トウガラシ果実に含まれる低辛味カプサイシン類似物質とその生合成について

Capsaicinoids are acid amides of vanillylamine and fatty acids, and are the main spicy component in chili peppers. Although capsaicinoids show beneficial biological activities, their utilization is limited due to intense pungency. The research on various chili pepper strains have identified two groups of low-pungency analogs (capsinoid and capsiconinoid). While capsinoids are esters of vanillyl alcohol and fatty acids, capsiconinoids are esters of coniferyl alcohol and the identical fatty acids. They exhibit similar biological properties to capsaicinoid, and have potential for food utilization, due to low pungency. The content of the low-pungency analogs varies greatly among the chili pepper strains. The mutations in putative aminotransferase (pAMT) gene have been identified as the key factor to accumulate capsinoid. The loss-of-function of pAMT suppresses the production of vanillylamine and capsaicinoid from vanillin, and accumulates vanillyl alcohol and capsinoids instead. Recently, it has been demonstrated that the synthesis of vanillyl alcohol from vanillin is carried out by cinnamyl alcohol dehydrogenase (CAD), which is ubiquitously involved in the lignin biosynthesis pathway in plants. The low-pungency analogs may be regarded as "by-products", which is produced when ubiquitous enzymes are involved in the biosynthetic pathway of specific secondary metabolites. Further understanding of capsaicinoid biosynthesis pathway may lead to rational manipulation of the biosynthesis pathway to increase low pungency analogs and the industrial value of chili pepper fruit.