BIOSINTESIS MENTHOL PADA BERBAGAI PERIODE PENCAHAYAAN TANAMAN MENTHA (Mentha piperita L.)

ABSTRAK<br />Penelitian ini bertujuan untuk mengkaji mekanisme sintesis menthol<br />pada berbagai periode pencahayaan tanaman M. piperita L. Penelitian<br />dilakukan di Instalasi Penelitian Balai Penelitian Tanaman Obat dan<br />Aromatik, Lembang, Jawa Barat, dari bulan Januari 2000 hingga Juli 2000.<br />Penelitian dilakukan tiga tahap. Tahap pertama membuat variasi<br />lingkungan cahaya, tahap kedua penyulingan dan analisis komponen<br />minyak dengan kromatografi gas spektrometer massa dan tahap ketiga<br />merunut lintasan biosintesis menthol. Penelitian menggunakan rancangan<br />acak kelompok 5 perlakuan, yaitu L 0 (panjang hari normal sebagai<br />kontrol), L 1 (pemutusan periode gelap 1 jam, pukul 21.00-22.00 mulai<br />umur 30 hari), L 2  (pemutusan periode gelap 1 jam, pukul 21.00-22.00<br />mulai umur 60 hari), L 3 (penambahan cahaya 4 jam, pukul 18.00-22.00<br />mulai umur 30 hari), dan L 4 (penambahan cahaya 4 jam, pukul 18.00-<br />22.00 mulai umur 60 hari). Hasil penelitian menunjukkan bahwa<br />perubahan lingkungan mempengaruhi mekanisme sintesis menthol di<br />dalam tanaman Mentha piperita L. Perubahan lingkungan mengubah<br />lintasan menthol yang selanjutnya mengubah komponen minyak dan mutu<br />menthol. Tingginya kadar menthol dan rendahnya menthofuran pada<br />penambahan cahaya 4 jam terjadi melalui penghambatan pembentukan<br />senyawa menthofuran dengan mereduksi pulegon menjadi menthol,<br />sehingga menthol meningkat, sedangkan pada perlakuan kontrol terjadi<br />oksidasi pulegon ke menthofuran sehingga menthol rendah. Penambahan<br />cahaya 4 jam mulai umur 30 hari setelah tanam menghasilkan minyak<br />dengan kadar menthol paling tinggi yaitu 54,89% dan menthofuran paling<br />rendah yaitu 7,83%.<br />Kata kunci :  Mentha, Mentha piperita L., periode pencahayaan, hasil,<br />komposisi minyak, Jawa Barat<br />ABSTRACT<br />The effect of photoperiod on menthol sysnthesis of<br />Mentha piperita L.<br />Research on the effect of photoperiod on menthol synthesis of<br />Mentha piperita L, was carried out at the Experimental Garden of Institute<br />Reseach for Medicinal and Aromatic Crops, Lembang, West Java, from<br />January until July, 2000. The objective is to study the machanism of<br />menthol synthesis in relation with the manipulation of light periode, three<br />steps were taken: The first step was manipulation of environment using TL<br />lamps (two experiments), the second step was distillation and analisis of<br />peppermint oil from their products with gas chromatography and mass<br />spectrometry, and the third step was tracing the pathway on menthol<br />biosynthesis. At the first experiment, 5 treatments were given i.e. (1)<br />control or normal light period, (2) four hours light supplement at the age of<br />30 days and 60 days after planting, and (3) one hour interruption of dark<br />period at the age of 30 days and 60 days. The result showed that the effect<br />of light period manipulation can change the pathway of menthol<br />biosynthesis and oil component and finally the quality of menthol. Four<br />hours light supplement at the age of 30 days after planting could enhance<br />the menthol content and reduce menthofuran by blocking the reaction from<br />pulegone to menthofuran, so the pulegone was reduced into menthon and<br />menthol. Four hours light supplement at 30 days after planting showed the<br />highest menthol content (54.89%) and the lowest menthofuran (7.83%).<br />Control treatment (normal light period) showed the lowest menthol<br />content, due to no reduction of pulegone into menthon, but pulegone was<br />oxidized into menthofuran. Without additional light the menthol content<br />decreased and the menthofuran content increased.<br />Key words : Mentha, Mentha piperita L., oil composition, photoperiod,<br />yield, West Java