to the manufacturer's formulation, interaction of the volatile components with the different types of container lining, or foreign material introduction. Light intensity and temperature are also thought to influence off-odor development. Increased shelf life in varying light and temperature conditions may stimulate oxidative reactions resulting in the degradation of terpenoid compounds. The purpose of this study is to demonstrate the ability of the Short Path Thermal Desorption System in conjunction with Purge and Trap techniques for the flavor profile analysis of wines, wine coolers and consumer beverages, compare the flavor profiles of different manufacturers' brands over time and quantify the volatile organics within these products.

INSTRUMENTATION

All experiments were conducted using a Scientific Instrument Services model TD-2 Short Path Thermal Desorption System accessory (1&2) connected to the injection port of an HP 5890 Series II GC interfaced to an HP 5971 Mass Selective Detector. The mass spectrometer was operated in the electron impact mode (EI) at 70eV and scanned from 35 to 350 daltons during the GC run for the total ion chromatogram.

A short 0.5 meter by 0.53 mm diameter fused silica precolumn was attached to the injection port end of a 30 meter x 0.25 mm i.d. DB-5MS capillary column containing a 0.25 um film thickness. The GC injection port was set to 250 degrees C and a 50:1 split was used during the injection step. The GC oven was maintained at -40 degrees C during the desorption and extraction process, after which the oven was temperature programmed from -40 degrees C to 300 degrees C at a rate of 10 degrees per minute for the total ion chromatogram.

EXPERIMENTAL

Two brands of wines, a red and a burgundy, and several wine coolers were analyzed to compare the flavor profiles of different manufacturers' brands and to quantify the volatile organics to determine their relationship to off-odor/off-taste development. Two homemade wines, a 30 year old grape and a 2 year old dandelion were also analyzed. For quantification, an internal standard was spiked into the adsorbent traps, after the sample had been isolated. No correction for extraction efficiency or recovery is achieved using this technique; however, it functions as a useful means of quantifying the levels of components present on the adsorbent traps (3). The commercial wines and wine coolers were opened, sampled, then corked/recapped for a period of 6 months and 1 month, respectively, and reexamined to determine any changes in the volatile organic concentrations. Only fresh samples of the homemade wines were analyzed.

Sample sizes of 2.5 ml of commercial and homemade wine diluted into 25 ml of distilled H2O were pipetted into a 50 ml test tube. Twenty-five ml aliquots were used as the sample size for the wine coolers. Samples were sparged with high purity helium at 15 to 20 ml/min with an additional 15 to 20 ml/min dry purge for 10 minutes using a Scientific Instrument Services Liquid Purge System (Figure 1). All sampling was done at 24 degrees C. Volatile analytes were gas extracted and carried to a preconditioned 4.0 mm i.d. glass-lined stainless steel desorption tube packed with 100 mg of Tenax® TA. Once the samples were collected, they were spiked with 400 ng of d-14 cymene internal standard by injecting 1 µl of a 400 ng/µl of a d-14 cymene stock solution in methanol by syringe injection into the Tenax matrix.

Figure 1

Figure 1 - Purge & Trap System

The desorption tubes with sample and internal standard were then attached to the Short Path Thermal Desorption System and a syringe needle attached. The desorption tube was injected into the GC injection port and thermally desorbed in the GC injection port at desorption block temperatures of 150 degrees C for 10 minutes at a purge flow of 50 ml/min, and a GC injection split ratio of 50:1.

RESULTS AND DISCUSSION

Flavor compounds were identified in each of the two wines examined such as: ethyl acetate, ethyl butyrate, ethyl caproate and ethyl caprylate. Additional compounds which were found in the red and burgundy wines included the alcohols isobutyl and isoamyl (impure), as well as isoamyl alcohol acetate (Figures 2 - 5). Isopropyl butyrate and 3-methyl ethyl butyrate were also detected in the burgundy wine (Figure 4). There did not appear to be any significant changes in these compounds after 6 months (Table I); however, acetal was detected in both of the wines after 6 months (Figures. 3 & 5). This may be due to an acid catalysis reaction which occurred during the 6 month period after the wines were opened. This was supported by a lower pH found in the wines which were previously opened. The aromatic compound toluene was also detected in the red wine after 6 months (Figure 3). The presence of this compound may be the result of the manufacturing process or occur naturally from essential essences.


Table I. - Relative Amounts of Volatile Organics In Wine (ng/µl)

                         Red         Red     Burgandy    Burgandy   Grape     Dandelion

                         New       6 months     New      6 months  30 years     2 years

                       --------    --------   --------   --------   --------   ---------

Ethyl Acetate             578         656        551        600        3178        1287

Isobutyl Alcohol           36          42         78         62          89          61

Acetal                      -          11          -         20           -           -

3-Methyl Butanal            -           -          -          -          40           -

Ethyl Proprionaaate         -           -          -          -          10           -

1,1-Diethoxy-Ethane         -           -          -          -         138          22

Isoamyl Alcohol           746         737       1281       1108         413         470

Toluene                    -          54          -          -           -           -

Isopropyl Propionate        -           -         26         40          55          78

Ethyl Butyrate             20          29         12         11          27           -

Isopropyl Butyrate          -           -         10         10           9           -

3-Methyl Ethyl Butyrate     -           -         10         13          21           8

Isoamyl Alcohol Acetate    65          55         70         80          30          16

Ethyl Caproate            213         213         83         98          53           -

Limonene                    -           -          -         11           -           -

Butyl Carbitol             32           -          -          -           -           -

Ethyl Caprylate           582         751        263        304         112          20

Ethyl Pelargonate          47           -          -          -           -           -

Ethyl Caprate               -           -          -          -           -          73


Figure 2

Figure 2 - Red Wine (New), 2.5ml in 25 ml H2O Collected For 10 min At 15 ml/min With 15 ml/min Dry Purge and Thermally Desorbed At 150 Degrees C For 10 min

Figure 3

Figure 3 - Red Wine (6 mos. old), 2.5ml In 25 ml H2O Collected For 10 min At 15 ml/min With 15 ml/min Dry Purge and Thermally Desorbed At 150 Degrees C For 10 min

Figure 4

Figure 4 - Burgundy Wine (new), 2.5ml in 25 ml H2O Collected For 10 min At 15 ml/min With 15 ml/min Dry Purge and Thermally Desorbed At 150 Degrees C For 10 min

Figure 5

Figure 5 - Burgundy Wine (6 mons. old), 2.5ml in 25 ml H2O Collected For 10 min At 15 ml/min With 15 ml/min Dry Purge and Thermally Desorbed At 150 Degrees C For 10 min

Alcohol containing wine coolers were found to contain many common compounds such as the flavors: ethyl acetate, ethyl butyrate, 3-methyl ethyl butyrate, ethyl caproate and several monoterpenes with limonene as the most common (Figures 6 - 13). The alcohols isobutyl and isoamyl (impure) were also present in each of the flavored wine coolers (Figures 6 - 13). Additional compounds which were identified included aldehyde and alcohol derivatives. Relative amounts of these volatile organics are found in Table II. After 1 month, flavor concentrations generally decreased in each of the wine coolers with the exception of the lime-flavored wine cooler (Table II). These reductions are probably due to volatilization of the flavor compounds over the 1 month period after the wine coolers were opened.


Table II. - - Relative Amounts of Volatile Organics In the Wine Cooler (ng/µl)

                               Cooler           Strawberry            Lime             Berry         

                           New      1 mo.     New      1 mo.     New      1 mo.     New     1 mo.

                          -----    ------    ------    ------   ------   -------   ------  ------

Ethyl Acetate              1308      1000      2728     1200       78       117      116      86

Isobytyl Alcohol            119        50       136      144       23        41       83      83

Ethyl Propionate             10         -         -       16        -         -        -       -

Isoamyl Alcohol             542       290       520      528      257       302      375     443

Toluene                       -         -         -        -       10       161        -     216

Isopropyl Propionate         56        47        40       47        -         -        -       -

2-Methyl-methyl butyrate      -         -         -        -        -         -     2576    1232

Ethyl Butyrate               30        23      1576     1568      293        47      245     144

Isopropyl Butyrate            -         -       880      856      120        48      394     159

3-Methyl-ethyl butyrate      29        23       664      752       33        15      247     101

Myrcene                       -        13         -        -        -         -        -       -

Benzaldehyde                  -         -         -        -        -         -       49      80

Ethyl Caproate               27        20       512      552      261        45      123      58

Hexyl Acetate                18        14         -        -       96         -        -       -

Cymeme                      122       140         -        -       28         -        -       -

2-ethyl-1-hexanol             -         -         -        -        -        14        -       -

Limonene                    530       660         -        -       45         -        -       -

Benzyl Alcohol                -         -         -       22        -         -        -       -

1,8-Cineole                   -         -         -        -       20        22        -       -

3-methyl-n-butyl-n-butyrate   -         -         -        -        -         -      247      92

Propyl Acetate                -         -        77       68        -         -        -       -

Terpinene                   189       215         -        -       13         -        -       -

Terpinolene                  31        35         -        -        -         -        -       -

Linalool                      -         -         -        -        -         -        -      17

Nonanal                      54        45         -        -        -         -        -       -

Ethyl Benzoate                -         -         -        -       17       134        -      25

Butyl Carbitol              162        48         -        -        -         -        -       -

methyl-benzyl alcohol         -         -         -        -        -         -       30      43

Ethyl Caprylate               -         -         -        -        -       242        -       -

Ethyl Pelargonate             -         -         -        -        -         -       56       -

Decanal                      24        21         -        -        -         -        -       -

1-Terpineol                  27         -         -        -        -         -        -       -

Ionone                        -         -         -        -        -         -        -      27


Figure 6

Figure 6 - Wine Cooler (new), 25 ml Collected For 10 min At 15 ml/min With 15 ml/min Dry Purge and Thermally Desorbed At 150 Degrees C For 10 min

Figure 7

Figure 7 - Wine Cooler (1 mon. old), 25 ml Collected For 10 min At 15 ml/min With 15 ml/min Dry Purge and Thermally Desorbed At 150 Degrees C For 10 min

Figure 8

Figure 8 - Strawberry Wine Cooler (New), 25 ml Collected For 10 min At 15 ml/min With 15 ml/min Dry Purge and Thermally Desorbed At 150 Degrees C For 10 min

Figure 9

Figure 9 - Strawberry Wine Cooler (1 mon. old), 25 ml Collected For 10 min At 15 ml/min With 15 ml/min Dry Purge and Thermally Desorbed At 150 Degrees C For 10 min

Figure 10

Figure 10 - Lime Wine Cooler (New), 25 ml Collected For 10 min At 15 ml/min With 15 ml/min Dry Purge and Thermally Desorbed At 150 Degrees C For 10 min

Figure 11

Figure 11 - Lime Wine Cooler (1 mon. old), 25 ml Collected For 10 min At 15 ml/min With 15 ml/min Dry Purge and Thermally Desorbed At 150 Degrees C For 10 min

Figure 12

Figure 12 - Berry Wine Cooler (New), 25 ml Collected For 10 min at 15 ml/min With 15 ml/min Dry Purge and Thermally Desorbed At 150 Degrees C For 10 min

Figure 13

Figure 13 - Berry Wine Cooler (1 mon. old), 25 ml Collected For 10 min At 15 ml/min With 15 ml/min Dry Purge and Thermally Desorbed At 150 Degrees C For 10 min

The homemade wines contain many of the same flavors and alcohol compounds which were detected in the commercial wines (Figures 14 & 15). Both the 30-year-old grape wine and the 2-year-old dandelion wine exhibited a much higher concentration of ethyl acetate than the commercial wines, while isoamyl alcohol concentrations of the homemade wines were much lower than the commercial wines (Table I). An additional compound which was not present in the commercial wines, but detected in the homemade wines, was the natural product 1,1-diethoxy-Ethane (ethylene glycol diethyl ether), which contributes to the sweet taste of the wine.

Figure 14

Figure 14 - 30-Year-Old Grape Wine, 2.5 ml. in 25ml H2O Collected For 10 min At 15 ml/min With 15 ml/min Dry Purge and Thermally Desorbed At 150 Degrees C For 10 min

Figure 15

Figure 15 - 2-Year-Old Dandelion Wine, 2.5 ml. in 25ml H2O Collected For 10 min At 15 ml/min With 15 ml/min Dry Purge and Thermally Desorbed At 150 Degrees C For 10 min

CONCLUSION

Results indicate that acetal formation resulting from a lower pH over time may play a role in off-odor and unusual taste development in wine, although there appears to be very little, if any, volatilization occurring in the wines over the 6 month period. However, decreased flavor concentrations due to volatilization of the compounds in wine coolers appear to influence off-odor/off-taste development over time. In addition, oxidative reactions may occur which result in the degradation of terpenoid compounds and in the formation of by-products, as acetic acid and substituted alcohols. These may affect off-odor/off-taste development. High concentrations of the flavor ethyl acetate, as well as the presence of the natural product ethylene glycol diethyl ether in the homemade and older wines, possibly indicate a richer wine than the commercial wines analyzed. These richer and fuller wines may be due either to the aging of the wine or to the individual's recipe. The Short Path Thermal Desorption System used in conjunction with the Liquid Purge System permits the identification and quantification of trace levels of volatile organics in wines/wine coolers. This technique has also been applied to other applications such as: quantification of benzene and toluene in food products (3), and flavors and fragrances in food products (4&5), commercial products (6) and plant material (7).

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