1. Introduction
More than 300 types of toxic fungal metabolites have been identified, although the most relevant and known mycotoxins include the aflatoxins (AFs) (AFB
1, AFB
2, AFG
1, AFG
2), deoxynivalenol (DON), zearalenone (ZEN), ochratoxin (OTA), and fumonisins (FBs) (FB
1, FB
2, FB
3, among others), which are highly stable metabolites that can resist food processing
[1] and therefore remain in the final products. Consequently, various strategic pre-processing methods are adopted to reduce mycotoxins in the food chain
[2]. Due to their remarkable toxicity and associated health risks, the threshold levels for mycotoxins have been regulated worldwide
[1][3][4]. Numerous diagnostic tools are used to discriminate fungi by their genetic details and volatile signatures and determine mycotoxins in foodstuffs
[5][6], but the issues and gaps regarding mycotoxins’ persistence in the food chain remain unnoticed.
2. Mycotoxin Occurrence
The occurrence and contamination of fungi are major issues in the overall food system. A plethora of fungi occur and produce several toxins in the food and feed produced worldwide
[7][8][9][10]. These toxins transfer to humans directly via the ingestion of plant-based foods of any category, as well as animal-derived food products. In the latter case, whenever animals are fed with a diet potentially contaminated with toxins, the animals biochemically transform these toxins or distribute the unmetabolized forms in various edible tissues, which can be found in their derived milk, meat, liver, heart, and eggs
[11][12][13][14]. The consumption of mycotoxin-contaminated foods presents significant health risks in humans, considering the carcinogenic, immune-suppressive, estrogenic, and organ-target acute effects of these toxins
[10][14].
The occurrence levels of several mycotoxins in a range of foodstuffs recently reported in some countries are displayed in
Table 1. Mycotoxins occur in multiple food and feed items at varied levels, in which cereal grains and nuts are prominent. The origin of the products is diverse, where the data show that a high frequency and level of these toxins can occur regardless of the geographical location
[15][16][17]. The products shown are associated with cereals (wheat, corn, oat), nuts (peanuts, hazelnuts), animal-derived products (milk, meat, eggs), mixed food, and others, e.g., cocoa and soybean meal (
Table 1). These products (
N = 5146) have often been analyzed by high-performance liquid chromatography (HPLC) and mass spectrometry (MS), and a predominant number (
n = 4351) of the products mainly relate to cereals. This corroborates data presented in previous studies, where cereals with a widespread consumption were widely examined for mycotoxins
[15][18]. In search for mycotoxins, around 28 different metabolites comprising their (less or un)familiar, emerging, and conjugated forms were evaluated, in which several have properly regulated and estimated tolerable limits, with toxicity details for the specific ingredient of interest as
[19][20][21][22][23][24][25].
Table 1. Mycotoxin occurrence and levels in diverse foodstuffs recently reported in some countries.
Regarding the overall samples evaluated in studies conducted between 2017 and 2022 and detailed in Table 1, higher contamination rates were observed for trichothecene type B (TTB) toxins (58.53%), FBs (51.19%), ZEN (40.25%), and AFs (17%), as depicted in Figure 1. Importantly, trichothecene type B includes DON as a major toxin, and FBs were more notable in cereal products, while ZEN was more likely mainly in animal products (chicken and dairy) when compared with its low level in other items. Relevant to the sample positivity for the occurrence of one or more toxins, TTB appeared in 87.47% of the corn-based feed, 70.56% of the wheat as food, and 53.10% of oat grass. Mixed products associated with cereals and nuts, as well as corn, exhibited the highest percentage of contamination by FBs (77.35–81.55%). For ZEN, samples that exhibited high positivity were from dairy milk (99%), chicken meat (52.17%), and corn feed (51.48%). Concerning the contamination by AFs, all peanut meal (100%), 62.5% of milk formula, and 54.29% of mixed cereal- or nut-based foods showed positivity for AFs (Figure 1).
Figure 1. Overall percentage of positive samples of foods for mycotoxins recently reported (2017–2022). A, cereal-based infant foods; B, mix cereals and nut-based food; C, milk formula; D, fluid milk; E, chicken meat; F, eggs; G, corn as feed; H, wheat; I, soybean meal; J, peanut meal; K, oat grass; L, corn; M, dairy milk. AFs, aflatoxins; FBs, fumonisins; DON, deoxynivalenol; TTB, trichothecene type B; ZEN, zearalenone.
When it comes to TTB having DON as a key toxin, its prevalence and level in cereals and cereal-derived products appear to show consistency across different regions. This corroborates Khaneghah et al.
[31], who pointed out a higher occurrence and concentration of DON in cereal products worldwide. This observation is corroborated by additional studies. For instance, research from Algeria found that 33.3% of barley, corn, rice, and wheat samples had elevated levels of DON (ranging from 15–4569 µg/kg)
[32] In Egypt, approximately 70.2% of the wheat and corn products had high contamination by DON (ranging up to 853 µg/kg)
[33] A study in Brazil highlights widespread DON in various food items like rice (median 13.2 µg/kg), beans (51.3 µg/kg), wheat flour (408.2 µg/kg), corn flour (56.7 µg/kg), and cornmeal (51.8 µg/kg)
[9]. In line with FBs, this group of toxins show maximum probability with cereal products. For example, barley, corn, rice, and wheat from Algeria presented surprisingly higher incidence and levels of FBs (up to 48,878.00 µg/kg) in 21 samples that exceeded the maximum permitted limit (MPL, 1000 µg/kg) in these foodstuffs according to the European Union (EU)
[20][32] Regarding ZEN, it occurred in almost 100% of animal products while little in cereal commodities, indicating sample size variations (
Figure 1). However, further studies have shown ZEN occurrence with higher rates in cereal commodities. For example, in the cereal group, rice wheat, and corn products are likely to be more contaminated with maximum incidence of ZEN. This likelihood aligns with a higher ZEN level (8–474 µg/kg) in rice, wheat bread, and pasta, as well as in corn-based cake or meal from Brazil
[34]. Higher ZEN (median levels 57.9–70.9 µg/kg) occurrence was found in wheat grains, with varying frequencies (12–84%) in Brazil, where ZEN was above the MPL of the EU in numerous samples
[35]. In similar cereal products from Pakistan, 57% of the samples had ZEN positivity, with 31% of samples above the MPL (50 µg/kg)
[36]. The occurrence frequency of AFs was also high in the remaining products (
Table 1,
Figure 1). The data can be reinforced with the results from research describing the AFs most frequently occurring in these products
[15]. High positivity rates were recorded for milk products (63%) and peanut meal (100%). In general, it can be noted that the contamination levels of various toxins surveyed within five years were high in many products, mainly in China
[12], and in this case, a large variability may indicate the sample size. Compared to the established limits by the European Union, for example, the mean levels in 96 and 108 samples of corn from Croatia and Serbia during a four-year survey presented 11.87 µg/kg and 11.1 µg/kg of AFs that are above the established MPL for cereals
[21][29]. Contrarily, a survey in Chile using 24 to 26 samples of milk formulas and fluid milk presented a percent rate for AFM
1 positivity of 62.5% and 23.1%, respectively. The mean levels were 0.0038 and 0.0069 µg/kg, below the EU thresholds
[29][37]. These details shed light on the prevalence of multi-mycotoxin contamination with varied levels in numerous products, which can be a matter of exposure that causes health issues in humans and animals
[20][21][22][23][24][25].
Human exposure to these toxins based on their biomarkers in bodily fluids, e.g., urine, blood, and serum, has also been described
[37][38][39]. Exposure to these toxins can demonstrate high levels of positivity compared to non-exposed volunteers. In addition, the exposed group can present biomarkers with average levels higher than non-exposed ones
[40]. In epidemiological investigations, in non-occupational exposure, sample positivity percentages vary. This is in line with a study by Šarkanj et al.
[41] from Nigeria, where urine samples were evaluated for AFM
1, FB
1, OTA, DON, ZEN, and other less usual biomarkers, highlighting sample positivity of 72%, 71%, 78%, 19%, and 82%. Contrarily, Njumbe Ediage et al.
[40] found lower frequencies of biomarkers in human urine collected in Belgium, with 13%, 7%, 3%, 10%, 10%, and 10% for DON, OTα, CIT, β-ZEL, ZEN, and OTA, respectively. These results indicate that mycotoxin exposure frequency can differ according to several factors, including occupation, origin, biomarker monitoring, and exposure to toxins, mainly by ingesting contaminated food, inhalation, or other routes of exposure
[38]. These details indicate mycotoxins’ persistence and interactions in the foods, which should be concisely underlined. Such effort could be emphasized mainly in the cereals and nuts industry, with some possible biochemistry discussion regarding toxins’ occurrence, persistence, and interaction issues that can be relevant to the food industry and public health.
This entry is adapted from the peer-reviewed paper 10.3390/foods12234314