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return to Farmers
Independent Weekly
January
22, 2004
Manitoba
researchers help clean up Brazil nuts
by
Katia Arrus and Dr. Greg Blank, Department of Food Science
This
project was financially supported by the International Development
Research Council of Canada (IDRC).
Brazil
nuts originating from wild trees in the non-flooded areas
of the Guianas, Amazonian Brazil, Columbia, Venezuela, Peru
and Bolivia represent a major non-timber forest product. The
tree is one of largest in the Amazon basin ranging from 23
to 43 meters tall with branches and fruits or pods located
only near the top. The round pod resembles a woody-shelled
softball and contains approximately 10 to 25 Brazil nuts in
hard shells arranged concentrically in the capsule, similar
to orange segments. The pods are harvested after they fall
to the jungle floor and are opened using a machete.
The in-shell
nuts are placed in sacs and transported to processors where
they are shelled, sorted, graded and exported to various countries
including the United States, Canada and Europe to be eaten
raw or used for baking and confections.
This industry
continued for decades relatively unchanged until 1998 when
the European Community brought in stricter regulations on
microbiological standards and aflatoxin levels in Brazil nuts.
Under
hot, humid conditions, Brazil nuts are subject to contamination
with molds such as Aspergillus flavus which produce
proven carcinogens known as aflatoxins. Consumption of infected
nuts could cause various toxic effects in humans including
hepatic lesions, reduction of fertility, acute gastrointestinal
effects and cardiotoxicity.
The goal
of our research was to provide Brazil nut harvesters and processors,
particularly those located in Peru's province of Madre de
Dios, with information that could be used to reduce the incidence
and level of aflatoxin and disease-causing bacteria in Brazil
nuts. The research was divided into two main parts. Initially
we examined the influence of relative humidity and temperature
on aflatoxin production by Aspergillus flavus isolated
from Brazil nuts obtained from Peru. In the second part of
the study, we evaluated Brazil nuts from different stages
of processing.
We found
that the highest levels of aflatoxin occurred in nuts when
the relative humidity of the storage environment approached
97% and was accompanied by temperatures in the range of 25-30ºC.
At 10ºC or at a relative humidity level below 75% toxin
was not produced. Unfortunately, warm temperatures and a high
relative humidity are characteristics of the production areas
in the Amazon, especially during the harvesting season which
occurs from January to April and reducing relative humidity
and or temperature is not economically viable. We determined,
however, that reducing the moisture in the nuts to lower than
5.0 % could prevent aflatoxin production especially during
storage. Therefore, air and or mechanical drying of the nuts
following harvesting can be used to control mold growth, thereby
limiting toxin formation.
The microbiological
analysis performed on the Brazil nuts during various stages
of processing identified coliform bacteria and yeasts as well
as mold on the nuts even before they were harvested, since
the exterior of several Brazil nut pods were contaminated
while still on the tree. The cause for this contamination
remains unclear and requires additional investigation. Many
of the in-shell nuts received at the processing plant were
also contaminated with A. flavus. In order to prevent
or minimize aflatoxin formation, we concluded that the pods
should be opened as soon as they're harvested and that the
in-shell nuts be dried as soon as possible. Pathogens including
E. coli and salmonellae were not detected in any of
the nuts including those picked from trees.
In Peru,
in-shell Brazil nuts are soaked in water in order to soften
the shell. This facilitates cracking of the nut; however,
our study concluded that this process also contributes to
significant contamination. We recommended that alternative
methods be investigated such as steaming in order to avoid
external contamination.
Additional
studies are required in order to assess the microbiological
safety of Brazil nuts. Implementation of good manufacturing
practices, particularly those focused on hygiene, will be
of particular benefit since the processing of this nut involves
considerable handing. This information will help local harvesters
and producers maintain a viable export trade and contribute
to rainforest conservation.
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