story to find out more.
Chemist Russell Molyneux prepares walnut pellicle
samples for analysis of gallic acid content. Click the image for more
information about it.
Walnuts' Secret Defense Explored
By Marcia Wood
March 9, 2005
With their rich taste and pleasing
crunchiness, it's no wonder that walnuts are one of America's favorite tree
nuts. But walnuts, like several other kinds of crops, are vulnerable to attack
by fungi called Aspergillus flavus and A. parasiticus. Both
species can produce a natural compound called aflatoxin, which is thought to be
Though inspections ensure that the walnuts that make their way from orchards
to the home are free of harmful levels of aflatoxin,
Agricultural Research Service scientists
in Albany, Calif., want to do more to combat the fungi. For example, they've
compared the A. flavus resistance of nearly a dozen leading kinds of
English walnuts--the kind most widely marketed in the United States--and two
species of black walnuts, which are less widely grown because their thicker
shells are harder to open.
These laboratory experiments, led by ARS research chemist
J. Molyneux of the agency's
Regional Research Center at Albany, showed that a popularly grown walnut
known as Tulare was remarkably resistant to Aspergillus. Molyneux did
the work with chemist
E. Mahoney at the Albany laboratory and with
University of California,
Davis, collaborator Jim McKenna. Davis researchers Charles A. Leslie and Gale
H. McGranahan also participated.
Tulare's secret defense? It's gallic acid, found only in the nutmeat's thin
skin, or pellicle, according to Molyneux. Tulare walnuts contained
one-and-one-half to two times more gallic acid than, for instance, Chico
walnuts, the most Aspergillus-susceptible of the walnuts that the
Earlier, scientists elsewhere had shown that gallic acid has antimicrobial
effects. But Molyneux's team is likely the first to show that a crop
susceptible to an aflatoxin-producing Aspergillus can actually prevent
the Aspergillus from producing aflatoxin.
The work, published in 2003, paved the way for current Albany studies to
discover how gallic acid undermines Aspergillus.
more about the research in the March issue of Agricultural Research
ARS is the U.S. Department of
Agriculture's chief scientific research agency.