Analysis of aroma components in fruit of the new apple cultivar ‘Ruixue’ and several common cultivars

Abstract:【Objective】Seven apple varieties including‘Ruixue'‘Fuji'‘Pink Lady'‘Gala'‘Jonagold'‘Golden Delicious' and‘Orin'were selected as experimental materials in the present study. The differences in their aroma components at ripe stage were analyzed. The main aroma substances in‘Ruixue'were further explored in order to popularize the new apple variety.【Methods】Unbagged apple fruits of the seven varieties were taken from the Experimental Station of Northwest A&F University, Baishui County, Shaanxi Province, China in 2017. These apple trees had the same growth conditions and management levels. They were trained into spindle shape and single-row planted at 1.5 m × 4 m tree spacings. Starch dyeing, color and maturity of the fruits were determined based on sensory evaluations.‘Ruixue'‘Fuji'‘Pink Lady'‘Gala'‘Jonagold'‘Golden Delicious' and‘Orin'were harvested at190 d, 180 d, 195 d, 180 d, 125 d, 150 d, and 165 d after flowering, respectively. Six apple trees (n=6) for each cultivar were selected for fruit sampling. Fruit were harvested from the four sides of the crown of each tree. The sampled fruits were packed and transported to the laboratory. One quarter of each fruit was taken and cut into small pieces and mixed. The aroma components of the fruits were extracted by the headspace solid-phase microextraction (SPME) . One gram of sodium chloride and rotor were added to a 50 mL sample bottle, and 5 g sample and 10 μL 3-nonanone (0.04 μL · mL^-1) were added successively. The sample bottle was then sealed with tin foil, and balanced in a magnetic stirring heating plate for10 min. After that, the extraction head was inserted into the well balanced sample bottle for adsorption.After 40 min, the extraction head was inserted into a GC sample port at 250 ℃ for desorption. After desorption for 2.5 min, the extraction head was taken out to determinate the aroma components in fruits using the gas chromatography-mass spectrometry (GC-MSQP-2010) . Helium was used as the carrier gas at a flow rate of 1.0 mL · min^-1. A HP-INNOW capillary column of 60 m in length, 0.25 mm in inner diameter and 0.25 μm film thickness was used. Injection port temperature was 230 ℃ and a non-split injection mode was applied. The column temperature started from 40 ℃ (holding 3 min) and increased to150 ℃ at the rate of 5 ℃ · min^-1, then rose at 10 ℃ · min^-1 to 220 ℃, which was maintained for 5 min.The MC were equipped with an electron ionization (EI source) with an electron bombardment energy of70 eV, an ion source temperature of 240 ℃ and a transmission line temperature of 240 ℃.【Results】A total of 92 aroma substances were detected in the seven apple cultivars, including 53 esters, 12 aldehydes, 6 alcohols, 4 ketones, 9 olefins, and 8 other species. Among them, ‘Ruixue'contained 46, ‘Pink Lady'49, ‘Fuji'35, ‘Gala'49, ‘Jonagold'38, ‘Golden Delicious' 42, and‘Orin'42 of the aromatic components.‘Pink Lady'and‘Gala'had the largest total volatile matter, followed by‘Ruixue', and‘Fuji'had the lowest. Esters were the most abundant across the seven apple varieties, and it included20-30 species, while ketones and alcohols were the least, with only 2-5 species. The common aroma components of the seven apple varieties were butyl acetate, butyl butyrate, hexyl acetate, 2-methylbutyl, methyl butanoate, Hexyl 2-methylbutanoate, Hexyl hexanoate, Hexanal, 2-Hexanal and à-Farnesene, etc. The apple fruit of different varieties were clustered into different genomic groups according to the PCA score map. Based on the distance between the varieties, they were generally classified into three groups. The first group included‘Gala'and‘Pink Lady', located at the top left of the score chart. The second group contained‘Golden Delicious' ‘Fuji'and‘Orin', located at the bottom left of the score chart. The distance was small in this group, which indicated the great similarity among the three apple varieties. The third group included‘Jonagold'and‘Ruixue'on the right side of the score map. The second principal component showed that the distance between the two cultivars was large, and the relative content of volatile matter and material was quite different.【Conclusion】Compared with the other selected apple varieties, the new apple variety‘Ruixue'had more aroma components, including a higher level of hexyl 2-methylbutanoate (15.24%) , 2-hexenal (17.65%) and à-farnesene (27.88%) , while the content of 1-butanol, 2-methyl-, acetate and acetic acid, hexyl ester were lower, and these aroma components probably formed the unique flavor of‘Ruixue'apple.