**1. Introduction**

Wheat is the basic staple food and its global consumption is about 66 kg/per capita worldwide [1]. Various diseases can a ffect the heads of wheat, and severe infection can result in decreased grain yield and quality. Furthermore, wheat and its products can be contaminated with mycotoxins produced by di fferent fungi that can be found in the field and/or postharvest [2]. Among the most important risks associated with cereal consumption are mycotoxins, heavy metals, pesticide residues, and alkaloids. It is very important to monitor mycotoxins in all stages of wheat production from the field to end-use quality usage. Fusarium head blight (FHB), caused by several *Fusarium* species, mainly *Fusarium graminearum*, *F. culmorum*, and *F. avenaceum*, is a devastating disease of wheat, associated with mycotoxin contamination with a significant threat to animal and human health. The most important mycotoxins in wheat are mainly *Fusarium* toxins, such as deoxynivalenol (DON), with its acetylated forms (15 acetyl-deoxynivalenol or 15AcDON, and 3 acetyl-deoxynivalenol, or 3AcDON), zearalenone (ZEN), nivalenol (NIV), fumonisins (FB), T-2, and HT-2 toxins and its modified forms [2–4]. Beside *Fusarium* spp., species from the genera *Alternaria*, *Penicillium*, and *Aspergillus* are critical in the maintenance of food safety and can cause mycotoxin contaminations of cereals [5,6]. For example, *Aspergillus flavus* can infect wheat grain in the field but also contaminates stored grains when temperature and water activity are favorable [7].

The most common mycotoxin in wheat and wheat-based products in the European Union (EU) is the well-known type-B trichothecene, DON [8]. Moreover, a very limited number of mycotoxins are subject to legislation and regular monitoring. As far as cereals are concerned, aflatoxins, fumonisins, DON, zearalenone (ZEN), and ochratoxin A (OTA) are those most often analyzed [9]. For these reasons, the other mycotoxins, which until now have not received detailed scientific attention, are commonly indicated as 'novel' or 'emerging' mycotoxins [10,11]. Therefore, there is an urgen<sup>t</sup> need to acquire data on the presence and di ffusion of these emerging mycotoxins in field crops, in relationship to di fferent climatic conditions, in order to perform proper risk characterization, risk assessment, and afterwards propose maximum limits in the food chain. The European Union has established maximum levels for DON [12], where unprocessed wheat, cereal flour, bread and wheat-based foods for infants and young children must not contain more than 1250, 750, 500, and 200 μg/kg of DON, respectively. DON is known to cause food refusal, vomiting, and depressed immune function, resulting in poor weight gain [13]. Culmorins (CULMs) are tricyclic sesquiterpene diols that can be produced by *F. culmorum*, *F. graminearum*, and *F. venenatum* [14]. Nevertheless, CULM is considered an "emerging mycotoxin" whose synthesis and toxicology will be of greater interest for food safety consideration in the future [11]. It was also confirmed that CULM suppresses one of the important steps of DON detoxification—glucuronidation [15] and therefore can increase DON's toxic e ffect if it co-occurs with DON. Genes for CULM and trichothecene production co-occur in other fungal species closely related to *F. graminearum* [16]. Nivalenol (NIV) to some extent co-occurs with DON. Although NIV is less toxic to plants compared to DON, it has more severe toxic e ffects in animals and humans [17]. ZEN is often co-produced with DON by *Fusarium* spp. such as *F. graminearum* [18]. Moreover, recent studies revealed an increased presence of modified *Fusarium* mycotoxins and so-called emerging mycotoxins, particularly enniatins (Enns), beauvericin (BEA), and moniliformin (MON) [19,20] which are far less investigated. Enns can be produced by several fungal species including *Fusarium* spp., and the enniatin analogs enniatin A (EnnA), enniatin A1 (EnnA1), enniatin B (EnnB), enniatin B1 (EnnB1), and enniatin B2 (EnnB2) are reported to be the most prevalent ones in cereals in Europe [21,22]. Beauvericin (BEA) can co-occur with Enns, since they can be produced by the same *Fusarium* species [21]. Moniliformin (MON) often was found in *Fusarium*-damaged durum wheat grains due to *F. avenaceum* infection [23,24]. The European Union maximum limits for other *Fusarium* toxins (ZEN and fumonisins B1 and B2, and T-2 and HT-2 toxins) in cereals and cereal-based products have been established by Commission Regulation [12]. Di fferent reference points were established for mycotoxins as follows: the benchmark dose lower confidence limit of 10% (BMDL10) extra risk for aflatoxin B1 at 170 ng/kg per body weight (bw) per day; tolerable daily intake (TDI) of 2 μg/kg bw per day for fumonisins B1, B2, and B3; tolerable weekly intake (TWI) of 0.1 μg/kg bw per week for OTA; BMDL05 of 200 μg/kg bw per day for MON; and 90 μg/kg bw per day of BEA was established as a concentration with a low risk (for genotoxic carcinogens such as aflatoxins) or no risk (for other mycotoxins) [25]. The control of *Fusarium* fungal infection in the field by growing resistant cultivars could be the most e fficient method to control FHB [16] and mitigating mycotoxin accumulation in the end-use products. To reduce the risk of *Fusarium* contamination, the application of preventive agricultural practices is also important, such as crop selection, rotation, tillage, irrigation, and the proper use of fungicides, as partial control of FHB [26,27]. Furthermore, mycotoxin production by mycotoxigenic fungal species is dependent on water activity, temperature, and CO2 levels [28,29].

In addition to these better-known compounds, other secondary metabolites produced by *Fusarium* species may be detected and investigated using multi-analytic methods developed in recent years based on liquid chromatography coupled to mass spectrometry [30,31]. Modified and emerging mycotoxins which cover DON derivatives (DON-3-glucoside, acetyl-DONs, nor-DONs and deepoxy-DON), nivalenol, T-2 and HT-2 toxins, enns, BEA, moniliformin, and fumonisins are not regulated by EU law. Furthermore, multiple fungal metabolites including mycotoxins are frequently observed [32,33]. This is a topic of grea<sup>t</sup> concern, as co-contaminated samples might still exert adverse health e ffects due to additive/synergistic interactions of the mycotoxins.

This research summarizes the occurrence of the mycotoxins/metabolites produced by *Fusarium*, *Alternaria,* and *Aspergillus*, as well as several unspecific metabolites in naturally-infected and *Fusarium*-inoculated wheat samples. To our best knowledge, the majority of mycotoxins/metabolites analyzed in this study are poorly characterized [6], and their occurrence and concentration in commercially produced wheat varieties are mainly unexplored.
