Toward Safe Food Systems: Analyses of Mycotoxin Contaminants in Food and Preventive Strategies Thereof for Their Formation and Toxicity

Abstract

Mycotoxin contaminants in food pose a threat to human and animal health. These lead to food wastage and threaten food security that is already a serious problem in Africa. In addition, these affect trading and especially affect incomes of rural farmers. The broad impacts of these contaminants require integrated solutions and strategies. It is thus critical to not only develop strategies for analysis of these toxins but also develop removal and preventive strategies of these contaminants to ensure consumer safety and compliance with regulatory standards. Further within the aim of promoting food safety, there is need for operational policy framework and strategy on the management of these contaminants to promote their mitigation. This chapter discusses integrated strategies for monitoring and control of mycotoxin contamination in food matrices to promote their mitigation and build resilient food systems in Africa and thus reinforce efforts to reach sustainable food security.

1. Introduction

Food safety indirectly affects a wide range of social, economic, and environmental processes including food production and hence environmental impacts of agriculture, food trade, and energy use [1]. Foodborne illness, in particular, places an undue burden on health and socioeconomics of society, and this burden is the highest in developing countries especially in marginalized communities. Thus, the integration of food safety considerations is critical in achieving a wide range of sustainable development goals (SDGs) including SDG2 (End hunger, achieve food security and improved nutrition, and promote sustainable agriculture) [2]. It is important to make food safety a development priority and to ensure that food security policies and initiatives give attention to food safety.

In order for African Governments to make food safety a public health priority, there is need for rigorous analysis of food contaminants that would give evidence on the burdens of food safety and thus lead to establishing and implementing effective and resilient food safety systems [3]. Of concern is the presence of chemical contamination that poses an enormous threat to food safety and security, and these influence the development of African agri-food system. Chemical contamination imposes a huge economic burden across the health and other sectors [4]. Chemical contamination also leads to food loss, which could otherwise have served millions of people and assisted in achieving food security [5]. Food loss not only threatens food security but also represents the lost labor, capital, water, energy, land, and other resources that went into producing the food and thereby threatening sustainability [2]. Chemical contamination includes many substances such as agrochemicals, pesticides, heavy metals [6], persistent organic pollutants, and natural toxins [7]. Among chemical contaminants that are troublesome are naturally occurring toxins and these include mycotoxins, marine biotoxins, cyanogenic glycosides, and toxins occurring in poisonous mushrooms [8]. It is of particular interest to focus on mycotoxins due to their severity in Africa and their impact on agro-economies [9, 10, 11, 12, 13].

Mycotoxins are secondary metabolites of a range of filamentous fungi and saphrophytic molds [14]. Among all the toxic filamentous fungi species, Aspergillus, Fusarium, and Penicillium are important genera, producing regularly widely studied toxins including aflatoxins, patulin, ochratoxin A (OTA), deoxynivalenol (DON), trichothenes: T-2 toxin, fumonisin, tremorgenic toxins, ergot alkaloids, and zearalenone (ZON) [15]. Mycotoxins can contaminate food or food crops throughout the food chain, in the field or after harvest and during storage [16]. In addition to food- and feed-born intoxication, humans can also be affected through exposures via surface water contamination. Pathogenic fungi, including Fusarium species, have been demonstrated to be capable of continuing to produce their secondary metabolites in water [17], and this process has been indicated to be a potential route of human exposure to mycotoxins [18].

1.1 Impact of mycotoxins on public health

The consumption of mycotoxins-contaminated food/feed products has had an adverse impact on public health for many centuries [19]. Mycotoxins can be found in many food products including cereals, nuts, spices, dried fruits, apples, and coffee beans [20]. Exposure to mycotoxins can produce both acute and chronic toxicities ranging from death to deleterious effects on the central nervous, cardiovascular, pulmonary, and digestive systems of most farm animals and humans. Mycotoxins may also be carcinogenic, mutagenic, teratogenic, and immunosuppressive [12, 19].

Aflatoxins are among the most potent carcinogens of all mycotoxins. Studies have revealed that aflatoxins occur at extremely high levels in many African countries such as Ghana, Benin, Togo, Egypt, Guinea, and Gambia [20]. Repetitive incidents of aflatoxicosis, which, in severe cases, lead to death, have been reported. The greatest recorded fatal mycotoxin-poisoning outbreak occurred in Africa in 2004 where a 125 people in Kenya died due to consumption of contaminated maize [9]. A similar outbreak occurred in Eastern Kenya in 2005 where 75 cases were admitted in Hospital resulting in 25 deaths. Maize samples collected from these areas had high aflatoxin B1 (AFB1) levels with 55% contaminated above the Kenyan legal limit of 20 μg/kg [10].

AFB1 levels have been extensively linked to human liver cancer in which they act synergistically with HBV hepatitis B virus infection [10, 21]. There is up to 30 times greater risk of acquiring liver cancer from chronic infection with hepatitis B virus and dietary exposure to aflatoxin as compared with exposure to either of the two factors alone [21]. Both aflatoxin exposure and chronic hepatitis B infection predominate in rural Africa, which explains why the highest incidence of liver cancer occurs in Africa. In Tanzania, there was about 1480 per 100,000 persons cases of aflatoxin-induced liver cancer in 2016 [12]. Further AFB1 could also lead to increased susceptibility to infectious diseases such as malaria and HIV-AIDS [10].

Consumption of fumonisins has been associated with elevated human esophageal cancer incidence in various parts of Africa [10, 22]. Fumonisins have also been implicated in the high incidence of neural tube defects in rural populations of Eastern Cape province, the former Transkei region of South Africa [11, 22]. Fumonisins may also cause stunted growth in children. A study carried out to investigate the relationship between infant and young child growth and fumonisin exposure revealed that children with fumonisins intake of greater than the maximum tolerable daily intake (PMTDI) were significantly shorter (1.3 cm) and lighter (328 g) compared with children whose fumonisin intake is less than the PMTDI [20]. Recently, children in Tanzania showed impaired growth, which is associated with exposure to fumonisns from maize [23]. Another study done in sorghum grown in different parts of Northern Uganda showed that 80% of all samples contained aflatoxins, 93% fumonisins, and 67% OTA. The presence of mycotoxins in staple such as sorghum has been linked to the development of edema and kwashiorkor in undernourished children in this region [24].

Aflatoxin exposure in young children in West Africa has also been associated with Reye’s syndrome, child neurological impairment, Kwashiorkor, and stunted growth [25]. The chronic incidence of aflatoxin in diets is evident from the presence of aflatoxin M1 (AFM1) in human breast milk in Ghana, Nigeria, Sierra Leone, and Sudan as well as in umbilical cord blood samples in Ghana, Kenya, Nigeria, and Sierra Leone [9]. Another study on aflatoxin exposure in the Gambia revealed that aflatoxins can be transported from the mother to the infant. This shows a significant association between maternal exposure to aflatoxin and impaired infant growth [26].

1.2 Economic impact of mycotoxins

The economic impacts of mycotoxins to human society can be thought of in terms of the direct market costs associated with lost trade or reduced revenues due to contaminated food or feed, and the human health losses from the adverse effects associated with mycotoxin consumption covered in Section 1.1. Mycotoxins are known to affect almost one quarter (25%) of global feed and food output [27]. This leads to huge agricultural and industrial losses in billions of dollars [20]. About 10% of the 2010 Kenyan maize harvest was withdrawn from the food supply in a responsible move taken by the Kenyan government to protect public health, which translates to economic losses [16]. These toxins account for economic losses in the magnitude of millions of dollars due to reduced agricultural production. In Africa, factors such as poverty and climate change further complicate the mycotoxin situation; thus, the economic impact due to mycotoxins is alarming [19]. This impact includes high cost of research and regulatory activities aimed at reducing health risks because of the existence of causal relationships between mycotoxins and their impact on health.

In domestic markets, economic losses occur at various levels, from the commodity producers to the brokers, the processors, and the animal producers. Several countries, particularly some industrialized ones, have set specific regulations defining maximum admissible levels for major mycotoxins in numerous commodities. Limits for AFB1 in foodstuffs range from 0 to 30 μg/kg, while those for total aflatoxins range from 0 to 50 μg/kg [28]. As of 2003, only 15 African countries, accounting for approximately 59 percent of the continent’s population, are known to have specific mycotoxin regulations [29], and this is still the current status to date. In countries like Ethopia, only a few food commodities have mycotoxin legislation largely because they are exported to European and American markets [28]. While these regulations limit their presence in food and feed, these also adversely affects access to attractive export market for many developing countries due to the difficulty in meeting required standards [1]. For example, Africa could earn up to US$1 billion per year from groundnut exports by regaining the 77% share of the global groundnut export market it enjoyed in the 1960s instead of the current share of 4%, which is valued at just US$64 million [1].

1.3 Mycotoxin contamination: what is it to Africa?

Mycotoxin research has attracted huge interest among scientists, farmers, and policy makers and regulatory bodies alike. Despite mycotoxins being a much more pronounced problem in the developing world than in the developed world, much of the work in this area is concentrated in the developed world, while Africa, especially Sub-Saharan Africa, is lagging behind. Only few and fragmented studies have been conducted on mycotoxins in Africa (examples are shown in Table 1). This is of concern given that most of African countries rely on staple food such as sorghum and maize and other oil seeds such as groundnuts that are subject to contamination by a range of fungi, both in the field and after harvest. This predisposes a high number of populations in Africa to consumption of mycotoxin contaminated food products and thus increases the chance of chronic and detrimental exposure to mycotoxins [34]. Further, Africans rely on preservation of grains through traditional storage, where the grains stored for more than a few days are susceptible to fungal attack.

Country	Year	Mycotoxin(s)/fungal contamination	Matrix	References
Angola	2017	Aspergillus and penicillium	Arabica coffee and Robusta coffee	[5]
Botswana	2013	Aflatoxins and fumonisins	Peanuts, peanut butter, and sorghum	[30]
	2011	ZEA and fumonisins	Maize and sorghum grains and meals	[31]
Ghana	2021	Aflatoxins	Maize	[32]
	2019	Aflatoxins	cereals and cereal based foods	[33]
	2018	aflatoxins, fumonisins, DON, T-2 toxin, ZEA and ochratoxin	maize, maize silage, other cereals	[34]
Kenya	2021	Aflatoxin, citrinin, fumonisin, OTA, diacetoxyscirpenol, T2; HT2	Rice	[35]
	2020	Aflatoxins and fumonisins	Maize	[36]
Namibia	2019	Patulin, aflatoxins, and fumonisins	Sorghum malts	[37]
Namibia, Kenya, and Nigeria	2018	Aflatoxins, fumonisins, DONl, T-2 toxin, ZON, and ochratoxin	Maize, maize silage, other cereals	[34]
Nigeria	2020	DON, fumonisins, moniliformin, aflatoxins, and citrinin	Cheese balls, garri (cassava-based), granola, and popcorn	[38]
Rwanda	2019	Aflatoxins and fumonisins	Maize	[39]
	2018	Aflatoxins	Soybean (Glycine max L.)	[40]
South Africa	2018	Aflatoxins, fumonisins, ochratoxins, HT-2 toxin, T-2 toxin, ZON, DON, and 15-acetyl-DON	Maize	[41]
	2018	Aflatoxins, fumonisins, OTA, sterigmatocystin, 3-acetyl DON, roquefortine C	Food spices	[42]
Togo	2019	Aflatoxins, fumonisins, and trichothecenes	Maize and sorghum	[43]
	2020	Aflatoxins	Maize	[44]
Zambia	2017	Aflatoxins	Groundnut and maize	[45]
Zimbabwe	2013	Aflatoxins and fumonisins	Peanuts, peanut butter, and sorghum	[30]

Table 1.

Examples of mycotoxins studies in Africa.

Increased climate variability and harsh climate conditions in Africa such as high relative humidity and high temperatures conducive for mycotoxigenic fungal colonization and mycotoxin production pre- and/or post-harvest [46] may aggravate the situation. The stress of hot dry conditions, especially in places such as Botswana and Namibia, may result in significant mycotoxigenic fungal infections during the pre-harvest phase and hence mycotoxin production. Climate change can also increase host susceptibility to hull cracking [46]. As a result, this can lead to decreased phytoalexin production, which increases susceptibility of peanuts to mycotoxin and may compromise maize kernel integrity leading to increased mycotoxin contamination.

All these factors require a rigorous mycotoxin management system, especially the continued monitoring of mycotoxins in Africa. Thus, Africa is challenged with driving mycotoxin research to (a) provide scientific evidence for consumers from health and economic perspective; (b) to provide regulatory bodies with data for relevant risk of exposure and risk assessment to enable them to set regulatory legislations for mycotoxins in food commodities, as well as (c) to ensure that international regulatory levels are met. It is within this context that it is necessary to come up with cost-effective strategies in determining the identity and level of mycotoxins in food commodities as well as to come up with sustainable preventive strategies. Without an aggressive research program to prevent, treat, and contain outbreaks of mycotoxins in grain, grain producers will suffer the consequences of reduced marketability of their products. In this regard, nanotechnology-based solutions present themselves as attractive solutions and the use of affordable detections such as point-of-care (POC) diagnosis and electrochemistry are areas that present a lot of potential.

2. Analytical strategies toward mycotoxin adsorption and detection

The accurate and rapid qualitative and quantitative analysis for mycotoxins has been topic of interest by many researchers [47, 48]. A mycotoxin analysis method should be simple, rapid, reproducible, robust, accurate, sensitive, and selective to enable simultaneous determination. Analytical methods for the determination of mycotoxins commonly have the following steps: sampling, homogenization, extraction, and cleanup, which might include sample concentration and then detection [49].

2.1 Cost-effective strategies for adsorption of mycotoxins (either for extraction or for decontamination)

Several strategies on pre-harvest and post-harvest prevention of mycotoxin contamination have been reported including the use of resistant varieties, the use of biological and chemical agents, crop rotation, improved drying methods, good storage conditions, and irradiation. However, these methods do not solve the problem as mycotoxins still get detected in food ready for consumption [50]. Therefore, greater attention should be paid to mycotoxin adsorption or removal strategies as they have greater potential in complete elimination of mycotoxins from food commodities. These adsorption strategies are also very useful for extraction of mycotoxin in contaminated samples prior to instrumental analysis, needed especially for trace analysis. An efficient method for adsorption of mycotoxin should be inexpensive, able to adsorb or remove/inactivate the mycotoxins without producing toxic residues and affecting the technological properties, nutritive value, and palatability of products [51]. Several adsorption materials are discussed herein.

2.1.1 Zeolites

Zeolites are micro-porous crystalline-hydrated aluminosilicates structurally based on three-dimensional anionic network of SiO₄ and AlO₄ tetrahedra linked to each other by sharing all of the oxygen atoms [52]. The potential for using zeolites as mycotoxin adsorbents is based on their adsorption capacity, cation-exchange, dehydration-rehydration, and catalysis features. Zeolites can also be modified specifically to enhance selectivity of specific mycotoxins. Mycotoxins are structurally diverse; thus, they have varying chemical and physical properties. Some are polar, others are non-polar, and there are several that fall in between. This diversity can be resolved by such a material that can change its properties under various physicochemical conditions [52].

Surfactant-modified zeolites have proven to be effective adsorbents of mycotoxin and potential food additives due to their “non-toxic” traits. The clinoptilolite type that has been approved by European Food Safety Authority (EFSA) Panel on Food Contact Materials, Enzymes, Flavorings and Processing Aids (CEF) is one of the safe substances for feed and food additives [53]. The in vitro mycotoxins adsorption by natural clinoptilolite-heulandite rich tuff-modified with octadecyldimethyl benzyl ammonium chloride (Do) and dioctadecyldimethyl ammonium chloride (Pr) (organo-zeolites) has been investigated [54]. Results from the mycotoxin-binding studies showed that the organo-zeolites effectively adsorbed AFB1, ZON, OTA, and the ergopeptine alkaloids.

ZON adsorption by organozeolites prepared via treatment of the natural zeolites—organoclinoptilolites (ZCPs) and organophillipsites (PCPs) with cetylpyridinium chloride (CP), has also been studied [55]. Results showed that adsorption of ZON increases with increasing amounts of CP at the zeolitic surfaces for both ZCPs and PCPs even though the adsorption mechanism was different. The increased adsorption of ZON with increasing amount of organic cation at the zeolitic surface confirmed that CP at both zeolitic surfaces is responsible for ZON adsorption. Although there has not been much work done on multi-mycotoxin adsorption by zeolites, studies show that there is potential in that area.

Due to their adsorption efficiency, zeolites have also developed for the analytical determination of mycotoxins, especially aflatoxins and ZON. Aflatoxins in milk have successfully been determined with an ionic liquid-modified magnetic zeolitic imidazolate framework-8 (M/ZIF-8) [56] and the application potential of M/ZIF-8 was extended successfully for the trace liposoluble pollutants analysis in foodstuffs. Natural zeolite treated with benzalkonium chloride has also showed great potential as an OTA and ZON adsorbent [55].

2.1.2 Molecularly imprinted polymers (MIPs)

MIPs are synthetic polymers with a predetermined selectivity for a certain analyte or several analytes that are structurally similar, making them ideal for separation and adsorption purposes. MIPs have been widely investigated as suitable adsorbents for mycotoxin analysis and determination [57, 58, 59] and only have been applied to food commodities to solve the challenge associated with detecting trace quantity of mycotoxins in food. AFB1-specific molecularly imprinted solid phase extraction sorbent has been developed for the selective pre-concentration of toxic AFB1 in child-weaning food, tsabana. The MIPs successfully achieved a pre-concentration factor of 5 and therefore significantly increased AFB1 signal intensity for easier detection [59].

MIPs have also been applied to extract AFM1 from milk spiked with 0.5–50 ng/mL AFM1. The MIPs removed 87.3–96.2% of the AFM1 without any notable effects on the milk composition [60]. MIPs that constituted of (i) Fe₃O₄, to make the MIP magnetic, (ii) chitosan (CS), and SiO₂ to improve the biocompatibility, stability and dispersibility of the MIP, were developed for removal of patulin from apple juice. This Fe₃O₄@SiO₂@CS-GO@MIP demonstrated to be a promising adsorbent with the adsorption capacity of 7.11 mg/g maximally and ability to remove over 90% of the total patulin in apple juice [61].

2.1.3 Carbon nanomaterials

The application of nanotechnology in adsorbents is especially attractive due to increased adsorption capacities of nanomaterials. Nanotechnology is a field of science, which deals with production, manipulation, and use of materials ranging in nanometers [62] with unique and improved properties of commercial and scientific relevance such as large surface-to-volume ratio and improved physiochemical properties such as color, solubility, strength, diffusivity, toxicity, magnetic, optical, thermodynamic properties [63]. In particular, the large surface area-to-volume ratios of nanomaterials can greatly enhance the adsorption capacities of sorbent materials.

Carbon nanoforms have large surface area per weight, colloidal stability upon various pH [64], strength, elasticity, and great conductivity and thus have great potential as mycotoxin adsorbents [65]. Fullerene, an allotrope of carbon has been found to adsorb aflatoxins. Another form, nanodiamonds, has the same advantages as carbon nanomaterials and is considered inexpensive [65]. Furthermore, their chemical structure allows surface modifications including carboxylation, hydrogenation, and hydroxylation which could enable effective adsorption of mycotoxins. The binding and mechanism of mycotoxins and nanodiamonds have been studied. Nanodiamond aggregates (~40 nm) have been shown to adsorb AFB1 and OTA via electrostatic interactions with functional groups on their surfaces [66] and demonstrated adsorption capacities greater that clay mineral, which are conventional adsorbents for mycotoxins.

Single/multiwalled carbon nanotubes (CNT) have been utilized in solid phase extraction of various mycotoxins due to their good adsorption capacity. A multi-walled CNT-based magnetic solid-phase extraction sorbent for the determination of ZON and its derivatives were developed and applied in maize samples [67]. The main parameters affecting the cleanup efficiency were investigated using ultra-high-performance liquid chromatography–tandem mass spectrometry (LC–MS), and high purification efficiencies for all analytes were obtained. The method proved to be a powerful tool for monitoring ZON and its derivatives in maize. The good adsorption capacity of CNT has also been utilized in extraction of tricothecenes [68, 69] and aflatoxins [70].

2.2 Cost-effective methods for the detection and analysis of mycotoxins

There are numerous analytical methods having different technical details for accuracy, which have been developed for analysis of mycotoxins [71]. Commonly used methods to analyze mycotoxins are thin-layer chromatography, high-performance liquid chromatography with UV or fluorescence detection (FD), LC–MS [71], gas chromatography–mass spectroscopy, and immunoanalytical techniques with enzyme-linked immunosorbent assay (ELISA) being the most prevailing method [72]. Whereas these methods are offering good detection limits and exceptional specificities and sensitivities, they are still drawbacks associated with these methods. These methods are time-consuming, and they use expensive analytical instruments, and require a lot of technical knowledge and operational expertise. They are therefore unsuitable for point-of-care diagnosis and will certainly not be accessible to farmers and many developing country laboratories. Therefore, the development of rapid, simple, relatively easy to use, and possibly non-instrumental cost-effective and convenient sampling and accurate detection methods for mycotoxin analysis are extremely essential and desirable. Methods with such properties are especially attractive for routine laboratory and on-site screening by untrained personnel and could also be affordable to farmers and to African Laboratories.

2.2.1 Lateral flow immunoassays

The lateral flow immunoassay (LFIA) has gained increasing interest and exhibits promise as a tool to overcome the complexities associated with traditional methods of mycotoxin analysis [73]. With LFIA, expensive equipment is not required, less skill is involved in administering LFIAs, and there is easy interpretation of results. The user-friendly operation and easy storage of the LFIA platform allow them to be used at the POC or industry setting as well as for in-home diagnoses/farm diagnosis especially with remote settings, administered with little training and with little chance of error [73, 74]. The POC diagnosis would also enable the decentralization of laboratory testing to POC sites. LFIA also offers advantages of prolonged shelf-life, small volumes required, rapid screening, and sometimes sensitive detection. Rapid detection of mycotoxin levels in food is of key importance in both mycotoxin monitoring and exposure assessment [71].

Recently, LFIA has been studied to detect mycotoxins such as AFB1, ZON, OTA and T-2 toxin DON, and fumonisin B1 [73, 74]. A one-step lateral flow test has been developed for the quantitative determination of total type B fumonisins in maize with a test range up to 4000 μg/kg and a limit of detection of 199 μg/kg [75]. A multiplex LFIA with luminescent quantum dots as label was developed with cutoff limits of 1000, 80, and 80 μg/kg for DON, ZON, and T2/HT2-toxin, respectively. The LFIA gave within 15 minutes with a low false-negative rate of less than 5% [73]. Further, LFIA has been used for the determination of AFB1, ZON, DON where analysis of naturally contaminated maize samples showed high sensitivity of LFIA proven by a good agreement between the multiplex LFIA and LC–MS/MS (100% for DONs and AFs, and 81% for ZONs) [74].

While traditionally built commercial LFIAs have many advantages, issues including poorer sensitivity and lower specificity than laboratory tests such as LC–MS and HPLC affect their efficacy and availability to the full market potential. Decreasing these disadvantages and complexity of these tests may increase the availability of diagnostic testing and quality of food commodities to farmers unable to make it to expensive testing facilities. To overcome this, several strategies are currently being developed such as reducing the components utilized in the manufacturing of these tests, which will consequently reduce cost and increase the manufacturability, improving adsorption capabilities and improving detection capabilities [76].

2.2.1.1 Improvement of LFIAs using electrospun nanofibers

With LFIAs, bio-reagents are immobilized in defined areas of the strip, normally referred to as the membrane, where the formation of colored bands due to the accumulation of suitably labeled species yields a yes/no information [77]. In particular, the analytical response is observed in the test line (T-line), while a second control line (C-line) allows to verify that the test has been correctly performed and therefore that results are reliable. There is potential for use of electrospinning to develop adsorbent pad and the support membrane for use in lateral flow device to improve adsorption flow rate and hence decrease incubation time [78, 79]. In conventional LFIA, nitrocellulose is used as a solid phase support. These are affordable, simple to produce, and easy to use in remote settings. These same materials can be used in conjunction with electrospinning technology to develop novel platforms for the detection of mycotoxins.

Electrospinning is a technique that utilizes electrostatic force to process a variety of native and synthetic polymers into highly porous materials composed of nano-scale to micron-scale diameter fibers. By nature, electrospun materials exhibit an extensive surface area and highly interconnected pore spaces and thus offer the advantages of high surface area-to-volume ratio for active reaction sites, tunable porosity and morphology, and high mechanical strength. For the ability to directly regulate the physical properties of an electrospun material through the manipulation of the fundamental variables such as electrospinning solvent and the air gap distance, accelerating voltage affords considerable control over the process. Further electrospun nanofibers can be functionalized very easily and materials can easily be combined together to make fibers and thus manipulate nanofiber composition to get the desired properties and function. Electrospun fibers can also be deposited unto other surfaces such as microfibrious mats. Electrospinning has shown great potential including water and air filtration as well as a gateway to the development and fabrication of physiologically relevant tissue engineering scaffolds, hemostatic agents, wound care products, and solid phase drug and peptide delivery platforms. Despite the growing research in this area, electrospinning techniques have not been widely employed for the development of LFIAs. Although the potential application of combining electrospun nanofiber membranes and biosensing has been recognized, limited studies have been done in this area of LFIAs. To date, electrospinning has not penetrated to any great extent into product lines designed for diagnostic and research applications.

Electrospun materials, by nature, exhibit an extensive surface area-to-volume ratios and therefore increase chances of interaction with target analytes such as mycotoxins [63]. Increasing the surface area of the detector substrate offers the advantage of increasing the number of sensing sites available without increasing the amount of overall sample required. A small volume electrospun mat can provide a very large surface for sensing and easy access for mycotoxins to the sensing sites [63]. The sequential deposition of the discreet, individual fibers that are formed in this process also results in a unique and complex interconnected network of pores. Thus, exploiting these characteristic to fabricate LFIA platforms designed for mycotoxins detection is desirable. The electrospun membrane can then be manipulated with gold nanoparticles (NPs) and antibodies to achieve functionality required for the mycotoxin detection. Gold nanoparticles are the most preferred candidate materials and have been widely used for the fabrication of aflatoxin-sensing devices. Gold nanoparticles offer excellent compatibility with antibodies, and their functionality remains unaffected even after immobilization. A fiber-based immunoassay system could also be incorporated in multiple configurations, which may not necessitate individual housing and packaging of tests.

Developing a fiber-based immunoassay system, by incorporating immunoassay technology that is currently used for diagnostic tests into a fiber-based system, presents a great potential. This could increase the sensitivity, decrease the number of components in manufacturing, reduce cost, and facilitate simpler and more comfortable sample collection to simplify the procedure. Electrospun membranes have been tested as immunoassay substrates. Polycaprolactone on nitrocellulose has been successfully electrospun membrane to form a hydrophobic coating to reduce the flow rate and increase the interaction rate between the targets and gold NPs-detecting probes conjugates [79]. This resulted in the binding of more complexes to the capture probes. With this approach, the sensitivity of the PCL electrospin-coated test strip was increased by approximately 10-fold as compared with the unmodified test strip. The approach holds great potential for sensitive detection of targets at point-of-care testing.

2.2.1.2 Improvement of detection in LFIAs

As there is an increasing need for high-performing LIFA in the clinical, environmental, self-diagnosis, agriculture, and food safety areas, conventional LFIA having readout errors to the naked eye is up against some major problems such as poor quantitative discrimination and low analytical sensitivity. To make the most out of LFIA’s advantages such as rapid point-of-care diagnosis, LFIA readers measuring the optical densities of the LFIA detection area have been developed for point-of-care applications [80] provided for quantitative or semi-quantitative analysis.

Further to provide the basis for a global monitoring of mycotoxins, highly sensitive, low-cost diagnostic tests developed can also be linked to smart phones applications as shown in Figure 1. The resulting digital information can be transmitted to a database of mycotoxin occurrence developed country by country and thus improved communication channels within the food chain. This could lead to comprehensive information systems that can support farm management decisions and thus help producers of many crops to produce higher quality and/or avoid losses, and also increase consumer confidence in agro-food products. A simple, rapid, and accurate one-dot LFIA detection method for AFB1 has been developed for point-of-care diagnosis [80] using competition between colloidal gold-AFB1-BSA conjugates for antibody-binding sites in the test zone. This was coupled with smartphone application for quantitative or semi-quantitative analysis.

Figure 1.

Low-cost rapid mycotoxin test system combined with ICT solutions.

2.3 Electrochemical detection of mycotoxins

Electrochemistry provides powerful analytical techniques that are sensitive, reliable, portable, and low-cost procedures that are associated with food safety [81, 82]. Electrochemistry deals with relationship between electrical energy and chemical energy and inter-conversion of one form to another. To transform the toxin interaction to analytical signal, a variety of electrochemical techniques have been used.

Amperometry is an important electrochemical analysis method in food analysis. In amperometry, the potential of the working electrode is constant and the resulting current from Faradaic processes occurring at the electrode is monitored with the function of time. It has a working response over a wide range of mycotoxin concentrations that gives an improved signal to ratio since the current is integrated over relatively longer time intervals [83].

Voltammetry is another method in the analysis of mycotoxins. The current in the cell is measured with respect to the variation of the potential in the cell. Constant or varied potential is applied at the electrode surface, and the resulting current is measured with a three-electrode system (work, auxiliary, and reference electrode). Chemically modified electrodes are employed for highly sensitive electrochemical determination of mycotoxins. Hernandez-Hernandez et al. 2021 studied ZON using cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). The method for the determination ZON was developed and applied for the quantitative analysis with low detection limits and multiplex analysis [84].

2.3.1 Electrochemical sensors

A biosensor is an analytical device that incorporate a bio-component or bio-receptor such as isolated enzymes, whole cell, tissues, aptamers with a suitable transducing system to detect chemical compound [85]. The numerous examples in the literature illustrate the high potential of the electrochemical biosensors in mycotoxin analysis, contributing to their sensitive determination in a variety of food and commodities. Measurement of the signal is generally electrochemical for biological, and this bio-electrochemical serves as transduction component in electrochemical biosensors. The biological reaction generates change in signal for conductance or impedance, measurable current, or change accumulation, which can be measured by conductometric, potentiometric, or amperometric techniques. The interaction between the target molecule and the electrical signal of bio-component produced can be measured [86].

Immunosensors are devices based on the detection of analyte-antibody interaction. Three main groups have been developed, which are luminescent or colorimetric sensors, surface plasmon resonance, and electrochemical sensors. An electrochemical immunosensor for the simultaneous detection of fumonisin B1 and DON has been designed and fabricated, which attained very low detection limits [87]. Furthermore, a third-generation enzymatic biosensor for quantification of sterigmatocystin (STEH), which was based on modified glassy carbon electrode, has been developed. The biosensor was also used to determine STEH in corn samples inoculated with Aspergillus flavus, which is an aflatoxins fungus producer [88].

2.3.1.1 Nanosensors

In many situations, it is necessary to detect multiple analytes or pathogens simultaneously, especially in mycotoxins detection where various mycotoxins can contaminate one single product. This would not be possible with conventional sensors. Sensors in nanoscale are especially attractive for such purposes. Nanosensors are characterized by one of the following attributes: Either the size of the sensor or its sensitivity is on the nanoscale or the spatial interaction distance between the sensors and the object is given in nanometers. These have advantages of improved sensitivity, specificity, and limits of detection, and reduced assay complexity and cost. Relatively small amount of analyte is required to register a response due to the small area of the sensing surface. Recently, a CeO₂ NPs-based sensor to detect OTA was developed [89]. The biosensor was assembled by functionalizing CeO₂ particles with OTA-specific ssDNA aptamers resulting in higher dispersibility and activity. Changes in the redox properties at the CeO₂ surface upon binding of the ssDNA and its target, measured using TMB, enabled rapid visual detection of OTA. In the presence of OTA, the ssDNA aptamer changed its structure from loose random coils to a compact tertiary form following target binding. As a result, a decreased catalytic effect against TMB oxidation was observed. The system was able to detect as low as 0.15 nM OTA.

During fungal growth, carbon dioxide is secreted due to the metabolic activity of microorganisms. In particular, gas nanosensors can be applied to detect the presence of CO₂ [89]. The detection of CO₂ is critical for environmental monitoring, chemical safety control, and many industrial applications; hence, nanosensors have been developed to assess changes in CO₂ concentration [90]. Electrochemical CO₂ nanosensors have been developed based on the principle that when CO₂ comes in contact with a semiconductor nanomaterial layer, a surface interaction may occur through oxidation/reduction, electron charge transfer, adsorption, or chemical reaction. The chemical interaction of the adsorbate (CO₂) with adsorbent semiconducting nanomaterial causes a charge depletion layer with upward bending energy bands that lead to change in electrical properties [91]. Although literature is scarce on CO₂ nanosensors associated with mycotoxin monitoring, there is a great potential in the area.

3. Preventive strategies

3.1 Food packaging

It is important to maintain the integrity of the food during storage and transportation through the supply chain before reaching the end consumer. Food packaging is one of the most critical steps in the food industry to protecting and preserving food commodities from any unacceptable alteration in quality and safety [92]. Traditional packaging systems such as use of polyethylene, polypropylene, and polyethylene terephthalate have several limitations related to extending shelf-life and maintaining the safety of food products. Thus, food packaging continues to evolve along with the innovations in material science and technology critical for food commodity preservation and effective distribution. Moreover, the increased desire of both food producers and consumers for quality food is encouraging researchers to seek novel, innovative, and resourceful food packaging systems with committed food safety, quality, and traceability and also to find ways to improve food quality while least compromising nutrition product value [93]. Innovative packaging systems facilitate communication at the consumer levels. These interventions and developments in food packaging must be commercially feasible and effectively acceptable, which must meet regulatory guidelines along with a justified outcome that outweighs the associated expenses of added novel technology [93].

Nanotechnology, in particular, has brought advances in the domain of food packaging. It offers a variety of options in the improvement of food packaging based on functionality nanomaterials, which can significantly address the food quality, safety, and stability concerns and thus reduce food waste and economic losses associated with mycotoxin contamination.

Advanced technologies based on applications of nanomaterials for food packaging, including active and intelligent packaging systems, have been developed in response to increased concerns for food safety and stringent regulatory requirements, and market globalization [94].

3.1.1 Active packaging

An active packaging is a designed packaging system that incorporates components that would release or absorb material into or from the packaged food or the food environment [94] thereby stimulating actions, which extends the shelf-life, and improves or maintains food quality and safety and/or sensory properties of the food product. Nanotechnology can be used to incorporate the active constituent into a food package material. Active packaging incorporates robust ways to control oxidation, microbial growth, hydrolysis, and other degradation reactions. The most promising active packaging technologies applicable to mycotoxin control include antimicrobial packaging, which significantly improve the micro-biological safety, oxygen scavengers, and moisture regulators/absorbers [94].

3.1.1.1 Antimicrobial active packaging

An antimicrobial packaging in particular antifungal active packaging is attractive in dealing with mycotoxins. This packaging allows its interaction with the food product or the headspace inside to reduce, inhibit, or retard the growth of spoilage or pathogenic microorganisms that may be present on food surfaces [95] and thus extends food shelf-life. Antimicrobial packaging could be achieved either by incorporation of nanomaterial active agent onto or applying a coating layer onto or within the packaging material. The active agent can inhibit the essential metabolic pathways of microorganisms or destroy cell wall/membrane structure. Higher surface area-to-volume ratio of nanomaterials antimicrobial agents in comparison with classical material enables their efficient inhibitory activity against food microbes resulting in an enhanced reactivity as photocatalysts and improved interactions between NPs and microbial membranes.

Nanomaterials such as chitosan NPs, metal NPs (AgNPs, Copper NPs and gold NPs), and metal oxide NPs (TiO₂, ZnO, MgO, and CuO) and CNTs are suitable agents that are well known for their antimicrobial activity and thus show great potential in providing antimicrobial and scavenging activity to food packaging. AgNPs are known to be inhibitory against multiple fungi [62, 96]. The AgNPs have been shown to inhibit fungal growth, when they are deposited over multilayered linear low-density polyethylene (LLDPE), and this resulted in 70% reduction of Aspergillus niger [76]. In another study, the application of 45 ppm Ag NPs caused a decrease in mycotoxin production (up to 80%) and changes in the enzymatic profile in Aspergillus niger [97]. The biosynthesized AgNPs showed outstanding activities for inhibiting four mycotoxigenic fungal strains (including Alternaria alternata, A. ochraceus, Aspergillus flavus, and Fusarium solani) [98]. Chitosan/silver, chitosan/gold, and chitosan/cinnamaldehyde nanocomposite films have also demonstrated antimicrobial activity against Aspergillus niger [99]. TiO₂ NPs, used as a food additive and for food contact material, have been applied to food packaging [92]. ZnO NPs have been an extremely promising antifungal agents for inhibiting the growth of mycotoxin-producing fungi [98]. CuNPs with the size range of 3–10 nm have also been found to have a superior antifungal activity toward Fusarium oxysporum [100]. NPs are especially attractive when exploiting eco-friendly energy-efficient, cost-effective, and green approaches. The use of extract of Cymbopogan citratus (DC) stapf, commonly known as lemon grass [100] and leaf extract of Cinnamomum camphora [101] in NPs synthesis, has been reported and has been found to be efficient in terms of reaction time as well as stability of the synthesized NPs. Essential oil-loaded biopolymeric nanocarriers also show promising antimicrobial and antioxidant activity and are suitable material for active food packaging due to inhibition of microbial growth in different food products [102].

3.1.1.2 Incorporation of moisture repellents and moisture absorbers in food packaging

Excess water reduces food shelf-life as it can promotes fungal proliferation inducing undesired changes in food quality. Thus, the moisture absorbers that are active non-migratory packaging and anti-wetting agents can be used in food packaging to reduce food water activity and provide an environment less suitable for mycotoxin-causing fungi [94]. Anti-wetting/moisture repellents can be made up of hydrophobic coatings on the surfaces of packaging materials.

Another strategy could involve the preparation of nano-engineered silicate-based hybrids coated onto both the intercalated and exfoliated silicate-based nano-composites. These materials are known to play an important role as agents that prevent the permeability of gaseous agents (e.g., O₂, CO₂). An attractive feature of using nano-engineered silicate-based hybrids arises from the fact that they are among minerals that are widely found in nature abundantly. Silicate minerals can have the surface easily modified due to the high possibility of ion exchange whereby a hydrophobic silicate can be modified/converted to an organophilic by exchanging a cation on its surface with an organic cation.

3.2 Smart packaging/intelligent packaging systems

In processing facilities, packaged foods are tested randomly during a production run. The downside to this is that there is no assurance that unsampled packages meet quality and safety standards. Recent efforts have thus been directed to the development of intelligent packaging systems that allow for real-time monitoring of food quality and boosting communicating with suppliers or the consumer at any point of the supply chain, or at the time of use [103]. These give ability to continually monitor the content of a package headspace and also provide a means to assess the safety and quality of the contained food long after it has left the production chain [62]. This can assist in ensuring adequate control after delivery to the supermarket, which is often not possible.

Intelligent systems use different innovative communication methods, which include sensors (already discussed under 2.3.1.1), indicators, and data carriers, that can measure changes in the environmental conditions inside packaging. These systems are attractive in mycotoxin research. The inclusion of nanosensors especially in food packaging systems could help in detecting the spoilage-associated changes and mycotoxin-causing fungi and thus can be alerted consumer and producer on food contamination [104]. These selective and sensitive nanosensors have been efficiently incorporated into food packaging, applied as labels or coatings to add an intelligent function to food packaging [105].

4. Conclusion

Analytical detection methods for mycotoxin that are affordable, easy to operate, and including LFIAs and electochemistry have been discussed. LFIA especially offers point-of-care diagnosis, which could be affordable to laboratories and farmers. The means of improving the LFIAs such as using electrospinning for production of membrane are recommended for increasing the acceptability LFIA. Food packaging is recognized as a means of preventing/controlling formation of mycotoxins. Aggressive research programs and yet affordable are needed to prevent, treat, and contain outbreaks of mycotoxins in grain, and grain producers and thus increase marketability of African products.