Volatile Constituents of Some Myrtaceous Edible and Medicinal Fruits from the Brazilian Amazon

Native and exotic fruits from the Amazon have varied characteristics, with aroma being a decisive factor in their acceptance for medicinal use as a nutraceutical supplement. This work aimed to analyze the chemical constituents of the volatile concentrates of some Myrtaceous fruit species sampled in the Brazilian Amazon. The fruit’s pulps were subjected to simultaneous distillation–extraction, and gas chromatography–mass spectrometry was used to analyze their volatile chemical composition. In the volatile concentrate of Eugenia stipitata (Araçá-boi) α-pinene (17.5%), citronellyl butanoate (15.6%), and pogostol (13.5%) were identified as primary constituents; Eugenia uniflora (Ginja) concentrate comprised curzerene (30.5%), germacrone (15.4%), atractylone (13.1%), and (E)-β-ocimene (11.1%); in Myrciaria dubia (Camu-Camu), α-pinene (55.8%), (E)-β-ocimene (13.1%), and α-terpineol (10.0%) were present; in Psidium guajava (Goiaba) were (2E)-hexenal (21.7%), hexanal (15.4%), caryophylla-4(12),8(13)-dien-5-β-ol (10.5%), caryophyllene oxide (9.2%), and pogostol (8.3%); and in Psidium guineense (Araçá), limonene (25.2%), ethyl butanoate (12.1%), epi-β-bisabolol (9.8%), and α-pinene (9.2%) were the main constituents. The analyzed volatile concentrates of these fruit species presented a significant diversity of constituents with a predominance of functional groups, such as monoterpenes, sesquiterpenes, and fatty acid derivatives, originating from the plant’s secondary metabolism and playing an important role in their nutritional and medicinal uses.


Introduction
The Amazon region is the last stronghold of potentially valuable plants awaiting domestication and economic exploitation.The use of exotic fruits that have been introduced worldwide, such as apples and oranges, has undergone improvement across centuries in a continuous process, the memory of whose initiation has already been lost to time.Humanity began to domesticate plants around ten thousand years ago, while the history of the domestication of Amazonian fruits has only begun to be written [1].
Several fruit species native to the Amazon have been commercialized and consumed for medicinal and nutritional purposes.They are known for having a pleasant flavor and juicy pulp, representing significant economic potential; however, they still require domestication and genetic improvement studies.These studies must be resumed urgently due to increases in deforestation, which introduces a high risk of species extinction, in addition to the fact that some of these fruits still need to be adequately studied and scientifically classified [2][3][4][5][6][7].
A significant variety of fruits are consumed in Brazil, representing one of the primary sources of vitamins, minerals, fiber, aromas, and antioxidants in the diet of the native population.In this context, Brazil is considered one of the great centers of global biodiversity, A significant variety of fruits are consumed in Brazil, representing one of the primary sources of vitamins, minerals, fiber, aromas, and antioxidants in the diet of the native pop ulation.In this context, Brazil is considered one of the great centers of global biodiversity and has many tropical fruits with different and pleasant flavors [2].Due to its territoria extension, geographical position, climate, and soil, Brazil produces fruits in tropical, sub tropical, and temperate areas, being the third largest fruit producer in the world, after China and India, with 42 million tons produced per year and more than 2.2 million hec tares of fruit crops planted across the country.More than 30% of fresh fruits produced in Brazil are exported to different parts of the world [3,4].
Given this context, the region of the Middle Amazon River, spanning the State of Pará and made up of the municipalities of Óbidos, Juruti, Oriximiná, Terra Santa, and Santa rém, has made available several species of native fruits, some produced on a large scale and sold for different purposes, in addition to others fruits unnoticed by consumers, re sulting from limited stocks and logistics (IBGE, 2019) [8].In addition to nutritional value other attributes existing in native fruits and those cultivated in this region of the Middle Amazon River are their outstanding aromas, composed of a significant diversity of differ ent volatile constituents which, despite representing a low percentage of the total mass o the fruit (around 0.05% to 1.0%), contribute to the taste, flavor, and acceptability of these fruits.Furthermore, scientific knowledge of the chemical constituents responsible for the characteristic aromas of tropical fruits is justified by the importance they can play in the quality of their products.The attractive tropical fruit flavor has stimulated growing con sumer interest around the world.In this context, the Amazon stands out for its outstand ing natural diversity of fruits, with characteristic flavors that require the identification o their volatile constituents, also representing a promising area for research into the typica aromas of this region [7].
In fruits, the biosynthetic routes for forming volatile constituents involve enzymatic reactions, producing volatile components such as terpenes, sulfur compounds, derivatives of fatty acids, derivatives of amino acids, and those originating from fermentation.The enzymatic generation of volatile constituents derived from fatty acids is one of the main routes that leads to the formation of the characteristic flavor of fruits.As reactions occur the aroma of the fruit can change, and aldehydes and ketones, for example, can be con verted into the corresponding alcohols, presenting more prominent aromas [9].
The selection of fruits was made considering their seasonality and maturity, integral characteristics, natural shape without deformations, and absence of microbiological contamination.The fruits were washed in running water, measured, and weighed, and their pulp (edible part) was processed to remove seeds and skins.Then, the fruit pulps were frozen for subsequent analysis.

Obtaining and Analyzing Volatile Concentrates
The fruit pulps were subjected to microdistillation-extraction in a Likens and Nickersontype apparatus (30 g in total, 2 h, duplicate) to obtain their volatile concentrates, using n-pentane (99% HPLC grade, 3 mL) as the solvent [10].
The volatile concentrates were subjected to GC and GC-MS analysis.This was performed on a GCMS-QP2010 Ultra system (Shimadzu Corporation, Tokyo, Japan), equipped with an AOC-20i auto-injector and the GCMS-Solution software (Shimadzu, Japan) containing the Adams (2007) and Mondello (2011) libraries [11,12].An Rxi-5ms (30 m × 0.25 mm; 0.25 µm film thickness) silica capillary column (Restek Corporation, Bellefonte, PA, USA) was used.The conditions of analysis were as follows: injector temperature, 250 • C; oven temperature programming, 60-240 • C (3 • C min −1 ); helium as the carrier gas, adjusted to a linear velocity of 36.5 cm s −1 (1.0 mL min −1 ); split mode injection (split ratio 1:20) of 1.0-2.0µL of the n-pentane solution; electron ionization at 70 eV; and ionization source and transfer line temperatures of 200 and 250 • C, respectively.The mass spectra were obtained by automatically scanning every 0.3 s, with mass fragments in the range of 35-400 m/z.The retention index was calculated for all volatile components using a homologous series of C8-C40 n-alkanes (Sigma-Aldrich, Milwaukee, WI, USA) according to the linear equation of van den Dool and Kratz (1963) [13].Individual components were identified by comparing their retention indices and mass spectra (molecular mass and fragmentation pattern) with those existing in the GCMS-Solution system libraries [11,12].The quantitative data regarding the volatile constituents were obtained using a GC2010 Series gas chromatograph, operated under conditions similar to the GC-MS system.The relative amounts of individual components were calculated by peak-area normalization using a flame ionization detector (GC-FID).Chromatographic analyses were performed in duplicate.

Multivariate Statistical Analysis
Principal component analysis (PCA) was applied to verify the interrelationship of the samples of volatile concentrates analyzed with the classes of identified compounds, including monoterpene hydrocarbons (MH), oxygenated monoterpenes (OM), sesquiterpene hydrocarbons (SH), oxygenated sesquiterpenes (OS), benzenoids/phenylpropanoids (BP), and fatty acid derivatives (FA).The data matrix was standardized for multivariate analysis by subtracting the mean and dividing it by the standard deviation.Hierarchical cluster analysis (HCA), considering the Euclidean distance and complete linkage, was used to verify the similarity of the samples based on the distribution of the constituents selected in the PCA analysis (Software Minitab, free version 390, Minitab Inc., State College, PA, USA) [14].

Eugenia stipitata McVaugh-Myrtaceae
Botanical description: It is an ornamental leafy tree or shrub known as Araçá-boi.It is 3.0-15.0m tall, densely branched, and lacks apical dominance.The stem is brown to reddish-brown, the bark is flaky, and young branches are covered with short, velvety, brown hairs that are lost with age.Leaves are arranged in an opposing formation, and are simple and without stipule.The petiole is short, at 3 mm long; the leaf blade is ovate to somewhat broadly elliptic, and is 8-19 cm long and 3.5-9.5 cm wide.The apex of the leaves acuminates, while the base is rounded and often subcordate.The leaf margins are entire, and the leaves are dull in color; they are dark green on top, with 6-10 pairs of impressed lateral veins, and pale green, shortly pilose, with scattered hairs underneath.The inflorescence racemose pedicles are long, and the bracteoles are linear and 1-2 mm long.The calyx lobes are rounded, broader than long, and overlap in the bud.There are five petals, which are white in color, obovate and ciliate, and 7-10 mm long and 4 mm wide.There are about 70 stamens of 6 mm in length.There are four locules, each locule containing 5-8 ovules that are 5-8 mm long.The fruits are oblate or spherical berries measuring 2-10 × 2-12 cm, weighing 50-750 g.They are light green at first, and turn pale or orange-yellow when ripe.They are soft, with a thin, velvety skin enclosing a juicy, thick pulp that accounts for as much as 60% of the fresh fruit.There are approximately 12 seeds in each fruit (see Figure 2) [15].They fruit from November to May in all Amazon regions.The pleasant-tasting Araçá-boi fruit is rich in vitamins A, B1, and C, and it is used in soft drinks, juices, ice creams, and sweets.
Botanical description: It is an ornamental leafy tree or shrub known as Araçá-boi.I is 3.0-15.0m tall, densely branched, and lacks apical dominance.The stem is brown to reddish-brown, the bark is flaky, and young branches are covered with short, velvety brown hairs that are lost with age.Leaves are arranged in an opposing formation, and are simple and without stipule.The petiole is short, at 3 mm long; the leaf blade is ovate to somewhat broadly elliptic, and is 8-19 cm long and 3.5-9.5 cm wide.The apex of the leaves acuminates, while the base is rounded and often subcordate.The leaf margins are entire and the leaves are dull in color; they are dark green on top, with 6-10 pairs of impressed lateral veins, and pale green, shortly pilose, with scattered hairs underneath.The inflo rescence racemose pedicles are long, and the bracteoles are linear and 1-2 mm long.The calyx lobes are rounded, broader than long, and overlap in the bud.There are five petals which are white in color, obovate and ciliate, and 7-10 mm long and 4 mm wide.There are about 70 stamens of 6 mm in length.There are four locules, each locule containing 5-8 ovules that are 5-8 mm long.The fruits are oblate or spherical berries measuring 2-10 × 2-12 cm, weighing 50-750 g.They are light green at first, and turn pale or orange-yellow when ripe.They are soft, with a thin, velvety skin enclosing a juicy, thick pulp that ac counts for as much as 60% of the fresh fruit.There are approximately 12 seeds in each frui (see Figure 2) [15].They fruit from November to May in all Amazon regions.The pleasant tasting Araçá-boi fruit is rich in vitamins A, B1, and C, and it is used in soft drinks, juices ice creams, and sweets.Geographic distribution: It is a fruit tree native to the Peruvian Amazon.It is found in the wild in many areas of the region, and it has proliferated across the Ucaiali Rive basin in Peru.In the state of Amazonas, Brazil, it is cultivated on a domestic scale by the caboclo and indigenous populations of the Solimões River [5].See Table 1 concerning the volatile constituents identified in Eugenia stipitata.[5].
Geographic distribution: It is a fruit tree native to the Peruvian Amazon.It is found in the wild in many areas of the region, and it has proliferated across the Ucaiali River basin in Peru.In the state of Amazonas, Brazil, it is cultivated on a domestic scale by the caboclo and indigenous populations of the Solimões River [5].See Table 1 concerning the volatile constituents identified in Eugenia stipitata.

Eugenia uniflora L.-Myrtaceae
Botanical description: It is a shrub standing at between 1.5 and 8.0 m tall that branches from the base.It is known as Ginja or Pitanga.The leaves are simple, arranged opposite to each other, chartaceous, ovate, 1.5-5.0m long and 1.0-3.5 m wide, dark green and shiny, and shortly petiolate; they have a rounded base, and a short obtuse-acuminate apex.Flowers are solitary or in groups of 2 to 3, axillary, and with filiform pedicels 2-3

Eugenia uniflora L.-Myrtaceae
Botanical description: It is a shrub standing at between 1.5 and 8.0 m tall that branches from the base.It is known as Ginja or Pitanga.The leaves are simple, arranged opposite to each other, chartaceous, ovate, 1.5-5.0m long and 1.0-3.5 m wide, dark green and shiny, and shortly petiolate; they have a rounded base, and a short obtuse-acuminate apex.Flowers are solitary or in groups of 2 to 3, axillary, and with filiform pedicels 2-3 cm long.The corolla of the flower has four white petals, is slightly fragrant, and has numerous stamens.The fruit has an oblate berry 2-3 cm in diameter with 7-10 longitudinal buds, a persistent calyx, and smooth, shiny skin that is red when ripe.The orange pulp is juicy, has a sweet flavor, is a little astringent, and contains 1-2 greenish-white seeds [5] (Figure 4).Fruiting has been observed throughout the year.The Ginja, or Pitanga, fruit has a pleasant flavor and is consumed fresh, in salads, and in the preparation of jellies and ice creams.

Myrciaria dubia (Kunth) McVaugh-Myrtaceae
Botanical description: Known as Camu-Camu, it is a small shrub typically measuring 1-3 m, but it can reach up to 8 m in height.The leaves are simple and oriented opposite to one another.They are elliptical or broadly ovate in shape, 6-10 cm long and 1.5-3.0cm wide, and have an obtuse or rounded base, long-acuminate apex, and delicate lateral veins.Axillary inflorescences are formed by subsessile flowers arranged in decussate pairs, and the flowers are white and fragrant.The fruit is a spherical berry measuring 2.0-2.5 cm in diameter, with thin, smooth, shiny skin that is red to blackish-purple in color.It has a slightly pinkish juicy pulp that contains two seeds [5] (Figure 6).This species fruits from November to March in all Amazon regions.The Camu-Camu fruit has an acidic flavor due to its vitamin C content and is used in soft drinks, ice cream, liqueur, jellies, and sweets.

Myrciaria dubia (Kunth) McVaugh-Myrtaceae
Botanical description: Known as Camu-Camu, it is a small shrub typically measuring 1-3 m, but it can reach up to 8 m in height.The leaves are simple and oriented opposite to one another.They are elliptical or broadly ovate in shape, 6-10 cm long and 1.5-3.0cm wide, and have an obtuse or rounded base, long-acuminate apex, and delicate latera veins.Axillary inflorescences are formed by subsessile flowers arranged in decussate pairs, and the flowers are white and fragrant.The fruit is a spherical berry measuring 2.0-2.5 cm in diameter, with thin, smooth, shiny skin that is red to blackish-purple in color.It has a slightly pinkish juicy pulp that contains two seeds [5] (Figure 6).This species fruits from November to March in all Amazon regions.The Camu-Camu fruit has an acidic flavor due to its vitamin C content and is used in soft drinks, ice cream, liqueur, jellies, and sweets.Geographic distribution: This species is distributed northwest of the Brazilian Amazon, and across Peru and Venezuela, in semi-flooded areas.See Table 3 concerning the volatile constituents identified in Myrciaria dubia.
Franco and Shibamoto (2000) [16] also identified α-pinene, limonene, and β-caryophyllene as the major constituents of the volatile concentrate of Camu-Camu fruit collected in Manaus, Brazil.Furthermore, Quijano and Pino (2007) [28] highlighted limonene, α-terpineol, and α-pinene as significant components of a volatile concentrate extracted from fruits sampled in Caquetá, Colombia.The characterization of the aroma of Camu-Camu was recently reported, and limonene, (E)-caryophyllene, a-pinene, and isoamyl acetate were the compounds that most contributed to the fruity, herbal, citrus, and woody notes of the M. dubia fruit, also collected in Caquetá, Colombia [29].The essential oil from M. dubia leaves sampled in Belém, Brazil exhibited α-pinene, (E)-caryophyllene, and caryophyllene oxide as its primary constituents [30].Franco and Shibamoto (2000) [16] also identified α-pinene, limonene, and β-caryophyllene as the major constituents of the volatile concentrate of Camu-Camu fruit collected in Manaus, Brazil.Furthermore, Quijano and Pino (2007) [28] highlighted limonene, αterpineol, and α-pinene as significant components of a volatile concentrate extracted from fruits sampled in Caquetá, Colombia.The characterization of the aroma of Camu-Camu was recently reported, and limonene, (E)-caryophyllene, a-pinene, and isoamyl acetate were the compounds that most contributed to the fruity, herbal, citrus, and woody notes of the M. dubia fruit, also collected in Caquetá, Colombia [29].The essential oil from M. dubia leaves sampled in Belém, Brazil exhibited α-pinene, (E)-caryophyllene, and caryophyllene oxide as its primary constituents [30].

Psidium guajava L.-Myrtaceae
Botanical description: It is a small tree, ranging in height from 10-12 m.The stems are irregular, tortuous, very branched, and light green, with quadrangular branches.The bark is thin, smooth, and greenish-brown, and exfoliates frequently.The leaves are simple, opposite in orientation, and have a short petiole.The texture of the leaves is sub-coriaceous, and they are elliptical in shape, 5-15 cm long, and 4-6 cm wide, with an obtuse, acute, or sub-acuminate apex, and an obtuse-rounded base.The lateral ribs are parallel, conspicuous, and straight.The flowers are axillary, solitary, and have a tubular-swollen hypanthium and thick greenish-white sepals.Each flower has four to five white petals, which are rounded and very deciduous, and there are numerous white stamens.The ovary is positioned inferiorly.The fruit is a rounded, ovoid, or pyriform berry of varying size, with greenish or yellow skin and numerous seeds.It is fleshy and edible [5] (Figure 8).Fruiting in two periods, from April to June/July and from November to January/February, the Goiaba is much appreciated in its natural state, with its sweet, aromatic pulp.Its primary uses are in sweets, jams, jellies, juices, and ice creams.Geographic distribution: It is a fruit of pre-Columbian culture, originating from Mexico to Brazil, currently cultivated in almost all New and Old-World tropical countries.See Table 4 concerning the volatile constituents identified in Psidium guajava.Geographic distribution: It is a fruit of pre-Columbian culture, originating from Mexico to Brazil, currently cultivated in almost all New and Old-World tropical countries.See Table 4 concerning the volatile constituents identified in Psidium guajava.

Psidium guineense Sw.-Myrtaceae
Botanical description: It is a species of variable size, ranging in height from 0.7 to 6.0 m.The leaves are elliptical or obovate, 8-15 cm long and 4-7 cm wide, with an obtuse or rounded apex and base.The underside surface of the leaf is more hairy, and the lateral veins exist in 8-10 pairs.The inflorescences are isolated flowers or small axillary dichasia containing up to three flowers.The flowers comprise a white corolla with free shellshaped petals facing downwards, and around 200 stamens.The fruit is a yellowish-white globose berry, about 4 cm in diameter, containing numerous 2-3 mm seeds, hard test, and a creamy-white pulp, which is quite acidic [6] (Figure 10).It flowers from June to December, and fruits from October to March.The fruits are naturally consumed in soft drinks, ice cream, sweets, and liqueur.Mahattanatawee and co-workers (2005) [32] identified hexanal and (E)-caryophyllene as the major constituents of the volatile concentrate of Goiaba fruit sampled in Florida, USA.Also, Chen, Sheu, and Wu (2006) [33] highlighted (E)-caryophyllene, globulol, αpinene, 1,8-cineole, hexanal, and ethyl hexanoate as significant components in the volatile concentrate of Goiaba fruit collected in Linnei, Taiwan.The odor-active compounds of a Goiaba specimen sampled in Alquizar, Cuba, comprised (E)-caryophyllene, hexanal, and 1-hexanol as the principal constituents [34].In Brazil, the behavior of Goiaba fruit volatile compounds was found to change throughout the maturation stages: in immature fruits, the aldehydes (E)-2-hexenal and (Z)-3-hexenal predominated, and in mature fruits, the esters (Z)-3-hexenyl acetate and (E)-3-hexenyl acetate, and the sesquiterpenes (E)-caryophyllene, α-humulene, and β-bisabolene were the primary constituents [35].The major constituents of the essential oil of leaves and fruits from a specimen of Goiaba sampled in Cairo, Egypt, were (E)-caryophyllene and limonene for the fruit, and (E)-caryophyllene and selin-7(11)en-4α-ol for the leaves [36].

Psidium guineense Sw.-Myrtaceae
Botanical description: It is a species of variable size, ranging in height from 0.7 to 6.0 m.The leaves are elliptical or obovate, 8-15 cm long and 4-7 cm wide, with an obtuse or rounded apex and base.The underside surface of the leaf is more hairy, and the lateral veins exist in 8-10 pairs.The inflorescences are isolated flowers or small axillary dichasia containing up to three flowers.The flowers comprise a white corolla with free shell-shaped petals facing downwards, and around 200 stamens.The fruit is a yellowish-white globose berry, about 4 cm in diameter, containing numerous 2-3 mm seeds, hard test, and a creamywhite pulp, which is quite acidic [6] (Figure 10).It flowers from June to December, and fruits from October to March.The fruits are naturally consumed in soft drinks, ice cream, sweets, and liqueur.Geographic distribution: Araçá occurs in regions ranging from Mexico to the West Indies, passing through Brazil and reaching Argentina.The species has an African name due to a mistake by Swartz, who assumed it was introduced to the Antilles from Africa.Araçá is cultivated, and also occurs spontaneously, throughout the Amazon region in open areas, fields, and pastures.See Table 5 concerning the volatile constituents identified in Psidium guineense.Geographic distribution: Araçá occurs in regions ranging from Mexico to the West Indies, passing through Brazil and reaching Argentina.The species has an African name due to a mistake by Swartz, who assumed it was introduced to the Antilles from Africa.Araçá is cultivated, and also occurs spontaneously, throughout the Amazon region in open areas, fields, and pastures.See Table 5 concerning the volatile constituents identified in Psidium guineense.In the volatile concentrate of P. guineense, monoterpene hydrocarbons (36.4%), fatty acid derivatives (29.8%), oxygenated sesquiterpenes (18.9%), and sesquiterpene hydrocarbons (12.1%) predominated, complemented by a minor content of benzenoids/phenylpropanoids (1.1%) and oxygenated monoterpenes (0.4%).The primary constituents of Araçá were limonene (25.2%), ethyl butanoate (12.1%), epi-β-bisabolol (9.8%), α-pinene (9.2%), and ethyl hexanoate (5.9%), comprising 62.2% of its volatile concentrate (see Figure 11).main constituents of the fruits and leaves of an Araçá specimen collected in Hidrolândia, Goiás, Brazil, were also reported, including (2Z,6E)-farnesol, α-copaene, δ-cadinene, γhimachalene, and cubenol in the fruits, and (2Z,6E)-farnesol, α-copaene, muurola-4,10( 14)-dien-1-β-ol, and epi-α-cadinol in leaves [39].Volatile compounds isolated from Araçá leaves from various locations have also been reported, with β-bisabolene and αpinene forming the main constituents of a specimen sampled in Tempe, AZ, USA [40], high levels of spathulenol being found in leaf samples collected in Dourados, Mato Grosso do Sul, Brazil [41], and limonene, α-pinene, β-bisabolol, epi-α-bisabolol, epi-β-bisabolol, βbisabolene, α-copaene, and (E)-caryophyllene appearing in specimens collected in the Amazon region of Brazil [42,43].A review of essential oils from the leaves of Psidium species, emphasizing the description of monoterpenes and sesquiterpenes from P. guineense, was recently reported [44].

Fruit Scent: Chemistry and Ecological Function
Like other plant parts, fruits are also composed of secondary metabolites.These related compounds act ecologically, attracting frugivorous and seed-dispersing small animals and repelling other so-called fruit antagonists.It has been said that secondary metabolites in fruits act mainly as defensive agents for the plant.The discussion about the defense of fruits by secondary metabolites has attributed this phenomenon to molecules with higher molecular weights and non-volatile characteristics.On the other hand, less attention has been paid to volatile organic compounds and lighter, odorous hydrophobic constituents.The volatile organic compounds not only play a role in the defense of fruits, but are also responsible for their aroma and attractiveness to human consumers [45].
Fruit aroma is a significant contributor to fruit quality.In the wild, the aroma of volatile organic compounds released from fruits influences herbivore behavior.It attracts animal dispersers, such as fruit bats, that recognize ripe and non-ripe fruits based on the emitted volatiles.Additionally, volatile organic compounds from fruits have biological activities against bacteria and fungi.For example, volatiles extracted from citrus species exhibit significant antifungal and antibacterial activities against pathogenic strains [46].
Fruits are generally classified into berries, melons, citrus fruits, drupes (fruits with stones), pomes (apple and pear types), and tropical fruits, as in the present case of Myrtaceous species.Most fruits release a wide range of volatile organic compounds, which determine the profile of their aromas and which, in general, are fatty acid derivatives (esters, ketones, aldehydes, lactones, and alcohols), terpenoids (mono-and sesquiterpenes, benzenoids, and phenylpropanoids (aromatic compounds).Each species of fruit has a characteristic aroma based on the mixture of its volatile organic compounds [9].

Fruit Scent: Chemistry and Ecological Function
Like other plant parts, fruits are also composed of secondary metabolites.These related compounds act ecologically, attracting frugivorous and seed-dispersing small animals and repelling other so-called fruit antagonists.It has been said that secondary metabolites in fruits act mainly as defensive agents for the plant.The discussion about the defense of fruits by secondary metabolites has attributed this phenomenon to molecules with higher molecular weights and non-volatile characteristics.On the other hand, less attention has been paid to volatile organic compounds and lighter, odorous hydrophobic constituents.The volatile organic compounds not only play a role in the defense of fruits, but are also responsible for their aroma and attractiveness to human consumers [45].
Fruit aroma is a significant contributor to fruit quality.In the wild, the aroma of volatile organic compounds released from fruits influences herbivore behavior.It attracts animal dispersers, such as fruit bats, that recognize ripe and non-ripe fruits based on the emitted volatiles.Additionally, volatile organic compounds from fruits have biological activities against bacteria and fungi.For example, volatiles extracted from citrus species exhibit significant antifungal and antibacterial activities against pathogenic strains [46].
Fruits are generally classified into berries, melons, citrus fruits, drupes (fruits with stones), pomes (apple and pear types), and tropical fruits, as in the present case of Myrtaceous species.Most fruits release a wide range of volatile organic compounds, which determine the profile of their aromas and which, in general, are fatty acid derivatives (esters, ketones, aldehydes, lactones, and alcohols), terpenoids (mono-and sesquiterpenes, benzenoids, and phenylpropanoids (aromatic compounds).Each species of fruit has a characteristic aroma based on the mixture of its volatile organic compounds [9].
Many factors regulate the aromas emitted by fruits, while the genotype of the fruit influences the flavor.The final fruit flavor profile is affected by environmental conditions, such as climate, sunlight, soil, fruit ripening, harvesting time, and post-harvesting processes.For example, environmental stresses (high temperature and drought) influence the metabolism of fruit and the aromatic compound content [47].The volatile organic compound profiles of fruits change according to the maturation stage.Terpenoids dominate the aroma profile in some fruits, such as apples, apricots, and peaches, during ripening, while in grapes, some phenylpropanoids increase with maturation.Furthermore, fatty acid and amino acid-related compounds increase during the maturation of apples and apricots.Therefore, maturation is vital for the emission of volatile organic compounds in fruits and affects commercial production [46].
As seen, fruit aromas serve as a signal to their pollinators or eaters.However, most horticultural varieties and cultivars have been selected according to human preference.Identifying volatile organic compounds relevant to human sensory preferences is essential to meet consumer demand for fruits.Furthermore, biotechnological modification of the aromatic characteristics of fruits or the engineering of synthesis pathways in microbial cell factories could increase the production of their aromatic metabolites for commercial exploitation [48].

Conclusions
The present study contributed to improved knowledge of the chemotaxonomy of Myrtaceae fruit species, of which there are few reports in the existing literature.The main classes of compounds in the studied species were determined as follows: in Eugenia stipitata, monoterpene hydrocarbons, oxygenated monoterpenes, sesquiterpene hydrocarbons, oxygenated sesquiterpenes, and fatty acid derivatives were highly represented; in E. uniflora, there existed an absence of oxygenated monoterpenes and fatty acid derivatives; in Myrciaria dubia, there were only monoterpene hydrocarbons and oxygenated monoterpenes; in Psidium guajava, sesquiterpene hydrocarbons, oxygenated sesquiterpenes, and fatty acid derivatives predominated; and in P. guineense, we observed an absence of oxygenated monoterpenes.Therefore, these findings contribute to a better understanding of the chemical profiles of Myrtaceae fruit species.

Figure 1 .
Figure 1.Location of fruit collection areas in the Brazilian Amazon.

Figure 1 .
Figure 1.Location of fruit collection areas in the Brazilian Amazon.

Figure 7 .
Figure 7. Ion-chromatogram of the Myrciaria dubia fruit volatile concentrate.3.4.Psidium guajava L.-Myrtaceae Botanical description: It is a small tree, ranging in height from 10-12 m.The stems are irregular, tortuous, very branched, and light green, with quadrangular branches.The bark is thin, smooth, and greenish-brown, and exfoliates frequently.The leaves are simple, opposite in orientation, and have a short petiole.The texture of the leaves is sub-coria-

Figure 12 .
Figure 12.Hierarchical cluster analysis (HCA) of the Myrtaceae fruit volatile concentrates, based on their classes of compounds.

Figure 13 .
Figure 13.Principal component analysis (PCA) of the Myrtaceae fruit volatile concentrates, based on their classes of compounds.

Figure 12 .
Figure 12.Hierarchical cluster analysis (HCA) of the Myrtaceae fruit volatile concentrates, based on their classes of compounds.

Foods 2024 , 20 Figure 12 .
Figure 12.Hierarchical cluster analysis (HCA) of the Myrtaceae fruit volatile concentrates, based on their classes of compounds.

Figure 13 .
Figure 13.Principal component analysis (PCA) of the Myrtaceae fruit volatile concentrates, based on their classes of compounds.

Figure 13 .
Figure 13.Principal component analysis (PCA) of the Myrtaceae fruit volatile concentrates, based on their classes of compounds.

Table 1 .
Constituents identified in the volatile concentrate of Eugenia stipitata fruits.

Table 1 .
Constituents identified in the volatile concentrate of Eugenia stipitata fruits.

Table 2 .
Constituents identified in the volatile concentrate of Eugenia uniflora fruits.

Table 2 .
Constituents identified in the volatile concentrate of Eugenia uniflora fruits.

Table 3 .
Constituents identified in the volatile concentrate of Myrciaria dubia fruits.

Table 4 .
Constituents identified in the volatile concentrate of Psidium guajava fruits.

Table 4 .
Constituents identified in the volatile concentrate of Psidium guajava fruits.

Table 5 .
Constituents identified in the volatile concentrate of Psidium guineense fruits.

Table 5 .
Constituents identified in the volatile concentrate of Psidium guineense fruits.

Table 6 .
Classes of compounds identified in the Myrtaceae fruits and used in the multivariate statistical analyses.