Analysis of aroma compounds in 9 jackfruit varieties

Abstract：【Objective】This study analyzed the aroma components in nine jackfruit varieties and classified the varieties based on aroma components using principal component analysis and cluster analysis.The characteristic aromatic components detected in jackfruits were quantified using the odour activity value (OAV) , ratio of concentration of the volatile compound to its odour threshold. Aroma components with the aroma value greater than or equal to 1 were regarded as characteristic aroma.【Methods】The aroma components in the nine jackfruit varieties were analyzed by headspace solid-phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS) . The flesh tissue was homogenized with beater in liquid nitrogen. Flesh (0.2 g) was weighed in 20 mL jaws and added with 5 mL of saturated sodium chloride solution to extract aroma ingredients for 40 min. Aroma ingredients were detected by SHIMADZU QP2010-Plus gas chromatography-mass spectrometer with an automatic injection. A 65μm PDMS/DVB solid phase microextraction extraction head was aged at 250 ℃ for 1 hour in the gas chromatographic inlet before injection. The chromatography was equipped with a DB-5 capillary column (30 m × 0.25 mm × 0.25 μm) and the column temperature was raised following the procedure: initial 40 ℃ for 1 min, an increase to 100 ℃ at 3.5 ℃·min-1, and to 180 ℃, and a further increase at 5 ℃·min-1 to 250 ℃, which was maintained for 3 min. The inlet temperature was kept at 250 ℃. There was no shunt. The carrier gas was helium at a flow rate of 1.0 mL · min-1. Desorption of the extractor at the inlet was allowed for 2 min. The mass spectrometry conditions included an electron impact ion source (EI) , an ion source temperature of 230 ℃, an interface temperature of 280 ℃, a detector voltage 350 V, an electron energy 70 e V and a scanning quality range of 35-335 amu. The external standards were methylisovalerate, butyl isovalerate, ethyl isovalerate, butyl acetate, isoamyl acetate, n-propyl acetate, butyl butyrate, benzaldehyde, n-hexanal, isovaleraldehyde, active amyl alcohol, 1-pentanol, isoamyl alcohol, nbutanol, isobutyl isovalerate and isoamyl isovalerate, which were of HPLC purity grade and purchased from Sigma. Sodium chloride (AR) was provided by Sinopharm Chemical Reagent.【Results】There were 130 volatile components in the nine jackfruit varieties, including 71 esters, 16 alcohols, 19 aldehydes, 8 ketones, 3 acids, 6 hydrocarbons and 7 other substances. The nine varieties were dominated by ester-based substances, followed by alcohol substances, acid substances and so on. The major aroma components in the nine varieties included 12 components, namely isoamyl isovalerate, isopentyl isooctanoate, propyl isovalerate, amyl valerate, butyl isovalerate, amyl valerate, esters, isobutyl isovalerate, phenylpropionaldehyde, isoamyl alcohol, ethyl isovalerate and isoamyl acetate. The characteristic aroma was different among the nine varieties. The principal component analysis and cluster analysis (intergroup connection) were used to classify the nine cultivars. The case system cluster analysis was carried out based on the Euclidean distance. When the distance was 9, 6 varieties including the‘Haida 2'‘No.20'‘Siji'‘No. 28'‘No. 45'and‘Red flesh 327'were grouped together in a class, which displayed obvious difference with the other three varieties. When the distance was 11, the 9 varieties could be divided into two categories, ‘No. 92'alone as a class, and the other eight as the other class. And the distance between‘No. 92'and the other eight varieties was the greatest (25) . The main aroma components in‘Haida 2'‘No. 20'‘Siji'‘No. 28'‘No. 45'‘Red flesh 327'‘305'and‘Soft type'were isoamyl isovalerate, amyl isovalerate, butyl isovalerate, ethyl isovalerate, propyl isovalerate and heptanoic acid heptyl ester, without isoamyl octanoate. The main aroma components in‘No. 92'were isovalerate butyl ester and isoamyl octanoate, which was unique in‘No. 92'. The comprehensive scores of the aroma components in the nine jackfruit varieties were in order of‘No. 92'>‘No. 45'>‘305'>‘Soft type'>‘No. 20'>‘Haida 2'>‘No. 28'>‘Red flesh 327'>‘Siji'. There were more than 40 esters in‘305'‘Soft type'‘No. 28'‘No. 45'and‘Siji'. However, in‘Red flesh 327'there were only 30 esters, but alcohol substances, aldehydes, hydrocarbons and other substances were most abundant among the nine varieties. There were isovaleraldehyde, isovalerate, isoamyl alcohol, isovaleric acid and phenylethyl alcohol in‘Haida 2';ethyl 2-methyl butyrate, ethyl isovalerate, isopentyl alcohol and isovaleric acid in‘305'; ethyl 2-methyl butyrate, isoamyl acetate, ethyl isovalerate, isoamyl alcohol and isovaleric acid in‘Soft type'; ethyl isovalerate and isoamyl alcohol in‘No. 28'; isoamyl acetate, ethyl isovalerate and isoamyl alcohol in‘No. 45'; isovaleraldehyde, alcohols and isovaleric acid in‘No. 20'; isovaleraldehyde, isoamyl acetate, isovalerate, isoamyl alcohol and phenylethyl alcohol in‘Red flesh 327'; isoamyl alcohol in‘Siji'; and isovaleraldehyde, (Z) -2-decenal, isoamyl alcohol, phenylethyl alcohol and isovaleric acid in‘No. 92'.【Conclusion】Although the aroma components of the nine varieties of jackfruit were different, the important aroma components of the nine cultivars were esters, which accounted for more than half of the total aroma and formed the major flavor substances in jackfruit. Isoamyl alcohol was the characteristic aroma substance in the nine cultivars according to the results of OAV value analysis. Isooctanoate was a unique aroma ingredient of‘No. 92', which was quite different from the other eight varieties.‘Red flesh 327'had the least amount of esters, but it contained the largest variety of substances including the specific component of 1-chloropentane, which provides a special aroma of this cultivar.