Absorption and Degradation of Individual Intact Glucosinolates in the Digestive Tract of Rodents

Abstract

Degradation of intact glucosinolates or their transformation into other products and glucosinolate absorption from the gastrointestinal tract were investigated by in vivo and in vitro experiments with rats. The absorption of intact glucosinolates in the form of active and passive transport across the intestinal wall was investigated in vitro using the intestine of rat and hamster as everted sacs. Individual glucosinolates as well as rapeseed meal with and without heat inactivation of myrosinase activity were used for the experiments. Analyses were based on HPLC and HPCE after group separation, purification and concentration of intact glucosinolates and their on-column desulfatation products. The in vivo experiments showed 3- to 20-fold lower concentrations of glucosinolates in the content from the stomach and the first parts of the small intestine compared to the concentrations in the applied feed. The glucosinolate concentrations increased again in contents from the distal part of the small intestine, and were reduced to very low values in contents from caecum and colon, with great variations between the individual animals. In vitro studies of glucosinolate degradation during 24 h periods revealed limited degradations when tissue homogenates of the stomach and small intestine and contents therein were used, whereas appreciable degradations were found when the caecum and/or colon contents were used. Heat inactivation of myrosinase activity in the rapeseed meal fed to a group of rats did not affect in vitro glucosinolate degradation in contents from stomach or small intestine, whereas the degradation seemed to be prevented in contents from caecum or colon, indicating an effect from dietary fibres or myrosinase associated to the dietary fibres. None of the glucosinolates was absorbed actively across the intestinal walls in vitro for any parts of the gastrointestinal tract investigated, as found with glucose, whereas passive or facilitated transport was found to be appreciable. The presence of glucosinolates did not affect the active glucose transport. The results obtained showed an appreciable in vivo absorption of intact glucosinolates in the upper gastrointestinal tract and degradation/transformation of the remaining glucosinolates in the distal gastrointestinal tract of rats.

Key Words:

• intestinal contents
• intestinal wall
• everted sacs
• active transport
• facilitated transport
• passive transport
• rapeseed
• dietary fibres
• myrosinases