Researchers from the University of Porto report that the outer skin of Castanea sativa Miller, the most commonly consumed chestnut, offers a rich source of polyphenols, compounds with potent antioxidant activity.
"As far as we know, this is the first report concerning the antioxidant activity of five different chestnut extracts," wrote Joao Barreira in the journal Food Chemistry
"The results obtained indicate a high potential of application for these chestnut extracts, traditionally considered as disposable byproducts."
The use of natural alternatives to synthetic preservatives, such as like BHA and butylhydroxytoluene (BHT), to slow down the oxidative deterioration of food is gaining interest.
According to a 2003 report by Frost and Sullivan, the synthetic antioxidant market is in decline, while natural antioxidants, such as herb extracts, tocopherols (vitamin E) and ascorbates (vitamin C) are growing, pushed by easier consumer acceptance and legal requirements for market access.
This natural antioxidant range could potentially include the polyphenol-rich extract from chestnuts.
Barreira and co-workers extracted polyphenols and flavonoids from the skins, flower, fruit and leaves, and measured antioxidant activity using a battery of tests, including the DPPH (2,2-diphenyl-1-picrylhydrazyl) radical-scavenging activity, the 2,2'-azobis(2-amidinopropane)dihydrochloride (AAPH) assay, and the thiobarbituric acid-reactive substances (TBARS) inhibition of lipid peroxidation.
They report that the outer skins (510 mg/g), followed by the inner skins (475 mg/g), were the richest source of the antioxidants. The fruit contained the least (3.73 mg/g).
For all the tests performed the order of efficacy always placed outer and inner skins top, with the fruit extracts performing worst.
"Other tree nuts have potential antioxidant activity, namely: walnuts and hazelnuts," wrote the researchers. "The results obtained with chestnut flower, leaf, and skins extracts were excellent compared to the results obtained by us for walnut and hazel leaves."
The Portuguese harvest of chestnut produces 20,000 tons of fruit per year.
Source: Food Chemistry (Elsevier)
Volume 107, Issue 3, Pages 1106-1113
"Antioxidant activities of the extracts from chestnut flower, leaf, skins and fruit"
Authors: J.C.M. Barreira, I.C.F.R. Ferreira, M.B.P.P. Oliveira and J.A. Pereira