Determination of the molecular weight distribution of non-enzymatic browning products formed by roasting of glucose and glycine and studies on their effects on NADPH-cytochrome c-reductase and glutathione-S-transferase in Caco-2 cells.
After thermal treatment of a mixture of glucose and glycine for 2 h at 125 degrees C, about 60% of the starting material was converted into non-soluble, black pigments, whereas 40% of the mixture was still water-soluble. Dialysis of the latter fraction revealed 30.4% of low molecular weight compounds (LMWs; MW < 10,000 Da) and 10.0% high-molecular weight products (HMWs; MW > or = 10,000 Da). The water-soluble Maillard reaction products (MRPs) were separated by gel permeation chromatography and ultrafiltration, revealing that 60% of the water-soluble products of the total carbohydrate/amino acid mixture had MWs < 1,000 Da and consisted mainly of non-coloured reaction products. MRPs with MWs between 1,000 and 30,000 Da were found in comparatively low yields (about 1.3%). In contrast, about 31.1% of the MRPs exhibited MWs > 30,000 Da, amongst which 14.5% showed MWs > 100,000 Da, thus indicating an oligomerisation of LMWs to melanoidins under roasting conditions. To investigate the physiological effects of these MRPs, xenobiotic enzyme activities were analysed in intestinal Caco-2 cells. For Phase-I NADPH-cytochrome c-reductase, the activity in the presence of the LMW and HMW fraction was decreased by 13% and 22%, respectively. Phase-II glutathione-S-transferase activity decreased by 15% and 18%, respectively, after incubation with the LMW and the HMW fractions. Considering the different yields, 30% and 10%, respectively, of the LMW and the HMW fractions, the total amount of the LMW fraction present in the glucose-glycine mixture is more active in modulating these enzyme activities than that of the HMW fraction.
Hofmann
T
T
Deutsche Forschungsanstalt für Lebensmittelchemie, Lichtenbergstrasse 4, D-85748 Garching, Germany. Thomas.hofmann@lrz.tu-muenchen.de
Ames
J
J
Krome
K
K
Faist
V
V
D018938:Caco-2 Cells; D002850:Chromatography, Gel; D003956:Dialysis; D005947:Glucose / Q000378:metabolism* / Q000494:pharmacology; D005982:Glutathione Transferase / Q000187:drug effects / Q000378:metabolism*; D005998:Glycine / Q000378:metabolism* / Q000494:pharmacology; D006358:Hot Temperature; D006801:Humans; D015416:Maillard Reaction; D008970:Molecular Weight; D009251:NADPH-Ferrihemoprotein Reductase / Q000187:drug effects / Q000378:metabolism*; D013997:Time Factors; D014462:Ultrafiltration
D009251:NADPH-Ferrihemoprotein Reductase; D005982:Glutathione Transferase; D005947:Glucose; D005998:Glycine