Identification of Characteristic Aroma Components of Mate - American

Chapter 12

Identification of Characteristic Aroma Components of Mate (Ilex paraguariensis) Tea

Downloaded by COLUMBIA UNIV on July 27, 2012 | http://pubs.acs.org Publication Date: December 4, 2006 | doi: 10.1021/bk-2007-0946.ch012

Patricio R. Lozano, Keith R. Cadwallader, and Elvira G o n z á l e z de Mejia Department of Food Science and Human Nutrition, University of Illinois at Urbana-Champaign, 1302 West Pennsylvania Avenue, Urbana, I L 61801

Mate (Ilex paraguariensis), native to South America, has been used for centuries by the South American Indians as a source for a tonic and a stimulating drink, and recent discoveries have associated its phenolic content with the inhibition of tumor growth. Despite the health promoting properties of Mate tea, its characteristic flavor is still not well-characterized. Three types of mate tea imported from Argentina were selected based on levels of polyphenols compounds, agronomic factors, and flavor characteristics (strong, medium, and weak flavor) determined by habitual Mate tea drinkers. Volatiles from hot water-infusions (brews) prepared from dried tea leaves were isolated by dynamic headspace analysis (DHA), solvent-assisted flavor evaporation-solvent extraction (SAFE— SE), and column adsorption extraction. Aroma-active components were identified by gas chromatography— olfactometry (GCO) and G C - M S . Predominant aroma components of Mate tea included geraniol, β-damascenone, 2methoxyphenol, linalool, β-ionone, eugenol, 2-acetyl-1— pyrroline, (E,Z) 2,6-nonadienal, and geranial. Aroma components of Mate tea are produced by lipoxygenase action and degradation reactions occurring during manufacture of the dried tea leaves.

© 2007 American Chemical Society

In Hispanic Foods; Tunick, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2006.

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Introduction Mate tea is a beverage prepared by the infusion of dried green Mate leaves and is traditionally consumed in the southeastern part of South America including Paraguay, Uruguay, Brazil, Argentina, and Bolivia. Mate is well known for its high content of alkaloids such as caffeine, which can have pharmaceutical applications. Caffeine intake due to Mate tea consumption by far exceeds intakes recorded in the literature for other beverages containing this alkaloid (7). Extraction of caffeine from Mate can be accomplished by use of supercritical C 0 , which gives the highest yield (2). Antioxidative properties have been found in Mate tea and its polyphenols compounds have been associated with inhibition of tumor growth (5) and nitrosative stress (4). Despite the importance of Mate tea leaves in the social and economic context of South America, the literature is scarce in relation to its characteristic flavor. Mate tea has a characteristic mature flavor, which is somewhat sweet, sour leaf-like and cigarette-like. This flavor is similar to that obtained from Camellia sinensis tea (5). Volatile components of Argentinean green Mate and Brazilian roasted Mate were investigated by Kawakami and Kobayashi (6). A total of 196 compounds were identified as volatile constituents of Mate in that study; however, no sensory (olfactometry) assessment was carried out. Therefore, the aroma significance o f these aroma compounds has not been fully addressed. The aim of the present study was to identify and characterize the major aroma components of mate tea using novel extraction techniques in combination with G C O and G C - M S .


2

Experimental Procedures

Materials Three samples of commercial Mate tea imported from Argentina. Cruz de Malta low ash, Kraus Organic Classic Mate, and Taragui low ash were selected for this study based on the levels of polyphenols compounds (5), agronomic conditions (7) and flavor characteristics suggested by traditional Mate drinkers, who classified the samples as having low, medium or high flavor intensity, respectively. The samples were sealed in plastic bags and frozen at -80°C until analysis.


145 Preparation of Mate Tea Infusion Sample brewing process was carried out following the protocol described by Chandra and Gonzalez de Mejia (5). Each tea (2.7 g) was mixed with 250 mL of boiling water at 98°C and held/stirred for 10 min. The tea extract was then filtered using Whatman paper #2.


Dynamic Headspace Dilution Analysis (DHDA) Ten mL of tea brew was placed in a glass three-neck purge and trap vessel (SIS, C A ) . A desorption tube containing 200 mg of Tenax T A (Supelco, Bellefonte, P A ) was attached to the vessel. The vessel was kept at 50°C for 10 min to allow equilibration of the headspace of the tea and then nitrogen at a constant flow of 50 mL/min was used to purge the headspace volatiles onto the Tenax trap. Serial dilutions were accomplished by varying the purging time from 25, 5, or 1 min, corresponding to flavor dilution factors of 1, 5, and 25 respectively (5). Prior to thermal desorption the trap was dry purged for 17 min (100 mL/min nitrogen flow) to remove excess moisture. A thermal desorption system (TDS2, Gerstel, Germany) was employed to desorb (220°C) and transfer the volatiles from the Tenax trap into a CIS 4 inlet (Gerstel) where they were cryofocused at -150°C. Splitless injection was made by ramping the CIS 4 temperature to 260°C at 12°C/s. G C O was performed on a 6890 G C (Agilent Technologies, Palo Alto, C A ) equipped with an OD2 olfactometry port (Gerstel) and Stabilwax-DA (Restek, Bellefonte, P A ) or DB5ms (J&W Scientific, Foison, C A ) capillary column (15 m χ 0.32 mm i.d. χ 0.5 μηι film). Analyses were carried out in duplicate.

Solvent Assisted Flavor Evaporation - Solvent Extraction (SAFE-SE) A modified solvent assisted flavor evaporation (SAFE) apparatus (P) was used for the extraction of the main aroma components of Mate tea brew. S A F E SE was selected because it allows for a representative aroma extract to be prepared without the formation of artifacts. Mate tea brew (800 mL) was spiked with 10 of internal standard solution (50 mg each of 2-undecanol, 6undecanone, teri-butylbenzene, and 2-ethyl butyric acid dissolved in 10 mL of methanol) and kept in an Erlenmeyer flask covered with aluminum foil to prevent any light affects on the chemical composition of the tea during the extraction time. The S A F E extraction was conducted under the following conditions: vacuum at 10" Torr, 45°C S A F E head temperature, and 40°C water 5


146 bath (sample flask) temperature. The receiving traps were kept in liquid nitrogen temperature (-196°C) throughout the distillation. The distillate was thawed at room temperature and extracted with ether (3 χ 50 mL). The ether extract was separated into acidic, neutral and basic fractions (10). Each fraction was dried over 2 g of sodium sulfate and then concentrated to 200 under a gentle stream of nitrogen.


Adsorptive Column Extraction Mate tea brew (800 mL) was passed through a column packed with 10 g of Porapak Q (50- 80 mesh, Waters Co., Milford, M A ) using the method described by Kumazawa and Masuda (11) and Maneerat et al. (12). The column was washed with 100 mL deodorized-deionized water and the adsorbed compounds were then eluted with 100 mL of methylene chloride. The elute was separated into neutral, acidic and basic fractions and each fraction was concentrated to 200 μL as earlier described.

Aroma Extract Dilution Analysis ( A E D A ) G C O was conducted using an Agilent 6890 G C equipped with a D A T U sniffing port (Geneva, N Y ) and flame ionization detector. Separations were performed using polar (Stabilwax D A ) and nonpolar (DB5ms) (15 m χ 0.25 mm i.d. χ 0.25 μπι film) columns. Serial dilutions (1:3) were prepared from each aroma fraction from SAFE-SE and column adsorptive extraction. Two μί, of each dilution was injected in the cool on-colum mode. Oven temperature was 35°C for 5 min, then ramped to 225°C at 4°C/min, with a final holding time of 20 min. The carrier gas was He at a constant flow of 1 mL/min.

Gas Chromatography-Mass Spectrometry ( G C - M S ) The G C - M S system consisted of an Agilent 6890 GC/5973 M S D equipped with a cool on-column injector. Separations were performed on a Stabilwax-DA column (30 m χ 0.25 mm i.d. χ 0.5 μπι; Restek). G C conditions were the same as for A E D A except that only 1 μL of each extract was injected. M S D conditions were as follows: 280°C interface temperature, ionization voltage was set at 200 V above standard tune value and mass range was 35 - 300 a.m.u. Compounds were positively identified by comparing their retention indices (on two columns) and mass spectra with authentic reference compounds. Tentative indentifications were based on matching RIs with literature values or


147 by comparing their mass spectra to a database (Wiley 138K Mass Spectral Database, Wiley and Sons, 1990).

Results and Discussion


Aroma Components Isolated by S A F E - S E Forty-two, 23, and 45 aroma compounds were detected in Cruz de Malta, Kraus Organic, and Taragui Mate tea infusions, respectively. However, some of the aroma compounds that were detected at the sniffing port could not be identified by G C - M S due to their low abundance. Table I shows only the major aroma compounds identified in these three Mate extracts. Although a higher number of compounds were detected in the Taragui Mate tea extract by using SAFE-SE, all of the Mate teas seemed to show similar aroma-active compounds, which provide the chracterisitic herbal/minty, grassy/hay and burnt/tabbaco aroma to the tea. Cruz de Malta tea, which was characterized by a smoky and tobbaco note, showed the lowest intensity in its aroma compounds, β-ionone, eugenol, 2methoxy-4-vinylphenol (p-vinylguaiacol), geraniol, 2-methoxy phenol (guaiacol), geranial, and 1,8-cineole were the major aroma contributors in this extract. From these compounds 2-methoxyphenol and 2-methoxy-4-vinylphenol have been reported previously in other types of teas as important contributors of roasted/smoky aroma notes (77). Taragui tea, which was classified by habitual mate consumers as having the strongest flavor among the three teas analyzed in this study, possessed more intense grassy and floral aroma notes besides the burnt and hay aroma discussed above. It appears that the presence of hydroperoxide breakdown products such as fî^-2-octenal (peanut), (%)-3-hexenal (grassy), l-octen-3-ol (mushroom), and f£,Z>2,6-nonadienal (cucumber) contribute to the grassy or green flavor in this type of Mate tea. These compounds were shown to be formed as a result lipoxygenase activity due to mild temperature treatment employed to inhibit leaf enzymes. In addition, geraniol (floral), geranial (fruity), 1,8-cineole (minty), linalool (floral), and eugenol (spicy) contribute to the higher herbal/minty character of the Taragui extract. These terpene alcohols are formed via hydrolysis of glycoside precursors (75). The aroma extract of Kraus-Organic mate tea contained a lower number of aroma compounds, generally at weaker intensities, than the other two tea extracts. This finding could be due to the different agronomic conditions applied to these leaves, which has been shown to influence the amount of aroma


148 Table I. Predominant Odorants Determined by SAFE-SE and AEDA of Hot-Water Infusions of Three Types of Mate Tea FD-factor Compound Rf Odor Description Fr Cruz Org Tard Geraniol 1864 Floral Ν 9 243 729 Guaiacol Ν 1853 Smoky, medicine 27 3 243 l-Octen-3-ol 1438 Mushroom Ν 3 27 1819 Cooked apple Ν 81 3 729 β-Damascenone Ν 81 1972 Fruity, floral 9 9 δ-Octalactone Skatole 2486 Urine, mothballs Ν 81 81 9 (Z)-3-Hexenal 1114 Green, cut-leaf Ν 27 3 27 l,8-Cineole 1171 Minty, eucalyptus Ν 9 3 27 2-Acetyl-1 -pyrroline Β 1319 Roasty, popcorn 3 27 27 Methional Ν 1465 Cooked potato

Identification of Characteristic Aroma Components of Mate - American

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