Sulfur metabolism in durian pulps: Factors contributing to the production of volatile sulfur compounds during fruit ripening

Abstract

Durian (Durio zibethinus L.), an economically important fruit crop in Southeast Asia, is known for its strong sulfuryl aroma resulting from the accumulation of sulfur-containing compounds. However, our understanding of sulfur metabolism in fruit remains limited. In this study, we focused on the functional characterization of durian methionine γ-lyase (DzMGL), the key enzyme in volatile sulfur compound (VSC) production. In addition, to gain a better insight into sulfur metabolism, we profiled metabolites related to this process using various methods and assessed the expression of relevant genes through reverse transcription-quantitative PCR. Our gene and metabolite analyses revealed that sulfur metabolism is activated during ripening. Interestingly, DzMGL exhibited a higher efficiency in using L-cysteine than Arabidopsis MGL. The differential levels of the produced VSCs explained the aroma intensity-related differences between the two commercial Thai cultivars ‘Chanee’ and ‘Monthong’. Furthermore, the cysteine availability-related differences between the two cultivars could contribute to this variation, with ‘Chanee’ containing higher cysteine levels than ‘Monthong’. Our findings indicated that γ-glutamylcysteine was the preferred form of sulfur storage in durian pulps, with a potential recycling process providing intermediates that flux methionine toward ethylene biosynthesis and VSC production. This study provides novel insights into sulfur metabolism in durian fruit.