Recent Understanding of the Biosynthesis of Capsaicinoids and Low-pungent Analogs towards Quality Improvement of Chili Pepper

Chili pepper (Capsicum spp.) is an economically important crop used as a spice and vegetable. The striking feature of chili pepper fruits is their pungency, which is attributed to capsaicin and its analogs (collectively called capsaicinoids). Capsaicinoids are unique compounds synthesized only in Capsicum fruits, and their biosynthesis exhibits temporal- and spatial-specific patterns in the placental septum tissue. Capsaicinoids are biosynthesized through the condensation of vanillylamine (produced in the phenylpropanoid pathway) and a fatty acid moiety (produced from branched amino acids). Capsaicinoids have beneficial bioactivities, such as thermogenetic and anti-obesity properties, and thus they are regarded as health-promoting compounds. Furthermore, low-pungent capsaicinoid analogs (capsinoids and capsiconinoids) have been discovered in chili pepper fruits. They exhibit similar physiological activities to pungent capsaicinoids and are promising compounds with high economic value because of their low-pungency. Huge variation in capsaicinoid and analog contents among Capsicum accessions has been observed. Research using various Capsicum accessions has identified important genetic factors in the biosynthesis of capsaicinoids and low-pungent analogs. This review provides an overview regarding the biosynthesis of capsaicin and its analogs. Furthermore, future options to enrich the quality of chili pepper fruits are discussed.