Ripening-Associated Branched-Chain Amino Acid Metabolism Correlates With Branched-Chain Ester Accumulation in "Chanthaburi 1" Durian, a Mild-Scent Cultivar.

Abstract

Durian exhibits pronounced cultivar-dependent variation in aroma intensity during ripening. This study investigated volatile composition and associated metabolic regulation in "Chanthaburi 1," a low-aroma durian cultivar. Fruits displayed typical climacteric behavior, with respiration peaking at 375 mg CO₂ kg^-1 h^-1 on Day 4 and ethylene production reaching 28 µL kg^-1 h^-1 on Day 5 during the storage of mature green fruit at 25°C and 65%-75% relative humidity. Dehiscence occurred on Day 7, coinciding with marked pulp softening. Total volatile content increased by 240% from the unripe to overripe stages. Alcohol dehydrogenase and alcohol acyltransferase activities rose approximately three- and over fourfold, respectively, indicating enhanced esterification capacity during ripening. Aroma development featured a marked shift from straight-chain to branched-chain esters, with their ratio decreasing from 51.1 at the ripe stage to 2.38 at the overripe stage. Characteristic branched-chain esters, including ethyl 2-methylbutanoate, methyl 3-methylbutanoate, and propyl 3-methylbutanoate, were predominant in overripe fruit. Leucine and valine decreased at the ripe stage and increased again at the overripe stage, whereas methionine accumulated continuously. These findings demonstrate that ripening activates branched-chain amino acid catabolism as a programmed precursor-supplying pathway, which together with terminal esterification contributes to aroma development in "Chanthaburi 1" durian. PRACTICAL APPLICATIONS: This research provides aroma profile information in a milder aroma durian cultivar. Identified key volatiles and biochemical precursors can guide optimized harvest timing, and postharvest handling for durian traders. The findings also provide useful biochemical and volatile phenotypic references for breeding programs targeting reduced fruit pungency, by identifying key aroma compounds and metabolic pathways associated with the mild-scent phenotype of Chanthaburi 1.