Comparison of fruit quality and volatile compounds between Golden Delicious apple and the new strain originated from its occasional seedling (SGP-1)

Abstract:【Objective】Golden Delicious is one of the main apple cultivar in the alpine plateau in Southwest China. It is popular for high eating quality. However, its fruit surface is easily rusty. The fruits of new strain SGP^-1 selected from occasional seedling of Golden Delicious have less rust, lower acidity and stronger aroma. The purpose of this study was to investigate the differences in fruit quality and volatile substances of Golden Delicious and its offspring SGP^-1 in order to provide a theoretical basis for the possible use of the new strain.【Methods】The rust index, the peel color, single fruit weight, the fruit index, hardness, soluble solids, titratable acid, vitamin C, sugar and acid components of Golden Deli-ious and SGP^-1 were detected by conventional methods. The volatiles of the fruits were analyzed qualitatively and quantitatively by gas chromatography-mass spectrometry.【Results】(1) The fruit surface of SGP^-1 was densely waxy, smooth and less rusted, the fruit spots was small and thin, besides, the sunny side was bright and red. The main quality indexes of the two materials had significant differences. Compared with Golden Delicious apple, the pulp firmness, sugar-acid ratio, color value L and a* of SGP^-1fruits were respectively increased by 9.94%, 80.91%, 6.31%, 27.14%, the rust index and titratable acid respectively decreased by 80.0% and 52.8%. (2) A total of 44 volatile substances were identified in the two materials, mainly composed of compounds such as esters, alcohols, and terpenes. SGP^-1 had 38 volatile substances, including 25 kinds of esters, 5 kinds of terpenes, 3 kinds of alcohols, 2 kinds of ethers, 1 kind of aldehydes, 1 kind of phenols, and 1 kind of aromatic hydrocarbons; the content of esters was 76.51% , the content of terpenes was 12.69% , and the content of alcohols was 7.04%; phenols were unique substances, accounting for only 0.19%. There were 13 kinds of volatile substances with relative content over 1.00% in the fruits of SGP^-1. There were 34 volatile substances, including 20 kinds of esters, 4 kinds of terpenes, 4 kinds of alcohols, 2 kinds of ethers, 2 kinds of aldehydes, 1 kind of ketones, and 1 kind of aromatic hydrocarbons in the fruits of Golden Delicious; the relative content of esters was 53.87%; followed by alcohols (20.21% ) and terpenes (10.55% ); ketones were unique substances, accounting for only 0.10%. There were 14 kinds of volatile substances with relative content over 1.00% in the fruits of Golden Delicious. The above showed that the components and contents of volatile substances of the two materials were quite different, resulting in a unique and rich aroma of SGP^-1 fruits. (3) The Variable Importance of Projection (VIP) was used to analyze the contribution of each volatile substance in the PLS-DA model to the difference between the two materials. A total of 27 volatile compounds were identified as differential volatiles. The 24 compounds such as Hexanoic acid, the methyl ester, Butanoic acid, 2-methyl-, propyl ester, Butanoic acid, ethyl ester, Acetic acid, butyl ester, Butanoic acid, propyl ester, Butanoic acid, 2-methyl-, 2-methylbutyl ester, 1-Butanol, 2-methyl-, acetate, Octanoic acid, ethyl ester, Hexanoic acid, ethyl ester, 2- Butanoic acid, 2-methyl-, ethyl ester, Hexanoic acid, butyl ester, Estragole, 2-Butenoic acid, 2-methyl-, 4-methylpentyl ester, (E)-, Butanoic acid, 2-methyl-, heptyl ester, Hexanoic acid, pentyl ester, Hexanoic acid, 2-methylbutyl ester, Butanoic acid, 2-methyl-, pentyl ester, Octanoic acid, hexyl ester, Eugenol, Butanoic acid, 2-methyl-, hexyl ester, Butyl 2-methylbutanoate, Alpha-Patchoulene, Acetic acid, pentyl ester and Hexanoic acid, and hexyl ester in the fruits of SGP- 1 were higher than those of Golden Delicious (p＜0.05) and had higher contribution values. The contents of 5-Hepten-2-one, 6-methyl-, 1-Hexanol, 2-ethyl- and Butanoic acid, butyl ester in the fruits of Golden Delicious were higher, and their contribution values were higher than those of SGP^-1(p＜0.05).【Conclusion】Compared with Golden Delicious apple, the fruit rust index, acid content and sugar-acid content of SGP^-1 fruits were significantly improved, and the aroma components were rich in the fruits of SGP^-1, and the comprehensive characters of SGP^-1were better than Golden Delicious. The molecular mechanism of less rust, low acidity and rich aroma in SGP^-1 apple need to explore in the near future.