Increasing the alkyl glucosinolate level in Broccoli by leafstalk infusion of methionine

Alkyl glucosinolates such as glucoraphanin and glucoiberin are secondary plant products derived from amino acids. Some of their breakdown products potentially contribute to positive effects on human health. Broccoli (Brassica oleracea convar. botrytis var. italica) contains considerable amounts of these alkyl glucosinolates and in order to increase these amounts, methionine was added to broccoli plants via leafstalk infusion. Methionine was applied in five different concentrations at the developmental stage of head formation. The percentage of the alkyl glucosinolates on total glucosinolates were on average 80 %. The alkyl glucosinolate concentration increased in the highest methionine treatment by 16 % due to significant increases of glucoraphanin and the cultivar specific glucosinolate glucoiberin, while glucoalyssin and glucoerucin remained unaffected. Twenty percent of the detected glucosinolates were indole glucosinolates, which were not changed by the methionine treatment.