in the Aroma of and : A Review

J. MARAIS

Viticultural and Oenological Research Institute, Private Bag X5026, 7600 Stellenbosch, Republic of South Africa. The author would like to express his thanks and appreciation to Dr. P. 1. Williams of the Australian Research Institute, Glen Osmond, South Australia for critically reading the manuscript. Submitted for publication: August 1983 Accepted for publication: October 1983

This paper reviews some aspects of terpenes and derivatives in grapes and wines, such as the identification of these compounds, their use in the identification of and differentiation between cultivars, the effect of maturity and wine-making techniques on terpene concentrations and wine quality, as well as transformations of terpenes in grapes and wine.

Wine quality is determined by a complex balance of A number of prominent aroma components of grapes all the wine aroma components as perceived by sensory and wine, which are of terpenic origin, are also of great evaluation. Although several sensory parameters may importance, Some are listed in Table 2. play a role in the acceptance and enjoyment of wine, the The most prominent terpene compounds occurring flavour of wine is possibly the most important factor. generally and in high concentrations in and Flavour is the result of the interaction between certain aroma related grapes and wines are , , chemical compounds in wine and the senses of smell and nerol, oc.-terpineol and hotrienol. Of equal importance of the consumer. Approximately 550 volatile com­ is the great number of terpene compounds which occur ponents have been identified in grapes and wine, and in micro concentrations but which have significant many of these components contribute to the aroma effects on aroma. Different complex combinations of (Schreier, 1979). A large number of components appear terpene compounds are responsible for the characteris­ in micro concentrations in wine, and in many cases these tic aromas of different muscat and aroma related have the most· significant effect on wine quality. With cultivars. These subtle differences in terpene profiles respect to their origin, wine aroma components may be may also occur within the same cultivar originating classified into four groups (Schreier, 1979). from different areas. Typical aroma descriptions of - Originating from the grapes. some important terpenes are floral, rose-like (geraniol, - Produced during the crushing of the grapes by the nerol, rose oxides), coriander (linalool), camphoraceous action of certain enzymes. (linalool oxides), green (nerol oxide) and herbaceous - Produced during fermentation. (Meilgaard, 1975; Simpson, 1979 b). - Produced during maturation of wine. Several studies have been undertaken regarding the A typical cultivar bouquet in wine can be attributed to chemistry of terpenes, their synthesis, systematic classi­ the bouquet of the corresponding grape cultivar and is fications, etc. (Pinder, 1960; Klouwen & Ter Heide, caused by: 1962; Ter Heide, 1968; Ter Heide, 1976). Devon & Scott - Compounds typical of the grape cultivar which are (1972) presented a classification of 4 000 components of transferred from the grape to the wine without being terpenic nature. Of these components, 400 are mono­ affected by the fermentation process. terpenes and 1 000 sesquiterpenes. and - Compounds equally typical of the grape cultivar sesquiterpenes are characteristic components of the

which are formed from a precursor(s) during fermen­ essential oils produced by plants. Monoterpenes (C 10 ) tation (Condonnier & Bayonove, 1978). and sesquiterpenes (C 15 ) are the lower molecular weight representatives of the terpenoid components and com­ GENERAL prise two and three isoprene units, respectively. A general representation of the biosynthesis of mono­ The wine aroma components responsible for the terpenes and sesquiterpenes, as well as some enzymatic characteristic aroma of muscat and aroma related transformations such as oxidation, reduction and wines, are mainly derived from the grape and are known dehydration, has been summarised by Croteau (1975). as terpene compounds. True muscat cultivars include Terpene concentrations in grapes and wine would Muscat d' Alexandrie, Morio Muscat, and Muscat obviously depend on various factors, such as cultivar, blanc, whereas aroma related cultivars include Weisser region and wine-making techniques. Since the majority , Bukettraube, Gewiirztraminer, FeriJ.ao Pires of the terpene compounds occur in micro concentra­ and . Terpene compounds may also contri­ tions in grapes and wines, their quantification is quite bute to the aromas of other non-muscat cultivars. Near­ difficult. Consequently, their concentrations are ly 50 terpene compounds in grapes and wine are known normally expressed as relative amounts. Examples of at this stage, of which 46 were identified in grapes and absolute terpene concentrations in muscat and aroma 30 in wines (Table 1). They include only monoterpenes related grapes and wines, as well as some aroma and sesquiterpenes. threshold values, are shown in Table 3.

S. Afr. J. Enol. Vitic., Vol. 4. No. 2. 1983

49 50 Review: Terpenes in the aroma of grapes and wines TABLE I Monoterpenes and sesquiterpenes in grapes and wines.

Terprn•

,.C.ryophyU.i>e ~ 2 ~ ~ ~

2 ~ ~

5:0• 3,7-0.me1hykt01a-l,?-dir1>-3,6""iol R t" J,7-D1methyloc1-J ...... J.7-diol r

cio·S-Hydroxy-2.6,Mrimetbyl-l..,lnyl­ ~· ie1rahydropynn(cis-l'yranllialooloxidol

traru-5-Hydn>•Y·l,6,C.-lrim

References to these terpenes are available in Supplements 5 (1980, wine) and 6 (1981, grape) to the Fourth Edition of "Volatile Compounds in Food" (Van Straten, De Beauveser & Visscher, 1977), except for: XI Rapp & Knipser, 1980. X indicates presence in either grapes or wines.

S. Afr. J. Enol. Vitic., Vol. 4. No. 2. 1983 Review: Terpenes in the aroma of grapes and wines 51 TABLE 2 Some terpene derivatives in grapes and wines.

Ttrprnold Grapoo

1.l,6-TrlmethyH.2-dihr'-,n•phth.ol•"" ~o~ f"/ c:t::>, t"~ ~ ~),

References to these terpene derivatives are available in Supplements 5 (1980, wine) and 6 (1981, grape) to the Fourth Edition of "Volatile Compounds in Food" (Van Straten, De Beauveser & Visscher, 1977), except for: XI Schreier & Drawert, 1974 b. X2 Schreier, Drawert & Junker, 1976 b. X3 Rapp & Knipser, 1980. X indicates presence in either grapes or wines.

Identification and role of terpene compounds in grapes, are indications that more terpenes other than linalool wine and grape leaves: Considerable research has been and geraniol contribute to muscat and related aromas. done in respect of the identification"-and contribution of Available literature since 1974 indicate that the follow­ terpene compounds to the muscat aroma of muscat ing new terpenes had been identified. Schreier, Drawert grapes and wines. Austerweil (1946) was the first to & Junker (1974) identified 3,7 - dimethylocta - 1,5,7 - suggest that the aroma of muscat grapes can be ascribed trien - 3 - ol (hotrienol) in grape and wine aromas of the to terpene compounds, especially linalool and its deriva­ cultivars Weisser Riesling, Gewiirztraminer, Ruliinder, tives. Cordonnier (1956) investigated the aroma of Muller Thurgau, Scheurebe, Optima and Rieslaner. muscat wines and tentatively identified linalool, Rapp & Knipser (1979) identified 3, 7 - dimethyl - octa - geraniol,

S. Afr. J. Enol. Vitic., Vol. 4. No. 2. 1983 52 Review: Terpenes in the aroma of grapes and wines

TABLE 3 Aroma threshold values and concentrations* of some terpenes in muscat and aroma related grapes (G) and wines (W).

Terpene Aroma Reference Occur- Concentration ( µ..gl I) Reference threshold rence ( µ..g/ /) min. max. Citronellol w 5 7 Geraniol 130 G 89 1059 I G 2 240 2 G 34 237 6 w (+) 69 3 w 14 187 7 Hotrienol 110 4 G (+) 120 2 G 7 77 6 w 3 237 3 w 3 I 17 7 Linalool 100 G 62 1506 1 G II 77 2 G 167 823 6 w 6 375 3 w (+) 29 5 w 8 93 7 Nero! 400-500 G II 447 I G (+) 43 2 G 15 57 6 w (+) 36 3 w 3 43 7 ex -Terpineol 400-500 G 19 145 I G (+) 14 2 G 3 23 6 w 5 399 3 w 7 52 7 3,7 - Dimethylocta - 1,5 - dien - G 125 1497 6 3,7 - diol <._ w 24 I 174 7 3,7 - Dimethylocta - 1,7 - dien - 3,6 - diol G 18 228 6 Nero! oxide 100 4 w (+) 86 3 w I 17 7 Rose oxides w (+) 19 3 ~is - Furan linalool oxide > 6000 G IO 247 1 G (+) 20 2 w 2 258 3 w 5 21 7 trans - Furan linalool oxide > 6000 G 21 400 I G (+) 15 2 w (+) 156 3 w 2 9 7 cis - Pyran linalool oxide 3000-5000 G 10 232 1 G 3 73 2 G 20 66 6 w (+) 74 3 w I 7 7 trans - Pyran linalool oxide 3000-5000 G 20 349 I G 5 89 2 G 67 271 6 w 16 58 7 2,6,6 - Trimethyl - 2 - vinyl - tetrahydropyran w 3 64 5 p - Cymene w 5 35 5 Limonene w 3 30 5 Mvrcene G (+) 9 2 ~ Terpinene w 6 35 5 * The concentration ranges represent the sum of different cultivars analysed. ( +) = Traces. I. Ribereau-Gayon, Boidron & Terrier, 1975 (Muscat d'Alexandrie, Muscat blanc, Saint Vallier, Italia and Muscat Hambourg). 2. Schreier, Drawert & Junker, 1976 a (Rulander, Gewiirztraminer, Scheurebe and Weisser Riesling). 3. Schreier, Drawer! & Junker, 1977 (MUiler Thurgau, Weisser Riesling, Morio Muscat, Gewiirztraminer, Rulander and Scheurebe). 4. Simpson, 1979. 5. Noble, Flath & Forrey, 1980 (Weisser Riesling). 6. Di Stefano, 1981 (A series of white Muscat grapes from ). 7. Versini, lnama & Sartori, 1981 (Weisser Riesling).

amongst others included linalool presented a threshold & Cordonnier (1971) found linalool, cx-terpineol, value of 91 µ..git (Ribereau-Gayon et al., 1975). citral, citronellol, nerol and geraniol to occur in I 0 to Terpene compounds were also found in minor quanti­ I 00 times larger concentrations in muscat than in the ties in some non-muscat cultivars (Stevens, Bomben & non-muscat grape cultivars, Auxerrois, Weisser Riesling McFadden, 1967; Prillinger & Madner, 1970). Bayonove and blanc but in approximately similar relative

S. Afr. J. Enol. Vitic., Vol. 4. No. 2. 1983 Review: Terpenes in the aroma of grapes and wines 53 ratios. Theauthorsalsofoundthattheadditionoftheseter- and aroma related cultivars (Hardy, 1970; Terrier et al. pene compounds to a neutral grape juice medium in the 1972 b; Cordonnier, 1974; Rapp et al. 1978). Bayonove same ratios in which they had been found in muscat culti- & Cordonnier (1970 a,b) established that in the case of varspresentedacharacterwhichcorrespondedwithmuscat several muscat cultivars linalool is absent in the unripe aroma, but lacked balance. Consequently, the terpene grapes, appears at the beginning of ripening at the same compounds mentioned above do contribute to muscat time as the muscat aroma, increases in concentration aroma, but do not represent the complete aroma spectrum. until maturity is reached and then decreases in concen- Terpene compounds were also identified in grape tration with over-ripeness. Bayonove & Cordonnier leaves. Wildenradt et el. (1975) reported that pentane (1971) observed increases in concentrations, similar to extracts of leaves contained terpenes and that of linalool, of other terpenes until maturity is their derivatives as prominent compounds apart from reached. Ripe grapes contained about six times more the grassy C6 - compounds. Myrcene, linalool, ex: -ter- linalool, five times more cx:-terpineol, four times more pineol, iso-pulegone, citral, geraniol, nerol and ex:- and nerol and 1,4 times more geraniol than unripe grapes, B-ionone were identified. Augustyn & Rapp (1982) fail- while citral and citronellol occurred in nearly the same ed to find measurable concentrations of terpenes in the concentrations in the unripe and ripe grapes. Versini et berries of Chenin blanc, and the question arises whether al. (1981) determined terpenes in Weisser Riesling and which biochemical processes are involved in the grapes during the final ripening period (about one possible translocation of terpene compounds from the month) and observed increases as well as decreases in leaves to the grapes. different terpene concentrations. These studies clearly indicated that the maximum aroma can be attained Identification of and differentiation between cultivars, before all the sugar has been accumulated. using terpenes: Generally, it is difficult to differentiate In contrast to the above-mentioned findings, prelimi­ analytically between grape cultivars. An exception in this nary investigations (A. Rapp, 0. P. H. Augustyn & L. regard is muscat and aroma related cultivars, since Engel, 1980; personal communication) indicated cultivar-typical grape aroma components, such as terpene decreases in the concentrations of certain terpenes of compounds, are quite suitable for the analytical differen­ some muscat and aroma related cultivars in South tiation between some cultivars (Schreier, 1979). Terpene Africa with an increase in grape maturity. Reasons for composition, as well as their concentrations differ between these contradicting tendencies must still be found, but cultivars and are responsible for differences in aroma. By may possibly be ascribed to, amongst others, the warm employing mathematical techniques, considerable South African climatic conditions. research has been done in order to identify cultivars and to Wagner et al. (1977), Cordonnier & Bayonove (1978) distinguish between them on the basis of their terpene com­ and Simpson (1979 b) stressed the importance of harves­ position and concentrations. These analyses were useful in ting grapes at the correct maturity. In order to exploit establishing which compounds were cultivar-typical, such the aromatic potential of muscat and aroma related as terpenes, as well as in determining their effect on the grapes, they should be harvested before maximum sugar quality of grapes and wine (Wagner, Dirninger & Fuchs, accumulation, at least before over-ripeness, but not too 1974; Rapp&Hastrich, 1976; Schreier, Drawert&Junker, early in order to prevent the detrimental effect of com­ 1976 a; Rapp & Hastrich, 1978 b). ponents derived from unripe grapes on wine quality. Terrier et al. (1972 b) demonstrated cultivar-typical The optimum maturity of grapes in terms of the opti­ distribution patterns of geraniol, nerol, oc-terpineol and mum terpene composition must still be determined. the linalool oxides in different white V. vinifera cultivars. Schreier et al. (1976 c) and Drawert & Schreier (1978) suc­ The effect of certain wine-making techniques on terpene ceeded in distinguishing mathematically between the concentrations and wine quality: In general, there is cultivars Rulander, Morio Muscat, Gewi.irztraminer, proportionately higher concentrations of nerol in Scheurebe, Weisser Riesling and Mi.iller Thurgau using muscat grapes with small berries compared to those with the concentrations of the terpene compounds linalool, larger berries, such as Muscat d' Alexandrie. Geraniol hotrienol, geraniol, nerol, cx:-terpineol, nerol oxide, the and linalool represent approximately 7 5 OJo to 80% of the rose oxides and the linalool oxides of grapes as well as total terpene content of grapes and wine, and the largest wines. In this case, the rose oxides and nerol oxide emerg­ amounts were found in the case of Muscat d' Alexandrie ed as the aroma components with the most significant (Cordonnier & Bayonove, 1978). The volatile compo­ discriminating abilities. Rapp, Hastrich & Engel (1977), nents of the berry are mainly found in the skin and the Rapp & Hastrich (1978 a) and Rapp et al. (1978) under­ solid parts of the cells. In the case of terpene com­ took detailed investigations into the aroma ("finger­ pounds, Bayonove, Cordonnier & Ratier (1974), print") patterns of different cultivars. By employing the Cordonnier & Bayonove (1978) and Cordonnier & concentrations of certain terpene compounds the authors Bayonove (1981) indicated that in Muscat d' Alexandrie could differentiate between the cultivars Sylvaner, grapes, 94% of geraniol and 96% of nerol are located in Weisser Riesling and Morio Muscat and the cross B 6 - 18 the skin, whereas linalool is almost equally distributed irrespective of grape maturity, year and origin. between the juice (50%) on the one hand and the skin More subtle differentiations ("fine pattern") were also (26%) and cellular debris (24%) on the other. Versini possible between Weisser Riesling grapes cultivated in et al. (1981) found similar trends for geraniol, nerol and different wine areas. citronellol in the case of Weisser Riesling grapes, name­ ly the occurrence of high concentrations in the skins. The effect of grape maturity on terpene concentrations: Linalool also occurred in greater concentrations in Several studies were undertaken to determine the effect the skins, namely 60%. The linalool oxides appeared of grape maturity on terpene concentrations in muscat in evenly distributed concentrations between the skins

S. Afr. J. Enol. Vitic., Vol. 4. No. 2. 1983 54 Review: Terpenes in the aroma of grapes and wines and the juice plus cellular debris, whereas hotrienol, and geraniol were also increased. Bound terpenes are oc-terpineol and 3,7 - dimethylocta - 1,5 - dien - 3,7 - discussed in more depth in the next section. Usseglio- diol mainly occurred in the juice plus cellular debris. Tomasset (1981) investigated the effect of heat- Bayonove et al. (1976) found the distribution of treatment on terpene concentrations of Muscat blanc hotrienol in Muscat blanc to be 14,5% in the cmllular juice and wines, and found decreases in linalool and in- debris, 30% in the skin and 55% in the juice. In other creases in hotrienol, oc-terpineol, nerol and geraniol words, the aromatic profile of the skin differs from that concentrations. Although nuances of the wine-aromas of the juice, and skin-contact may affect wine quality by were modified, the overall quality and aroma intensities affecting the intensity as well as the quality of the were improved. aroma. The quick removal of juice from the skins in the Ethanol may play an important role in the extraction conventional technique of -making, which is of terpenes from the grape particles (Cordonnier & designed to limit phenolic compounds as far as possible, Bayonove, 1981). Even when present in low concen- may lead to ignoring of the fact that important aroma trations during , ethanol may act as an components are located in the skin (Cordonnier & Bayo- extraction solvent. Strauss & Williams (1983) found that nove, 1981). during the distillation of Muscat d' Alexandrie wine the Different techniques may affect the terpene presence of ethanol caused the formation of linalyl, composition of juice and quality of wines significantly. oc-terpinyl, neryl and geranyl ethyl ethers. Generally speaking, pressed juice contains terpene in two to four times higher concentrations than Transformations of terpene compounds in grapes and the corresponding free-run juice. Nerol and geraniol wine: It is well-known that transformations of terpenes especially show distinctly higher concentrations in press may take place during the storage of grapes and the pro­ juice than in free-run juice (Cordonnier & Bayonove, duction and maturation of wines. Muscat and aroma 1981). Kinzer & Schreier (1980) compared the effect of related wines may lose their cultivar characters to a large different pressing systems, namely the screw press, the extent during maturation (Wenzel & De Vries, 1968; cylindrical Willmess press and a combination of the Simpson, 1979 a). Vitispirane (Simpson, Strauss & Willmess press and a chemical pressing-aid material on Williams, 1977) and 1, 1,6 - trimethyl - 1,2 - dihydro­ the composition of volatile constituents in unfermented naphthalene (responsible for the kerosene flavour, musts and wines. The free-run juice and the press frac­ Simpson, 1978) which are of terpenic origin, were found tions were compared in each case. It was found that, in to develop in Weisser Riesling wines during maturation the case of Morio Muscat musts ~nd wines, concentra­ and affect wine aroma and quality significantly. tions of compounds of cultivar origin, such as terpenes, Terpene compounds in grapes and wines are sensitive increased with an increase in pressure. Sensory evalua­ to acidic conditions and to increases in temperature and tion of the wines were not performed. storage time. Under these conditions they are trans­ Versini et al. (1981) systematically compared terpene formed to compounds which may be more or less aroma concentrations of Weisser Riesling grapes and the intensive and which may present a different character in corresponding musts and wines. Pressing of the grapes wine (Terrier & Boidron, 1972 a,b; Terrier et al., 1972 increased terpene concentrations markedly from the a,b; Whittaker, 1972). An example in this respect is the grapes to the musts (7-8 times for geraniol, nerol and acid-catalysed rearrangement of nerol and linalool to a citronellol), as well as in the wines (5-10 times for mutual carbo-cation which could further be stabilised to linalool, nerol, hotrienol, oc-terpineol and the furan OC·terpineol, terpinolene and limonene. Ribereau­ linalool oxides). Furthermore, the authors investigated Gayon et al. (1975) stated that linalool can easily be oxi­ the effect of maceration, which included different con­ dised via an epoxide into four oxides, namely cis- and tact times, a C02 atmosphere, the use of pectolytic trans- furan linalool oxides and cis- and trans- pyran enzymes and heating of the pressed juice on terpene linalool oxides. Furthermore, geraniol is transformed concentrations. Although individual terpenes behaved into oc-terpineol, and nerol, the isomer of geraniol, may differently, generally increases in terpene concentra­ react similarly. Bezzubov et al. (1980) and Batiashvili et tions were observed. The evaluation of the effects of al. (1980) discussed the oxidation of terpenes, such as these treatments on wine quality, as well as statistical linalool and geraniol in grapes and wines and found as a correlations of terpenes with wine quality were still in result losses in wine aroma. Castino & Di Stefano (1981) progress at the time of publication. investigated the effect of storage temperature on the Heat-treatment or pasteurisation of grape juice may characteristics of Asti Spumante wines and found signi­ have a highly significant effect on the concentrations of ficant decreases in terpene concentrations of the specific terpenes in the juice and the wines produced wines stored at 20°C, compared to storage at 10°C. It is from it. Bound terpenes in the juice, such as linalool, clear that some of the most intense aromatic terpene hotrienol and oc-terpineol may be released, and this compounds with low aroma threshold values may be may result in an increase in the concentrations of these transformed into terpenes with high aroma threshold terpenes. Hotrienol mainly occurs in its bound form in values, and these re-arrangements may result in the loss the juice of the berry and only in small quantities in the of muscat and related aromas during storage of grapes skin itself (Usseglio-Tomasset & Di Stefano, 1979). and wine. Usseglio-Tomasset & Di Stefano (1979) and Usseglio­ Williams et al. (1980 a) identified four new hydrox­ Tomasset & Di Stefano (1980) in fact demonstrated gas ylated linalool derivatives in the chloroform extracts of chromatographically that the concentration of linalool Muscat d' Alexandrie grapes and suggested their possi­ doubled, that of oc-terpineol increased eightfold and ble formation from 6, 7 - epoxydihydrolinalool by that of hotrienol hundredfold after steam distillation of means of a series of enzyme-mediated transformations. must for one hour at 70°C. The concentrations of nerol Williams et al. (1980 b) demonstrated the non-enzymatic

S. Afr. J. Enol. Vitic., Vol. 4. No. 2. 1983 Review: Terpenes in the aroma ofgrapes and wines 55 rearrangements of these four hydroxylated linalool It is clear that some terpene compounds which are derivatives at the pH of the grape juice (3,2) to give almost odourless, may be rearranged during acid- several volatile terpenes. Heating Muscat d' Alexandrie catalysed hydrolysis to yield increases in the concentra- grape juice for 1·11}5 minutes at 70°C resulted in an in- tions of existing terpenes as well as the formation of new crease in the concentrations of cis- and trans-furan terpene compounds with quite low aroma threshold linalool oxides, nerol oxide, hotrienol and CX:-terpineol. values. The formation of large amounts of certain Simultaneously seven new terpene compounds were terpenes from limited amounts of linalool derivatives identified as grape aroma components. Acid-catalysed could however not be explained. Cordonnier & Bayo- hydrolysis of model solutions of the four hydroxylated nove (1974) suggested that terpenes occur in bound linalool derivatives is illustrated in Figure 1. forms in muscat grapes, namely as carbohydrate derivatives. However, no terpene glucosides were OH isolated. They believed that under certain conditions .£!U.,4 during maturation of grapes and fermentation, these bound terpenes release additional quantities of volatile OH terpenes which may contribute significantly to the 6 muscat aroma. For example, a fraction of 5 Muscat d' Alexandrie grapes may release linalool by 0H means of enzyme-mediated hydrolysis (Cordonnier & pH3,2 Bayonove, 1974). "-----? Ck=- + )>-·" 0 ,,_ Usseglio-Tomasset & Di Stefano (1979) indicated that 2OH linalool, cx:-terpineol and hotrienol mainly occur in ~ their bound forms in grape musts. During'fermentation 2 7 8 a modest liberation of terpenes, especially cx:-terpineol, takes place, and increases in their concentrations in wines are consequently observed. Usseglio-Tomasset & OH~ .CY=+,~ Di Stefano (1980) further discussed the existence of OH Hof 0 HO.y...... 0---·-, bound precursor terpenes and demonstrated the trans­ OH formations of individual pure commercial terpenes to 3 9 10 other terpenes in an aqueous lOOJo alcohol solution, sub­ jected to heat-treatment at wine pH. It is clear that heat~ treatment of grape juice gives rise to changes in the Ao" ~ ::O<=, + V-< terpene composition, and cx:-terpineol and hotrienol are some of the major products. Di Stefano (1981) deter­ *OH 11 12 ', mined terpene and terpenoid concentrations in white 4 Muscat grapes and mentioned that two-thirds of the linalool content often occur in the combined form. He also demonstrated reaction mechanisms for the produc­ tion of linalool, cx:-terpineol, nerol and geraniol from a linalool precursor. In the same context, Williams, Strauss & Wilson 13 14 15 (1981) investigated the presence of non-volatile, bound (conjugated) precursor terpenes and volatile free terpenes in Muscat d' Alexandrie grapes. Factors such as temperature and acid hydrolysis induced the re­ arrangement of bound terpenes into free terpenes. Grape juice was extracted with pentane seven times. These pentane extracts contained the free terpenes. The 16 17 pentane-stripped juice was further extracted with Freon FIGURE 1 11, and this extract contained the more polar, poly­ Acid hydrolysis products of grape polyols 1-4 (Williams, Strauss & hydroxylated monoterpenes which are also viewed as Wilson, 1980 b). free terpenes; The pentane-freon-stripped juice contain­ I. 3,7 - Dimethylocta - 1,5 - dien - 3,7 - diol. ed the remaining highly water-soluble bound terpenes 2. 3,7 - Dimethylocta - 1,7 - dien - 3,6 - diol. and this juice, when heated to 70°C at low pH, induced 3. 3,7 - Dimethyloct - 1 - en - 3,6,7 - trio!. 4. 3, 7 - Dimethyloct - 1 - en - 3,7 c diol. the transformation of bound terpenes into free terpenes. 5. Hotrienol. Some of the major products formed at pH 3,0 were 6. Nero! oxide. hotrienol, linalool, cx:-terpineol and the furan linalool 7. trans - Anhydrofuran linalool oxide. oxides. When the pH of the juice was adjusted to 1,0 8. cis - Anhydrofuran linalool oxide. and the juice heated to 70°C, myrcenol and cis- and 9. trans - Furan linalool oxide. 10. cis - Furan linalool oxide. trans-ocimenol were major products. Furthermore, cis­ 11. 2,6,6 - Trimethyl - 2 - vinyl - tetrahydropyran. and trans - 1,8 - terpin, which had not yet been identi­ 12. 2,2 - Dimethyl - 5 - (1 - methyl-propenyl) tetrahydrofuran. fied in grapes and wine, also emerged as prominent 13. Linalool. terpenes. The mechanisms by which these rearrange­ 14. Myrcenol. 15. cis - Ocimenol. ments occurred were then not clear. The authors specu­ 16. trans - Ocimenol. lated that the different oxidation levels of the terpene 17. CX:- Terpineol. compounds possibly played an important role in this

S. Afr. J. Eno!. Vitic., Vol. 4. No. 2. 1983 56 Review: Terpenes in the aroma of grapes and wines regard. In view of the presence of bound terpenes and Yeasts are able to produce terpenes. Drawert & their incomplete rearrangements into free terpenes Barton (1978) demonstrated the formation of during different wine-making procedures as well as citronellol, linalool and geraniol by the yeast during extraction procedures of grape juice at normal Kluyveromyces /actis in aerobic submerged culture. By juice pH, quantitative results of terpene concentrations changing the culture conditions, the yield of in grape juice and wines should be interpreted with monoterpenes such as citronellol was affected. Fagan, caution (Williams et al., 1981). Kepner & Webb (1981) reported the production of It became evident from the above-mentioned research linalool, cis- and trans-nerolidol and trans, trans­ that concentrations of terpene compounds and conse­ farnesol by the wine yeast Saccharomyces fermentati. quently the aroma of wine, would definitely be affected This was carried out by the yeast growing for 10 weeks by certain wine-making techniques such as heat­ as a film on the surface of a simulated fino , treatment of grapes and must. which contained ethanol as the only volatile carbon Williams et al. ( 1982 a) confirmed the occurrence of containing compound. bound terpenes as glucosidic derivatives and isolated Terpene transformations which involve the actions of them from grape juice and wines by means of C18 - enzymes has been discussed by Croteau (1975) who bonded reversed-phase liquid chromatography. This concluded that, in spite of limited knowledge in this type of chromatography allowed separation of gluco­ respect, several highly specific enzymes are involved in sidic precursors of monoterpenes at different oxidation terpene metabolism and transformations. The enzyme levels. Simultaneously, precursors of the important nor­ trans- cis-isomerase seems to be a key enzyme in terpene isoprenoid grape and wine aroma components, namely metabolism, since it functions at the conditions where vitispirane, 1, 1,6 - trimethyl - 1,2 - dihydronaphthalene geranyl pyrophosphate is transformed into cyclic mono­ and damascenone were identified. When the grape juice terpenes, while further condensation to farnesyl pyro­ was subjected to drastic conditions, namely pH 1,0 and phosphate is prevented. Another key reaction in the 70°C, the formation of various terpenes, which have biosynthesis of monoterpenes appears to be the not yet been identified in grapes and wine, was induced. enzymatic dehydration of cx:-terpineol to terpinolene They were amongst others 1,4 - cineole, 1,8 cineole, and limonene. cx:-Terpineol is mainly dehydrated to cx:-terpinene, cis- and trans-ocimene, terpinolene, terpinolene in the case of extracts of carrot roots and to terpinen-l-ol and trans- 2,6-dimethylocta -3, 7 - dien -2,6 limonene in the case of peppermint leaves. During the - diol. Di Stefano (1982) isolated a linalool precursor crushing of grapes, intense enzymatic activities occur. from white Muscat of Piemonte ,which, by acid hydro­ The enzymatic liberation of terpenes from sugar lysis, mainly produced linalool and arabinose. molecules by specific enzymes, such as .fJ-glucosidase Williams et al. (1982 b) identified the glycosidic may possibly occur, which may affect wine aroma signi­ precursors of the geraniol oxidation state monoterpenes ficantly (Cordonnier & Bayonove, 1981). of both Muscat d' Alexandrie and Weisser Riesling Due to the relative instability of terpene compounds, grapes and wines and thus clarified the origin of the free transformations of terpenes may also occur as a result terpenes involved. They were found to be a complex of vigorous and lengthy extraction procedures (Williams mixture of disaccharides namely jJ - rutinosides and et al., 1980 b). As already mentioned, factors such as an 6-0-cx:-L-arabinofuranosyl - .fJ-D-glucopyranosides of increase in temperature and acid conditions result in several monoterpene alcohols. These findings were marked increases in the concentrations of some existing confirmed by hydrolysis studies of synthetic neryl, gera­ terpenes as well as the formation of new terpene com­ nyl and linalyl .fJ-D- glucopyranosides (Williams et al., pounds. In other words, terpenes may also be produced 1982 c). as artefacts which consequently do not represent the Boidron (1978) investigated the effect of Botrytis original aroma profile of grapes and wine (Usseglio­ cinerea infection on the decomposition of terpenes in Tomasset & Di Stefano, 1979; Williams et al., 1980 b). grape juice and found decreases in the concentrations of More accurate and mild isolation techniques, such as linalool, cx:-terpineol, geraniol, nerol, hotrienol and headspace methods, which involve the sampling and terpene oxidation products, as well as an eventual dis­ concentration of aroma components in the headspace appearance of the majority of the terpene compounds above wines, appear to be the most acceptable. These and the distinct muscat aroma with an increase in infec­ techniques should produce an aroma profile which is tion. Shimizu, Uehara & Watanabe (1982) demon­ more representative of those volatiles of grape juice and strated the transformations of some monoterpenes to wine which actually enter the nose when the product is other terpenes when added to artificially botrytized being smelt (Williams, 1982). Rapp & Knipser (1980) grape must. The concentration of a mixture of cis- and described a method for the enrichment of headspace trans-furan linalool oxides remained unchanged, components of wine in which the mild conditions whereas the concentrations of linalool, terpinen - 4 - ol involved prevent the formation of artefacts as far as and cx:-terpineol decreased markedly. When only practically possible. linalool was added to the must, 12 terpenes were Research indicates clearly that terpene compounds produced. They were .fJ-pinene, cis- and trans-furan are responsible for some of the most important and linalool oxides, p-menthane-l-en-3-one, cx:-terpineol, prominent aromas in grapes and wines. Technological cis- and trans-pyran linalool oxides, geraniol, development of analytical instruments make it possible p-menthane-1,8-dien-9-ol and three unidentified to gain deeper insight into the nature of terpenes. monoterpenes. When only terpinen - 4-ol was added to Factors such as cultivar, climatic conditions, grape the must, only one terpene, namely geranial, was maturity, pH, enzymes, lengthy storage times, extrac­ produced. Botrytis cinerea did not produce terpene tion procedures and wine-making procedures such as compounds in grape must lacking terpenes. maceration, heat-treatment and pressing may have a

S. Afr. J. Enol. Vitic., Vol. 4. No. 2. 1983 Review: Terpenes in the aroma ofgrapes and wines 57 significant effect on the volatile terpene content of DI STEFANO, R., 1982. Presenza di precursori de! Iinalolo nel grapes and wines and on wine quality. By improving Moscato bianco de! Piemonte. Vignivini IX, 45-47. quantification of terpenes, and utilisation of available DRAWERT, F. & BARTON, H., 1978. Biosynthesis of flavor com- k 1 d h d b·1· · · pounds by micro-organisms. 3. Production of monoterpenes by now e ge, t e a apta l lty of different cult1vars to the yeast Kluyveromyces lactis. J. Agric. Food Chem. 26, 765-766. different climatic regions may be utilised better, and DRAWERT, F. & SCHREIER, P., 1978. caracterisation des raisins high quality wines with more specific aroma styles may et des vins a !'aide de certains constituants remarquables. Ann. be produced. Technol. Agric. 27, 367-375. FAGAN, G. L., KEPNER, R. E. & WEBB, A. D., 1981. 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SCHREIER, P., DRAWERT, F. & JUNKER, A., 1976 a. USSEGLIO-TOMASSET, L. & DI STEFANO, R., 1980. Profilo Gaschromatographisch - massenspektrometrische Differenzie­ aromatico de! Moscato bianco de! Piemonte. Riv. Vitic. Eno!. rung der Traubenaromastoffe verschiedener Rebsorten von Vitis 33, 58-68. vinifera. Chem. Mikrobiol. Technol. Lebensm. 4, 154-157. VANSTRATEN, S., DE BEAUVESER, J.C. & VISSCHER, C. A. SCHREIER, P., DRAWERT, F. & JUNKER, A., 1976 b. Identi­ 1977. "Volatile Compounds in Food'', Supplement 5 (1980, fication of volatile constituents from grapes. J. Agric. Food wine), 70.1-70.9 and Supplement 6 (1981, grape) 9.1-9.6 to the Chem. 24, 331-336. Fourth Edition. Central Institute for Nutrition and Food SCHREIER, P., DRAWERT, F., JUNKER, A. & REINER, L., 1976 c. Research TNO, Zeist, The Netherlands. Anwendung der multiplen Diskriminanzanalyse zur Differen­ VERSINI, G., INAMA, S. & SARTORI, G., 1981. A capillary zierung von Rebsorten an Hand der quantitativen Verteilung column gaschromatographic research into the terpene fliichtiger Weininhaltsstoffe. Mitt. Klosterneuberg. 26, 225-234. constituents of "Riesling Renano" (Rhine Riesling) wine from SCHREIER, P., DRAWERT, F. & JUNKER, A., 1977. Gaschro­ Trentino Alto Adige: Their distribution within berries, their matographische Bestimmung der Inhaltsstoffe von Giirungsge­ passage into must and their presence in the wine according to triinken. X. Quantitative Bestimmung von Weinaromastoffen in different wine-making procedures. Organoleptic considerations. myg/1-Bereich. Chem. Mikrobiol. Technol. Lebensm. 5, 45-52. Vini Ital. XXlll, 189-211. SHIMIZU, J., UEHARA, M. & WATANABE, M., 1982. Trans­ WAGNER, R., DIRNINGER, N. & FUCHS, V., 1974. Resultats formation of terpenoids in grape must by Botrytis cinerea. preliminaires concernant I' etude genetique de substances Agric. Biol. Chem. 46, 1339-1344. odorantes decelees par chromatographie en phase gazeuse dans SIMPSON, R. F., 1978. l,l,6-Trimethyl-1,2-dihydronaphthalene: Jes fruits d'une descendance de L. Colloque an important contributor to the bottle aged bouquet of wine. C.N.R.S. "Facteurs et regulation de la maturite des fruits". Chem. Ind., 37. 335-339. SIMPSON, R. F., 1979 a. Aroma composition of bottle aged white WAGNER, R., DIRNINGER, N., FUCHS, V. & BRONNER, A., wine. Vitis 18, 148-154. 1977. Study of the intervarietal differences in the concentration of volatile constituents (linalool and geraniol) in the aroma of SIMPSON, R. F., 1979 b. Some important aroma components of the grape. Interest of such analyses for the appreciation of the white wine. Food Technol. Aust. 31, 516-522. quality of the . Int. Symp. Qua/. Vintage. Cape Town, SIMPSON, R. F., STRAUSS, C. R. & WILLIAMS, P. J., 1977. 137-142. Vitispirane: a C 13 spiro-ether in the aroma volatiles of grape WEBB, A. D. & KEPNER, R. E., 1957. Some volatile aroma juice, wines and distilled grape spirits. Chem. Ind., 663-664. constituents of Vitis vinifera var. . Food STEVENS, K. L., BOMBEN, J., LEE, A. & McFADDEN, W. H., Res. 22, 384-395. 1966. Volatiles from grapes. Muscat of Alexandria. J. Agric. WEBB, A. D., KEPNER, R. E. & MAGGIORA, L., 1966. Gas chro­ Food Chem. 14, 249-252. matographic comparison of volatile aroma materials extracted STEVENS, K. L., BOMBEN, J. & McFADDEN, W. H., 1967. from eight different muscat-flavored varieties of Vitis vinifera. Volatiles from grapes. Vitis vinifera (Linn.) cultivar . Am. J. Eno!. Vitic. 17, 247-254. J. Agric. Food Chem. 15, 378-380'..< WENZEL, K. W. 0. & DE VRIES, M. J., 1968. An investigation STRAUSS, C. R. & WILLIAMS, P. J., 1983. The effect of distillation of muscat aroma. S. Afr. J. Agric. Sci. 11, 273-280. on grape flavour components, Flavour of Distilled Beverages Symp. I-4th June. Univ. of Stirling, Scotland, U.K. WHITTAKER, D., 1972. The monoterpenes. Newman, A. A. ed. Chemistry of terpenes and terpenoids. Academic Press, London, TER HEIDE, R., 1968. Studies on terpenes. II. Characterization of 11-87. monoterpene by gas and thin-layer chromatography. Z. Anal. Chem. 236, 215-227. WILDENRADT, H. L., CHRISTENSEN, E. N., STACKLER, B., CAPUTI, Jr., A., SLINKARD, K. & SCUTT, K., 1975. Volatile TER HEIDE, R., 1976. Studies on terpenes. III. Gas chromatography constituents of grape leaves. I. Vitis vinifera variety 'Chenin of acyclic monoterpene alcohols. J. Chrom. 129, 143-154. blanc'. Am. J. Eno!. Vitic. 26, 148-153. TERRIER, A. & BOIDRON, J. N., 1972 a. Identification des derives WILLIAMS, A. A., 1982. Recent developments in the field of wine terpeniques dans Jes raisins de certaines varietes de Vitis vinifera. flavour research. J. Inst. Brew. 88, 43-53. I. Techniques experimentales. Connaiss. Vigne Vin. l, 69-85. WILLIAMS, P. J., STRAUSS, C. R. & WILSON, B., 1980 a. New TERRIER, A. & BOIDRON, J. N., 1972 b. 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L'aroma di moscato nelle uve e WESTROPP, R. A., 1982 a. Use of C reversed-phase liquid nei vini. lndustr. Agrar. 4, 216-244. 18 chromatography for the isolation of monoterpene glycosides and USSEGLIO-TOMASSET, L., 1969. I costituenti aromatici delle nor-isoprenoid precursors from grape juice and wines. J. uve. Riv. Vitic. Eno/. 22, 223. Chrom. 235, 471-480. USSEGLIO-TOMASSET, L., 1981. Les substances aromatiques du WILLIAMS, P. J., STRAUSS, C. R., WILSON, B. & MASSY­ vin et la possibilite de Jes augmenter par de traitements WESTROPP, R. A., 1982 b. Novel monoterpene disaccharide thermiques. Int. Oenol. Symp., (Pap.), 6th, 353-361. glycosides of Vitis vinifera grapes and wines. Phytochemistry 21, USSEGLIO-TOMASSET, L., ASTEGIANO, V. & MATTA, M., 2013-2020. 1966. II linalolo composto responsabile dell' aroma delle uve e dei WILLIAMS, P. J., STRAUSS, C. R., WILSON, B. & MASSY­ vini aromatici. lndustr. Agrar. 4, 583-584. WESTROPP, R. A., 1982 c. 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S. Afr. J. Eno!. Vitic., Vol. 4. No. 2. 1983