Analysis of fruit flavor and quality variation of Luli apple from different regions

Abstract: 【Objective】Apple planting area is widely distributed in China, involving 25 provinces. Affected by soil characteristics, altitude and climate, fruit quality indexes such as weight, color and sugars and acids differ in different growing areas, which lead to the flavor differences between producing areas. Fruit flavor is the internal quality of fruit, which is related to taste sense and olfactory sense. Taste perception is based on sweet and sour tastes, while olfactory sense is the smell of a mix of large number of volatile aromatic substances in the fruit. There have been few reports on the performance of new varieties in different producing areas, and there is a lack of objective and scientific evaluation system of fruit flavor. In this study, sugars, acids and aroma components of Luli apple fruit from 17 regions were determined, and the difference in fruit quality of the new variety in different regions was clarified. The study provides technical support for the promotion and application of the new variety.【Methods】Fruit samples were collected from 12 regions in Shandong province and 5 in other provinces. During the ripening period of Luli apples in each region, 50 apple fruit were randomly selected from representative orchards. The quality indexes, such as single fruit weight, shape index, soluble solid content, titratable acid content, soluble sugar content, and sugar to acid ratio, were determined. High performance liquidchromatography (HPLC) was used to determine sugars and acids, and the aroma components of fruit were determined by headspace solid phase extraction (HS-SPME) and gas chromatography-mass spectrometry (GC-MS). The data were statistically analyzed with SPSS.19.0, and Origin 2018 was used for heat map.【Results】The average single fruit weight in each region was 196.71 g. The fruit shape index in different regions had little difference, ranging from 0.83 to 0.99. The variation coefficient of fruit shape index was only 4.53%. Fruit hardness of fruit from Aksu, Guangrao and Pingdu was higher than 10.00 kg·cm^-2 . Aksu had the highest value in soluble solids, soluble sugars and titratable acids. The contents of soluble solids and soluble sugars in fruit from Taian and Yanggu were low, but titratable acid content was high. Sugar to acid ratio was the highest in fruit from Mengyin (67.46) and the lowest in those from Tai 'an (12.61). Among the sugar components in fruit, fructose was the highest, and its content ranged from 30.94 to 55.08 mg · g^{- 1} . Glucose content was the second highest, with an average of 18.05 mg·g^-1 . Sucrose content in fruit varied greatly and was highest in Mengyin (22.84 mg·g^-1 ), which was 6.78 times that of the fruit from Tai’an, which was the lowest. The content of sorbitol in fruit in all regions was low, and the average content was 4.64 mg·g-1 . Malic acid was the main organic acid in apple fruit, and its content was the highest among organic acids, with an average value of 2547.81 μg·g^-1 , followed by tartaric acid content, ranging from 321.58 to 564.11 mg·g-1 . Fruit from Aksu and Guangrao had a higher tartaric acid content than the other areas. The average contents of oxalic acid, citric acid and succinic acid were 138.01 μg·g^-1 , 107.09 μg·g^-1 and 85.57 μg·g^-1 , respectively. A total of 65 aroma components were detected from fruit samples from the 17 regions, including 31 esters, 22 alcohols, 6 aldehydes, 2 terpenes and 4 other aroma components. Fruit from Tai 'an had the most abundant aroma components, with 41 aroma components detected, followed by Guangrao with 38 components. Fruit from Jieshou was least in aroma abundance with only 17 detected. There were 13 common aroma components in Luli fruit from the 17 regions. The main aroma components in samples from Jieshou and Yanggu were aldehydes and alcohols, accounting for 48.49% and 37.01% of the total aroma components, respectively. Esters were the main volatile substances in Luli fruit from the other 15 regions, accounting for more than 48% of the total aroma. The typical correlation analysis of fruit aroma components and sugar and acid contents showed that glucose, citric acid, succinic acid and sucrose were closely related to the aroma, while fructose and malic acid had limited effects on the aroma.【Conclusion】 The fruit appearance quality, sugar, acid, aroma and other flavor quality indexes of Luli apple from different regions were compared and analyzed. The single fruit weight was the largest in fruit from Penglai. The hardness and soluble solids content of Luli apple were higher than those of mid-early maturing apples in the Chinese national standard《Fresh apple》. Fructose was higher in fruit from Huangsanjiao, Wanrong, and Guangrao. Fruit from Aksu, Pingdu and Huangsanjiao contained higher malic acid. Luli apple was rich in aroma substances, with a total of 65 species were detected. This paper preliminarily reported the quality performance of Luli apple in different regions of our country, which has certain reference significance for determining suitable areas for production of Luli apple in our country.