Abstract:

Citrus is one of the major sources of dietary flavonoids that are polyphenolic compounds biosynthesized in secondary metabolism pathways. Possibly due to their strong antioxidant activity，flavonoids have many health-promoting properties，including anticancer，antiviral，anti-inflammatory and antimicrobial functions. The types of flavonoids detected in Citrus so far consist of flavanones，flavones，flavonols，dihydrochalcones and anthocyanins. Flavanone glycosides are the most abundant flavonoids in Citrus. Flavonoid composition varied significantly between different Citrus species and between tissue types，i.e. pummelo fruit contains large amounts of the bitter compound neohesperidosides，while sweet orange and mandarin have tasteless rutinosides as their dominant flavonoids. So far，our understanding of flavonoid metabolism is mostly on the structural genes in main biosynthesis pathways，while information on genes regulating the pathways and enzymes involving in glycosylation，acylation and methylation of flavonoid are relatively scarce. Future researches in flavonoid biosynthesis in citrus will reveal more genetic mechanisms controlling the synthesis，modification and distribution of the flavonoids. A better understandingof these mechanisms will provide guidance for citrus breeding programs to produce functional fruit with enhanced levels of flavonoids.

Key words: citrus, flavonoids, composition, metabolism