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Abstract Mycotoxins are a kind of secondary metabolites and the most polluting biotoxins in food and feed pollution， causing great losses to peoples lives and economy. This study analyzed the residues of mycotoxins in foods and feeds in a certain area， so as to understand the food safety situation in the region and provide a strong basis for food and drug supervision and management. Quality control in the analysis process is the basis for ensuring real and effective data. This study carried out a specific analysis on the contamination of mycotoxins and the quality control in the process.
Key words Cereals; Mycotoxins; Pollution; Quality control
Mycotoxins were first discovered in Europe in the 11 th century， when it was called ergotoxine. These toxins mainly include deoxynivalenol （DON）， zearalenone （ZEN）， aflatoxins （AFs）， ochratoxins （OTA） and fumonisins （FBs）. According to statistics， about 25% of crops are infected with mycotoxins every year， and 2% of the grains are causing huge economic losses due to serious pollution. According to incomplete statistics， 30% of maize and 5% of soybean meal were positive for aflatoxins. However， when livestock and poultry eat contaminated feed， it will cause a mycotoxin poisoning phenomenon and thus pose a great impact on livestock and poultry. At the same time， mycotoxins are also extremely toxic， causing certain damage to human body. They can cause hallucinations， and even necrosis in severe case[1-2]， and also cause teratogenesis and carcinogenesis， mutagenesis and other hazards[3]. Therefore， the research on the contamination of mycotoxins in foods and feeds can not only prevent people and even animals from poisoning， but also provide a strong basis for peoples health.
In the 10 years from 2001 to 2011， among the violation events of exporting food to the EU in China， the events of mycotoxin exceeding the standard accounted for 28.6%， which was a high proportion in single events. As a kind of highly toxic and carcinogenic toxins， mycotoxins can contaminate almost all types of food and forage products. According to the Food and Agricultural Organization， about 25% of the worlds grain and oil is contaminated with mycotoxins every year. In recent years， the problem of mycotoxin contamination in agricultural products has been a hot food safety concern in all countries of the world.
The production process of mycotoxins is complicated， and the quality control can be performed from pre treatment and data analysis. In this study， quality control was performed from above aspects to ensure that people eat safely. Materials and Methods
Sampling
This experiment collected 150 cereals from supermarkets， shopping malls， canteens， grain and oil stores， farmers markets， growers and other places in a certain area， involving maize， rice， wheat， millet， flour and other common foods. Since the proportions of the mycotoxin contaminated parts in the foods are small and the distribution is not uniform， it is necessary to ensure the uniformity of samples during the preparation of the samples， so as to avoid excessive data error. At the same time， a part of representative feeds were also taken to detect the content.
Detection
The technical requirements were judged according to GB 2761 "Maximum levels of mycotoxins in foods". In this experiment， aflatoxin B1 and deoxynivalenol were analyzed by liquid chromatography tandem mass spectrometry （LC MS/MS）， and fumonisin and ochratoxin were determined by LC. The results were statistically analyzed. Through the sampling and detection of mycotoxins in foods and feeds， the specific statistical results are shown in Fig. 1.
In 2009， a survey of cereals and feeds in 11 provinces across the country found that the detection rate of mycotoxins was 95.8% ， with higher levels in barley， wheat and maize， and lower levels in rice and sorghum. In the study， the unqualified rate of mycotoxins in wheat and maize was the highest through the monitoring of cereals， and the unqualified rate of deoxynivalenol was the highest among these mycotoxins. The unqualified rate of aflatoxins in peanuts was also the highest. However， peanuts and maize are the main raw materials for animal feeds， so they are samples that need to be monitored （Table 1-2）.
Quality control
Each of the planting， storage and processing links cannot be missed
Mycotoxins are produced through mildew. They are secondary metabolites produced by fungi. From maize， peanuts to fruits， Chinese herbs， feeds， etc.， mycotoxins are ubiquitous in our lives， and they almost pollute all kinds of foods and feeds. They can cause pollution during planting， storage and processing. Therefore， these links need to be strictly controlled.
Crops are likely to be infected by fungi during their growth， thereby producing mycotoxins. Therefore， effective control during planting can reduce the probability of mycotoxin infection. After research， the Chinese Academy of Sciences invented an antifungal injection that inhibits the production of fungi. Injecting this kind of injection into crops during the planting process can effectively reduce the risk of mycotoxin contamination and prevent and control it from the source. Mycotoxins are extremely prone to occur during storage. The climate difference between the north and the south is relatively large. The climate difference between the north and the south is relatively large. The crops in the rainy south cannot be dried or may be wetted in the preservation process， which will cause the growth of mold to produce mycotoxins， and these toxins are difficult to eliminate in the later process. Therefore， the storage conditions are urgently needed to be solved. A drying equipment designed by Nanjing Research Institute for Agricultural Mechanization， Ministry of Agriculturethe can effectively solve the fungal pollution caused by improper storage. The Jiangxi Academy of Agricultural Sciences has also optimized the storage bag and introduced a new type of plastic bag for vacuum packaging that is protected from light， and as long as the cereals and grain feeds are placed inside， they will not be damp and mildew.
The processing of foods and feeds is more complicated， involving multiple links and equipment， which is a difficult point in the prevention and control of mycotoxins. Any bad work done can cause pollution， so it is difficult to strictly control each link. To this end， the testing centers and the Chinese Academy of Sciences are studying how to prevent it. The Chinese Academy of Sciences has specially developed technologies， products and equipment for removing the contaminated raw materials by screening， processing and biosorption. They can be used to degrade and remove mycotoxins and achieve good monitoring.
Control during detection
Sample preparation process
Uneven sampling or inadequate preparation （such as particle size not fine enough during grinding） can cause data deviation. Therefore， in the whole experiment process， the sample preparation must be carried out in strict accordance with the requirements stipulated in the standard. Sampling should be performed by the quartering method， and how the sample is ground and how many mesh of the screens are required after grinding are all rigidly stipulated. No link can be neglected because of saving time or trouble.
Solvent system
When extracting mycotoxins from foods and feeds， the type of mycotoxins， the nature of the toxins， the solubility of the toxins in the extraction solvent and the like are all conditions for extracting solvent selection. In principle， a solvent system with low toxicity， high polarity and low cost is selected. The basis for evaluating the extraction effect of a solvent system is the recovery and extraction time. The excellent solvent system should have high recovery of toxins， less interference impurities and short extraction time. The extraction solvent generally selected is a mixed solution of an organic solvent and water， methanol water or acetonitrile water. For example， it has been studied that almost all deoxynivalenol （DON） can be extracted with acetonitrile water in foods and feeds， while for fumonisins， it was found that natural fumonisins can be extracted from maize and its products with methanol water. The extracting solvents most used in the national standards for extracting mycotoxins from plant foods， grains， vegetable oils， feeds and other substrates are methanol water and acetonitrile water. This shows that the two extraction solvents can quickly extract the targetss and obtain a high extraction rate at the same time， which is necessary for the accuracy of the data during the whole experiment. Therefore， the choice of the extracting solvent is generally methanol water or acetonitrile water. Purification process
At present， the purification of mycotoxins in foods and feeds on national standards mainly depends on immunoaffinity column， solid phase extraction column， purification powder， and QuEChERs purification. The most commonly used purification methods at present are immunoaffinity columns and QuEChERs purification. The immunoaffinity column is characterized by strong specificity. In use， the required toxins are immobilized on the column， the undesired components can be eluted by solvents， and some impurities can be discarded by the eluent. This purification method is strong in immunity and clean， but the price is relatively high. The QuEChERS purification technology is an emerging purification technology that not only acts on agricultural residues， but also on the extraction of mycotoxins. Its principle is mainly to use the interaction between the filler and the interfering substances in the matrix to achieve the purpose of rapid purification. The fillers are mainly PSA， ODS， C18 and the like.
The technology is simple， fast， effective， and stable， and is suitable for a variety of substrates， so it is currently the second most used purification method. The recovery of the immunoaffinity column is 69.6%-97.3%， while the QuEChERS purification is 75.5%-113.4%. Comparing from the data， QuEChERS purification is better. Therefore， in order to better monitor the data， it is recommended to select QuEChERS purification during the purification process.
Detection method
There are many methods for detecting mycotoxins， which are summarized by liquid chromatography， liquid chromatography mass spectrometry， and enzyme linked immunosorbent assay. The most common methods are liquid chromatography tandem mass spectrometry and liquid chromatography. The comparative analysis of the instruments used is shown in Table 3.
Conclusions
Mycotoxins can cause serious damage to humans and animals， so quality control of mycotoxins is extremely important during experiments. This study monitored the preparation of samples， the selection of solvents， and the selection of methods during planting， processing， storage and experiment processes. Mycotoxins have the characteristics of relatively complicated production mechanism， easy contamination during the detection process and difficult removal. Therefore， all aspects of the mycotoxin quality control process should be monitored as much as possible. In general， there is still a certain gap between us and the international level. Meanwhile， the limit of mycotoxins is not perfect. Therefore， there are many difficulties in the process of monitoring. We still need to continue to work hard and try to achieve complete monitoring.
References
[1] ZHENG Y， WANG XY， LI JJ. Determination of aflatoxins in food by liquid chromatography tandem mass spectrometry[J]. Food Sci， 2010， 31（24）： 385-388. （in Chinese）
[2] HUONG BTM， TUYEN LD， TUAN DH， et al. Dietary exposure to aflatoxin B1， ochratoxin A and fuminisins of adults in Lao Cai province， Viet Nam： A total dietary study approach [J]. Food Chem Toxicol， 2016， 98（PtB）： 127-133.
[3] LONG XD， YAO JG， ZENG Z， et al. Polymorphisms in the coding region of X ray repair complementing group 4 and aflatoxin B1 related hepatocellular carcinoma[J]. Hepatology， 2013， 58（1）： 171-181.
Key words Cereals; Mycotoxins; Pollution; Quality control
Mycotoxins were first discovered in Europe in the 11 th century， when it was called ergotoxine. These toxins mainly include deoxynivalenol （DON）， zearalenone （ZEN）， aflatoxins （AFs）， ochratoxins （OTA） and fumonisins （FBs）. According to statistics， about 25% of crops are infected with mycotoxins every year， and 2% of the grains are causing huge economic losses due to serious pollution. According to incomplete statistics， 30% of maize and 5% of soybean meal were positive for aflatoxins. However， when livestock and poultry eat contaminated feed， it will cause a mycotoxin poisoning phenomenon and thus pose a great impact on livestock and poultry. At the same time， mycotoxins are also extremely toxic， causing certain damage to human body. They can cause hallucinations， and even necrosis in severe case[1-2]， and also cause teratogenesis and carcinogenesis， mutagenesis and other hazards[3]. Therefore， the research on the contamination of mycotoxins in foods and feeds can not only prevent people and even animals from poisoning， but also provide a strong basis for peoples health.
In the 10 years from 2001 to 2011， among the violation events of exporting food to the EU in China， the events of mycotoxin exceeding the standard accounted for 28.6%， which was a high proportion in single events. As a kind of highly toxic and carcinogenic toxins， mycotoxins can contaminate almost all types of food and forage products. According to the Food and Agricultural Organization， about 25% of the worlds grain and oil is contaminated with mycotoxins every year. In recent years， the problem of mycotoxin contamination in agricultural products has been a hot food safety concern in all countries of the world.
The production process of mycotoxins is complicated， and the quality control can be performed from pre treatment and data analysis. In this study， quality control was performed from above aspects to ensure that people eat safely. Materials and Methods
Sampling
This experiment collected 150 cereals from supermarkets， shopping malls， canteens， grain and oil stores， farmers markets， growers and other places in a certain area， involving maize， rice， wheat， millet， flour and other common foods. Since the proportions of the mycotoxin contaminated parts in the foods are small and the distribution is not uniform， it is necessary to ensure the uniformity of samples during the preparation of the samples， so as to avoid excessive data error. At the same time， a part of representative feeds were also taken to detect the content.
Detection
The technical requirements were judged according to GB 2761 "Maximum levels of mycotoxins in foods". In this experiment， aflatoxin B1 and deoxynivalenol were analyzed by liquid chromatography tandem mass spectrometry （LC MS/MS）， and fumonisin and ochratoxin were determined by LC. The results were statistically analyzed. Through the sampling and detection of mycotoxins in foods and feeds， the specific statistical results are shown in Fig. 1.
In 2009， a survey of cereals and feeds in 11 provinces across the country found that the detection rate of mycotoxins was 95.8% ， with higher levels in barley， wheat and maize， and lower levels in rice and sorghum. In the study， the unqualified rate of mycotoxins in wheat and maize was the highest through the monitoring of cereals， and the unqualified rate of deoxynivalenol was the highest among these mycotoxins. The unqualified rate of aflatoxins in peanuts was also the highest. However， peanuts and maize are the main raw materials for animal feeds， so they are samples that need to be monitored （Table 1-2）.
Quality control
Each of the planting， storage and processing links cannot be missed
Mycotoxins are produced through mildew. They are secondary metabolites produced by fungi. From maize， peanuts to fruits， Chinese herbs， feeds， etc.， mycotoxins are ubiquitous in our lives， and they almost pollute all kinds of foods and feeds. They can cause pollution during planting， storage and processing. Therefore， these links need to be strictly controlled.
Crops are likely to be infected by fungi during their growth， thereby producing mycotoxins. Therefore， effective control during planting can reduce the probability of mycotoxin infection. After research， the Chinese Academy of Sciences invented an antifungal injection that inhibits the production of fungi. Injecting this kind of injection into crops during the planting process can effectively reduce the risk of mycotoxin contamination and prevent and control it from the source. Mycotoxins are extremely prone to occur during storage. The climate difference between the north and the south is relatively large. The climate difference between the north and the south is relatively large. The crops in the rainy south cannot be dried or may be wetted in the preservation process， which will cause the growth of mold to produce mycotoxins， and these toxins are difficult to eliminate in the later process. Therefore， the storage conditions are urgently needed to be solved. A drying equipment designed by Nanjing Research Institute for Agricultural Mechanization， Ministry of Agriculturethe can effectively solve the fungal pollution caused by improper storage. The Jiangxi Academy of Agricultural Sciences has also optimized the storage bag and introduced a new type of plastic bag for vacuum packaging that is protected from light， and as long as the cereals and grain feeds are placed inside， they will not be damp and mildew.
The processing of foods and feeds is more complicated， involving multiple links and equipment， which is a difficult point in the prevention and control of mycotoxins. Any bad work done can cause pollution， so it is difficult to strictly control each link. To this end， the testing centers and the Chinese Academy of Sciences are studying how to prevent it. The Chinese Academy of Sciences has specially developed technologies， products and equipment for removing the contaminated raw materials by screening， processing and biosorption. They can be used to degrade and remove mycotoxins and achieve good monitoring.
Control during detection
Sample preparation process
Uneven sampling or inadequate preparation （such as particle size not fine enough during grinding） can cause data deviation. Therefore， in the whole experiment process， the sample preparation must be carried out in strict accordance with the requirements stipulated in the standard. Sampling should be performed by the quartering method， and how the sample is ground and how many mesh of the screens are required after grinding are all rigidly stipulated. No link can be neglected because of saving time or trouble.
Solvent system
When extracting mycotoxins from foods and feeds， the type of mycotoxins， the nature of the toxins， the solubility of the toxins in the extraction solvent and the like are all conditions for extracting solvent selection. In principle， a solvent system with low toxicity， high polarity and low cost is selected. The basis for evaluating the extraction effect of a solvent system is the recovery and extraction time. The excellent solvent system should have high recovery of toxins， less interference impurities and short extraction time. The extraction solvent generally selected is a mixed solution of an organic solvent and water， methanol water or acetonitrile water. For example， it has been studied that almost all deoxynivalenol （DON） can be extracted with acetonitrile water in foods and feeds， while for fumonisins， it was found that natural fumonisins can be extracted from maize and its products with methanol water. The extracting solvents most used in the national standards for extracting mycotoxins from plant foods， grains， vegetable oils， feeds and other substrates are methanol water and acetonitrile water. This shows that the two extraction solvents can quickly extract the targetss and obtain a high extraction rate at the same time， which is necessary for the accuracy of the data during the whole experiment. Therefore， the choice of the extracting solvent is generally methanol water or acetonitrile water. Purification process
At present， the purification of mycotoxins in foods and feeds on national standards mainly depends on immunoaffinity column， solid phase extraction column， purification powder， and QuEChERs purification. The most commonly used purification methods at present are immunoaffinity columns and QuEChERs purification. The immunoaffinity column is characterized by strong specificity. In use， the required toxins are immobilized on the column， the undesired components can be eluted by solvents， and some impurities can be discarded by the eluent. This purification method is strong in immunity and clean， but the price is relatively high. The QuEChERS purification technology is an emerging purification technology that not only acts on agricultural residues， but also on the extraction of mycotoxins. Its principle is mainly to use the interaction between the filler and the interfering substances in the matrix to achieve the purpose of rapid purification. The fillers are mainly PSA， ODS， C18 and the like.
The technology is simple， fast， effective， and stable， and is suitable for a variety of substrates， so it is currently the second most used purification method. The recovery of the immunoaffinity column is 69.6%-97.3%， while the QuEChERS purification is 75.5%-113.4%. Comparing from the data， QuEChERS purification is better. Therefore， in order to better monitor the data， it is recommended to select QuEChERS purification during the purification process.
Detection method
There are many methods for detecting mycotoxins， which are summarized by liquid chromatography， liquid chromatography mass spectrometry， and enzyme linked immunosorbent assay. The most common methods are liquid chromatography tandem mass spectrometry and liquid chromatography. The comparative analysis of the instruments used is shown in Table 3.
Conclusions
Mycotoxins can cause serious damage to humans and animals， so quality control of mycotoxins is extremely important during experiments. This study monitored the preparation of samples， the selection of solvents， and the selection of methods during planting， processing， storage and experiment processes. Mycotoxins have the characteristics of relatively complicated production mechanism， easy contamination during the detection process and difficult removal. Therefore， all aspects of the mycotoxin quality control process should be monitored as much as possible. In general， there is still a certain gap between us and the international level. Meanwhile， the limit of mycotoxins is not perfect. Therefore， there are many difficulties in the process of monitoring. We still need to continue to work hard and try to achieve complete monitoring.
References
[1] ZHENG Y， WANG XY， LI JJ. Determination of aflatoxins in food by liquid chromatography tandem mass spectrometry[J]. Food Sci， 2010， 31（24）： 385-388. （in Chinese）
[2] HUONG BTM， TUYEN LD， TUAN DH， et al. Dietary exposure to aflatoxin B1， ochratoxin A and fuminisins of adults in Lao Cai province， Viet Nam： A total dietary study approach [J]. Food Chem Toxicol， 2016， 98（PtB）： 127-133.
[3] LONG XD， YAO JG， ZENG Z， et al. Polymorphisms in the coding region of X ray repair complementing group 4 and aflatoxin B1 related hepatocellular carcinoma[J]. Hepatology， 2013， 58（1）： 171-181.