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Influence of plant and bacterial myrosinase activity on the metabolic fate of glucosinolates in gnotobiotic rats

Published online by Cambridge University Press:  09 March 2007

Gabrielle Rouzaud ,
Sylvie Rabot ,
Brian Ratcliffe  and
Alan J. Duncan
Gabrielle Rouzaud
Affiliation:
Macaulay Institute, Craigiebuckler, Aberdeen AB15 8QH, UK
Sylvie Rabot
Affiliation:
INRA, Unité d'Ecologie et de Physiologie du Système Digestif, Centre de Recherche de Jouy en Josas, 78 352 Jouy en Josas, France
Brian Ratcliffe
Affiliation:
Robert Gordon University, Queen's Road, Aberdeen AB15 4PH, UK
Alan J. Duncan*
Affiliation:
Macaulay Institute, Craigiebuckler, Aberdeen AB15 8QH, UK
*
*Corresponding author: Dr Alan J. Duncan, fax +44 1224 311556, email a.duncan@macaulay.ac.uk
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Abstract

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The breakdown of glucosinolates, a group of thioglucoside compounds found in cruciferous plants, is catalysed by dietary or microbial myrosinase. This hydrolysis releases a range of breakdown products among which are the isothiocyanates, which have been implicated in the cancer-protective effects of cruciferous vegetables. The respective involvement of plant myrosinase and gut bacterial myrosinase in the conversion, in vivo, of glucosinolates into isothiocyanates was investigated in sixteen Fischer 344 rats. Glucosinolate hydrolysis in gnotobiotic rats harbouring a whole human faecal flora (Flora+) was compared with that in germ-free rats (Flora−). Rats were offered a diet where plant myrosinase was either active (Myro+) or inactive (Myro−). The conversion of prop-2-enyl glucosinolate and benzyl glucosinolate to their related isothiocyanates, allyl isothiocyanate and benzyl isothiocyanate, was estimated using urinary mercapturic acids, which are endproducts of isothiocyanate metabolism. The highest excretion of urinary mercapturic acids was found when only plant myrosinase was active (Flora−, Myro+ treatment). Lower excretion was observed when both plant and microbial myrosinases were active (Flora+, Myro+ treatment). Excretion of urinary mercapturic acids when only microbial myrosinase was active (Flora+, Myro− treatment) was low and comparable with the levels in the absence of myrosinase (Flora−, Myro− treatment). No intact glucosinolates were detected in the faeces of rats from the Flora+ treatments confirming the strong capacity of the microflora to break down glucosinolates. The results confirm that plant myrosinase can catalyse substantial release of isothiocyanates in vivo. The results also suggest that the human microflora may, in some circumstances, reduce the proportion of isothiocyanates available for intestinal absorption.

Keywords

GlucosinolatesIsothiocyanatesExcretionMyrosinaseHuman colonic microflora
Type
Research Article
Information
British Journal of Nutrition , Volume 90 , Issue 2 , August 2003 , pp. 395 - 404
Copyright
Copyright © The Nutrition Society 2003

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