Fruit quality evaluation on eight apple germplasm accessions

【Objective】Apple (Malus × domestica) is widely grown all over the world and one of the most common fruits in our daily life. China has a large number of apple germplasm resources that can be excavated and utilized, which are widely distributed in Xinjiang, Shaanxi, Shandong and other places in China. Fruit quality is an important aspect of apple germplasm resources that can be tapped and utilized. It is of great significance for breeding varieties with excellent flavor and functionality. The flavor quality of fruits is related to the content of sugar, acid and aroma substances. In this study, the fruit quality of 8 apple germplasm accessions was evaluated, and the relationship between phenolic substances and antioxidant capacity and the screening of aroma components were analyzed, so as to understand the differences in fruit traits, quality and flavor of different apple germplasm resources, and provide reference for their utilization.【Methods】In this study, eight apple germplasm accessions including P5, L51, L37, LC36, L7, LC54, ZN18 and C31 were used as experimental materials. The appearance quality was determined by the electronic analytical balance, vernier caliper and colorimeter. The soluble solids contents were determined by sugar-acid integrated machine. The titratable acid of fruit was determined by acid-base titration. The contents of soluble sugar, malic acid and aroma substances were determined by TSQ 9000 triple quadrupole GC-MS. The ascorbic acid content, total flavonoid content, total phenol content and antioxidant capacity of apple germplasm accessions were determined by corresponding kits. Phenolic compounds were determined by HPLC-MS. The fruit quality of 8 apple germplasm accessions was evaluated, and the difference in aroma substances and the relationship between phenolic content and antioxidant capacity were analyzed.【Results】Among the 8 apple germplasm accessions,P5, L51, L37, LC36, LC54 and C31 were small fruit-sized, while ZN18 and L7 were large fruit-sized. There were significant differences in the appearance quality of each apple germplasm accession. The soluble solids and titratable acid contents were significantly different. The soluble solids content of LC36 was significantly higher than that of other germplasm accessions, and the titratable acid content of L37 was significantly higher than that of other germplasm accessions. The types of soluble sugars were mainly fructose and sucrose. The fructose contents of P5, L51, L37 and LC54 were close to the sucrose contents, which were between 42.08 and 47.24 mg·g-1 . The fructose content of LC36 was slightly higher than its sucrose content, which was 66.26 mg · g- 1 and 48.07 mg · g- 1 , respectively. However, the fructose contents of L7, ZN18 and C31 were nearly double higher than its sucrose content. The ascorbic acid, total flavonoid and total phenol contents of different apple germplasm resources were significantly different. The ascorbic acid contents of LC54 and C31 were significantly higher than those of other germplasm accessions. The total flavonoid and total phenol contents of L51 were significantly higher than those of other germplasm accessions. The total flavonoid and total phenol contents of ZN18 were significantly lower than those of other germplasm accessions. Chlorogenic acid is the main phenolic substance in 8 apple germplasm accessions. LC54, L51 and LC36 had the strongest antioxidant capacity, and ZN18 had the weakest antioxidant capacity. Based on the fruit quality index of each apple germplasm accessions, the membership function value was calculated, and the fruit quality evaluation was carried out based on the average value of the membership function value of each apple germplasm accession. The average membership function value of each apple germplasm resource was calculated by synthesizing 37 indicators. The results showed that the average membership function value of L51 was the largest, indicating that the average fruit quality of L51 was the best, and the average membership function value of ZN18 was the smallest, indicating that the average fruit quality of ZN18 was the worst. Therefore, we concluded that the fruit quality of each apple germplasm accession was: L51＞ C31＞LC54＞LC36＞P5＞L37＞L7＞ZN18.【Conclusion】The appearance quality and internal quality of the 8 apple germplasm accessions were significantly different, and the 8 apple germplasm resources had their unique utilization value in terms of quality. For example, L37 could be used as a characteristic aroma material, and L51, LC36 and LC54 could be used as materials with high antioxidant capacity. Therefore, these 8 apple germplasm resources could be preserved and utilized as characteristic materials in the follow-up work.