Six fragrant ingredients were identified in fully-ripened Katsura-uri (Japanese pickling melon; Cucumis melo var. conomon). Four of them were sulfur-containing compounds [methylthioacetic acid ethyl ester (MTAE), acetic acid 2-methylthio ethyl ester (AMTE), 3-methylthiopropionic acid ethyl ester (MTPE), and acetic acid 3-methylthio propyl ester (AMTP)]; and the others were benzyl acetate and eugenol. The newly identified MTAE and AMTP possessed antimutagenic activity as determined by their ability to inhibit the UV-induced mutation in repair-proficient E. coli B/r WP2. MTAE and MTPE (esters with thiocarbonic acid and alkyl alcohol) induced the differentiation of human colon cancer cells (RCM-1 cells), but AMTE and AMTP (esters with carbonic acid and thioalkyl alcohol) did not. A specific thioester motif containing a thiocarbonic acid and alkyl alcohol correlated with these compounds ability to induce differentiation. AMTE, MTPE, AMTP, and eugenol had higher oxygen radical absorbing capacity than the antioxidative vitamin, ascorbic acid. The quantity of MTPE, AMTP and eugenol increased 49-fold, >1175-fold and 11-fold, respectively, in the fully-ripened fruit as compared to the mid-ripened fruit.
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