Microbiological and aflatoxin evaluation of Brazil nut pods and the effects of unit processing operations

Harvesting of Brazil nuts not only helps to preserve the Amazon rainforest but also provides income to individuals who would otherwise have little means of making a livelihood. Recently, the European Community has tightened the quality requirements for Brazil nuts, particularly with regard to aflatoxin levels and microbiological contamination. The objectives of this research were to gain a better understanding of the origin of aflatoxins on Brazil nuts and to microbiologically evaluate some of the operations involved in processing. In this regard, five Brazil nut pods were aseptically picked from trees located in each of three concessions of the Peruvian Amazon rainforest (Madre de Dios province). The exteriors of the pods and the nuts were examined for yeast and molds, including Aspergillus flavus and Aspergillus parasiticus, and for bacteria, including Salmonella and Escherichia coli. Brazil nuts obtained from various commercial process operations located in Peru were similarly evaluated. Exteriors of all Brazil nut pods did not contain A. parasiticus, and only pods from one concession yielded A. flavus isolates. All isolates tested were aflatoxigenic (630 to 915 ppb total aflatoxin). Coliforms, E. coli, and salmonellae were not recovered from any of the pods. Whole, in-shell nuts obtained after opening the pods yielded no A. flavus or A. parasiticus. Aflatoxins were not detected (detection limit 1.75 ppb) in any of the nuts. Whole, in-shell and shelled nuts from various process operations were all positive for A. flavus but negative for E. coli and salmonellae. Soaking of whole, in-shell nuts before cracking or shelling increased coliform numbers, whereas levels of A. flavus decreased. In order to gain a better understanding of the sanitary performance of the unit process operations, additional evaluations should be conducted on product lots processed on different days. Also, the microbiology of product processed from common lots should be followed through the various unit operations and compared.