Evaluation on fruit flavor quality in two second-generation hybrid apple lines

Abstract: 【Objective】Functional apple is defined as a kind of health-promoting apple with high content of flavonoids and can be fresh consumed or processed. Breeding for functional apple is to realize integration of multiple quality traits (genes) , which requires multiple parental crosses and repeated backcrosses and selection. In this study, we investigated the flavor quality of two functional apple lines using the conventional cultivar‘Gala'as the control.【Methods】The 2 functional apple lines were‘Hongxin 7'and‘Hongxin 9', which were the second generation of hybrid between‘Gala'and a hybrid F₁ plant from the population of Malus sieversii f. neidzwetzkyana × conventional cultivars (‘Fuji'‘Golden Delicious' ‘Starkrimson'‘Hanfu', etc.) . Relevant indicators of flavor substances were measured and analyzed. The contents of calcium, iron and zinc were determined with atomic spectrophotometer. Aroma substances were extracted by the solid phase microextraction (SPME) and detected with a GC/MS-QP2010 gas chromatography-mass spectrometer (Shimadzu, JPN) . The characteristic aroma components were determinedusing index of aroma value with lg (aroma value) > 0 assigned as the characteristic aroma component. Aroma value was the ratio of a compound content to the aroma threshold of the compound. Sugar and acid components were measured using high performance liquid chromatography (510, Water, US) . The flavonoid components were also determined with high performance liquid chromatography (Dionex, US) . The firmness and brittleness were measured with a TA.XT plus texture analyzer (Stable Microsystems, Godalming, U.K.) . The taste evaluation of fruits was carried out by a group of seven people.【Results】There were significant differences in some fruit traits among the three tested materials. Some traits, such as fruit size, fruit shape index, brittleness and soluble solids were of no defined pattern. The content of anthocyanins, fruit firmness and antioxidant power in‘Hongxin 7'and‘Hongxin 9'were significantly higher than those in‘Gala'. The contents of calcium, iron and zinc in‘Hongxin 7'and‘Hongxin 9'were significantly higher than those of‘Gala', and calcium in‘Hongxin 7'and‘Hongxin 9'was 1.93 and 1.96 times of that of‘Gala', respectively. Four sugars and seven organic acids were detected from the 3 materials, and the contents of fructose and malic acid were the highest among sugar and acid components, respectively.Sucrose, lactic acid and acetic acid, and other sugars and acids in‘Hongxin 7'and‘Hongxin 9'were significantly higher than those in‘Gala'. Therefore, the two functional apple lines had significantly higher contents of total sugars and acids than‘Gala'. Total sugar content was the highest in‘Hongxin 7', while total acid content highest in‘Hongxin 9'. The ester compounds were the highest aromatic compounds in the 3 tested materials, but the categories and contents of aroma components and characteristic aroma components were different. The numbers of aroma components and characteristic aroma components in‘Hongxin 9'were the highest; but their contents in‘Gala'were the highest, while their numbers and contents in‘Hongxin 7'were the lowest. Flavanoids such as flavanols, dihydrochalcones and flavonols were detected in the 3 tested materials, but their contents differed among the tested materials. Eleven components were detected in‘Hongxin 9'and the total content of flavonoids was (299.49±13.30) mg·kg^-1, while nine components were detected in‘Hongxin 7'and the total content of flavonoids was (229.21±9.55) mg·kg^-1.The flavonoid content in‘Hongxin 7'and‘Hongxin 9'was significantly and 3.1 and 2.3 times higher than that of‘Gala', respectively. Based on taste evaluation, ‘Hongxin 9'tasted sour, while‘Hongxin 7'and‘Gala'was sweet and sour.【Conclusion】Sugar and acid compositions were consistent in the three detected materials, but the antioxidant power and the contents of flavonoids, anthocyanin, calcium, iron and zinc in‘Hongxin 7'and‘Hongxin 9'were significantly higher than those in‘Gala'.‘Hongxin 7'was hard-crispy and juicy with low categories and contents of aroma components and characteristic aroma components. Similar to‘Gala'‘ Hongxin 7'tasted sweet-sour with very light astringency and had a good flesh quality that is highly acceptable among the majority of consumers. Therefore, we can select functional apple cultivars with excellent comprehensive quality from hybrid or backcross progeny segregating populations of Malus sieversii f. neidzwetzkyana.