A review published in the Journal of Cereal Science suggested that while evidence on the antioxidant potential of wholegrain cereals is plentiful, further research – importantly in vivo – needs to be conducted to discover the true antioxidant potential.
“The in vitro antioxidant capacity of cereals is only an approximate reflection of their in vivo antioxidant effect due to differences in antioxidant solubility/bioavailability within the digestive tract and the metabolism/conjugation of compounds such as polyphenols,” the researchers wrote.
“During digestion, the antioxidant capacity of cereals is increased and is likely to provide a favorable antioxidative environment for the epithelium tract, notably in the large intestine,” they continued.
Antioxidant potential likely underestimated
The researchers said that while extensive research has measured the in vitro antioxidant potential of wholegrain cereals, refined cereals, brans and other various cereal products, the antioxidant capacity of these grains has likely been underestimated.
Un-physiological extraction methods using solvents – used in most published in vitro studies – does not completely release all the antioxidant compounds, they said. There is an important fraction of antioxidant micronutrients, especially insoluble phenolic acids, which is strongly bound to the fiber fraction of the grain outer layers, they added.
“…It is therefore difficult to predict the in vivo efficiency of an antioxidant or of a cereal product based solely on in vitro measurements. Numerous factors may influence the antioxidant action of the defined compound in vivo, such as digestibility, bioavailability and metabolism – for example conjugation for polyphenols.”
“Thus, the relationship between the antioxidant capacity measured in vitro and the real health benefits of cereals and cereal products is not really known,” they said.
Activity in humans not fully understood
While wholegrain cereals seem to provide an antioxidant protection throughout the intestinal tract - this should be confirmed by in vivo studies.
“While the antioxidant capacity of cereals is believed to contribute to a better antioxidant status in vivo, the mechanisms involved remain poorly understood, and it is difficult to associate the effect of a given micro-constituent with a particular metabolic effect.”
The review also noted that strong in vitro antioxidant potential was not always an indication of a strong in vivo effect.
Human studies remain scarce…
Animal studies have been conducted, along with a few in humans, the review said.
However, investigation into the antioxidant potential of cereal in animals and humans remains “scarce in view of the numerous in vitro studies”.
Source: Journal of Cereal Science
Published online ahead of print, doi: 10.1016/j.jcs.2008.01.002
“Is the in vitro antioxidant potential of whole-grain cereals and cereal products well reflected in vivo?”
Authors: A. Fardet, E. Rock and C. Rémésy