Research improves the control of Brazil nut contamination by mycotoxins

Study also helped to set more realistic national and international ceilings on toxic substances produced by fungi in Brazil nuts.

By Elton Alisson | Agência FAPESP – Brazil nuts are highly susceptible to contamination by mycotoxins – toxic substances produced by fungi – from the moment that they fall to the ground from the parent tree Bertholletia excelsa in the Amazon rainforest to the moment that they reach the consumer.

To investigate the critical points of Brazil nut contamination by mycotoxins, a group of researchers at the Food Technology Institute (ITAL) in Campinas, Brazil, in collaboration with colleagues at the Technical University of Denmark (DTU), tracked the potentially poisonous fungi present in Brazil nuts from the forest to the supermarket. ITAL is an agency of the São Paulo State Department of Agricultural & Food Supply.

The results of the study, supported by FAPESP through a grant for a project under its BIOTA Program, helped to diagnose the problem and contributed to the development of strategies to control the contamination of Brazil nuts by mycotoxins. These results also served as inputs for national and international standards regulating the maximum acceptable limits of these poisonous substances in the product.

The study was described in two articles published by Food Microbiology and International Journal of Food Microbiology.

“Our research identified the critical points in the contamination of Brazil nuts by aflatoxins [a type of mycotoxin produced by fungi of the genus Aspergillus] and helped to establish measures to reduce contamination by means of improvements throughout the supply chain,” said Marta Hiromi Taniwaki, a researcher at ITAL and principal investigator for the project, in an interview with Agência FAPESP.

According to Taniwaki, the study was motivated by a problem with exports of Brazil nuts to the European Union (EU). Brazil is the world’s largest producer of this type of nut. In 2003, the EU halted imports of Brazil nuts because they allegedly contained higher levels of aflatoxins than allowed by its rules, which set a maximum of 4 micrograms (µg) of total aflatoxins per kilo of Brazil nuts, or 2 µg of aflatoxin B1 per kilo. Aflatoxin B1 is the most toxic aflatoxin and is considered a carcinogen.

“The EU set very low ceilings for acceptable levels of aflatoxins. On the other hand, Brazil nuts are collected in the wild and have a highly complex supply chain. Control of contamination was not effective at the time, and Brazil lacked its own standards for acceptable levels of mycotoxins,” Taniwaki said.

Control strategy

In order to establish a contamination control strategy, the researchers decided to begin by analyzing the supply chain and identifying the fungi responsible for producing the aflatoxins found in the product. If the stages at which they were most abundant could be pinpointed, measures to minimize contamination could be proposed.

Samples were collected from the Amazon rainforest, harvester communities, street markets and processing plants in Pará and Amazonas States, as well as from supermarkets in São Paulo State, with the aim of verifying which samples had high levels of contamination and why this occurred.

The analysis showed the presence of a huge diversity of fungi in the generaAspergillus and Penicillium, in addition to Eurotium spp., Zygomycetes, dematiaceous or “black” fungi, and toxins produced by some species of Aspergillus in the Brazil nuts collected from all these sites.

The highest levels of contamination by aflatoxins were detected in samples collected from processing plants before sorting and from street markets in Pará and Amazonas.

“We concluded that manual or mechanical sorting and drying eliminated more than 98% of total aflatoxins,” Taniwaki said. “Sorting is a very effective way of reducing contamination of Brazil nuts by aflatoxins.”

Sources of contamination

The researchers also discovered that the aflatoxin-producing fungi came both from forest soil and undergrowth and from bees that visit the Brazil nut trees and scatter fungal spores throughout the environment. They also found that high temperatures and humidity, as well as the long time spent by Brazil nuts on the forest floor before harvesting, favored the growth of these fungi.

After falling from trees that can be as tall as 60 m, the almost coconut-sized pods can remain for weeks on the forest floor, which is often very wet, especially during the Amazon’s rainy season (November-April), until they are harvested and transported to storage or processing. Aflatoxin-producing fungi may develop during the period in which the pods are wet, the researchers noted.

“Depending on the time taken to transport the nuts to a processing facility for drying, they may be contaminated to a greater or lesser extent by these toxigenic fungi,” Taniwaki said. “So, the sooner they’re transported and dried to a point we identified as being safe, the more feasible it will be to prevent the development of fungi and the production of toxins.”

The researchers found that some communities of forest harvesters dried the nuts themselves. However, humidity is so high in the Amazon that they were unable to do so to a point considered safe. For this reason, drying by processing plants in purpose-built equipment is recommended.

“After our study, dryers were installed in some forest harvester communities,” Taniwaki said. “The problem is that these dryers are expensive, and forest communities lack a reliable power supply. So it’s important to ship the nuts as soon as possible from the forest to the processing units for drying, sorting and storage.”

Contributions to legislation

The results of the study helped Brazil to ensure that more realistic maximum tolerance levels for contamination of Brazil nuts by aflatoxins were established in the Codex Alimentarius, a collection of standards recognized by the World Trade Organization (WTO) as a benchmark in settling disputes over food safety and consumer protection.

The tolerance levels now set in the Codex Alimentarius are more in line with the requirements of the producer countries, which include Bolivia and Peru, as well as Brazil. These levels are 15 µg of total aflatoxins per kilo of Brazil nuts before processing and 10 µg of total aflatoxins per kilo of Brazil nuts ready for consumption.

The EU has revised its own standards to harmonize them with the Codex and has resumed imports of Brazil nuts from Brazil.

“With these new tolerance levels, if Brazil has any problems with exports of Brazil nuts due to contamination by aflatoxins, it can appeal to the WTO, which will enforce the international standards in the Codex,” Taniwaki said.