(+)-Methyl Jasmonate-Induced Bioformation of Myricetin, Quercetin and Kaempferol in Red Raspberries

The effect of postharvest treatment with enantiomers of methyl jasmonate (MJ) in conjunction with ethanol on bioformation of myricetin, quercetin and kaempferol in red raspberry was studied. For comparison, postharvest treatment with the commercial stereoisomeric mixture of MJ in conjunction with ethanol was simultaneously accomplished. The levels obtained were contrasted with those determined in untreated (control) samples. Exogenous (+)-MJ induced an enhancement in the levels of myricetin, quercetin and, particularly, kaempferol whereas the exposition to (-)-MJ exhibited the opposite effect. Enzymatic assays were carried out in presence and absence of (-)-MJ and (+)-MJ to evaluate possible changes in the activity of the enzymes regulating the bioformation of flavonols in red raspberries as a consequence of the treatments. From the results of the assays both (-)-MJ and (+)-MJ inhibited the activity of flavanone 3 beta-hydroxylase (FHT) and flavonol synthase (FLS), which are directly involved in the formation of flavonols from (-/+)naringenin. From these results, it is speculated that the activity of phenylalanine ammonia lyase (PAL) regulating the formation of (-/+)-naringenin from L-phenylalanine by (+)-MJ in conjunction with ethanol is promoted. Postharvest treatment of red raspberry with (+)-MJ in ethanol is proposed as a mean to increase flavonol content in red raspberries.