| Summary: | This study was to investigate chemical properties and associated biological effects of
monosaccharide pentose, aldo- and keto-hexose generated Maillard reaction (MR) products
(MRPs) in both sugar-lysine (Lys) and sugar-casein MR models. Different reaction rates of
three sugar-Lys MR models corresponded to differential yields of high molecular weight
(HMW) (> 3,500) MR products (MRPs). The reaction rate of ribose (Rib) was greater than that
for glucose (Glc), which in turn was greater than that for fructose (Fru). Greater bioactivity,
such as antioxidant and cytotoxic activities of MRPs were associated with HMW MRPs.
Similarly, sugar-modified casein MRPs also exhibited different reaction rates depending on
sugar source, but changes in antioxidant and cytotoxic activity of native casein was minimal.
The present study demonstrated antioxidant activity of sugar-Lys MRPs in both hydrophilic
and hydrophobic systems. Differences in l,l-diphenyl-2-picryl-hydrazyl scavenging activity
were observed between three sugar-generated MRPs derived from both sugar-Lys and sugar-casein
MRPs. Antioxidant activity of MRPs was further investigated in a human intestinal
epithelial model, i.e., Caco-2 cells. The sugar-Lys MRPs was shown to protect Caco2-cells
from H2O2 and 2,2'-azobis-(2-amidinopropane)dihydrochloride (AAPH) induced cytotoxicity,
and moreover, from ferrous ion and cupric ion induced cytotoxicity. There.was no significant
difference in MRP protection among three sugar-generated MRPs. The sugar-casein MRPs
were also shown to protect Caco2-cells from AAPH, ferrous ion, and cupric ion induced
cytotoxicity. The cell protective effect of sugar-modified caseins was, however, comparable to
native casein.
Sugar-Lys MRPs were shown to reduce the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl
tetrazolium bromide (MTT) response of Caco-2 cells, adversely affect cellular antioxidant
enzyme activities for superoxide dismutase (SOD), catalase, glutathione peroxidase (GSH-Px), and lower glutathione content. These changes corresponded to an altered cell proliferation
cycle, but no change in cellular lactate dehydrogenase leakage. A greater reduction in cell
MTT response occurred for Rib-Lys MRPs, compared to Glc- and Fru-Lys MRPs. Sugar-casein
MRPs did not affect cell MTT response and antioxidant enzyme activities in Caco-2
cells. A more pronounced cytotoxic effect of sugar-casein MRPs was obtained on embryonic
Int-407 cell, with a decrease in antioxidant enzyme activities of SOD and GSH-Px observed
for Glc- and Fru-caseins, but not Rib-casein.
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