The scientists found that the phenolic acids in the Blackadder variety - cultivated by the New Zealand Institute for Plant and Food Research which funded the research - caused a near total inhibition (96%) of monoamine oxidase B (MAO-B) enzymes.
Blocking these enzymes, which regulated serotonin and dopamine concentrations in the brain, meant reduced oxidative stress - essential for normal cognitive function and mood, said the authors.
MAO inhibitors have been used for several decades in the pharmaceutical world to treat depressive disorders and neurodegenerative diseases, and have been shown to improve cognitive processing when given to early-onset Parkinson patients.
“This is the first demonstration of a clinically significant inhibition of MAO-B following blackcurrant supplementation,” wrote the authors.
“Although the current study measured MAO-B inhibition only in peripheral tissue, if the inhibition could be shown to be centrally active, the clinical applications of a MAO inhibitor from a commonly consumed fruit could be enormous.”
The researchers said this was the first study looking at the improvement of cognitive function in young healthy adults, while Roger Hurst of Plant & Food Research said the ultimate aim of the research was to develop new functional foods.
"Understanding what, and how, foods affect mental performance could lead to the development of new foods designed for populations or situations where mental performance or mental decline is a factor, such as older people or those suffering from stress, anxiety or other mood disorders,” he said.
In study 36 healthy participants aged between 18 and 35 years were assigned to one of three groups.
Two groups received a 142 ml intervention drink derived from either the Blackadder blackcurrant variety or the DelCyan variety, both containing 5 mg of polyphenols per 60 kg of bodyweight, or a placebo which contained no polyphenols but matched the juices for taste and sucrose.
After waiting 60 minutes to let the antioxidants be absorbed, the subjects completed various tasks commonly used in nutritional intervention studies to measure cognitive performance, flexibility and mood scale.
The researchers found that the varieties had slightly difference effects – subjects who drank the DelCyan had better Rapid Visual Information Processing (RVIP) accuracy whilst those who drank Blackadder juice scored better for alertness and vigilance.
Subjects who drank both blackcurrant juices reported a reduction in mental fatigue. For mood, they reported feeling more alert but not calmer or more content.
"This research shows how New Zealand blackcurrants can potentially add value, both for the food industry and for people looking for foods that naturally support their own health aspirations," said Hurst.
Source: Journal of Functional Foods
Published online ahead of print, http://dx.doi.org/10.1016/j.jff.2015.06.005
“Acute supplementation with blackcurrant extracts modulates cognitive functioning and inhibits monoamine oxidase-B in healthy
Authors: A. Watson, C. F. Haskell-Ramsay and D. O. Kennedy