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Analysis of aroma compounds of nine autochthonous and non-autochthonous loquat cultivars grown in Sicily

Diego Planeta, Vittorio Farina, Paola Bambina, Ilenia Tinebra, Roberta Passafiume, Luciano Cinquanta, Onofrio Corona*

Department of Agricultural, Food, and Forest Sciences (SAAF), Università degli Studi di Palermo, Viale delle Scienze, Palermo, Italy

Abstract

Loquat cultivation in Sicily is mainly based on nonnative cultivars and local ecotypes characterized by high nutraceutical value and appreciable physicochemical characteristics. Increased interest in commercial loquat production has increased the intention to provide premium quality loquat cultivars that include volatile substances capable of conditioning the sensorial properties and, therefore, the acceptability of fruits by consumers. This study determined the content of volatile compounds in nonnative and local loquat fruits grown in Sicily. Analyses were performed on five international cultivars and four local cultivars.

Key words: international and local cultivars, loquat, volatile compounds

*Corresponding author: Onofrio Corona, Department of Agricultural, Food and Forest Sciences (SAAF), Università degli Studi di Palermo, Viale delle Scienze, Palermo, 90128 Italy. Email: [email protected]

Received: 23 July 2021; Accepted: 15 October 2021; Published: 11 November 2021

DOI: 10.15586/ijfs.v33i4.2104

© 2021 Codon Publications

This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0). License (http://creativecommons.org/licenses/by-nc-sa/4.0/)

Introduction

In recent years, there has been a growing demand for fruit products from tropical and subtropical countries. Among the attractive characteristics that fuel this demand from consumers is the increased interest in products with a high nutraceutical value, importantly their characteristic taste and flavour (Gentile et al., 2019). It is well known that the taste and quality of food are determined by aromatic compounds, which in turn, influence consumer preferences and attract the attention of farmers who require more information and analytical tools to enable them to select the most suitable cultivars to grow (Baldwin, 2004; Schwab et al., 2008). The aroma is a critical quality parameter that differentiates one fruit from the other and it is associated with many volatile compounds (Lo Bianco et al., 2010; Ye et al., 2017; Yuan et al., 2018) belonging to different chemical groups, such as esters, alcohols, terpenes, ethers, aldehydes, etc.

One of the fruits belonging to the subtropical species, which is well adapted to the temperate zones of the Mediterranean and whose production is concentrated in Spain and Italy, is the Loquat (Eriobotrya japonica Lindl). It is an evergreen subtropical species (Family Rosaceae - Subfamily Mathat loideae) that originates from Southern China. Today, 90% of the cultivation is concentrated in the region of Sicily, particularly in the province of Palermo (Farina et al., 2016), with an extended harvest period (from April to June) based on several cultivars and local ecotypes (Farina et al., 2011; Gentile et al., 2016). Loquat cultivation in Sicily is based especially on nonnative cultivars and local ecotypes characterized by a high nutraceutical value (Gentile et al., 2019) and appreciable physico-chemical characteristics. Today, the interest in loquat commercial production has risen, and it is geared towards loquat cultivars of premium quality (Badenes et al., 2013). The most important characteristic for the market is fruit size. The value of the crop (Goulas et al., 2014) is in line with the commercial classification (Testa et al., 2020). As a result, fruits are divided into four classes based on their diameter: GGG for fruits over 53 mm; GG for fruits between 46 and 52 mm; G for fruits between 32 and 45 mm; and M for fruits between 31 and 28 mm. Quality is a complex of chemical and physical parameters and aromatic composition. Volatile flavor compounds are likely to play a key role in determining the perception and acceptability of products by consumers (Pott et al., 2020). Fruits produce a range of volatile compounds that make up their characteristic aromas and contribute to their flavor. The differences in volatile compounds may be because of their ripening phase during the harvest time (Agozzino et al., 2007) and differences in the studied cultivars (Farina et al., 2020). Many studies on the volatile component of many fruits can be found in literature, while only a few studies have been conducted to date for the Mediterranean loquat. In this regard, Shaw and Wilson (1982) identified the following volatile compounds in loquat fruits; 2-phenylethanol, 3-hydroxy-2-butanone, phenylacetaldehyde, isomeric hexen-1-ols, ethyl acetate, methyl cinnamate, and β-ionone. Hexanal and (E)-2-hexenal and benzaldehyde have also been identified by Fröhlich and Schreier (1990). Chen et al. (2011) reported that β-ionone, decanoic acid, propanoic acid, bicycle nonane, and heptadecane are the major volatile compounds in the Zaozhong 6 cultivar. These studies highlighted that volatile compounds such as 2E-hexenol, 3Z-hexenol, and hexanol contribute to green notes; methyl cinnamate and eugenol contribute to the spicy note; ethyl and methyl 2-methylbutanoates are responsible for fresh fruity notes; a sweet watery aroma was also detected by traces amount of phenylacetaldehyde, vanillin, and β-ionone (Hideki et al. 1998). Finally, Takahashi et al. (2000) reported that the Tanaka cultivar presents phenylacetaldehyde as the most aromatic compound, while small traces of hexanal, (E)-2-hexanal, hexanoic acid, and β-ionone have also been found. Nevertheless, many other volatile compounds are present in traces which can be detected not only by analytical instruments but also by human olfaction (Goff et al., 2006).

The aim of this study was to determine for the first time the content of volatile compounds in non-native and local loquat fruits grown in Sicily.

Material and Methods

Plant material

Two hundred and seventy loquat fruits (Eriobotrya japonica Lindl.) were harvested in an experimental orchard located in Santa Maria di Gesù (Palermo, Italy, 38°04’N, 13°22’E, 150 m a.s.l.) between April and June at commercial ripening, using fruit peel color as a ripening index (807-809 degree of Biologische Bundesantalt, Bundessortenamt and Chemische Industrie (BBCH) Scale). The analyses were carried out on four local cultivars (BRT20, Claudia, Sanfilippara, and Nespolone di Trabia) and five international cultivars (Algerie, Bueno, El Buenet, Golden Nugget, and Peluche). A sample of 30 fruits per cv was submitted for laboratory analyses.

Commercial classification

Primarily the loquat fruits were divided into international and local cultivars and later were classified based on the flesh color (yellow and white) and diameter (GGG, GG, G, and M), according to Testa et al. (2020).

Volatile compounds analysis

Three replicates of the pulp (about 200 g) of 10 fruits were separated from the peel and seeds with the addition of 100 mg of sodium metabisulfite. The pulps were crushed with a laboratory blender by a high-speed Ultra-Turrax T25 (IKA Labortechnik, Staufen, Germany) and centrifuged twice at 4500gand 4°C for 15 minutes and later the solid residue was washed with 70 mL of ethanol:water solvent (12:88). The final extract (250 mL) was then clarified with 0.1 g of the pectolytic enzyme without secondary glycosidase activity (Rapidase X-Press, DSM, The Netherlands) at room temperature for 2 hours. 1-Heptanol was added as internal standard (0.2 mL of 40 mg/L in 10% ethanol) to the samples and was loaded onto a 5-g C18 reversed-phase solid-phase extraction (SPE) cartridge (Isolute, SPE Columns, Uppsala, Sweden), previously activated with 20 mL of methanol,50 mL of deionized water using a flow-rate of ca. 3 mL/min, and then rinsed with 100 mL of deionized water to eliminate sugars, acids, and other low molecular weight polar compounds. The free aromatic fraction was then eluted with 25 mL of dichloromethane. The eluate was dried over anhydrous sodium sulfate (Na2SO4) and was concentrated to about 0.2 mL under a stream of nitrogen. This extract, containing free volatile compounds, was immediately analyzed by gas chromatography/mass spectrometry (GC/MS). Then, the glycoconjugates aromas were finally eluted from the cartridge with 20 mL of methanol, and the eluate was concentrated to dryness using a vacuum rotary evaporator set at 30 °C (Buchi R-210, Switzerland). These dried glycosides extract were dissolved in 5 mL of citrate-phosphate buffer (0.2 M, pH 5) and subjected to enzymatic hydrolysis with 50 mg of an AR-2000 commercial preparation with glycosidase side activities (DSM Oenology, The Netherlands) at 40 °C for 24 hours. Later, 0.2 mL of 1-heptanol was added as internal standard, and the volatiles generated by the enzymatic hydrolysis of glycosylated precursors were then extracted following the SPE method previously described. The dichloromethane extract obtained was dried using anhydrous Na2SO4, concentrated to 0.2 mL, and kept at −20 °C until further analysis. GC/MS analysis was performed with an Agilent 6890 Series GC system and Agilent 5973 Network Mass Selective Detector (Agilent Technologies, Palo Alto, CA) equipped with a DB-WAX column (30 m, 0.250 mm i.d., film thickness 0.25 μm; Agilent Technologies).

The GC-MS conditions used were as reported by Corona et al. (2019). The detection was carried out by electron impact mass spectrometry in total ion current (TIC) mode using ionization energy of 70 eV. The mass acquisition range was m/z 30–330. Volatile organic compounds were identified by comparing their mass spectra and GC retention times with those of the pure commercial standard compounds and those within the NIST/EPA/NIH Mass Spectral Library database (Version 2.0d, build 2005). The concentration (µg/kg pulp) of volatile compounds was determined as 1-heptanol equivalents.

All solvents and reagents were purchased from WWR International (Milan, Italy).

Statistical analysis

The data were presented as mean ± standard deviation and analysed using the Tukey test at P ≤ 0.05. All statistical analysis was conducted using XLSTAT software version 9.0 (Addinsoft, Paris, France).

Results And Discussion

Commercial classification

According to commercial classification, our data showed that local ecotypes sizes were larger than international ecotypes (Amorós et al., 2003; Testa et al., 2020). However, only Peluche had the highest value as a well-known large fruit cultivar (Barone et al., 2010).

Varieties with a larger size are more appreciated by consumers because of their small portion size and high sugar/acid ratio. (Agusti et al. 2000; Testa et al. 2020). More sugar in local fruits versus international cultivars shows an increased degree of acidity (Gentile et al., 2016).

In this study, all the international cultivars had yellow flesh, whereas, among the local cultivars, only Nespolone di Trabia showed more similar behavior with that of the international cultivars (yellow flesh). On the other hand, BRT 20, Claudia, and Sanfilippara, showed white flesh with highest commercial classification (Table 1).

Table 1. Commercial classification based on origin, size, and color of analyzed loquat fruits: GGG> 53mm, GG 46-52mm, G 32-45 mm, and M 31-28 mm.

Origin Cultivars Commercial classification Color classification
Local BRT 20 GGG White flesh
Claudia GGG White flesh
Sanfilippara GG White flesh
Nespolone di trabia GG Yellow flesh
International Algerie GG Yellow flesh
Bueno G Yellow flesh
El buenet G Yellow flesh
Golden nugget GG Yellow flesh
Peluche GGG Yellow flesh

Volatile compounds analysis

GC-MS analysis of the concentrated flesh extract of SPE was performed to evaluate the aromatic compounds of loquat fruit flesh, and 35 free volatile compounds (Table 2) and 17 glycosylated compounds (Table 3) were detected. Of which, 14 were acids, 10 alcohols, two aldehydes, one benzenoid, and eight esters. Among which four were terpenes, four C13-norisoprenoids, and nine benzenoids. The latter were released after enzymatic hydrolysis from aromatic precursors linked to sugars.

Table 2. Free volatile compounds released by enzymatic hydrolysis of glycosylated precursors (μg/kg pulp).

Compounds Local cultivars* International cultivars*
BRT 20 Claudia Sanfilippara Nespolone di trabia Algerie Bueno El buenet Golden Nugget Peluche
Acids
Butyric acid 4.0 ± 0.0 6.2 ± 0.1 0.6 ± 0.0 0.7 ± 0.1 0.4 ± 0.1 3.6 ± 0.2 6.4 ± 0.4 n.d. 0.5 ± 0.1
Pentanoic acid 10.3 ± 1.6 7.2 ± 0.1 3.5 ± 0.1 9.4 ± 0.3 8.1 ± 0.7 5.5 ± 0.5 15.7 ± 1.8 8.9 ± 0.7 8.5 ± 0.7
Hexanoic acid 1060.9 ± 44.7b 1190.9 ± 31.0b 554.4 ± 34.3a 511.1 ± 29.4a 475.2 ± 57.6ab 645.8 ± 49.3ab 358.4 ± 7.3a 598.5 ± 50.4ab 506.1 ± 34.9ab
Heptanoic acid 2.2 ± 0.6b 2.2 ± 0.2b 2.2 ± 0.1b 0.8 ± 0.0a 0.1 ± 0.0a 3.4 ± 0.2b 3.8 ± 0.2b 0.8 ± 0.0a 0.4 ± 0.0 a
Octanoid acid 13.6 ± 1.3b 11.9 ± 1.1b 9.9 ± 0.1a 11.9 ± 0.2b 13.8 ± 2.0b 10.5 ± 1.6ab 12.1 ± 0.7ab 4.2 ± 0.2a 10.1 ± 0.7 ab
Nonanoic acid 18.4 ± 1.7b 17.4 ± 1.9 17.4 ± 0.7 16.4 ± 1.2 13.2 ± 1.5 20.4 ± 1.5 18.9 ± 1.8 20.8 ± 1.3 19.0 ± 1.5
Decanoic acid 16.8 ± 1.0b 8.0 ± 0.1a 8.2 ± 0.5a 17.4 ± 0.2b 33.5 ± 1.3b 12.0 ± 0.7a 8.0 ± 0.3a 20.1 ± 0.8ab 11.4 ± 1.1a
Dodecanoic acid 3.9 ± 0.1a 2.4 ± 0.3a 4.2 ± 0.1a 9.9 ± 0.1b 13.3 ± 0.8ab 8.4 ± 0.6ab 39.1 ± 3.6b 12.8 ± 0.2ab 4.4 ± 0.1a
Tetradecanoic acid 7.5 ± 0.1 1.9 ± 0.2 3.7 ± 0.2 3.2 ± 0.0 7.4 ± 0.4 14.1 ± 1.4 15.6 ± 1.2 6.7 ± 0.7 1.8 ± 0.2
Pentadecanoic acid 7.6 ± 0.3a 19.8 ± 1.2b 15.9 ± 0.2b 45.3 ± 1.0c 4.0 ± 0.0a 10.8 ± 0.8abc 5.3 ± 0.2ab 25.9 ± 0.1d 1.3 ± 0.1a
Hexadecanoic acid 240.6 ± 17.4a 219.4 ± 21.1a 444.9 ± 95.5b 341.7 ± 21.3b 636.4 ± 16.0b 667.6 ± 26.8b 617.8 ± 13.7b 525.0 ± 10.5ab 105.0 ± 4.2a
Heptadecanoic acid 4.3 ± 0.2 n.d. 0.3 ± 0.0 2.1 ± 0.1 5.4 ± 0.1 3.4 ± 0.1 3.8 ± 0.3 1.5 ± 0.1 n.d.
Octadecanoid acid 124.5 ± 11.6 120.3 ± 10.2 133.4 ± 21.7 116.1 ± 4.8 143.4 ± 4.2b 171.7 ± 12.0b 137.0 ± 10.3b 118.8 ± 13.7b 73.9 ± 2.6a
Benzoic acid 1053.3 ± 53.0b 1185.2 ± 130.4b 547.8 ± 33.5a 504.5 ± 25.7a 464.2 ± 55.2ab 640.5 ± 61.0ab 353.6 ± 7.9a 594.4 ± 40.2ab 502.8 ± 35.2ab
Total 2567.8 ± 133.6b 2792.8 ± 197.9b 1746.3 ± 187.0a 1590.6 ± 84.4a 1818.4 ± 138.9ab 2217.4 ± 157.7ab 1595.3 ± 49.7ab 1938.4 ± 118.9ab 1245.2 ± 81.4a
Alcohols
1-Pentanolo 2.4 ± 0.0b 2.9 ± 0.1b 1.6 ± 0.1a 2.7 ± 0.0b 1.7 ± 0.1ab 1.7 ± 0.1ab 5.6 ± 0.2b 2.7 ± 0.0ab 4.3 ± 0.2ab
3-Heptanol 0.6 ± 0.0 n.d. 0.4 ± 0.0 n.d. 0.3 ± 0.0a 0.7 ± 0.0a 2.8 ± 0.1b n.d.a 0.2 ± 0.0a
2-Hexanol 1.3 ± 0.0 n.d. 0.4 ± 0.0 1.6 ± 0.0 1.3 ± 0.1a 54.7 ± 4.3b 6.3 ± 0.2ab 1.3 ± 0.1a 2.0 ± 0.1a
1-Hexanol 1.5 ± 0.0a 1.4 ± 0.0a 4.7 ± 0.1b 5.5 ± 0.0b 12.4 ± 0.3b 2.0 ± 0.0a 3.9 ± 0.1a 3.5 ± 0.1a 3.3 ± 0.2a
3-Ethyl-3-heptanol 0.3 ± 0.0 n.d. n.d. n.d. n.d. 0.2 ± 0.0 0.2 ± 0.0 n.d. 0.3 ± 0.1
Cis-3-hexen-1-ol 2.0 ± 0.0a 12.5 ± 0.1bc 6.7 ± 0.1b 22.2 ± 1.2c 20.0 ± 1.4ab 5.9 ± 0.3ab 2.8 ± 0.1a 5.7 ± 0.2ab 4.8 ± 0.0ab
2-Butoxyethanol 5.4 ± 0.0b 3.4 ± 0.1a 3.5 ± 0.0a 2.4 ± 0.0a 5.0 ± 0.1ab 3.9 ± 0.1ab 2.0 ± 0.0a 2.3 ± 0.1ab 3.3 ± 0.3ab
Trans-3-hexen-1-ol 2.7 ± 0.0a 6.5 ± 0.1b 4.0 ± 0.0a 9.4 ± 2.6b 26.5 ± 0.3c 11.2 ± 0.2ab 8.1 ± 0.1ab 7.5 ± 0.2ab 14.6 ± 0.2b
2-Ethyl hexanol 5.3 ± 0.0 2.4 ± 0.0 3.9 ± 0.1 2.3 ± 0.0 5.6 ± 0.2 4.7 ± 0.2 2.5 ± 0.1 3.3 ± 0.1 2.8 ± 0.1
Total 21.6 ± 0.0a 29.1 ± 0.4a 25.4 ± 0.4a 46.2 ± 3.9b 72.5 ± 2.5c 85.1 ± 5.1bc 34.2 ± 0.9abc 26.5 ± 0.8abc 35.6 ± 1.2abc
Aldehydes
Cis-2-hexenal 6.2 ± 0.1a 8.7 ± 0.1a 9.2 ± 0.2 a 20.5 ± 0.2b 92.1 ± 8.9b 7.9 ± 0.6a n.d.a 5.0 ± 0.1a 30.3 ± 1.7ab
Nonanal 1.6 ± 0.0 ab 3.5 ± 0.1b 2.4 ± 0.1ab 1.0 ± 0.0ab 0.6 ± 0.0a 1.8 ± 0.1ab 0.4 ± 0.0a 1.4 ± 0.2ab 1.3 ± 0.2ab
Total 7.8 ± 0.1a 12.3 ± 0.2ab 11.6 ± 0.3ab 21.5 ± 0.2b 92.7 ± 8.9b 9.7 ± 0.7ab 0.4 ± 0.0a 6.4 ± 0.3a 31.6 ± 1.9ab
Benzenoids
Vanillin 11.7 ± 0.2b 8.7 ± 0.1a 8.0 ± 0.1a 8.2 ± 0.0a 11.1 ± 1.1ab 27.9 ± 2.4b n.d.a 11.8 ± 0.2ab 10.1 ± 0.1ab
Esters
Ethyl hexanoate 1.9 ± 0.1a n.d.a 5.0 ± 0.1ab 0.6 ± 0.0a 3.3 ± 0.5a 3.8 ± 0.4a 9.6 ± 0.3b 1.0 ± 0.0 a 3.2 ± 0.2a
Ethyl octanoate 3.4 ± 0.0a 1.4 ± 0.0a 9.4 ± 0.3a 3.7 ± 0.0a 11.3 ± 1.8a 6.7 ± 0.3a 25.2 ± 0.3b 3.1 ± 0.2a 7.4 ± 0.2a
Ethyl-3-hydroxy butyrate 230.8 ± 8.7d 10.0 ± 0.1a 181.1 ± 9.6cd 7.1 ± 0.1a 83.3 ± 4.5b 203.9 ± 23.1d 120.8 ± 10.8c 5.2 ± 0.3a 4.6 ± 0.0a
Ethyl decanoate 0.2 ± 0.0a 0.2 ± 0.0a 1.3 ± 0.0ab 1.2 ± 0.0ab 2.8 ± 0.2b 0.5 ± 0.0a 2.4 ± 0.1b 0.6 ± 0.0a 0.5 ± 0.1a
Diethyl succinate 0.8 ± 0.0a n.d.a 1.3 ± 0.1ab 0.1 ± 0.0a 3.3 ± 0.1b 0.7 ± 0.0a 0.3 ± 0.0a 0.2 ± 0.0a 2.5 ± 0.1b
Butanoic Acid-2-methyl 137.4 ± 10.9a 118.7 ± 9.1a 8.7 ± 0.1a 65.7 ± 1.8a 623.9 ± 7.1c 415.1 ± 36.2b 308.0 ± 28.6b 7.3 ± 0.2a 301.3 ± 3.8b
Hexadecanoic acid methyl ester 4.4 ± 0.4a 25.3 ± 0.2b 2.7 ± 0.2a 7.4 ± 0.2a 4.3 ± 0.3a 4.6 ± 0.3a 2.9 ± 0.1a 1.6 ± 0.1a 6.4 ± 0.2b
Hexadecanoic acid ethyl ester 1.6 ± 0.0 2.6 ± 0.0 1.4 ± 0.1 2.4 ± 0.2 7.0 ± 0.3 1.5 ± 0.1 5.4 ± 0.2 2.4 ± 0.2 2.8 ± 0.1
Total 380.5 ± 20.1cd 158.2 210.9 ± 10.5abc 88.1 ± 2.3a 739.3 ± 14.8c 636.7 ± 60.4c 474.7 ± 40.4b 21.5 ± 1.0a 328.8 ± 4.7b

*Mean ± standard deviation (n = 3). Different superscripted letters indicate significant differences for P ≤ 0.05 (analysis of variance or Tukey test). n.d., not determinable.

Table 3. Glycosylated volatile compounds released by enzymatic hydrolysis of glycosylated precursors (μg/kg pulp).

Local cultivars* International cultivars*
Compounds BRT 20 Claudia Sanfilippara Nespolone di trabia Algerie Bueno El buenet Golden nugget Peluche
Terpenes
Trans-8-diidrolinalool 6.1 ± 0.0b 8.0 ± 0.1b 4.0 ± 0.0a 3.3 ± 0.0a 10.7 ± 0.2c 6.9 ± 0.0b 3.4 ± 0.1ab 6.1 ± 0.2b 1.4 ± 0.0a
Trans-8-hydroxylinalool 5.5 ± 0.1a 15.1 ± 0.3 b 7.0 ± 0.2a 15.5 ± 0.3b 12.8 ± 0.1bc 9.5 ± 0.2b 7.1 ± 0.2b 16.0 ± 1.4c 1.0 ± 0.0a
Cis-8-hydroxylinalool 1.5 ± 0.0a 4.1 ± 0.1 ab 8.5 ± 0.2b 7.6 ± 0.3b 3.2 ± 0.0b 4.3 ± 0.2bc 5.7 ± 0.1c 3.7 ± 0.2b 1.1 ± 0.0a
Geranial 3.4 ± 0.0ab 2.6 ± 0.2a 6.9 ± 0.2b 4.2 ± 0.2ab 6.0 ± 0.0bc 3.8 ± 0.1a 4.8 ± 0.1b 7.6 ± 0.2c 5.6 ± 0.2b
Total 16.5 ± 0.1a 29.8 ± 0.7b 26.4 ± 0.6b 30.6 ± 0.8b 32.7 ± 0.3c 24.5 ± 0.5b 21.1 ± 0.5b 33.4 ± 2.0c 9.2 ± 0.2a
C13-norisoprenoids
3-oxo-a-ionol 59.2 ± 4.8a 62.4 ± 1.2a 94.4 ± 4.9ab 207.5 ± 23.0b 461.0 ± 41.5d 286.6 ± 19.8c 217.9 ± 19.3b 373.4 ± 34.0c 112.3 ± 9.8a
3-4-dihydro-3-oxo-a-ionol 19.8 ± 1.1a 41.9 ± 1.1ab 32.7 ± 2.9ab 74.1 ± 14.0b 92.1 ± 7.2c 55.6 ± 4.2b 27.7 ± 2.0a 72.9 ± 17.1bc 24.8 ± 1.1a
3-OH-b-ionone 2.0 ± 0.0a 28.5 ± 1.3ab 34.1 ± 1.6b 64.7 ± 3.7c 23.4 ± 2.9c 13.0 ± 1.8bc 7.8 ± 1.0ab 22.2 ± 1.6c 2.6 ± 0.1a
Vomifoliol 135.0 ± 10.4a 149.2 ± 0.8a 178.0 ± 12.2a 283.4 ± 23.8b 581.6 ± 26.7c 79.9 ± 2.2a 101.2 ± 9.1a 283.8 ± 10.9b 120.0 ± 11.5a
Total 215.9 ± 16.3a 281.9 ± 4.4ab 339.2 ± 21.6b 629.6 ± 64.5c 1158.1 ± 78.3c 435.1 ± 28.0ab 354.5 ± 31.4a 752.3 ± 63.6bc 259.7 ± 22.5a
Benzenoids
Eugenol 32.3 ± 1.6 a 21.7 ± 0.1b 15.9 ± 0.2a 27.9 ± 0.3b 55.0 ± 3.6b 59.2 ± 4.1b 24.7 ± 1.9a 121.3 ± 9.5c 16.1 ± 0.2a
4-vinylguaiacol 54.4 ± 4.1c 35.2 ± 0.3b 30.1 ± 0.2ª 32.5 ± 0.4a 29.0 ± 2.4a 25.1 ± 2.1a 21.4 ± 0.7a 78.0 ± 8.4b 16.9 ± 0.9a
Isoeugenol 2.6 ± 0.1a 7.3 ± 0.1b 7.9 ± 0.1b 5.2 ± 0.1a 23.0 ± 0.1c 22.0 ± 1.0c 24.5 ± 1.5d 10.8 ± 0.7ab 7.0 ± 0.1a
Methylvanillate 30.5 ± 0.2a 192.5 ± 11.9b 24.7 ± 0.2ª 45.1 ± 0.4a 194.9 ± 10.7c 32.0 ± 2.9a 19.8 ± 1.7a 134.8 ± 0.4b 11.8 ± 0.2a
Benzylalcohol 5.9 ± 0.2a 7.9 ± 0.2a 6.8 ± 0.1a 12.2 ± 0.2b 11.3 ± 1.1c 3.4 ± 0.2ab 4.8 ± 0.2b 12.2 ± 0.1c 2.5 ± 0.1a
2-phenylethanol 225.4 ± 13.6b 443.8 ± 24.3c 177.4 ± 13.7a 234.1 ± 21.1b 285.1 ± 18.7c 92.4 ± 2.1b 84.7 ± 2.0b 241.7 ± 13.0c 77.2 ± 6.2a
Vanillin 18.8 ± 0.2c 13.8 ± 0.7b 3.9 ± 0.2a 13.4 ± 1.8b 12.4 ± 0.8ab 10.2 ± 1.0ab 9.1 ± 0.7ab 25.4 ± 2.3c 2.8 ± 0.1a
Methoxyeugenol 5.7 ± 0.2b 5.3 ± 0.1b 3.9 ± 0.1a 2.2 ± 0.2a 2.3 ± 0.0b 3.4 ± 0.1c 5.6 ± 0.3d 0.4 ± 0.0a 3.8 ± 0.1c
Syringaldehyde 56.3 ± 0.4ab 4.6 ± 0.1a 45.9 ± 2.2ab 36.8 ± 3.2ab 68.7 ± 3.4b 16.7 ± 0.9ab 26.3 ± 1.9ab 10.2 ± 0.7 ab 7.0 ± 1.0a
Total 431.9 ±20.6b 732.3 ± 37.8c 316.5 ± 17.0a 409.4 ± 27.7b 681.7 ± 40.8c 264.3 ± 14.4ab 221.0 ± 10.9ab 634.8 ± 35.1c 145.1 ± 8.9a

*Mean ± standard deviation (n=3). Different superscripted letters indicate significant differences for P ≤ 0.05 (analysis of variance or Tukey test). n.d., not determinable.

During maturation, the volatile compounds of the two cultivars, Algerie and Golden nugget, have been studied, and a strong similarity was identified in terms of aroma, flavor, and parameters related to physiological-qualitative traits (Pino et al., 2002; Besada et al., 2013, 2017).

The heritability of loquat aromas was assessed by Jiang et al. (2014) by examining the composition of the volatile compounds of Xiantgtian and Jiefangzhong cultivars and two-hybrid progenies (Xiangzhong No.11 and Zhongxiang No. 25). They concluded that the level of volatile compounds in the fruit of the progeny was like the values known in their parents. Previous studies showed that the maturity stage determines the qualitative and quantitative volatile substances of many fruit species (Mattheis et al. 1992; Perez et al. 1992), for loquat, very little is known about their association with other ripening or quality characteristics that vary between cultivars (Jiang et al., 2014).

Free volatile compounds

Among the free volatile compounds, minimal presence of volatile compounds that can characterize the aroma of loquat fruit was observed. It is a predominance of compounds belonging to the class of acids and alcohols, followed by esters, aldehydes, and finally a benzenoid (vanillin only, according to Hideki et al. 1998). The identified acids range from C4 to C18, the esters from C4 to C10 and C16; they contribute to the taste sensations perceptible in the mouth during tasting and eating of the flesh, giving taste, fat sensation, and different aromatic sensations, ranging from fruity to floral (Table 4). The greater acids concentration are: hexanoic (1060.9±44.7 in BRT20, local cultivar), benzoic (1185.2 mg/kg flesh fruit in Claudia, local cultivar), hexadecanoic (667.6 mg/kg flesh fruit in Bueno, international cultivar), and octadecanoic (171.7 mg/kg flesh fruit also in Bueno cultivar).

Table 4. Odor descriptor and odor threshold volatile compounds.

Compuonds Odor descriptor Odour threshold (ppb) Reference
Acids      
Butyric acid Rancid, cheese 173 Fariña et al. (2015)
Pentanoic acid Sweet 70 Pino and Mesa (2006)
Hexanoic acid Fatty, cheese 420 Fariña et al. (2015)
Heptanoic acid Waxy, cheese, fruity www.thegoodscentscompany.com/
Octanoic acid Fatty, cheese 500 Fariña et al. (2015)
Nonanoic acid Green, fatty 3000 Pino and Mesa (2006)
Decanoic acid Rancid, fatty 1000 Fariña et al. (2015)
Dodecanoic acid Fatty, waxy www.thegoodscentscompany.com/
Tetradecanoic acid Waxy, oily, fatty www.thegoodscentscompany.com/
Pentadecanoic acid Waxy www.pherobase.com
Hexadecanoic acid Oily www.pherobase.com
Heptadecanoic acid Oily www.pherobase.com
Octadecanoid acid Oily www.pherobase.com
Benzoic acid Balsamic  
Alcohols      
1-Pentanol Green, grassy, powerful 4,000 Pino and Mesa (2006)
3-Heptanol Herbal www.thegoodscentscompany.com/
2-Hexanol Chemical, winey 500 Pino and Mesa (2006)
1-Hexanol Fatty, green, resin, flower, sweet 500 Bonneau et al. (2016)
3-Ethyl-3-heptanol    
cis-3-hexen-1-ol Green, moss, fresh 110 Bonneau et al. (2016)
2-butoxyethanol    
trans-3-hexen-1-ol Green, grass, fruity 70 Bonneau et al. (2016)
2-Ethyl-hexanol Oily, rose, sweet Li et al. (2011)
Aldehydes      
Trans-2-hexenal Green, banana-like 17 Pino and Mesa (2006)
Nonanal Fatty, citrus, green, floral, sweet, soapy 1 Bonneau et al. (2016)
Benzenoid      
Vanillin Vanilla-like, sweet 25 Bonneau et al. (2001)
Esters      
Ethyl hexanoate Apple peel, fruity 1 Pino and Mesa (2006)
Ethyl octanoate Fruity, fat 194 Pino and Mesa (2006)
Ethyl-3-hydroxy butyrate Fruity, grape 1000 Moyano et al. (2002)
Ethyl decanoate Sweet, oily, nutlike, grape 6300 Pino and Mesa (2006)
Diethyl succinate Overripe melon, lavender 100,000 Fariña et al. (2015)
2-methylbutanoic acid Cheese 250 Fariña et al. (2015)
Methyl hexadecanoic Waxy www.thegoodscentscompany.com/
Ethyl hexadecanoic Waxy www.thegoodscentscompany.com/

In terms of bad tastes, the highest values of butyric and decanoic acid, commonly detectable in cheese and fat notes was observed only in Bueno and El buenet (both international cultivars).

Among the esters, higher amounts of ethyl-3-OH-butyrate and 2-methyl-butanoic acid were observed.

The very limited presence of C6 alcohols, deriving from the enzymatic activities of lipoxygenase, highlights how loquat is poorly endowed with these enzymes, which lead to the formation of herbaceous aromas that are not always pleasant, or that the sample preparation was done correctly. The different cultivars examined show significant differences in ester and alcohol content: international Algerie and Bueno cultivars tend to have the highest values.

The total contents of acids, aldehydes and benzenoids show a similar profile in most cultivars. Significant differences were recorded for total acid content in Claudia (local cultivar) which represent the highest values (2792 mg/kg flesh fruit) and in Peluche (international cultivar), which represent the lowest values (1245 mg/kg flesh fruit); in total aldehydes, Algerie has significantly higher values and BRT 20, El buenet and Golden nugget are lower; finally, benzenoids are present in higher amounts in Bueno.

Glycosylated volatile compounds

A limited number of glycosylates, released by enzymatic hydrolysis, have been recorded in the studied cultivars, demonstrating that loquat does not have a high supply of sugar-related flavors, which can be released and perceived after swallowing the flesh (flavor).

Among the identified glycosylates, there is a clear predominance of compounds belonging to the class of benzenoids and C13-norisoprenoids followed by terpenes, the latter is present at low concentrations and with significant differences between cultivars.

Among the benzenoids, the presence of eugenol, 4-vinylguaiacol, vanillin, syringaldehyde, methylvanillate, and 2-phenylethanol was shown according to the study outcome of Chen et al. (2011) and Shaw and Wilson (1982). Among the C13-norisoprenoids and terpenes presence of vomifoliol and 3-oxo-α-ionol and their dehydroxylated forms is recorded. Important compounds that contribute to aromatic sensations range from fruity to floral (Table 5). The international cultivars tend to have a higher concentration of these compounds, especially Algerie and Golden nugget. Among the local cultivars, Claudia has the highest values. Higher values for total benzenoids are observed in Claudia (local cultivar), Golden nugget, and Algerie (international cultivars); Higher C13-norisoprenoids in Algerie and Golden nugget; the latter also had higher total terpenes. As in all cultivars, the synthesis of terpene compounds is shifted towards dehydroxylated forms (trans-8-Hydroxylinalool and cis-8-Hydroxylinalool), and geraniol is present only among monohydroxylates.

Table 5. Odor descriptor and odor threshold volatile compounds.

Compounds Odor descriptor Odor threshold (ppb) Reference
Terpenes      
Linalool Floral, lavender 6 Pino and Mesa (2006)
Trans-8-hydroxy-linalool Sweet, floral, creamy www.thegoodscentscompany.com/
Cis-8-hydroxy-linalool Sweet, floral, creamy www.thegoodscentscompany.com/
Geranial Citrus-like, flowery, fruity 32 Pino and Mesa (2006)
C13-norisoprenoids      
3-oxo-a-ionol Spicy, woody, violet www.pherobase.com
3,4-dihydro-3-oxo-actinidol 1   www.pherobase.com
3-OH-b-ionone Flower, violet www.thegoodscentscompany.com/
Vomifoliol Fruity www.pherobase.com
Benzenoids      
Eugenol Clove, spicy, balsamic 6 Pino and Mesa (2006)
4-Vinylguaiacol Clove, curry 3 Pino and Mesa (2006)
Isoeugenol Flower 6 Escudero et al. (2007)
Methyl vanillate Caramel, butterscotch, vanilla 990 Escudero et al. (2007)
Benzylalcohol Sweet, flower www.pherobase.com
2-Phenylethanol Hawthorne, honey, sweet 1100 Pino and Mesa (2006)
Methoxyeugenol Sweet, flower www.pherobase.com
Syringaldehyde Sweet, cocoa, chocolate 50,000 Escudero et al. (2007)

Conclusion

Among local cultivars, only cv Claudia had higher values of glycosylated compounds highlighting the floral and acidic notes that are appreciated in the market. Regarding the international cultivars, all yellow fleshed cultivars had a higher number of free aromatic compounds that showed cheese and fat notes (butyric and decanoic acid) and other odors and flavors less appreciated by consumers. They have fewer acids and a greater number of glycosylated compounds that showed characteristic floral and woody notes. This article tends to highlight the importance of local and international cultivars in Mediterranean environments that are grown with the best market characteristics.

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