S16 - Session P2 - Profiling and ratio of main sugar and phenolic component in early developing apple fruitlets

Authors: Milica Fotiric Aksic, Tomislav Tosti, Uros Gasic, Nikola Horvacki, Radosav Cerovic, Zivoslav Tesic, Mekjell Meland *

Sugars are involved in nearly all fundamental processes within plant, and synthesis of many compounds, such as polyphenols. Both groups of compounds are important for plant metabolism and the regulation of fruit development. The aim of this study was to show developmental dynamics of sugar and phenolic metabolism together with its ratio in early developing apple fruitlets. The study was done on apple cultivar `Summered`, during two consecutive years (2015-2016) in Ullensvang, Hardanger district, western Norway. Early developing fruitlets were picked four times (every third day) starting when fruitlets were 8-10 mm in diameter (approximately two weeks after full bloom). Sugar analysis was done using high-performance anion-exchange chromatography (HPAEC) with pulsed amperometric detection (PAD), while phenolic analysis was done while using ultra-high performance liquid chromatography coupled to a linear ion trap-Orbitrap hybrid mass analyzer. The most abounded sugar components were glucose, fructose, sucrose and sorbitol followed by galactose and turanose. The ratio between glucose: fructose was 1:1.4-1.5, while glucose : sorbitol ratio was 1:3.5-4. Galactose : turanose and sucrose : sorbitol ratio was 1:1. The major polyphenolic components were phlorizin, quercetin_3-O-rhamnoside, quercetin and phloretin. Phlorizin : quercetin_3-O-rhamnoside ratio was 1: 2.6-3.1, while phlorizin : phloretin was 1: 2.4-2.9. The results suggest that `Summered` is a 'low-fructose-to-glucose-ratio' and 'low-phloretin-to-phlorizin-ratio' cultivar. This study is just a beginning of the comprehensive study of the mechanisms involved in sugar and polyphenolic metabolism in developing apple fruitlet.