T01027: Influence of cooking and processing of Brassica vegetables on release of beneficial and harmful metabolites of glucosinolates in the digestive tract

Study Duration: December 2002 to February 2006

Contractor: Macaulay Land Use Research Institute - subcontracts at Robert Gordon University/University of St Andrews

Brassica vegetable consumption is associated with a reduced incidence of cancer. Glucosinolates, a group of natural products found in Brassica vegetables (green cabbage, cauliflower, broccoli and Brussel sprouts), have been implicated as mediators of this phenomenon. Glucosinolates are metabolised following plant cell damage, to yield a range of biologically active metabolites including isothiocyanates and nitriles. Isothiocyanates appear to be involved in chemo-protection by a variety of mechanisms whereas nitriles are potentially toxic and have been shown to cause damage to liver and kidney tissue in rats. The manner in which Brassica vegetables are treated prior to consumption may influence the relative proportions of isothiocyanates and nitriles arising in the digestive tract. In particular, the method and extent of cooking may alter metabolic fate of glucosinolates. This project complements T01028.

The current project aims to develop urinary markers for estimation of in vivo production of glucosinolate hydrolysis products. These will then be used in human volunteer trials to determine the digestive fate of glucosinolates. Further work will study the way in which different methods of preparing and cooking Brassica vegetables influence the hydrolysis and resulting digestive fate of glucosinolates following their ingestion by humans. The first phase of the study will focus on the synthesis of glucosinolates using novel techniques previously developed at the University of St Andrews and other laboratories. This includes the synthesis of stable isotope labelled compounds for use in animal studies. Results from this part of the work will be used to identify urinary biomarkers, first in animal models and then in humans.

This project complements project no T01028
T01028

The initial stage of this project involved the synthesis of a number of stable isotope-labelled glucosinolates and their metabolites. Sequential feeding of rats with labelled and unlabelled glucosinolates under different conditions led to the identification of a series of urinary metabolites. This information was then used to seek out similar compounds in urine from humans consuming cabbage or broccoli using a range of conditions and matrices.

Specifically the project has:

• Developed methods for the synthesis of stable isotope labelled glucosinolates. This represents an important achievement for this project and will be useful for any future work with glucosinolates.
• Investigated the effect of different cooking methods on the levels of glucosinolates and active myrosinase (the enzyme that breaks down glucosinolates to isothiocyanates and other metabolites) in cabbage and broccoli. These data were then used to predict levels of glucosinolates and their breakdown products available from the diet. The findings suggest that lightly cooked brassica vegetables give the highest yields of glucosinolate metabolites. This was confirmed by the results of human volunteer trials.
• Data from these studies were used to establish the pattern and level of absorption in humans; and to assess the possible effects on glucosinolate metabolism of:
  the meal matrix; or the administration of probiotics.

The project has demonstrated that with the exception of boiling which inactivates myrosinase, cooking methods have little effect on glucosinolate concentrations. Meal matrix effects were minimal; similarly glucosinolate levels were not affected by prebiotic supplementation. The results of feeding volunteers pre-formed isothiocyanates as opposed to intact glucosinolates showed that inter-individual variation in isothiocyanate excretion was much less than when intact glucosinolates were eaten. The authors therefore concluded that there is significant inter-individual variation in glucosinolate hydrolysis in the digestive tract.

The final report is available from the Agency’s Information Centre.
To obtain a copy, please contact the Enquiry Desk, Information Services, Food Standards Agency (tel: 020 7276 8181/8182 or email: infocentre@foodstandards.gsi.gov.uk)

Fuller Z, Louis P, Mihajlovski A, Rungapamestry V, Ratcliffe B and Duncan AJ, (2007). Influence of cabbage processing methods and pre-biotic manipulation of colonic microflora on glucosinolate breakdown in man. Br. J. Nutr., 98(2), 364-72.

Morrison JJ and Botting NP, (2005). The synthesis of [phenyl-2H5]gluconasturtiin and its metabolites for metabolic studies. J. Labelled Comp. Radiopharm., 48, 897-907.

Morrison JJ and Botting NP, (2007). The synthesis of isotopically labelled glucoraphanin for metabolic studies. Tetrahedron, 48, 1891-4.

Rungapamestry V, Duncan AJ, Fuller Z, and Ratcliffe BR, (2006). Changes in glucosinolate concentrations, myrosinase activity and production of hydrolysis products of glucosinolates in cabbage (Brassica oleracea var. capitata) cooked for different durations. J. Agric. Food Chem., 54, 7628-34.

Rungapamestry V, Duncan AJ, Fuller Z and Ratcliffe B (2007). Effect of cooking brassica vegetables on the subsequent hydrolysis and metabolic fate of glucosinolates. Proceedings of the Nutrition Society March; 66(1):69-81

Song LJ, Morrison JJ, Botting NP and Thornalley PJ, (2005). Analysis of glucosinolates, isothiocyanates and amine degradation products in vegetable extracts and blood plasma by LC-MS/MS. Anal. Biochem., 347, 234-43.

For any enquiries concerning this research project, please contact the relevant Programme contact or email: science@foodstandards.gsi.gov.uk