Fungal and multi-metabolite contamination of retailed rice in open markets in two Nigerian States.

Abstract

Abtract: Rice is a significant source of both nutritional and economic sustenance in Nigeria, but contamination by fungi and their toxic metabolites in addition to naturally occurring phytotoxins may pose significant challenges to grain quality and consumer health. This study assessed the safety of 80 rice samples retailed in open markets in two Nigerian states by identifying fungal contaminants using phenotypic and molecular techniques and quantifying the secondary metabolites present in the grains through liquid chromatography tandem mass spectrometry. A total of 101 distinct colonies were recovered and identified as nine species belonging to six genera: Aspergillus, Cladosporium, Fusarium, Monascus, Penicillium and Talaromyces. At least one third (30.4%) of the identified species were Aspergillus flavus, while A. montevidensis, Cladosporium halotolerans, Monascus purpureus, Talaromyces islandicus and T. purpureogenus recorded the least incidences of 4.3%. Sixteen mycotoxins and 48 other secondary metabolites including diverse fungal and lichen metabolites, plant toxins and phytoestrogenic phenols were detected in the rice samples. Moniliformin (MON) and beauvericin were the most common mycotoxins, present in 43% of samples, with MON reaching a maximum concentration of 19,391 µg/kg. Aflatoxins contaminated 18% of samples, generally below Nigeria's 10 µg/kg regulatory limit but in one case exceeding the European Union's threshold of 4 µg/kg. This study emphasizes the need to expand chemical contaminant monitoring in foods beyond the regular aflatoxin detection to include a wider spectrum of secondary metabolites and also to comprehensively review and enhance grain handling and retail practices in local/open markets to protect consumer health.