Understanding changes in volatile compounds and fatty acids of Jincheng orange peel oil at different growth stages using GC-MS

XIE Jiao,CAO Qi,WANG Wen-jun,ZHANG Hong-yan,DENG Bing

1 The Key Laboratory of Environmental Pollution Monitoring and Disease Control,Ministry of Education/Guizhou Provincial Engineering Research Center of Ecological Food Innovation,School of Public Health,Guizhou Medical University,Guiyang 550025,P.R.China

2College of Food Science/Food Storage and Logistics Research Center,Southwest University,Chongqing 400715,P.R.China

Abstract Jincheng orange (Citrus sinensis Osbeck) is widely grown in Chongqing,China,and is commonly consumed because of its characteristic aroma contributed by the presence of diverse volatile compounds. The changes in aroma during the development and maturation of fruit are indicators for ripening and harvest time. However,the influence of growth stages on the volatile compounds in Jincheng orange remains unclear. In addition,volatiles originate from fatty acids,most of which are the precursors of volatile substances. On this basis,gas chromatography-mass spectrometry (GC-MS) was performed to elaborate the changes in volatile constituents and fatty acids as precursors. This study tested proximately 60 volatiles and 8 fatty acids at 9 growth and development stages (AF1-AF9). Of those compounds,more than 92.00%of total volatiles and 87.50% of fatty acids were terpenoid and saturated fatty acids,respectively. As shown in the PCA plot,the AF5,AF6,and AF9 stages were confirmed as completely segregated and appeared different. In addition,most of the volatiles and fatty acids first increased at the beginning of the development stage,then decreased from the AF6 development stage,and finally increased at the AF9 maturity stage. Moreover,the highest contents of terpenoid,alcohols,aldehydes,ketones,and saturated fatty acids in Jincheng orange peel oil were d-limonene,linalool,octanal,cyclohexanone,and stearic acid during development stages,respectively. Our results found that the growth stages significantly affected the volatile constituents and precursors in Jincheng orange peel oil.

Keywords: Jincheng orange,volatile compounds,fatty acids,growth stages

1.Introduction

Citrus is one of the most widely grown fruits worldwide,with more than 100 countries located in the tropical and subtropical regions cultivating the plant (Nayaket al.2015;FAO 2020;Duanet al.2022;Huanget al.2023).According to the global citrus statistics in 2020,the highest output of citrus varieties was the sweet orange,and China is one of the leading producers (Liuet al.2019;FAO 2020;Liet al.2022). Chongqing is one of the top 10 major citrus-producing regions in China,and the Jincheng orange,a subgroup ofCitrussinensisOsbeck,is the main sweet orange variety in Chongqing due to its attractive flavor and aroma (Fanet al.2009).

Sweet orange is a known source of essential oil,in particular its peel (Parastaret al.2012;Taoet al.2014;Renet al.2015;Louet al.2017). Essential oils usually are comprised of a complex combination of volatile compounds that are one of the important indexes for measuring fruit quality,especially the perceived odor and aroma (Mastelloet al.2015;Tianet al.2018;Wanget al.2022). These volatile compounds,in general,include terpene-hydrocarbons (e.g.,d-limonene,α-pinene,sabinene,β-myrcene,γ-terpinolene,α-thujene,cis-β-ocimene,α-cubebene,β-caryophyllene,andβ-farnesene),alcohols (e.g.,3-hexanol,β-terpineol,linalool,and citronellol),aldehydes (e.g.,octanal,nonanal,citronellal,decanal,and geranial),ketones(e.g.,cyclohexanone,nootkatone,pulegone,verbenone,and (-)-carvone),oxides (e.g.,caryophyllene oxide,(Z)-limonene oxide,and (E)-limonene oxide),esters(e.g.,neryl acetate and geranyl acetate),and others(e.g.,toluene and ethylbenzene) (Casilliet al.2014;Xieet al.2018;Yuet al.2018). Of the different compounds identified,terpenoids account for more than 85.0% of the total volatile constituents in orange peel essential oils (Espinaet al.2011;Zhanget al.2017). In addition,certain physicochemical changes occur during the development and maturation of the fruit,including the changes in flavor and aroma that are the indicators of the ripening and harvest time of fruit (Rodriguezet al.2013;Chaudharyet al.2018). Therefore,the factor of maturity can affect the composition and content of volatiles (Jiet al.2019;Houet al.2020;Wanget al.2022). Moreover,the determination of appropriate harvest maturity can promote the yield and development of citrus components due to the differences in citrus composition at different growth stages (Penget al.2009;Houet al.2020). However,little information is available regarding the influence of different growth stages on volatile compounds in Jincheng orange. Thus,it was essential to explore the changes in volatile constituents at different growth stages.

At present,previous studies have revealed that plant volatiles are derived from fatty acids,most of which were the precursors of the volatile substances as in the case of hexanal and 3-pentanol (Schwabet al.2008;Stitzet al.2014;Wanget al.2015;Dhandapaniet al.2017;Al-Juhaimiet al.2018). Fatty acids in orange fruits mainly contain saturated fatty acids (e.g.,lauric acid,myristic acid,pentadecanoic acid,palmitic acid,and stearic acid) and a range of unsaturated fatty acids(e.g.,oleic acid) (Letaiefet al.2016;Zhouet al.2017). In conclusion,to comprehend the changes in the content of volatile compounds at different growth stages,the fatty acid in Jincheng orange peel should be analyzed.In this study,the samples of Jincheng orange fruit at 9 growth and development stages were collected,and gas chromatography-mass spectrometry (GC-MS) was utilized to analyze the changes of volatile constituents and fatty acids. Our research mainly focused on probing the critical development stage and the terpenoid in peels that were responsible for the major changes at different growth stages in Jincheng orange. The final goal was to reveal the chemical features and provide a reference for the best harvest period in Jincheng orange.

2.Materials and methods

2.1.Plant materials and preparation

The Jincheng orange (C.sinensisOsbeck ‘Beibei 447’)was harvested and collected on 75 d (AF1),100 d (AF2),125 d (AF3),140 d (AF4),155 d (AF5),170 d (AF6),185 d(AF7),200 d (AF8),and 215 d (AF9) after flowering in an orchard located in the Beibei District of Chongqing,China in 2016 (Fig.1). Three biological replicates for each of the 9 development stages of the fruit were analyzed for the predefined quality parameters.

The fruits were transported to the laboratory immediately after harvest,washed with potable water,and air-dried at room temperature. The peels were cut along the equator of the fruit without touching the edible segment,immediately ground in liquid nitrogen,and frozen at -80°C until further extraction.

Fig. 1 The samples of citrus fruits. AF1-AF9,75,100,125,140,155,170,185,200,and 215 days after flowering,respectively.

Fig. 2 PCA of terpene hydrocarbons in peel oil during the development of Jincheng orange fruit. A,score plot of PC2 against PC1.B,variable plot of PC2 against PC1. AF1-AF9,75,100,125,140,155,170,185,200,and 215 days after flowering,respectively.

2.2.Chemicals and reagents

The ethyl decanoate,C7-C30saturated alkanes and volatile standards of sabinene,β-myrcene,β-farnesene,α-farnesene,valencene,and citronellal were purchased from Sigma Co.,Ltd.(St.Louis,MO,USA). Methyl tertbutyl ether (MTBE,HPLC grade) for extraction of volatiles and volatile standards ofd-limonene,γ-terpinolene,α-terpinolene,β-caryophyllene,nonanal,decanal,geranial,dodecanal,undecanal,linalool,β-terpineol,α-terpineol,citronellol,geraniol,neryl acetate,geranyl acetate,(-)-carvone was obtained from Tokyo Chemical Industry (TCI) Development Co.,Ltd.(Shanghai,China).Anhydrous sodium sulfate and dichloromethane were acquired from Kelong Co.,Ltd.(Sichuan,China). Other volatile standards ofα-pinene and limonene oxide were provided by Dr.Ehrenstorfer (Augsburg,Germany)and Wako Pure Chemical Industries (Osaka,Japan),respectively.

2.3.Volatiles and fatty acids extraction

The volatiles and fatty acids of samples in peel essential oil during Jincheng orange development were extracted as previously described by Liuet al.(2012) and Xieet al.(2018) with some modifications. Approximately 1.00 g of frozen peel sample was extracted using 5 mL MTBE and added with 42.50 μg of ethyl decanoate as an internal standard. The samples were extracted for 1 h in an ultrasonic bath (model KQ5200DE,Kunshan Ultrasonic Instruments Co.,Ltd.,Kunshan,China);the organic layer was dried over Na2SO4and then concentrated to a volume of 0.30 mL at 4°C by using a vacuum centrifugal concentrator (model ZLS-1,Shanghai Jingxue Science Apparatus Co.,Ltd.,Shanghai,China). Subsequently,the samples were filtered with a 0.22-μm microporous filter for further GC-MS analysis.

2.4.GC-MS analysis

Exactly 1 μL of the sample was injected into GC-MSQP2010 Plus (Shimadzu,Japan). The GC was analyzed at a 10:1 split ratio using a DB-5 MS column (30 m×0.25 mm×0.25 μm film thickness;J&W Scientific,Folsom,CA,USA). Helium (99.99%) was used as carrier gas at a flow rate of 0.8 mL min-1. The temperatures of the injector and ion source were set to 250 and 230°C,respectively. The column temperature was set at 40°C,increased to 70°C at a rate of 3°C min-1,held at 70°C for 3 min,then increased to 160°C at a rate of 3°C min-1,kept at 160°C for 1 min,and finally increased to 220°C at a rate of 8°C min-1,held at 220°C for 2 min. Mass spectrometry parameters in electron ionization mode were set at 70 eV. Total ion current (TIC) spectra were obtained with am/zrange of 30-400.

2.5.Identification and quantification of volatiles and fatty acids

Volatile constituents and fatty acids of peel oil during Jincheng orange development were identified based on the NIST Chemistry WebBook (http://webbook.nist.gov/chemistry),Mass Spectral Library (NIST08,NIST08s)database,and data from literature reports. The retention index (RI) was obtained by making use of a standard series of saturatedn-alkanes (C7-C30) analyzed on the DB-5 MS column. The volatiles and fatty acid were identified in the TIC. The characteristic fragment (CF,RI,and that analyzed on the DB-5 MS column) and identification approach for each identified compound are shown in Table 1. In the semi-quantification for individual constituents of volatiles and fatty acids,the value of relative content was the ratio of peak areas between the composition and internal standard (Kelebeket al.2015).

Table 1 Identification of the volatiles and fatty acids in citrus peel oil by GC-MS1)

2.6.Statistical analysis

The statistical analysis was used for IBM SPSS Statistics 22.0,and graphs were processed using GraphPad Prism 7(GraphPad Software Inc.,CA,USA) and Photoshop 6.0.The principal component analysis (PCA) was performed by R Software (R i386 ver.3.3.3). Duncan’s multiple comparisons were used to compare the statistical study of characteristic changes in the content of volatile constituents and fatty acids during growth stages.Statistical significance was recognized asP＜0.05.

3.Results and discussion

3.1.ldentification of volatile compounds

A total of 60 volatile compounds were identified in peel oil during Jincheng orange development,of which the number of terpenoids,alcohols,aldehydes,ketones,oxides,esters,and others were 23,11,13,5,3,2,and 3,respectively (Table 2). Among these compounds,26 were identified successfully by matching with the relevant standards of MS spectra and RI (Table 1) (Watanabeet al.2008;Mesa-Arangoet al.2010;Silvaet al.2010;Cuiet al.2011;Jáno?kováet al.2014;Xieet al.2018).Further,the qualitative analysis of the rest of the volatiles was based on database searching,MS spectra in NIST Chemistry WebBook,and comparing the values of RI reported in the literature (Mockut?et al.2003;Chenget al.2005;Varletet al.2006;Cajkaet al.2007;Lozanoet al.2007;Noudogbessiet al.2008;Zhuet al.2008;Patilet al.2009;Suet al.2009;Wanget al.2012;Shinet al.2015) (Table 1). The results regarding the relative content of volatiles (Tables 2 and 3),d-limonene,β-myrcene,α-pinene,sabinene,octanal,decanal,and geranial were the major chemical,and terpenoid accounted for the most proportion of the peel oil of Jincheng orange fruit (above 92.00%),similarly to the result found in sweet orange (Fanet al.2009;Renet al.2015).

Changes in the relative content of terpenoidAmong the identified terpenoids,ylangene andγ-muurolene were not detected from the AF1 to AF6 development stages of Jincheng orange fruits. Subsequently,along the last 3 development stages,the ylangene andγ-muurolene were identified,and the relative content gradually increased over time (Table 2). In addition,γ-selinene and valencene were first detected at AF4,and the relative content at AF9 was the highest,approximately 200.00 and 433.33%of that at AF4,respectively. From the observed results,the maximum content of the mentioned four compounds was at the maturity of fruit or AF9. Of them,the variation characteristics of valencene were not detected at the early developmental stage and had the highest content at AF9,which was consistent with the literature of Chaudharyet al.(2018) and Houet al.(2020). Moreover,α-terpinolene andβ-gurjunene were not detected in the initial phase,consistent with Houet al.(2020). The two compounds above were detected at AF2,showed a gradual upward trend from AF2 to AF5,decreased the relative content at AF6,and then increased until they finally peaked in the ripening stage. By comparing the changes along the development stages,the maximum contents ofα-terpinolene andβ-gurjunene were found at AF5,approximately 300.00 and 800.00% of that at AF2,respectively.

Among the quantified terpenoids in peel oil of the Jincheng orange fruit,the contents ofα-pinene,sabinene,β-myrcene,d-limonene,α-cubebene,α-copaene,β-elemene,β-caryophyllene,germacrene D,and cadinene exhibited similar change patterns. The contents of these compounds increased from AF1 to AF5,decreased from AF6 to AF8,and then increased at AF9. In addition,AF5 exhibited the highest contents ofα-pinene,sabinene,β-myrcene,d-limonene,α-cubebene,α-copaene,β-elemene,β-caryophyllene,germacrene D,and cadinene,approximately 628.79,316.13,671.73,359.85,1 150.00,950.00,650.00,500.00,700.00,and 650.00% of those at AF1,respectively. Moreover,it was worth noting thatd-limonene was the composition with the highest content of all terpenoids in nine development stages,and the second one wasβ-myrcene and sabinene.Similar results that limonene is the component with the highest content of terpenoid,followed byβ-myrcene and sabinene,have been reported in citrus peels by Gucluet al.(2022). Of the other quantified terpenoids,styrene,α-thujene,γ-terpinolene,β-farnesene,andβ-sesquiphellandrene have exhibited similar tendencies in changes along the developmental stages,and which had the highest content all found at AF5,approximately 275.00,250.00,166.67,214.29,and 350.00% of those at AF1,respectively. In addition,the contents ofα-thujene,γ-terpinolene,andβ-sesquiphellandrene had not changed much before and after AF5. Moreover,the contents of styrene andβ-farnesene both gradually increased until AF5 except theβ-farnesene at AF1,styrene remained stable at 0.04 until AF9,andβ-farnesene decreased until AF9,following which the content was stable at 0.09.Furthermore,the content ofcis-β-ocimene was stable from AF1 to AF4,the content reached the maximum at AF5,approximately 437.50% of that at AF1,and then the content decreased until AF8 and increased again at the mature. The changing trend of first rising,then falling,and rising in the content of terpenoids,such asγ-terpinolene andβ-caryophyllene,was similar to that of the values observed in the peel oil of navel orange during the development stages (Cai 2015;Chaudharyet al.2018). From the results above,most of terpenoids in Jincheng orange showed the highest content at the mid-development stage (AF5),which was contrary or inconsistent with navel orange having the highest content almost at maturity and the red grapefruit at the early developmental stage (Chaudharyet al.2018;Houet al.2020). The reason might lie in the difference in varieties.

Principal component analysis of terpenoidsIn this study,the contents of terpenoids accounted for more than 92.00% of the total amount of volatile. PCA method (Fanet al.2009;Renet al.2015) was performed to explore the correlation and segregation of terpene hydrocatbons in peel oil during the development of Jincheng orange.Considering the results of PCA,3 principal components(PCs) contributed to about 92.37% of the total variance,of which PC1 and PC2 explained 64.62 and 21.88% of the total variance,respectively. Fig.2 shows that AF5 was in the upper right quadrant in the development of Jincheng orange,demonstrating that AF5 positively correlated with PC1. Similar results were also observed for AF6 and AF9 (Fig.2-A). However,AF1,AF2,AF3,AF4,AF7,and AF8 were negatively related to PC1. As for PC2,AF1,AF2,AF3,AF4,and AF5 were found to be positively correlated,whereas AF7,AF8,AF9,and AF6 were negatively related. These results demonstrated that the AF5,AF6,and AF9 stages of Jincheng orange fruit were completely segregated and exhibited differences.In other words,the terpenoids played a vital role in the semi-maturity stage and maturity. In addition,theβ-myrcene,sabinene,andd-limonene provided a large contribution for terpenoids at the whole growth stages(Table 2). However,the highest relative content was found at AF5 and AF6,and the low relative content was found at AF9,which might be due to the interactions between genetic (biotic) and environmental (Drobyet al.2008;Houet al.2020). Moreover,the decrease ind-limonene at AF9 might be associated with the increase ofα-terpinolene and valencene. Therefore,the 3 stages of AF5,AF6,and AF9 played an important role in the formation of aromatic substances during the growth and development of Jincheng orange. Of the variable PC1 (Fig.2-B),α-thujene,sabinene,cis-β-ocimene,γ-terpinolene,α-farnesene,andβ-sesquiphellandrene were positively correlated with PC1 and PC2 and were close to those at AF5. In addition,styrene,α-pinene,β-myrcene,d-limonene,α-cubebene,α-copaene,β-elemene,β-caryophyllene,germacrene D,β-gurjunene,α-terpinolene,γ-selinene,and cadinene were positively related to PC1 and were in the same quadrant as AF6.Valencene,γ-muurolene,and ylangene compounds were positively correlated with PC1 and were found to be in the same quadrant as AF9. In addition,as for the terpenoid,the relative quantities of which were significantly changed during AF5,AF6,and AF9,as shown in Fig.2.

Changes in the relative content of alcohols,aldehydes,ketones,oxides,esters,and other terpene hydrocarbonsAmong the identified alcohols in the peel oil of Jincheng orange fruits,trans-p-mentha-2,8-dienol and terpene-4-ol were not detected from AF1 to AF5 and AF1 to AF3,respectively (Table 2). The contents oftrans-pmentha-2,8-dienol were first detected at AF6,increased at 0.09 at AF7,decreased at AF8,and reached 0.04 at AF9. However,the content of terpene-4-ol was stable between 0.1 and 0.3 from AF4 to AF9. Additionally,the elemol was not detected at AF1,the content of which exhibited an increasing tendency between AF2 and AF6,decreased between AF7 and AF8,and finally increased at AF9 compared to AF8. Of those stages above,the content of elemol had the highest content at AF6,approximately 257.14% of that at AF1. Regarding the quantified alcohols,the contents of diketone alcohol and 3-pentanol had not changed much in all development stages of Jincheng orange fruits. Moreover,the contents ofp-menthan-8-ol,3-hexanol,β-terpineol,linalool,α-terpineol,and citronellol gradually increased until AF5,decreased from AF6 to AF8,and finally increased at fruit maturity. Furthermore,the maximum content of those compounds above was found at AF5,approximately 250.00,208.11,283.33,247.58,363.16,and 588.89%of those at AF1,respectively. The highest content of alcohols in peel oil at the nine development stages of Jincheng orange was observed to be linalool,followed by 3-hexanol andα-terpineol.

The results in Table 3 show that the compound tetradecanal was not detected in the initial four stages but identified at AF5,and it had a stable value between 0.02 and 0.03 in the last four stages. In the comparison of the changes in the quantified aldehydes at the development stages of Jincheng orange fruit,the contents of (E)-3-hexenal,hexenal,octanal,nonanal,citronellal,decanal,neral,geranial,and perilla aldehyde increased from AF1 to AF5,except for perilla aldehyde which was not detected at AF1 and showed decreasing contents until AF8 and increasing contents at the fruit maturity. Of these results,the maximum contents of those aldehydes above all existed at AF5,approximately 425.00,300.00,640.00,553.85,500.00,1 262.50,446.67,and 371.43%of the content of (E)-3-hexenal,hexenal,octanal,nonanal,citronellal,decanal,neral,and geranial at AF1,and 457.14% of the content of perilla aldehyde at AF2,respectively. In addition,the undecanal and dodecanal had a similar change pattern with the aldehydes above,except that these contents exhibited stable levels during AF6 and AF8. Finally,α-sinensal exhibited a different change pattern compared to other aldehydes,wherein the contents were observed to be increasing until AF5 and decreased at the last development stages until fruit maturity. Octanal was found in the highest quantities,followed by decanal and geranial in peel oil at all the selected stages of development in Jincheng oranges.

Among the identified ketones in the peel oil of Jincheng orange fruit,nootkatone was only found at the fruit maturity. In addition,pulegone and (-)-carvone were both found during the development stages of AF5.The pulegone content showed stable between 0.01 and 0.03,whereas the (-)-carvone content gradually increased along the stages of development,and the highest content of (-)-carvone was at the fruit maturity stage,approximately 250.00% of that at AF5. Moreover,verbenones were found at the last 3 development stages but showed stable quantities between 0.05 and 0.06.As for cyclohexanone,the content increased during the development stages from AF1 to AF5 and then decreased until AF8,followed by an increase at fruit maturity or AF9. The highest content of cyclohexanone was found at AF5 and AF9,approximately 228.57% of that at AF1.

Regarding the identified oxides,caryophyllene oxide was detected at the last two developmental stages and showed the highest content at the fruit maturity,approximately 325.00% of that at AF8. Based on the results of the quantified oxides in peel oil during the development stages of Jincheng orange fruit,the contents (Z)-limonene oxide and (E)-limonene oxide were relatively stable along different stages.Among these identified esters,neryl acetate and geranyl acetate were found at the last 3 development stages,with the content of neryl acetate gradually increasing and having the highest relative content of 0.04 at fruit maturity,whereas geranyl acetate remained relatively stable between 0.01 and 0.02. In the quantified other terpene hydrocarbons in peel oil during the development stages of Jincheng orange fruit,the content of toluene gradually increased and had the highest relative content of 0.12 at AF5 and then decreased until the fruit maturity. In addition,ethylbenzene andp-xylene exhibited similar changes in peel oil during the development stages,with the exception of the last 3 development stages,where the quantities remained relatively stable.

All the changes in the contents of volatiles such as linalool,β-terpineol,nonanal,citronellal,nootkatone,and caryophyllene oxide were in agreement with the peel oil in navel orange during different development stages (Houet al.2020).

3.2.ldentification of fatty acids

Eight fatty acids were identified in peel oil during Jincheng orange development,of which seven were saturated fatty acids and one was unsaturated fatty acids (Table 1). The qualitative analysis of these compounds was based on database searching,MS spectra in NIST Chemistry WebBook,and comparing the values of RI with the reports in the literature (Silvaet al.2010;Felixet al.2012;Wanget al.2012;Caiet al.2013;Xia and Li 2018).

Changes in the relative content of fatty acidsAmong the identified seven saturated fatty acids in peel oil (Table 4),the content of lauric acid decreased during AF1 and AF6 and then gradually increased until fruit maturity. Of these changes,the lowest content of lauric acid (0.04)was found at AF6. In addition,myristic acid,pentadecanoic acid,palmitic acid,3,5-di-t-butyl-4-hydroxyphenyl propionic acid,stearic acid,and eicosanoic acid exhibited a similar change pattern,with their contents decreasing until AF4,tending to increase at AF5,and thereafter decreasing until fruit maturity. Of the results,the highest content in peel oil of Jincheng orange fruits was found at AF5 except for that pentadecanoic acid which had the highest content of 0.26 at AF1,i.e.,114.29,119.01,112.50,210.53,105.00% of the content of myristic acid,palmitic acid,3,5-di-t-butyl-4-hydroxyphenyl propionic acid,stearic acid and eicosanoic acid at AF1,respectively. In addition,the content of stearic acid in peel oil had the highest content of 0.20 at AF9. Based on the quantified unsaturated fatty acids in the peel oil of Jincheng orange,oleic acid exhibited similar change patterns as that of the saturated fatty acid,pentadecanoic acid. From these results,the changed tendency of fatty acids in peel oil was similar to most volatiles above at different growth stages in Jincheng orange fruits. This result was the same with most plant volatiles originating from fatty acids(Schwabet al.2008;Stitzet al.2014;Wanget al.2015;Dhandapaniet al.2017;Al-Juhaimiet al.2018).

4.Conclusion

The changes in volatiles and fatty acids in the peel oil of Jincheng orange fruit were characterized by GCMS during the development stages. Approximately 60 volatiles and 8 fatty acids were identified in this study.The results identified more than 92.00% of the total volatiles as terpenoids. Utilizing the PCA plot,the AF5,AF6,and AF9 development stages of Jincheng orange fruit were identified to be completely segregated and exhibited differences. Also,the most obvious changes in terpene hydrocarbons in peel oil were found at AF5,AF6,and AF9,whereas most of the volatiles and fatty acids exhibited maximum contents at fruit maturity. In conclusion,the fruit growth of Jincheng orange exhibited significant effects on the volatile constituents and on the precursors of fatty acids.

Acknowledgements

This research was supported by the Guizhou Provincial Science and Technology Projects,China (ZK[2022]391),and the Cultivation Project of National Natural Science Foundation of Guizhou Medical University,China(21NSFCP20).

Declaration of competing interest

The authors declare that they have no conflict of interest.