Fungal Diversity and Mycotoxins in Low Moisture Content Ready-To-Eat Foods in Nigeria

Abstract

Low moisture content ready-to-eat foods vended in Nigerian markets could be prepackaged or packaged at point of sale. These foods are widely and frequently consumed across Nigeria as quick foods. Despite their importance in the daily diets of Nigerians, a comprehensive study on the diversity of fungi, fungal metabolite production potential, and mycotoxin contamination in the foods has not yet been reported. Therefore, this study assessed the diversity of fungi in 70 samples of low moisture content ready-to-eat foods [cheese balls, garri (cassava-based), granola (a mix of cereals and nuts) and popcorn] in Nigeria by applying a polyphasic approach including morphological examination, genera/species-specific gene marker sequencing and secondary metabolite profiling of fungal cultures. Additionally, mycotoxin levels in the foods were determined by LC-MS/MS. Fungal strains (n = 148) were recovered only from garri. Molecular analysis of 107 representative isolates revealed 27 species belonging to 12 genera: Acremonium, Allophoma, Aspergillus, Cladosporium, Fusarium, Microdochium, Penicillium, Sarocladium, Talaromyces, and Tolypocladium in the Ascomycota, and Fomitopsis and Trametes in the Basidiomycota. To the best of our knowledge Allophoma, Fomitopsis, Microdochium, Tolypocladium, and Trametes are reported in African food for the first time. A total of 21 uncommon metabolites were found in cultures of the following species: andrastin A and sporogen AO1 in Aspergillus flavus; paspalin in A. brunneoviolaceus; lecanoic acid and rugulusovin in A. sydowii; sclerotin A in P. citrinum and Talaromyces siamensis; barceloneic acid, festuclavine, fumigaclavine, isochromophilons (IV, VI, and IX), ochrephilone, sclerotioramin, and sclerotiorin in P. sclerotium; epoxyagroclavine, infectopyron, methylorsellinic acid and trichodermamide C in P. steckii; moniliformin and sporogen AO1 in P. copticola; and aminodimethyloctadecanol in Tolypocladium. Twenty-four mycotoxins in addition to other 73 fungal and plant toxins were quantified in the foods. In garri, cheeseballs, popcorn and granola were 1, 6, 12, and 23 mycotoxins detected, respectively. Frontiers in Microbiology | www.frontiersin.org 1 April 2020 | Volume 11 | Article 615 Ezekiel et al. Fungi and Mycotoxins in Ready-to-Eat FoodsDeoxynivalenol, fumonisins, moniliformin, aflatoxins and citrinin contaminated 37, 31, 31, 20, and 14% of all food samples, respectively. Overall, citrinin had the highest mean concentration of 1481 µg/kg in the foods, suggesting high citrinin exposures in the Nigerian populace. Fungal and mycotoxin contamination of the foods depend on pre-food and post-food processing practices.

Diversity and toxigenicity of fungi and description of Fusarium madaense sp. nov. from cereals, legumes and soils in north-central Nigeria

“…In addition, averantinmethylether (9.4 µg/kg) and aspergillimide (21.3 µg/ kg) are two uncommon compounds found only in cultures of one strain of A. aflatoxiformans and A. flavus, respectively. Similar to a recent report (Ezekiel et al 2020), two of the four A. flavus strains, examined in this study, produced sporogen AO1 (mean: 974 µg/kg), confirming the production of this compound in A. flavus. One of the four A. flavus strains, DTO 421-G6, did not produce aflatoxins, any of its pathway metabolites, cyclopiazonic acid or kojic acid, but produced cyclosporins A, B, C and H. Cyclosporin production has been reported in Aspergillus terreus (Sallam et al 2003), Neocosmospora solani (Sawai et al 1981) and Tolypocladium (El-Enshasy et al 2008).…”

“…A. fijiensis) liberated several known extrolites: aspergillimide (mean: 30.1 mg/kg), emodin (mean: 541 µg/ kg), endocrocin (mean: 23 mg/kg), iso-rhodoptilometrin (mean: 340 µg/kg), meleagrin (mean: 7.6 mg/kg), oxaline (mean: 17.3 mg/kg), paraherquamide E (mean: 6 mg/kg) and secalonic acid D (mean: 64.7 mg/kg) (Varga et al 2011, Vesth et al 2018). However, citreorosein and tryprostatin B, two compounds recently reported to be produced by A. brunneoviolaceus from garri (farinated cassava) in Nigeria (Ezekiel et al 2020), were not detected in cultures of the present strains. Nonetheless, six uncommon compounds (aurasperon C, dimethylsulochrin (mean: 1.9 mg/kg), fellutanine A (152 µg/kg), methylorsellinic acid (mean: 1.2 mg/kg), nigragillin and pyrophen (mean: 190 µg/kg)) were produced by strains examined in the present study.…”

Distribution of fungi and their toxic metabolites in melon and sesame seeds marketed in two major producing states in Nigeria

“…Previously, we had shown the presence of aflatoxin M 1 in melon (Ezekiel et al 2016 ). Although these metabolites were previously regarded as products of endogenous biotransformation of aflatoxin B 1 by CYP450 enzyme, they are now detectable in food crops (Warth et al 2012 ; Adetunji et al 2014 ; Ogara et al 2017 ; Oyedele et al 2017 ; Ezekiel et al 2020b ); thus, suggesting possible release of and exogenous activity of the CYP enzymes by aflatoxigenic fungi during food storage.…”

“…In addition, both toxins were found in 12% of the sesame samples at mean concentrations of 6 and 4 μg kg −1 , respectively, which contrasts a recent report that did not find both toxins in 35 sesame samples collected in 2013 from markets in Nasarawa state (Ogara et al under review ). The disparity in the contamination data for sesame may be attributed to climate actions (especially increased rainfall that brings about increased moisture levels) and/or improved sensitivity of the analytical method as recently, citrinin is now commonly found in foodstuffs in Nigeria (Ojuri et al 2018 ; Ezekiel et al 2020b ). Similarly, low levels of both toxins were reported in melon (Somorin et al 2016 ) and sesame (Ezekiel et al 2012 ).…”

Mycotoxin exposure biomonitoring in breastfed and non-exclusively breastfed Nigerian children

“…Although CIT/DHC was not detected in the examined complementary foods in the present study it was found in 74% of the urines of EB children. CIT levels in grains (especially maize) and complementary food in Nigeria have recently been shown to be high reaching 16,000 µg/kg (Okeke et al 2015, 2018; Ojuri et al 2018, 2019; Ezekiel et al 2020). Fermented cocoa beans in Nigeria, which could also be processed and used in the preparation of foods for infants and young children, have also recently been reported to contain CIT (Akinfala et al 2020).…”