Durian is economically significant in Southeast Asia due to its distinctive aroma and palatability. During fruit ripening, the flesh generates a substantial quantity of esters and some sulfur-containing compounds. This study aimed to analyze the ester profiles and characteristics of alcohol acetyltransferase (AAT; EC. 2.3.1.84) in the ripe flesh of two Thai durian (Durio zibethinus Merr.) cultivars, 'Chanthaburi 1' (a hybrid cultivar with a soft aroma) and 'Monthong' (a renowned cultivar with a medium scent). The primary esters responsible for the aromatic compounds found in durian are ethyl-2-methyl butanoate, ethyl hexanoate, and ethyl octanoate. The AAT's efficacy was assessed in its ability to catalyze the synthesis of acetate esters through the reaction between acetyl CoA and different alcohols. The AAT enzymes extracted from 'Chanthaburi 1' and 'Monthong' cultivars exhibited a notable affinity towards 3-methyl-1-butanol and hexanol as alcohol substrates. Propanol and butanol exhibited moderate activity as AAT substrates, whereas methanol and ethanol demonstrated the lowest. Both durians exhibited favorable enzyme activity at a temperature of 30 °C. However, 'Monthong' AAT demonstrated superior performance across a broader pH range compared to 'Chanthaburi 1' AAT. The partially purified proteins precipitated with ammonium sulfate and subsequently gel-filtered through a DEAE-Sephadex® column enhanced the potency of 'Chanthaburi 1' AAT, resulting in increased purity (1.20-fold) and specificity (1.08-fold) compared to 'Monthong'. The AAT of 'Chanthaburi 1' and 'Monthong' exhibited molecular weights of 39.52 and 41.51 kDa, respectively. This study presents the initial documentation of AAT in durians through an enzyme assay and activity staining technique.
Keywords: Acetate esters; Durio zibethinus Merr.; Ester production; In situ staining; Ripening.
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