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. 2024 Apr 19;29(8):1863. doi: 10.3390/molecules29081863

Chemical Composition of Volatile and Extractive Components of Canary (Tenerife) Propolis

Valery A Isidorov 1,*, Andrea M Dallagnol 2, Adam Zalewski 3
Editors: Maria da Graça Costa G Miguel, Ofelia Anjos, Carsten Müller
PMCID: PMC11053497  PMID: 38675683

Abstract

The vegetation of the Canary Islands is characterized by a large number of endemic species confined to different altitudinal levels. It can be assumed that these circumstances determine the characteristic features of the chemical composition of local beekeeping products, including propolis. We report, for the first time, the chemical composition of propolis from Tenerife (Canary Islands). The volatile emissions of three propolis samples collected from different apiaries are represented by 162 C1–C20 compounds, of which 144 were identified using the HS-SPME/GC-MS technique. The main group of volatiles, consisting of 72 compounds, is formed by terpenoids, which account for 42–68% of the total ion current (TIC) of the chromatograms. The next most numerous groups are formed by C6–C17 alkanes and alkenes (6–32% TIC) and aliphatic C3–C11 carbonyl compounds (7–20% TIC). The volatile emissions also contain C1–C6 aliphatic acids and C2–C8 alcohols, as well as their esters. Peaks of 138 organic C3–C34 compounds were recorded in the chromatograms of the ether extracts of the studied propolis. Terpene compounds form the most numerous group, but their number and content in different samples is within very wide limits (9–63% TIC), which is probably due to the origin of the samples from apiaries located at different altitudes. A peculiarity of the chemical composition of the extractive substances is the almost complete absence of phenylcarboxylic acids and flavonoids, characteristic of Apis mellifera propolis from different regions of Eurasia and North America. Aromatic compounds of propolis from Tenerife are represented by a group of nine isomeric furofuranoid lignans, as well as alkyl- and alkenyl-substituted derivatives of salicylic acid and resorcinol.

Keywords: propolis, chemical composition, volatile compounds, extractive components, terpenoids, resorcinol derivatives, lignans

1. Introduction

Propolis is one of the most valuable beekeeping products, but a honeybee colony’s need for it is not very great. Therefore, only a small proportion of worker bees are involved in collecting raw plant materials for its production. Meanwhile, the role of propolis in ensuring the survival of the colony in a far-from-sterile environment cannot be overestimated: it has high activity against various pathogens [1,2,3] and plays a key role in the ‘social immunity’ of bees [4,5].

In recent years, increasing attention has been paid to propolis as an antidote to human microbial pathogens. In terms of antisepticity, propolis stands out among most other beekeeping products, second only to bee venom in terms of potency [6,7,8]. It exhibits a wide range of medicinal properties, which are not limited to antimicrobial action, as reflected in a number of recent comprehensive reviews [9,10,11,12]. In particular, its beneficial effects on the human digestive system, in the treatment of a number of gynecological diseases, and in the healing of wounds and burns, as well as in dermatology and a number of oncological diseases, have been shown [13,14,15,16,17].

It is generally accepted that the antibacterial activity and other medicinal properties of propolis are due primarily to phenolic compounds of plant origin, flavonoids, phenolcarboxylic acids and their esters [9,10,18]. These natural compounds are found not only in plant tissues but also in their external secretions in the form of resin, exudates and leakage from wounded tissues, and perform protective functions against pathogens and parasites. It is these properties that encourage bees to collect these materials, in need of a means of combating pests and pathogens in their hives. Bees are selective and preferential in relation to plant sources of raw materials for the production of propolis [2,19,20,21], and when searching for them, they are guided by various insufficiently studied olfactory and optical signals. A consequence of the selectivity of bees that deliver raw materials is the existence of certain regional ‘types’ or varieties of propolis [22]. For example, the middle latitudes of Eurasia and North America are characterized by the ‘poplar type’, the plant precursor of which is exudates on the buds of different types of poplar containing the flavonoid aglycone, phenylcarboxylic acids and their derivatives [18,19,23]. In boreal regions, outside the growing range of poplar, bees collect resin from the buds of downy birch (Betula pubescens), which are not only rich in flavonoids but also contain large amounts of sesquiterpenol esters of phenylpropenoid acids [23,24]. Another source of resin are aspen (Populus tremula and P. tremuloides) buds, characterized by a high content of phenylpropenoid glycerides [23,25,26]. In the boreal zone, a mixed ‘birch-aspen type’ of propolis is often found [23], and on the border with the mid-latitude zone, poplar markers are also found in its composition [27]. In other phytogeographical zones and regions, there are local sources of resin acceptable to foraging bees, and there they produce specific types of propolis, such as green Brazilian propolis from the tropical zone [28] or Argentine Andean propolis [29]. The botanical predecessor of the former is Baccharis dracunculifolia, and that of the latter is Larrea nitida.

In isolated island areas, often rich in endemic plant species, one can also expect the existence of propolis with a specific chemical composition that allows it to be considered a separate variety. This applies to diterpenoids-rich propolis from the Greek islands [30] and to Pacific propolis from Okinawa and Taiwan [31]. Such isolated areas include the islands of the Canary archipelago, where beekeeping has long been practiced, but its products still remain poorly understood. In particular, there is only one report on the chemical composition of two propolis samples from the island of Gran Canaria [32]. Judging by the data presented, these samples demonstrate significant qualitative differences both from propolis from the temperate zone and from its known varieties of tropical origin. This is undoubtedly due to the presence on the island of specific plant sources of resins or other types of secretions that are attractive to the bees bred on it. It would be interesting to study the chemical composition of propolis from other Canary Islands, since each of them is characterized by biogeographical differences. This work reports for the first time the chemical composition of propolis from Tenerife, the largest of the islands of the archipelago and possessing plant species endemic only to this island [33].

2. Results

2.1. Composition of Volatile Components of Propolis

Determination of the volatile organic components (VOCs) of propolis was carried out using the method of solid phase microextraction combined with gas chromatography with mass spectrometric detection (HS-SPME/GC-MS). Chromatograms recorded using this method contained peaks of 162 C1–C20 compounds belonging to different classes of organic substances. Table 1 shows the composition of VOCs, grouped by class of organic compounds, as well as the substances included in each group in order of increasing retention index. The largest contribution to the total ion current (TIC) of the chromatograms was made by the group of terpenoids, numbering 72 compounds. The monoterpenoid subgroup, formed by 34 individual components (11 of them were found in all three samples), accounted for 27–56% of the TIC. However, 12 monoterpenoids were recorded in only one of the three samples. An even greater difference was observed in the subgroup of sesquiterpenoids: 27 out of a total of 36 were found in only one of the samples.

Table 1.

Relative group composition (% TIC) of volatile compounds in Canary (Tenerife) propolis.

Monoterpene/Monoterpenoids, Including: RI Exp RILit Sample
Pr-1 Pr-2 Pr-3
27.07 55.84 38.10
   tricyclene 919 921 0.19 0.16 0.21
   α-thujene 925 926 1.35 N.d. * 2.58
   α-pinene 936 936 6.43 10.07 18.68
   camphene 945 946 0.59 1.03 0.28
   dehydrosabinene 956 957 N.d. 1.49 N.d.
   sabinene 970 973 0.68 N.d. 5.55
   β-pinene 975 975 0.42 2.43 1.06
   myrcene 990 991 0.36 1.54 0.51
   3-carene 1010 1011 0.26 trace ** 1.76
   α-terpinene 1016 1017 0.18 N.d. 0.42
   limonene 1028 1028 13.36 4.77 1.49
   cis-β-ocimene 1044 1042 N.d. 0.56 N.d.
   trans-β-ocimene 1050 1048 N.d. 0.21 N.d.
   γ-terpinene 1056 1057 0.30 N.d. 0.86
   dihydromyrcenol 1071 1073 0.35 N.d. N.d.
   terpinolene 1086 1088 N.d. N.d. 0.57
   trans-sabinene hydrate 1096 1097 N.d. N.d. 0.19
   α-campholenal 1124 1226 N.d. 2.18 0.47
   trans-pinocarveol 1135 1140 0.54 1.97 0.35
   trans-verbenol 1142 1142 0.51 0.57 0.49
   pinocarvone 1161 1164 N.d. 1.22 N.d.
   borneol 1165 1168 0.36 1.01 N.d.
   isopinocamphone 1174 1175 N.d. 0.29 N.d.
   4-terpineol 1178 1178 0.11 0.84 1.16
   α-terpineol 1189 1191 0.12 7.82 0.23
   α-thujenal 1195 1190 N.d. 0.38 N.d.
   myrtenol 1198 1196 N.d. 1.26 N.d.
   verbenone 1209 1212 N.d. 2.20 N.d.
   trans-carveol 1220 1218 N.d. 2.40 N.d.
   cis-carveol 1230 1229 N.d. 0.59 N.d.
   carvone 1243 1245 N.d. 0.92 N.d.
   carvotanacetone 1246 1249 N.d. 0.47 N.d.
   bornyl acetate 1285 1287 N.d. 3.36 0.30
   piperitenone 1340 1340 N.d. 0.20 -
Sesquiterpene/sesquiterpenois, including: 16.50 12.18 3.78
   δ-elemene 1340 1342 N.d. N.d. 1.17
   α-cubebene 1350 1351 2.43 N.d. N.d.
   α-longipinene 1353 1357 N.d. 0.40 N.d.
   α-copaene 1376 1376 0.41 0.16 N.d.
   β-bourbonene 1383 1385 N.d. 1.21 N.d.
   sativene? 1388 1394 N.d. 0.27 N.d.
   β-cubebene 1391 1392 0.31 N.d. N.d.
   β-elemene 1393 1391 0.28 N.d. N.d.
   longifolene 1405 1405 N.d. 2.08 N.d.
   acora-3,7(14)-diene 1408 1408 N.d. 0.29 N.d.
   β-funebrene 1410 1412 N.d. N.d. 0.29
   β-caryophyllene 1417 1419 3.49 3.29 1.10
   β-copaene 1433 1432 N.d. 0.19 N.d.
   γ-elemene 1433 1433 N.d. N.d. 0.23
   α-humulene 1454 1454 0.30 1.16 N.d.
   γ-muurolene 1478 1479 0.39 0.21 N.d.
   β-selinene 1485 1486 0.55 N.d. N.d.
   valencene 1494 1493 0.47 N.d. N.d.
   α-selinene 1496 1496 0.31 N.d. N.d.
   α-muurolene 1503 1500 0.19 N.d. N.d.
   β-bisabolene 1509 1508 N.d. 0.13 N.d.
   γ-cadinene 1516 1515 0.41 0.19 N.d.
   δ-cadinene 1526 1524 0.96 N.d. 0.14
   selina-4(15),7(11)-diene? *** 1536 - 0.21 N.d. N.d.
   selina-3,7(11)-diene 1542 1541 0.25 N.d. N.d.
   elemol 1555 1550 0.45 N.d. N.d.
   germacrene B 1557 1557 N.d. N.d. 0.49
   caryophyllene oxide 1582 1583 0.66 1.39 N.d.
   cedrol 1600 1600 0.25 N.d. 0.37
   humulene epoxide II 1608 1606 N.d. 0.19 N.d.
   eremoligenol 1630 1630 1.71 N.d. N.d.
   caryophylladienol II 1635 1636 N.d. 0.12 N.d.
   β-eudesmol 1648 1650 1.15 N.d. N.d.
   α-eudesmol 1651 1653 0.92 N.d. N.d.
   14-hydroxy-β-caryophyllene? 1657 1667 N.d. 0.59 N.d.
   unidentified sesquiterpenol C15H22O2 1662 - 0.24 N.d. N.d.
Diterpene hydrocarbons, including: 0.40 N.d. N.d.
   unidentified diterpene C20H32 1762 - 0.15 N.d. N.d.
   unidentified diterpene C20H32 1805 - 0.25 N.d. N.d.
Aliphatic acid, including: 7.3 1.94 6.23
   formic acid 538 535 2.78 trace 1.32
   acetic acid 626 616 3.03 1.94 4.64
   isobutyric acid 765 762 0.72 trace N.d.
   isovaleric acid 842 848 0.32 N.d. 0.14
   2-methylbutanoic acid 862 868 trace N.d. 0.13
   hexanoic acid 983 989 0.27 N.d. N.d.
Aliphatic alcohol, including: 4.87 0.82 1.75
   ethanol 480 484 2.64 0.03 0.81
   isopentanol 730 734 0.26 trace 0.53
   2,3-butanediol, isomer 1 737 734 0.22 N.d. 0.15
   3-methyl-2-buten-1-ol (prenol) 770 771 0.81 N.d. N.d.
   2,3-butanediol, isomer2 782 779 0.52 N.d. 0.35
   1-hexanol 866 870 0.44 N.d. N.d.
   1-heptanol 970 968 N.d. 0.13 N.d.
   1-octanol 1070 1070 N.d. 0.40 N.d.
Esters, including: 2.96 N.d. N.d.
   n-propyl propionate 810 808 0.16 N.d. N.d.
   n-butyl butanoate 997 998 0.32 N.d. N.d.
   n-butyl hexanoate 1193 1192 1.68 N.d. N.d.
   ethyl octanoate 1199 1198 0.17 N.d. N.d.
   glycerol 1,2-diacetate? 1355 - 0.41 N.d. N.d.
   n-hexyl hexanoate 1387 1387 0.22 N.d. N.d.
Aliphatic carbonyls, including: 20.13 12.76 8.90
   acetone 500 501 2.73 2.31 2.28
   isopentanal 648 648 trace N.d. N.d.
   Acetol (hydroxyacetone) 667 673 N.d. N.d. 0.48
   acetoin (3-hydroxy-butanone) 722 722 0.51 N.d. 1.00
   3-methyl-2-butenal (prenal) 780 776 0.79 0.34 0.26
   hexanal 801 801 1.97 071 N.d.
   2-hexenal 851 853 N.d. 0.36 N.d.
   3-heptanone 885 890 N.d. N.d. 0.22
   heptanal 902 902 1.12 0.80 0.19
   trans-2-heptenal 954 956 N.d. 0.13 N.d.
   6-methyl-5-hepten-2-one 986 987 0.28 0.24 0.66
   octanal 1002 1004 0.52 1.68 1.42
   2-nonanone 1092 1089 N.d. 0.95 N.d.
   nonanal 1103 1104 6.34 3.17 1.91
   2,6-(E,Z)-nonadienal 1153 1156 N.d. 0.38 N.d.
   decanal 1208 1207 2.11 0.63 N.d.
   (E)-2-decenal 1261 1261 N.d. 0.40 N.d.
   2-undecanone 1296 1294 N.d. 0.66 N.d.
   undecanal 1309 1308 0.02 N.d. N.d.
Aromatics, including: 7.38 3.99 6.61
   toluene 761 761 2.80 0.37 1.03
   p-xylene 865 866 N.d. N.d. 0.16
   styrene 894 893 N.d. 2.65 N.d.
   benzaldehyde 964 960 0.11 0.46 N.d.
   p-cymene 1022 1023 4.44 0.52 2.14
   m-cymen-8-ol 1181 1184 0.02 N.d. N.d.
   p-cymen-8-ol 1184 1187 0.14 N.d. 0.28
Alkane & alkene, including: 6.00 9.33 32.48
   n-hexane 600 600 4.30 N.d. 1.50
   n-heptane 700 700 1.39 0.18 0.68
   1-octene 790 791 0.31 N.d. 0.30
   n-octane 800 800 N.d. N.d. 0.54
   n-nonane 900 900 trace trace 0.12
   2-methylnonane 962 962 N.d. N.d. 0.13
   n-decane 1000 1000 N.d. trace 6.03
   4-methyldecane 1060 1060 N.d. 0.40 0.25
   2-methyldecane 1063 1063 N.d. 0.18 1.55
   3-methyldecane 1070 1070 N.d. N.d. 0.48
   n-undecane 1100 1100 N.d. 0.45 2.05
   2,6-dimethyldecane 1109 1109 N.d. 0.63 N.d.
   2,9-dimethyldecane 1127 1126 N.d. N.d. 0.13
   6-methylundecane 1163 1062 N.d. N.d. 0.61
   1-dodecene 1190 1193 N.d. N.d. 0.22
   n-dodecane 1200 1200 N.d. 0.98 11.85
   4-methyldodecane 1260 1259 N.d. N.d. 0.15
   2-methyldodecane 1263 1263 N.d. N.d. 0.77
   n-tridecane 1300 1300 N.d. N.d. 0.78
   n-tetradecane 1400 1400 N.d. trace 2.28
   n-pentadecane 1500 150 N.d. 1.64 0.32
   n-heptadecane 1600 1600 N.d. N.d. 0.50
Other, including: 4.25 1.16 1.47
   chloroform 615 615 3.67 N.d. N.d.
   pyridine 742 742 N.d. N.d. 1.10
   furfural 830 834 0.33 0.17 N.d.
   γ-butyrolactone 916 914 N.d. 0.14 N.d.
   3,7,7-trimethyl-1,3,5-cycloheptatriene 967 970 0.25 N.d. 0.37
   γ-caprolactone 1056 1060 N.d. 0.39 N.d.
   4-acetyl-1-methylcyclohexene 1130 1131 N.d. 0.25 N.d.
   2-methylene-6,6-dimethylbicyclo [3.2.0]heptan-3ol 1156 1157 N.d. 0.21 N.d.
NN 4.55 1.98 2.68
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* N.d.—Not detected; ** trace—below 0.01% TIC; *** ?—tentatively.

The second largest group of VOCs was formed by C6–C17 alkanes and alkenes, the contribution of which to the TIC chromatograms varied greatly and ranged from 6% to 32%. It is interesting that even-numbered homologs predominated in terms of their contribution to the TIC. The VOCs contained 17 aliphatic carbonyl compounds, the proportion of which ranged from 7% to 20% of the TIC. The largest amounts were acetone, nonanal and heptanal. In addition, the fugitive emissions contained C2–C8 aliphatic alcohols and C1–C6 acids, as well as seven esters. However, the latter were found in only one of the samples (Pr-1). Of the seven aromatic compounds, toluene and p-cymene were present in the highest amounts in all three samples.

2.2. Extractive Components

Chromatograms of ether extracts of all three propolis samples were formed by peaks of 138 organic compounds, most of which contained polar groups and were recorded in the form of TMS derivatives. The identified compounds could be divided into 12 groups, as shown in Table 2. As in the case of VOCs, the largest group was formed by terpenoids, but its structure was different. It was formed by 10 sesquiterpenes, 22 diterpenes and 13 triterpenes. Sesquiterpenes were present only in small quantities (1.2–1.7% TIC) and only in extracts from two propolis samples. Without exception, all diterpenes were classified as resin acids and related C20 compounds (totarol and neoabietal). Three compounds with retention indices of 2515, 2665 and 2596 were conditionally assigned to this group based on the presence of characteristic ions in the mass spectra and the MS pattern of ion fragmentation. A subgroup of triterpenoids was represented by tetracyclic lanosterol, dihydrolanosterol and masticadienoic acid, as well as pentacyclic compounds of the oleanane, ursane and lupane group. The largest amount (21.4% TIC) and the largest number of triterpenes were found in the extract from sample 1.

Table 2.

Relative group composition (% TIC) of ether extracts of Canarian propolis.

Group of Compounds RI Exp RILit Sample
Pr-1 Pr-2 Pr-3
Sesquiterpene/Sesquiterpenoids, Including: 1.71 N.d. * 1.28
 β-caryophyllene 1417 1419 0.05 N.d. 0.07
 caryophyllene oxide 1583 1583 0.07 N.d. 0.06
 α-copaen-11-ol, TMS 1634 1636 0.13 N.d. N.d.
 elemol, TMS 1637 1638 0.06 N.d. N.d.
 τ-cadinol, TMS 1699 1701 0.05 N.d. N.d.
 α-acorenol, TMS 1723 1722 0.14 N.d. 0.05
 agarospirol, TMS 1734 1734 0.05 N.d. N.d.
 γ-eudesmol, TMS 1744 1741 0.76 N.d. 0.38
 β-eudesmol, TMS 1753 1750 0.40 N.d. 0.18
 (2E,6Z)-farnesol, TMS 1814 1811 0.05 N.d. N.d.
Diterpenoids, including: 10.42 55.18 2.48
 pimaric acid, TMS 2301 2302 0.60 5.47 N.d.
 sandaracopimaric acid, TMS 2319 2318 0.42 1.45 N.d.
 trans-communic acid, TMS 2325 2324 0.17 trace ** 0.11
 isopimaric acid, TMS 2332 2333 1.39 7.68 0.39
 totarol, TMS? *** 2338 3332 0.35 N.d. N.d.
 palustric acid, TMS 2360 3357 N.d. 4.78 N.d.
 diterpene aldehyde C20H30O (MW 286) 2367 - N.d. 0.40 N.d.
 communic acid, TMS 2377 3375 N.d. 3.58 N.d.
 dehydroabietic acid, TMS 2388 2386 1.76 6.93 0.20
 abietic acid, TMS 2414 2414 0.89 8.44 0.14
 13-epi-cupressic acid, di-TMS 2438 2435 0.63 N.d. 0.16
 podocarpic acid, di-TMS? 2482 N.d. 0.17 N.d. N.d.
 neoabietic acid, TMS 2508 2508 N.d. 3.55 N.d.
 unidentified diterpenoid, TMS 2515 N.d. N.d. 1.31 N.d.
 15-hydroxydehydroabietic acid, di-TMS 2540 2536 0.61 1.74 N.d.
 imbricatoloic acid, di-TMS 2550 2548 0.29 1.19 N.d.
 unidentified diterpenoid, TMS 2665 - N.d. 1.51 N.d.
 isocupressic acid, di-TMS 2592 2592 N.d. 0.86 1.48
 unidentified diterpenoid, TMS 2596 - 1.65 3.60 N.d.
 pinifolic acid, di-TMS 2640 2644 0.82 N.d. N.d.
 7a,15-dihydroxydehydroabietic acid, tri-TMS 2748 2744 0.09 0.61 N.d.
 15-hydroxy-7-oxodehydroabietic acid, di-TMS 2787 2789 0.08 N.d. N.d.
Triterpenoids, including: 21.4 7.48 5.31
 unidentified triterpenoid, TMS (393,73,149,69) 3265 - 0.61 N.d. N.d.
 dihydrolanostreol, TMS? 3292 - 0.17 N.d. N.d.
 β-amyrone? 3307 - 0.53 0.12 N.d.
 lanosterol, TMS 3332 3335 0.25 trace 0.30
 β-amyrin, TMS 3350 3347 0.72 1.40 N.d.
 olean-18-en-3-ol ? TMS 3360 - 1.23 0.62 0.3
 α-amyrin, TMS 3380 3378 0.05 2.48 N.d.
 lupeol, TMS 3395 3401 N.d. 0.88 0.20
 cycloartenol? TMS 3407 - 1.16 0.75 N.d.
 9,19-cyclolanostan-3-ol, 24-methylene-? TMS 3468 - 0.68 0.16 N.d.
 -masticadienoic acid? TMS 3702 - 2.29 N.d. 1.04
 unidentified triterpenoid, TMS (95,511,189,526) 3776 - 1.79 N.d. N.d.
 unidentified triterpenoid, TMS 3807 - 1.79 N.d. 0.52
Resorcinol derivatives, including: 1.17 0.54 N.d.
 (Z,Z)-5-heptadec-9,12-dienylresorcinol, di-TMS 2877 2881 0.54 0.41 N.d.
 (5Z)-5-heptadecenylresorcinol, di-TMS 2903 2905 0.23 trace N.d.
 5-heptadecylresorcynol, di-TMS 2908 2911 0.05 trace N.d.
 5-nonadecenylresorcynol, di-TMS 3101 3102 0.35 0.13 N.d.
Salicylic acid derivatives, including: 1.22 N.d. N.d.
 ginkgolic acid, C15:1, di-TMS 2861 2862 0.13 N.d. N.d.
 salicylic acid, 6-heptadecadienyl-, di-TMS 3031 3026 0.10 N.d. N.d.
 ginkgolic acid, C17:1, di-TMS 3059 3056 0.27 N.d. N.d.
 salicylic acid, 6-heptadecyl-, di-TMS 3063 3061 0.11 N.d. N.d.
 salicylic acid, 6-(12-hydroxyheptadecyl)-, tri-TMS 3260 3261 0.61 N.d. N.d.
Lignans, including: 21.29 3.30 6.65
 (+)-epi-sesamin 3140 3140 2.27 0.35 0.73
 fargesin 3201 3202 3.03 0.64 1.02
 eudesmin? (pinoresinol, dimethyl ether) 3250 - 0.76 0.22 0.35
 aschantin 3333 3332 4.84 1.51 1.82
 magnolin 3369 3371 0.95 0.12 0.28
 (+)-magnolin 3388 3388 2.28 N.d. 0.76
 yangambin, isomer 1 3510 3510 1.44 0.27 0.29
 yangambin, isomer 2 3515 3519 2.18 0.69 1.41
 unidentified lignan (430,179,165,181,207) 3568 - 2.58 0.50 N.d.
Aliphatic acids, including: 15.85 10.99 21.18
 azelaic acid, di-TMS 1807 1806 0.13 0.14 0.05
 hexadecanoic acid, TMS 2052 2051 1.92 1.53 1.90
 linoleic acid, TMS 2215 2215 0.22 0.60 0.26
 oleic acid, TMS 2222 2222 2.18 4.14 2.66
 (E)-vaccenic acid, TMS 2229 2233 0.09 N.d. N.d.
 octadecanoic acid, TMS 2249 2250 0.58 0.16 0.40
 (Z)-11-eicosenoic acid 2420 2419 0.07 N.d. N.d.
 3-hydroxyoctadecanoic acid, di-TMS 2429 2429 0.07 N.d. N.d.
 eicosanoic acid, TMS 2448 2447 0.12 N.d. 0.15
 heneicosanoic acid, TMS 2548 2546 0.18 N.d. N.d.
 docosanoic acid, TMS 2644 2645 0.72 N.d. 1.50
 tricosanoic acid, TMS 2743 2747 0.23 N.d. 0.18
 tetracosanoic acid, TMS 2847 2845 3.08 2.84 5.96
 hexacosanoic acid, TMS 3044 3043 1.43 0.24 2.12
 23-hydroxytetradecanoic acid, di-TMS 3115 3118 0.22 0.11 0.24
 octacosanoic acid, TMS 3242 3241 1.24 trace 1.90
 triacontenoic acid, TMS 3422 - N.d. N.d. 0.22
 triacontanoic acid, TMS 3442 3440 1.68 N.d. 1.31
 dotriacontenoic acid, TMS 3623 - N.d. N.d. 0.20
 dotriacontanoic acid, TMS 3642 3641 0.60 N.d. 0.58
 tetratriacontanoic acid, TMS 3838 3838 0.86 N.d. 0.61
Aliphatic alcohols, including: 1.01 N.d. 2.99
 1-octadecanol, TMS 2164 2165 0.09 N.d. N.d.
 1-tetracosanol, TMS 2753 2754 0.43 N.d. 0.26
 1-hexacosanol, TMS 2949 2951 0.22 N.d. 0.20
 1-octacosanol, TMS 3148 3148 0.24 N.d. 0.36
 1-triacontanol, TMS 3346 3346 N.d. N.d. 1.13
 1-dotriacontanol, TMS 3546 3542 N.d. N.d. 0.66
 1-tetratriacontanol, TMS 3742 3741 N.d. N.d. 0.26
Aliphatic carbonyls, including: 0.43 N.d. N.d.
 tricosanal 2533 2534 0.36 N.d. N.d.
 hexacosanal 2835 2833 0.07 N.d. N.d.
Alkane & alkenes, including: 14.94 28.20 47.59
 n-heptadecane 1700 1700 N.d. N.d. 0.09
 n-nonadecane 1900 1900 0.14 trace 0.37
 n-eicosane 2000 2000 N.d. N.d. 0.07
 n-heneicosane 2100 2100 0.26 1.37 0.80
 9-(Z)-tricosene 2270 2271 N.d. N.d. 0.29
 n-tricosane 2300 2300 1.01 6.87 2.34
 n-tetracosane 2400 2400 0.17 N.d. 0.35
 9-pentacosene 2473 2475 0.09 0.51 0.35
 7-pentacosene 2478 2482 N.d. N.d. 0.09
 n-pentacosane 2500 2500 1.63 2.87 4.01
 n-hexacosane 2600 2600 0.36 N.d. 1.48
 n-heptacosane 2700 2700 3.94 0.70 8.37
 13-methylheptacosane 2731 2731 0.23 N.d. 0.40
 n-octacosane 2800 2800 0.27 N.d. 0.58
 2-methyloctacosane 2860 2858 N.d. N.d. 0.15
 9-nonacosene 2876 2875 N.d. N.d. 1.87
 7-nonacosene 2885 2882 N.d. 2.63 N.d.
 n-nonacosane 2900 2900 2.67 0.70 6.72
 9-triacontene 2983 2984 N.d. N.d. 0.33
 n-triacontane 3000 3000 0.19 N.d. 0.36
 9-hentriacontene 3073 3075 0.48 3.44 2.75
 7-hentriacontene 3081 3082 0.89 4.21 3.39
 n-hentriacontane 3100 3100 1.42 N.d. 4.09
 9-tritriacontane 3276 3277 0.82 4.24 5.49
 7-tritriacontane 3282 3282 0.26 N.d. N.d.
 n-tritriacontane 3300 3300 0.31 N.d. 0.56
Other, including: 4.10 5.48 0.14
 glycerol, tri-TMS 1293 1294 trace 2.11 0.14
 3,4,5-trimethoxybenzoic acid, TMS 1832 1833 0.18 N.d. N.d.
 quinic acid, penta-TMS 1900 1900 N.d. 0.61 N.d.
 1-O-octadecyl glycerol, di-TMS 2699 2695 N.d. 2.09 N.d.
 1-O-eicosyl glycerol, di-TMS 2892 2893 1.01 0.67 N.d.
 tetracosyl hexadecanoate >4000 - 2.91 N.d. N.d.
NN 6.84 10.50 3.49
Open in a new tab

* N.d.—Not detected; ** trace—below 0.01% TIC; *** ?—tentatively.

The second largest group was formed by 16 C17–C33 n-alkanes and 10 C23–C33 alkenes; the contribution of this group to the TIC was significant and amounted to 15–48%. The group of aliphatic acids (11–21% TIC) included 21 compounds with a number of carbon atoms from 9 (azelaic acid) to 34. Aliphatic compounds also included relatively small amounts of normal C18–C34 alcohols and aldehydes, and these were not detected in one of the samples (Pr-2).

The group of aromatic compounds included four substituted alkyl and alkenyl resorcinols, five alkyl and alkenyl salicylates and nine furofuranoid lignans. If representatives of the last subgroup were present in the extracts of all three propolis samples, then resorcinol derivatives were found in two of them and substituted salicylates only in one.

The contribution of compounds not assigned to any of the 12 groups amounted to 0.1–5.5% TIC, and the share of unidentified components accounted for 3.5–10.5% TIC.

3. Discussion

Until now, there has been only one report on the chemical composition of Canarian (Gran Canaria) propolis [32]. Although Tenerife and Gran Canaria are located close to each other, the composition of their vegetation cover is markedly different: they have many endemic species that are found only on one of them [33]. Therefore, it seems interesting to compare the chemical composition of propolis originating from these islands.

The data obtained on the composition of propolis from Tenerife and Gran Canaria differ in many aspects, and in some cases, this may be explained by differences in the experimental technique. For example, the list of VOCs shown in Table 1 determined by the HS-SPME/GC-MS method includes a much larger number of compounds than those isolated from propolis by hydrodistillation, which loses the most volatile compounds. The list of extracted compounds (Table 2) does not contain sugars and related sugar acids and alcohols, while in the work [32], their share in one propolis sample accounts for approximately 56% of TIC, and in the second, approximately 10% of TIC. This is due to the fact that the weakly polar diethyl ether we used for extraction dissolves practically no polar sugars, unlike 70% aqueous ethanol.

Another difference is that the authors of the cited work note that the chemical composition of the extracts from both Gran Canaria propolis samples is very similar, while the extracts from the three Tenerife samples show significant differences. For example, in the extract from sample Pr-2, sesquiterpenes, aliphatic alcohols and carbonyl compounds were not detected even at trace levels, while extract Pr-3 did not contain phenolic compounds. These differences may be due to the fact that the Tenerife propolis samples were collected from apiaries located at different altitudinal levels (from 600 to 1400 m above sea level) with different floristic compositions.

A distinctive characteristic of the chemical composition of the studied propolis samples from Tenerife is the presence of a large number and, in two out of three samples, a high content of diterpenoids, mainly resin acids, while in the case of propolis from Gran Canaria, one compound of this class was found with a relative contribution of 0.1% TIC. The most likely plant source of resin acids in propolis from Tenerife is the secretion of an endemic pine species, Pinus canariensis. There is no information in the available literature on the chemical composition of the resinous secretions of this species, and our assumption is based on the qualitative composition of diterpene acids in propolis, characteristic of resins of all pine species [34]. The lower boundary of closed pine forests in Tenerife lies at an altitude of 1000–1200 m above sea level, but individual trees are found in plantings right up to the coastline. Thus, the lowest content of resin acids in the extract of sample Pr-3, collected in the San Miguel region at an altitude of about 600 m a.s.l., can be explained by the limited availability of this source of resin for bees.

Another difference concerns the composition of phenolic compounds, represented in Tenerife propolis by alkyl derivatives of resorcinol and salicylic acid, but absent in propolis samples from Gran Canaria. A probable plant source of these lipids is Mangifera indica (Anacardiaceae), brought from Indonesia to the Canary Islands at the end of the 18th century and widely cultivated on all the islands of the archipelago. These compounds were first discovered in Indonesian propolis [35] and later in Thai propolis [36]. Both publications name M. indica as the source of these compounds. Their absence in sample Pr-3, as well as in propolis samples from Gran Canaria, can be explained by the inaccessibility of mango plants to bees. On the other hand, a similar feature of the chemical composition of propolis from Gran Canaria and Tenerife is the high content of furofuranoid lignans. However, the plant precursor of these compounds, which have beneficial effects on brain function [37,38,39], including protection against Parkinson’s disease, Alzheimer’s disease, stroke, and other neurodegenerative diseases, remains unknown.

Thus, based on our research and earlier results [32], we can preliminarily state that Canarian propolis is significantly different in chemical composition from known types of propolis from the mid-latitude and tropical zones, and its distinctive feature is a high content of furofuran lignans.

4. Materials and Methods

4.1. Chemicals and Material

Silylation agent, bis(trimethylsilyl)trifluoroacetamide (BSTFA) with addition of 1% of trimethylchlorosilane, was purchased from TriMen Chemicals (Lodz, Poland).

Propolis samples were collected by one of the authors of the article in January, April and August 2023 from hives in different apiaries. Two samples were obtained in the Santiago del Teide area. The first of them (Pr-1) comes from an apiary located at an altitude of 1020 m above sea level (28°8′ N–16°47′ W) and the second (Pr-2) from an apiary located at an altitude of 1440 m above sea level (28°17′ N–16°46′ W). The third sample (Pr-3) was obtained from an apiary in the San Miguel area at an altitude of about 630 m above sea level (28°05′ N–16°37′ W).

4.2. Determination of Volatiles

Determination of the volatile components of the propolis was carried out using HS-SPME/GC-MS. Dry propolis (1.0–1.5 g) was frozen at −18 °C, crushed to a particle size of 1–2 mm and placed in a 16 mL HS-SPME vial with a screw cap and a silicone membrane. The membrane was pierced with the needle of a SPME device with DVB/CAR/PDMS fiber. Every 15–20 min the contents of the vial were shaken to mix the gas phase. After 2 h of exposure at room temperature (21 ± 1 °C), the fiber was placed into the injection port of an HP7890A gas chromatograph with a 5975C VL MSD Triple-Axis Detector (Agilent Technologies, Santa Clara, CA, USA) for 15 min. The apparatus was fitted with an HP-5ms capillary column (30 m × 0.25 mm i.d., 0.25 μm film thickness) with electronic pressure control and a split/splitless injector. The latter was operated at 220 °C in splitless mode. The helium flow rate through the column was 1 mL min−1. The initial column temperature was 40 °C and rose to 180 °C at a rate of 3 °C min−1. The MSD detector acquisition parameters were as follows: the transfer line temperature was 280 °C, the MS source temperature was 230 °C, and the MS quad temperature was 150 °C. The EI mass spectra were obtained at 70 eV of ionization energy. Detection was performed in the full scan mode. After integrating and summing the areas of the recorded peaks, the fraction of separated components in the total ion current (TIC) was calculated. All analyses were carried out in duplicate.

In a separate experiment, the retention times of the n-alkanes used as standards in the calculation of chromatographic retention indices on the above-mentioned GC/MS equipment used were determined. From 0.5 to 10 µL of C5–C17 n-alkanes were injected into a 16 mL vial for HS-SPME with a silicone membrane containing 5 mL of pure glycerol using a 10 µL microsyringe, increasing the dose for each subsequent homologue. The mixture was thoroughly mixed, and DVB/CAR/PDMS fiber was introduced into the gas phase above it for 2–3 s. The chromatogram of reference alkanes was recorded under the above conditions.

4.3. Determination of Extractive Components

After concentrating the volatile compounds on the sorption fiber for SPME, the propolis was transferred from the vial to a 50 mL conical flask, and 25 mL of diethyl ether was added and stirred on a magnetic stirrer for 30 min. The solvent was separated, and the extraction was repeated twice. The combined extracts were filtered through a paper filter, and the ether was completely removed on a rotary evaporator. Five milligrams of the viscous residue was transferred into a 2 mL vial and dissolved in 220 µL of dry pyridine, 80 µL of BSTFA was added and the resulting solution was heated for 30 min at a temperature of 60 °C.

The resulting TMS derivatives were separated on the above-mentioned GC-MS apparatus, equipped with the same HP-5ms column. The initial temperature of the column thermostat was 50 °C and increased linearly at a rate of 3 °C min−1 to 320 °C. The chromatograph injector, heated to 280 °C, operated with a division of the carrier gas flow (1:10). The helium flow rate through the column was 1 mL min−1 in constant flow mode.

Under the given conditions, a calibration mixture of C10–C40 n-alkanes was separated, and the recorded retention times were used to calculate RIExp values in the chromatograms of the extracts.

4.4. Component Identification

To identify the components, mass spectrum and chromatographic retention index (RI) were used. The mass spectrometric identification of volatiles was carried out using an automatic system for GC-MS data processing supplied by the NIST 14 library, as well as by computer search libraries containing the spectra and RI values from Adams’ [40] and Tkachev’s [41] collections. The RI values of TMS derivatives were compared with those in the NIST collection [42], as well as with those presented in a recently published atlas containing mass spectra and retention indices of more than 1750 organic components of various origins in the form of TMS derivatives, including bee products [43]. An identification was considered reliable if the results of the computer search of the mass spectra library were confirmed by the experimental RIExp values, i.e., if their deviation from the published database values (RILit) did not exceed ±10 u.i. If the result of mass spectrometric identification was not confirmed chromatographically due to the absence of RI values in the available databases, or if the RIExp and RILit values differed by more than 10 u.i., the identification was considered tentative (the names of the tentatively identified compounds in Table 1 and Table 2 are followed by a question mark).

Acknowledgments

The study was carried out within the WZ/WB-INL/3/2021 framework and financed by science funds from the Ministry of Science and Higher Education in Poland.

Author Contributions

Conceptualization and writing–original draft preparation, V.A.I.; investigation and visualization, A.Z. and A.M.D.; resources and data curation, A.M.D. All authors have read and agreed to the published version of the manuscript.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The study did not report any data.

Conflicts of Interest

The authors declare that there no conflicts of interest and that they have no actual or potential competing financial interest.

Funding Statement

This research received no external funding.

Footnotes

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