Impact of postharvest processing on the fungal population contaminating African walnut shells (Tetracarpidium conophorum Mull. Arg) at different maturity stages and potential mycotoxigenic implications

African walnut (Tetracarpidium conophorum Mull. Arg) is commonly processed by boiling or toasting and consumed as a snack or used as a thickener in many West African soup preparations. The nuts are usually exposed to both high temperatures and high relative humidity in open markets which predisposes...

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Bibliographic Details
Published in:International journal of food microbiology 2015-02, Vol.194, p.15-20
Main Authors: Nkwonta, Chikere G., Medina, Angel, del Carmen Alamar, Maria, Terry, Leon A.
Format: Article
Language:English
Subjects:
Aflatoxins
African walnut
Chromatography, High Pressure Liquid
Food Microbiology
Foodborne Diseases - prevention & control
Fungi - chemistry
Fungi - isolation & purification
Juglans
Juglans - microbiology
Mycotoxins
Mycotoxins - analysis
Nuts - microbiology
Tetracarpidium conophorum
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Summary:African walnut (Tetracarpidium conophorum Mull. Arg) is commonly processed by boiling or toasting and consumed as a snack or used as a thickener in many West African soup preparations. The nuts are usually exposed to both high temperatures and high relative humidity in open markets which predisposes them to fungal growth. Hence, the dangers of spore inhalation and resultant mycosis cannot be over-emphasized as retailers and consumers are always in direct contact with these nuts during harvest, processing and consumption. So far, there is no reported research on potential mycotoxin contamination of African walnut and whether this risk might be accentuated by processing. African walnut, at early and late maturity stages, were processed by toasting, boiling or left unprocessed before being stored at 25°C and 37°C, respectively under controlled relative humidity for 7days. Nuts were cracked and shell pieces cultured in malt extract agar (MEA) and Dichloran Glycerol 18 (DG18) media and incubated at 25°C for 7days. Results revealed that potential mycotoxigenic species – Aspergillus section Nigri, Aspergillus flavus/parasiticus, Fusarium spp. and Penicillium spp. – were frequently isolated. When compared with unprocessed nuts, toasting completely prevented fungal contamination in shell pieces from nuts in the non-stored (NSN) group at the early maturity stage, while boiling significantly reduced the level of contamination to about 58% (p
ISSN:0168-1605
1879-3460
DOI:10.1016/j.ijfoodmicro.2014.10.024