Aflatoxins contamination in Pakistani brown rice: a comparison of TLC, HPLC, LC–MS/MS and ELISA techniques

A dual-signal aptasensor based on cascade amplification for ultrasensitive detection of aflatoxin B1

Aflatoxin B1 (AFB1) is considered as a serious carcinogenic mycotoxin that was widely detected in grains and foods, and its sensitive analysis is of key importance to avoid the health threats for consumers. In this study, a dual-signal aptasensor based on cascade of entropy-driven strand displacement reaction (ESDR) and linear rolling circle amplification (LRCA) was fabricated for ultrasensitive determination of AFB1. At the sensing system, the complementary strand would be released after the aptamer combined with AFB1, which will bring about the functional domains exposed, triggering the subsequent ESDR. Meanwhile, the two strands that were outputted by ESDR would incur the downstream LRCA reaction to produce a pair of long strands to assist in the generation of fluorescence and absorbance signals. Under the optimized conditions, the proposed aptasensor could achieve excellent sensitivity (limit of detection, 0.427 pg/mL) with satisfactory accuracy (recoveries, 92.8-107.9 %; RSD, 2.4-5.0 %), mainly ascribed to the cascade amplification. Importantly, owing to the flexibility design of nucleic acid primer, this analytical method can be applied in monitoring various hazardous substances according to the specific requirements. Our strategy provides some novel insights at signal amplification for rapid detection of AFB1 and other targets.

Mycotoxins in Rice Correlate with Other Contaminants? A Pilot Study of the Portuguese Scenario and Human Risk Assessment

Rice is the second most important cereal crop and is vital for the diet of billions of people. However, its consumption can increase human exposure to chemical contaminants, namely mycotoxins and metalloids. Our goal was to evaluate the occurrence and human exposure of aflatoxin B1 (AFB1), ochratoxin A (OTA), zearalenone (ZEN), and inorganic arsenic (InAs) in 36 rice samples produced and commercialized in Portugal and evaluate their correlation. The analysis of mycotoxins involved ELISA, with limits of detection (LODs) of 0.8, 1 and 1.75 μg kg^-1 for OTA, AFB1, and ZEN, respectively. InAs analysis was carried out by inductively coupled plasma mass spectrometry (ICP-MS; LOD = 3.3 μg kg^-1). No sample showed contamination by OTA. AFB1 was present in 2 (4.8%) samples (1.96 and 2.20 μg kg^-1), doubling the European maximum permitted level (MPL). Concerning ZEN, 88.89% of the rice samples presented levels above the LOD up to 14.25 µg kg^-1 (average of 2.75 µg kg^-1). Regarding InAs, every sample presented concentration values above the LOD up to 100.0 µg kg^-1 (average of 35.3 µg kg^-1), although none surpassed the MPL (200 µg kg^-1). No correlation was observed between mycotoxins and InAs contamination. As for human exposure, only AFB1 surpassed the provisional maximum tolerable daily intake. Children were recognized as the most susceptible group.

Comprehensive Review of Aflatoxin Contamination, Impact on Health and Food Security, and Management Strategies in Pakistan

Aflatoxins (AFs) are the most important toxic, mutagenic, and carcinogenic fungal toxins that routinely contaminate food and feed. While more than 20 AFs have been identified to date, aflatoxin B1 (AFB1), B2 (AFB2), G1 (AFG1), G2 (AFG2), and M1 (AFM1) are the most common. Over 25 species of Aspergillus have been shown to produce AFs, with Aspergillus flavus, Aspergillus parasiticus, and Aspergillus nomius being the most important and well-known AF-producing fungi. These ubiquitous molds can propagate on agricultural commodities to produce AFs in fields and during harvesting, processing, transportation, and storage. Countries with warmer climates and that produce foods susceptible to AF contamination shoulder a substantial portion of the global AF burden. Pakistan's warm climate promotes the growth of toxigenic fungi, resulting in frequent AF contamination of human foods and animal feeds. The potential for contamination in Pakistan is exacerbated by improper storage conditions and a lack of regulatory limits and enforcement mechanisms. High levels of AFs in common commodities produced in Pakistan are a major food safety problem, posing serious health risks to the population. Furthermore, aflatoxin contamination contributes to economic losses by limiting exports of these commodities. In this review, recent information regarding the fungal producers of AFs, prevalence of AF contamination of foods and feed, current regulations, and AF prevention and removal strategies are summarized, with a major focus on Pakistan.

Exposure Assessment of Aflatoxin B1 through Consumption of Rice in the United Arab Emirates

Rice is one of the most consumed staple foods worldwide and a major part of the diet for half of the global population. Being primarily cultivated in countries with warm and humid environments increases rice's susceptibility for mycotoxins contamination, especially the hepatotoxic and carcinogenic aflatoxin B1 (AFB1). Since no study was published before on the exposure to AFB1 from consuming rice in the UAE, our study aims to assess the levels of AFB1 in rice marketed in the country and determine the estimated daily exposure of the population for this carcinogenic metabolite and its associated liver cancer risk. All white, brown, and parboiled rice brands available in the retail markets in the UAE were procured twice. Using an enzyme-linked immunosorbent assay (ELISA) method, AFB1 was detected in 48 out of 128 rice samples (38%). The average contamination ± standard deviation of AFB1 among positive samples (above the detection limit) was found to be 1.66 ± 0.89 μg/kg, ranging from 1 μg/kg (detection limit) to 4.69 μg/kg. The contamination level in all the samples was below the limit set by the Gulf Cooperation Council Standardization Organization (≤5 μg/kg), while 10 (20.8%) of the positive samples had a contamination level above the maximum limit set by the European Union (≥2 μg/kg). The moisture content in all the assessed samples was ≤14%. Furthermore, there was a significant difference in AFB1 between samples in both collections (p-value = 0.043). However, the rice type, grain size, packing country, packing season, country of origin, collection season, and packing to purchasing time had no significant effect on AFB1. The calculated mean daily exposure level of the Emirati population to AFB1 from consuming rice was 4.83 ng/kg.

Aflatoxins in Cereals and Cereal-Based Products: Occurrence, Toxicity, Impact on Human Health, and Their Detoxification and Management Strategies

Cereals and cereal-based products are primary sources of nutrition across the world. However, contamination of these foods with aflatoxins (AFs), secondary metabolites produced by several fungal species, has raised serious concerns. AF generation in innate substrates is influenced by several parameters, including the substrate type, fungus species, moisture content, minerals, humidity, temperature, and physical injury to the kernels. Consumption of AF-contaminated cereals and cereal-based products can lead to both acute and chronic health issues related to physical and mental maturity, reproduction, and the nervous system. Therefore, the precise detection methods, detoxification, and management strategies of AFs in cereal and cereal-based products are crucial for food safety as well as consumer health. Hence, this review provides a brief overview of the occurrence, chemical characteristics, biosynthetic processes, health hazards, and detection techniques of AFs, along with a focus on detoxification and management strategies that could be implemented for food safety and security.

Mycotoxins in Cattle Feed and Feed Ingredients in Brazil: A Five-Year Survey

Mycotoxins are toxic secondary metabolites produced by a variety of fungi, which when ingested can cause several deleterious effects to the health of humans and animals. In this work, the detection and quantification of six major mycotoxins (aflatoxins-AFLA, deoxynivalenol-DON, fumonisins-FUMO, ochratoxin A-OTA, T-2 toxin-T-2 and zearalenone-ZON) in 1749 samples of feed and feed ingredients for cattle, collected in Brazil between 2017 and 2021, was carried out using enzyme-linked immunosorbent assay (ELISA). In total, 97% of samples were contaminated with at least one mycotoxin, yet, very few samples exceeded the lowest European Union guidance values for cattle, and the estimated daily intake also showed a low risk for the animals. However, co-occurrences were widely observed, as 87% of samples contained two or more mycotoxins at the same time, and the presence of more than one mycotoxin at the same time in feed can lead to interactions. In conclusion, the contamination of feed and feed ingredients for cattle with mycotoxins in Brazil is very common. Hence, the monitoring of these mycotoxins is of significant importance for food safety.

Aflatoxin B1 in Rice: Effects of Storage Duration, Grain Type and Size, Production Site, and Season

ABSTRACT

Our study evaluated aflatoxin B1 (AFB1) levels in packed rice marketed in Lebanon and determined the exposure to this toxin from rice consumption. A total of 105 packed white, parboiled, and brown rice bags were collected. Enzyme-linked immunosorbent assay was used to measure AFB1. A comprehensive food frequency questionnaire was completed by 500 participants to determine patterns of rice consumption and, subsequently, the exposure levels to AFB1 from rice consumption in Lebanon. AFB1 was detected in all rice samples (100%). The average concentration ± standard deviation of AFB1 was 0.5 ± 0.3 μg/kg. Contamination ranged between 0.06 and 2.08 μg/kg. Moisture content in all rice samples was below the recommended percentage (14%). Only 1% of the samples had an AFB1 level above the European Union limit (2 μg/kg). Brown rice had a significantly higher AFB1 level than white and parboiled rice (P = 0.02), while a significant difference was found between both collections for the same brands (P = 0.016). Packing season, packing country, country of origin, presence of a food safety management certification, grain size, and time between packing and purchasing had no significant effect. Exposure to AFB1 from rice consumption in Lebanon was calculated as 0.1 to 2 ng/kg of body weight per day.

HIGHLIGHTS

Ingenious Electrochemiluminescence Bioaptasensor Based on Synergistic Effects and Enzyme-Driven Programmable 3D DNA Nanoflowers for Ultrasensitive Detection of Aflatoxin B1

Aflatoxin B1 (AFB1), one of the most toxic mycotoxins, has undergone a wide range of studies over the years. The development of rapid, simple, and sensitive analytical methods remains a major challenge for the accurate detection of AFB1 in foodstuffs. In this study, we designed an enhanced and stable ingenious electrochemiluminescence bioaptasensor (IEC-BA) for ultrasensitive detection of AFB1 based on the synergistic effects and enzyme-driven programmable assembled 3D DNA nanoflowers (EPDNs). This synergistic effect was comprised by the competitive impact on auxiliary probes (AP) and the cutting effect of the Hae III. Compared to the traditional aptamer direct-competition method, the synergistic effects ensured that the aptamer was more efficiently and adequately competed away by the target. Also, the redundant double-stranded probes were removed, which greatly facilitates simple, quick, and sensitive detection of AFB1. Besides, a large chunk of positively charged Ru(II) complexes (Ru(bpy)₃²⁺) was accumulated by the utilization of EPDNs, which resulted in tremendous improvement of the sensitivity of the designed method. Thus, even in the presence of trace amounts of AFB1, a sharply visual electrochemiluminescent signal was generated. The proposed method can realize the quantification of AFB1 with a good linear range from 1 ppt (pg mL^-1) to 5 ppb (ng mL^-1) with a detection limit of 0.27 ppt. In addition, it can also be successfully applied for the analysis of AFB1 in a peanut and wheat, with total recoveries ranging from 93.7 to 106.6%. Furthermore, the IEC-BA also exhibited good selectivity, reproducibility, and stability, revealing prospective applications of food safety monitoring and environmental analysis.

Aflatoxins in rice: Worldwide occurrence and public health perspectives

Aflatoxins are fungal secondary metabolites that contaminate dietary staples worldwide, including maize, rice and groundnuts. Dietary exposure to aflatoxins is a public health concern due to their carcinogenic, acute and chronic effects. Rice is an important staple food consumed widely and consists of a major part of the diets for half of the world population. Human exposure to these mycotoxins is a serious problem especially in developing countries where hot and humid climates favor the fungal growth and where food storage conditions are poor and lack of regulatory limits enforcement. The recent developments of biomarkers have provided opportunities in assessing aflatoxins exposure and related health effects in the high-risk population groups. This review describes the worldwide occurrence of aflatoxins in rice during the period from 1990 to 2015 and biomarkers-based evidence for human exposure to aflatoxins and their adverse health effects. Aflatoxin is a potent hepatocarcinogen and humans may expose to it at any stage of life. Epidemiological studies reported an association between aflatoxin intake and the incidence of hepatocellular carcinoma in some sub-Saharan and Asian countries. Even daily high intake of rice with a low level of contamination is of health concern. Thus, it is necessary to implement effective strategies to prevent contamination and fungal growth in rice. A good agricultural and manufacturing practice should be applied during handling, storage and distribution of rice to ensure that aflatoxins contamination level is lower in the final product. Moreover, a regular survey for aflatoxins occurrence in rice and biomarkers-based studies is recommended to prevent and reduce the adverse health effects in the world population.

Occurrence of aflatoxins in rice and in cassava (Manihot esculenta) products (meal, bread) produced in Guyana

A survey was conducted on Guyana's main staple foods, rice, cassava meal and cassava bread to determine the presence and concentration of aflatoxins (AFs) using enzyme-linked immunosorbent assay (ELISA) and high-performance liquid chromatography (HPLC) with fluorescence detection for concurrence. Aflatoxins are secondary metabolites of the fungus Aspergillus and can be a health risk to humans and animals. Results were compared with European Union Commission (EUC) maximum levels of total aflatoxins of 10 μg/kg. Various types of rice (paddy, steamed paddy, cargo rice, white rice and parboiled rice) were randomly collected either directly from the field and rice mills in Guyana during the November 2015/March 2016 season. Of the total 186 composite samples of rice fractions collected from field and mills, 10% (19) had AF concentrations greater than the maximum EUC level of 10 μg/kg. Fifteen samples had aflatoxin concentrations ranging from 10 to 171 μg/kg, mean 54.4 μg/kg; four samples were outliers. Since Guyanese consume mainly white and parboiled rice, composite samples were taken along the marketing chain at points of sale to determine the presence of AFs. Of the sixty samples of white rice collected, 6.7% (4) had AF concentrations greater than the EUC regulatory limits ranging from 31.9 to 131 μg/kg, mean 80.8 μg/kg. For the 57 samples of parboiled rice, 3.5% (2) samples exceeded the limit with values of 72.6 and 407 μg/kg. Forty (40) samples each of cassava meal and cassava bread were analysed fresh and after 2 months of storage, and no sample exceeded the ELISA detection limit of 0.5 μg/kg.

Aflatoxin B1 Electrochemical Aptasensor Based on Tetrahedral DNA Nanostructures Functionalized Three Dimensionally Ordered Macroporous MoS2-AuNPs Film

In food safety evaluation, aflatoxin B1 (AFB1) is an important indicator. In this work, we developed an AFB1 electrochemical aptasensor based on a tetrahedral DNA nanostructures (TDNs) immobilized three dimensionally ordered macroporous MoS₂-AuNPs hybrid (3DOM MoS₂-AuNPs) recognition interface and horseradish peroxidase (HRP) functionalized magnetic signal amplifier. To greatly enhance the recognition efficiency, sensitivity, and stability of the aptasensor, the AFB1 aptamer-incorporated TDNs were ingeniously combined with the 3DOM MoS₂-AuNPs film for the construction of the sensing interface. The aptamers would release from the electrode surface after they reacted with AFB1, and then the hybridization-free TDNs formed. Thus, the biocomposite of DNA helper strands (H1)/HRP functionalized AuNPs-SiO₂@Fe₃O₄ nanospheres would combine with the hybridization-free TDNs due to the hybridization of H1 and TDNs. The more AFB1 existed in the solution, the more H1/HRP-AuNPs-SiO₂@Fe₃O₄ could be combined onto the 3DOM MoS₂-AuNPs surface. The current response coming from HRP-catalyzed reduction of H₂O₂ using thionine (Thi) as electrochemical probe was proportional with the AFB1 concentration. Upon optimal conditions, the aptasensor showed specificity for AFB1, achieving a good linear range of 0.1 fg/mL-0.1 μg/mL and the detection limit of 0.01 fg/mL. Furthermore, the developed aptasensor was also applied for detecting AFB1 content in rice and wheat powder samples, obtaining good results in conformity with those achieved from the high-performance liquid chromatography tandem mass spectrometry (HPLC-MS) method.

Development of an Ultrasonication-Assisted Extraction Based HPLC With a Fluorescence Method for Sensitive Determination of Aflatoxins in Highly Acidic Hibiscus sabdariffa

The high acidity and complex components of Hibiscus sabdariffa have provided major challenges for sensitive determination of trace aflatoxins. In this study, sample pretreatment of H. sabdariffa was systematically developed for sensitive high performance liquid chromatography-fluorescence detection (HPLC-FLD) after ultrasonication-assisted extraction, immunoaffinity column (IAC) clean-up and on-line post-column photochemical derivatization (PCD). Aflatoxins B₁, B₂, G₁, G₂ were extracted from samples by using methanol/water (70:30, v/v) with the addition of NaCl. The solutions were diluted 1:8 with 0.1 M phosphate buffer (pH 8.0) to negate the issues of high acidity and matrix interferences. The established method was validated with satisfactory linearity (R > 0.999), sensitivity (limits of detection (LODs) and limits of quantitation (LOQs) of 0.15-0.65 and 0.53-2.18 μg/kg, respectively), precision (RSD <11%), stability (RSD of 0.2-3.6%), and accuracy (recovery rates of 86.0-102.3%), which all met the stipulated analytical requirements. Analysis of 28 H. sabdariffa samples indicated that one sample incubated with Aspergillus flavus was positive with aflatoxin B₁ (AFB₁) at 3.11 μg/kg. The strategy developed in this study also has the potential to reliably extract and sensitively detect more mycotoxins in other complex acidic matrices, such as traditional Chinese medicines, foodstuffs, etc.

Aflatoxin B1 Contamination of Dairy Feeds after Storage in Farm Practice in Tropical Environmen

　The objective of this study was to determine the contamination of aflatoxin B1 (AF-B1) when keeping various dairy feeds in a farm environment. The study was carried out from March to May 2011 and involved 63 small holder dairy farms belonging to a single dairy cooperative in Chiang Mai province, Thailand. All feed samples used for milking cows including 4 commercial concentrates (CC1 to CC4), by-products from local corn processing factories fermented in plastic bags (SIL), and corn and cob meal or corn dust (CCD). Feed samples were collected 2 times at before and after storage. Farmers were requested to store CC1 to CC4 and CCD for a month and SIL for a week using their routine on-farm storage arrangements. All samples were measured for their AF-B1 concentrations by ELISA. Results showed that AF-B1 concentrations of CC1 to CC4, SIL and CCD before storage were 5.1, 4.1, 4.0, 4.2, 5.5 and 5.5 μg/kg, respectively, and after storage the concentration of AF-B1 were 9.7, 6.5, 9.8, 12.3, 11.4 and 20.0 μg/kg, respectively. CCD at after storage was the only feed that had mean level more than 20 μg/kg. Concentrations of AF- B1 at before storage in all feeds were significantly lower than after storage (P<0.01), and the increased ratio of AF-B1 levels was approximately 2 to 3 times. The study concluded that increased AF-B1 levels are related to feed types and farm conditions.

Aflatoxin M1 in Cow's Milk: Method Validation for Milk Sampled in Northern Italy

Aflatoxins (AFs) are mycotoxins produced by some species of Aspergillus. In dairy cows, ingested AFB1 is metabolized into carcinogenic AFM1 which is eliminated through milk, thus posing a risk for consumer health. Here we describe the set, validation, and application of screening (ELISA) and confirmatory (HPLC) tests carried out on milk samples collected through official control of mycotoxin levels in northern Italy over a three-year period (2012-2014). The limit of detection (LOD) was set at 5 ppt and 2 ppt for ELISA and HPLC, respectively, and the limit of quantification (LOQ) was 10 ppt for confirmatory HPLC. A total of 1668 milk samples were analyzed: ELISA identified 36 (2.2%) positive milk samples that were subsequently confirmed by HPLC. The level of AFM1 in the positive samples ranged between 18 ± 2 and 208 ± 27 ppt. Of the total samples, only eight (0.5%) were found non-compliant with the EU regulatory limit (50 ppt; range 74 ± 10 to 208 ± 27 ppt). Use of ELISA and HPLC tests in series allows for high-volume analysis of samples, thus saving time and money while guaranteeing high analytical precision and accuracy.