216: Pathway-Based Analysis Reveals Biosynthesis of Key Flavor Compounds in Apple: A Multiomics Approach

Introduction

Apple (Malus domestica Borkh.) is one of the most widely consumed fruits globally, known for its high sensory quality and nutritional benefits. According to our previous study, fruity esters (e.g., butyl acetate, butyl butyrate, 2-methylbutyl acetate) were strongly correlated with consumer-preferred apple flavor, while off-flavor compounds (e.g., furfuryl alcohol, furfural, 2-methyl-1-butanol) were primarily associated with lower hedonic ratings of apples. Despite extensive research on flavor differences among various apple cultivars, the mechanisms underlying flavor biosynthesis in Korean apple cultivars remain poorly understood. This study aims to elucidate the metabolic pathways involved in flavor biosynthesis in different Korean apple cultivars.

Methods

Apple fruits were harvested at commercial maturity from orchards in South Korea. For metabolomics, untargeted and targeted metabolomic approaches were conducted using LC-Q-TOF/MS. For transcriptomics, total RNA was extracted using CTAB method followed by RNA sequencing. The biological functions of differentially expressed genes (DEGs) were analyzed using KEGG enrichment and gene ontology (GO) analysis. Pearson correlation analysis was performed to investigate the correlation between major flavor precursors, metabolites, and DEGs in selected pathways.

Results

Metabolomic analysis identified 65 metabolites associated with apple flavor biosynthesis, including organic acids, sugars, amino acids, and volatile compounds. Pathway enrichment analysis revealed nine significantly enriched pathways critical for the biosynthesis of key apple flavor compounds. Transcriptomic analysis identified 4,648 DEGs with an FDR of 0.05 and |log2FC| ≥ 1 across four apple cultivars. An integrative transcriptomic and metabolomics analysis elucidated the regulatory mechanisms associated with key flavor compounds. The results showed that key metabolites from glycolysis, aspartate metabolism, butanoate metabolism, citrate cycle, and glutamate metabolism were partially responsible for the fruity flavors of apple fruits. Additionally, fructose and mannose metabolism, pentose and glucuronate interconversions, and ascorbate metabolism were implicated in the biosynthesis of off-flavor compounds. Furthermore, the DEGs exhibited differential expression across cultivars, and key genes were found to be associated with the major flavor biosynthetic pathways.

Significance

The present study provides evidence of the major metabolites contributing to the sensory qualities of apple fruits and elucidates the genomic trends underlying metabolite biosynthesis. These findings provide valuable resources for the continued improvement of overall apple fruit quality.

Authors: Keono Kim, Yuna Jeon, Min Jeong Kang, Eui-Joon Kil, Joon Hyuk Suh, Jeehye Sung