Occurrence of certain mycotoxins in corn and corn‐based products and thermostability of fumonisin B1 during processing

A total of 57 samples of corn and corn‐based products collected from various districts of Egypt were analyzed for Fusarium mycotoxins (T‐2, diacetoxyscripenol (DAS( deoxynivalenol (DON) and fumonisin B₁ (FB₁) and aflatoxins. FB₁ was detected in about 80%, 53.85%, 33.3%, and 28.57% of yellow corn, corn meal, white corn, and popcorn samples, respectively. The levels of FB₁ ranged from 10 to 780 μg/kg. T‐2 and DAS were detected in 5% and 10% of yellow corn samples, respectively, and DON was detected in white corn and popcorn samples at levels of 28.8 and 10.1 μg/kg, respectively. Starch samples were found to be free from Fusarium mycotoxins. Baking balady bread at 450°C/min reduced FB₁ to 72.4% while baking Franco bread at 250°C/20 min reduced FB₁ to 57.4%. Boiling of macaroni and corn in water completely removed FB₁ from contaminated samples. On the other side, corn flakes samples were found to be contaminated with aflatoxins B₁ and G₁ at levels ranging from 6 to 10 ppm, whereas 2.9% of samples were contaminated with aflatoxin B₁ > 35 ppm and G1 > 16 ppm.     

Mycotoxins in fuel ethanol co‐products derived from maize: a mass balance for deoxynivalenol

BACKGROUND: Three matrices—corn (maize) meal, distiller's dried grains with solubles (DDGS) and condensed distiller's solubles (CDS)—were sampled in sequence from a continuous dry‐milling process plant for the determination of mass balance of deoxynivalenol (DON). Four commercially available enzyme‐linked immunosorbent assay (ELISA) kits were evaluated for their ability to measure the presence of DON. Liquid chromatography/tandem mass spectrometry (LC/MS/MS) was used as standard method to detect DON and other Fusarium toxins. RESULTS: The concentrations of DON in DDGS and especially CDS were overestimated or underestimated by ELISA. However, for both matrices, all ELISA methods were not significantly different in their mean results from the LC/MS/MS standard, although the variability in results was much higher. DON concentrations in the CDS and the final DDGS co‐product were significantly higher (P ≤ 0.01) than in the starting material (corn grain). Toxin concentration increased by a factor of 3 on a dry weight basis in DDGS compared with the starting corn and by a factor of 4 in CDS. Mean concentration of DON in CDS was four times higher (7.11 mg kg^?1) than in corn grains (1.80 mg kg^?1) and 1.4 times higher than in DDGS (5.24 mg kg^?1). Mass balance calculations showed that CDS was the main source of contamination of DON, comprising ca 70% of the toxin found in the final product (DDGS). Most DON (87%) was accounted for by this analysis. CONCLUSION: Concentrations in the grain corn entering ethanol plants should be close to the dietary values recommended for swine in Canada and the USA for DON (1 mg kg^?1). Small amounts of acetyldeoxynivalenol and DON glucoside were also found in the three matrices along with a small amount of zearalenone. Unlike the situation for DON, the DON glucoside was not concentrated into DDGS and CDS, indicating that it was hydrolysed during the fermentation process. Copyright © 2009 Society of Chemical Industry     

毛细管气相色谱法测定小麦和玉米中脱氧雪腐镰刀菌烯醇

本文采用毛细管气相色谱法测定了小麦和玉米中脱氧雪腐镰刀菌烯醇(deoxynivalenol,DON)的含量,小麦、玉米样品分别用乙腈-水(84:16,V/V)提取,小麦样品提取液用硅镁型吸附剂净化,玉米样品提取液用硅镁型吸附剂和活性炭二步净化,采用N-七氟丁酰咪唑(HFBI)为衍生剂,带电子捕获检测器的GC进行检测。DON加标量为0．5～1．5mg/kg时,5次重复实验的平均回收率:小麦样品为82．2%～98．5%,玉米样品为86．0%～103．4%,相对标准偏差(RSD)分别为6．2%～7．6%和6．4%～8．0%,该法DON的最低检出限为0．01mg/kg,线性范围为0．075～15mg/k8。用该法对21个小麦样品与20个玉米样品中DON的含量进行检测,其中小麦样品中DON含量为0．153～4．618mg/kg,污染率为47．6%,超标率为9．5%;而玉米样品中DON含量为0．116～3．004mg/kg,污染率为85%,超标率为20%。     

Occurrence of certain mycotoxins in corn and corn-based products and thermostability of fumonisin B1 during processing

A total of 57 samples of corn and corn-based products collected from various districts of Egypt were analyzed for Fusarium mycotoxins (T-2, diacetoxyscripenol (DAS), deoxynivalenol (DON) and fumonisin B1 (FB1) and aflatoxins. FB1 was detected in about 80%, 53.85%, 33.3%, and 28.57% of yellow corn, corn meal, white corn, and popcorn samples, respectively. The levels of FB1 ranged from 10 to 780 microg/kg. T-2 and DAS were detected in 5% and 10% of yellow corn samples, respectively, and DON was detected in white corn and popcorn samples at levels of 28.8 and 10.1 microg/kg, respectively. Starch samples were found to be free from Fusarium mycotoxins. Baking balady bread at 450 degrees C/min reduced FB1 to 72.4% while baking Franco bread at 250 degrees C/20 min reduced FB1 to 57.4%. Boiling of macaroni and corn in water completely removed FB1 from contaminated samples. On the other side, corn flakes samples were found to be contaminated with aflatoxins B1 and G1 at levels ranging from 6 to 10 ppm, whereas 2.9% of samples were contaminated with aflatoxin B1 > 35 ppm and G1 > 16 ppm.     

Occurrence of bound deoxynivalenol in Fusarium head blight-infected barley (Hordeum vulgare L.) and malt as determined by solvolysis with trifluoroacetic acid

Fusarium head blight occurs worldwide in barley production, and the Fusarium mycotoxins, particularly deoxynivalenol (DON), have become a major concern for barley products, such as beer. This study investigated the content of bound DON in barley samples that were naturally infected with Fusarium head blight. Free DON was determined by gas chromatography-electron capture detection after standard acetonitrile:water extraction, while total DON was determined using treatment with trifluoroacetic acid. Bound DON is the difference between the total and free values. Bound DON was detected in approximately 40% of the samples analyzed, and represented 6 to 21% of free DON. A preliminary study indicated that both free and bound DON decrease significantly during the steeping phase of malting. These results suggest that bound DON, like the free form, may be water-soluble.     

Further survey on the Fusarium mycotoxins in Korean cereals

Fifty-one samples of cereals from the 1984 harvest from Korea were analyzed for nivalenol (NIV), fusarenon-X (FX), deoxynivalenol (DON) and 3-acetyl-DON by gas chromatography (GC) utilizing a 63Ni electron capture detector (ECD), and were quantitated for zearalenone (ZEN) by high-performance liquid chromatography (HPLC) with a fluorescence detector (FD). Trichothecenes and ZEN in the positive samples were confirmed by GC-mass spectrometry (MS). Out of 51 samples, 51, 46 and 42 were positive for NIV, DON and ZEN, respectively, and one malt sample was heavily contaminated with NIV (2675 ng/g) and DON (246 ng/g), and one wheat sample was heavily contaminated with NIV (3169 ng/g). Neither FX nor 3-acetyl-DON was detected in any of the samples. The data reported here indicates that Korean cereals harvested in 1984 are simultaneously contaminated with NIV, DON and ZEN, and the incidences and levels are similar to those observed in the cereals harvested in 1983.     

2020年我国粮食及其产品中脱氧雪腐镰刀菌烯醇毒素污染情况与分布特征

摘要：目的 本研究旨在了解脱氧雪腐镰刀菌烯醇(Deoxynivalenol, DON)毒素在各种粮食和在全国各地区的污染情况及分布规律。方法 将粮食样品充分研磨,采用ELISA酶联免疫吸附测定法进行检测,在包被了DON毒素的微孔中加入标本,标准品和抗体。温育并洗涤之后,用酶标仪测定吸光度,计算样品浓度。 结果 在不同种类的粮食中,玉米中DON毒素含量与大米、绿豆、红豆相比差异有意义(p＜0.05)。玉米不同加工产品中的毒素含量玉米面与玉米渣,玉米与玉米渣之间有显著性差异(p＜0.01)。玉米DON毒素含量西北与北方,西北与南方比较差别有意义(p＜0.05);面粉DON含量北方与南方比较差别有意义(p＜0.05);大米中DON含量西北与南方,北方与南方比较差别有显著性意义(p＜0.01)。 结论 不同粮食毒素的含量不同,玉米中的毒素含量较高。玉米不同加工方式生产的产品毒素的含量有所不同。粮食中DON毒素含量的分布情况与环境气候有较大关系。     

Differentiation of raw spirits of rye, corn and potato using chromatographic profiles of volatile compounds

BACKGROUND: The origin of the raw spirits influences the sensory quality of rectified spirits that are subsequently used for the production of vodka. The aim of this research was to evaluate the effectiveness of two methods based on the comparison of profiles of volatile compounds [solid phase microextraction–gas chromatography–mass spectrometry (SPME‐GC‐MS) and gas chromatography with flame ionisation detection (GC‐FID)] for the determination of origin of raw spirits obtained from rye, corn (maize) and potato. RESULTS: Profiles obtained for the volatile compounds by using these methods were different and were influenced by the sample introduction method. The main groups of volatiles obtained using SPME‐GC‐MS method were fatty acid ethyl esters, while in the case of GC‐FID fusel alcohols and ethyl acetate dominated. Data obtained from these methods were treated using principal component analysis and linear discriminant analysis to test the possibility of sample differentiation and classification. It was relatively easy to differentiate potato spirits from the remainder; however, it was not possible to fully distinguish the corn samples from rye samples. The classification ability of the SPME‐GC‐MS method was 95% but the prediction ability was 97.4%. For the GC‐FID method the classification ability was 90.1%, whereas the prediction ability was 94.27%. CONCLUSIONS: The methods presented can be used for reliable differentiation of potato spirits from corn and rye spirits. Copyright © 2012 Society of Chemical Industry     

Survey of the presence of the Fusarium mycotoxins nivalenol, deoxynivalenol and T-2 toxin in Korean cereals of the 1989 harvest.

Twenty eight samples of rice, barley, millet, corn and Indian millet harvested in Korea in 1989 were subjected to assay for contamination of nivalenol (NIV), deoxynivalenol (DON) and T-2 toxin by using gas chromatography and gas chromatography-mass spectrometry. Seven samples were found to be positive for NIV and DON in the ranges of 189-624 micrograms/kg and 168-506 micrograms/kg, respectively. Of the contaminated samples, three samples, one barley, one Indian millet and one corn sample were contaminated simultaneously with both NIV and DON. T-2 toxin was not detected in any samples.     

Guaiacol and 4‐methylguaiacol accumulate in wines made from smoke‐affected fruit because of hydrolysis of their conjugates

Background and Aims: Taint in smoke‐exposed grapes have been associated with elevated levels of guaiacol and 4‐methylguaiacol. Previous research has reported guaiacol and 4‐methylguaiacol in both fruits and wines. In some cases, these compounds were not detected, or were detected at low levels in the fruit while high levels were subsequently identified during or after winemaking. Later research indicated that this was due to the presence of glycosidic conjugates. Here we report a method for the routine analysis of guaiacol and 4‐methylguaiacol released after acid hydrolysis of glycoside precursors. Methods and Results: Chardonnay, Merlot, Shiraz, Sangiovese and Cabernet Sauvignon fruits were collected following bushfire events in 2006–2007 in the King Valley wine region of NE Victoria, Australia. Gas chromatography‐mass spectrometry (GC‐MS) was used to detect free guaiacol and 4‐methylguaiacol in both fruits and wines. Low levels of free and bound forms were present in fruit not exposed to smoke. Substantial levels of free guaiacol and 4‐methylguaiacol were detected in the wines made from the smoke‐affected fruits. These compounds increased during bottle storage. Acid hydrolysis of wines and berries resulted in a several‐fold increase in free guaiacol and 4‐methylguaiacol. Conclusions: The validated GC‐MS method is suitable for monitoring free and glycosidically bound guaiacol and 4‐methylguaiacol after acid hydrolysis in both fruits and wines. Acid hydrolysis of wines provided evidence that bound volatiles, most probably glycosidically, act as reserve for guaiacol and 4‐methylguaiacol, which are released during ageing of wines. Significance of the Study: This is the first study published in a refereed journal to demonstrate that smoke taint‐associated volatiles increase during ageing of wine and bound forms of guaiacol and 4‐methylguaiacol represent an aroma reserve for smoke taint in ageing/bottled wines.     

Antioxidants from barley husks impregnated in films of low-density polyethylene and their effect over lipid deterioration of frozen cod (Gadus morhua)

BACKGROUND: The changes in quality of cod fillets packaged in films with and without antioxidants during 12 months of frozen storage at ? 20 °C were investigated in the present study. The following parameters were determined in order to study lipid hydrolysis and primary and secondary lipid oxidation in the samples during frozen storage: peroxide value, conjugated dienes, conjugated triene hydroperoxides, free fatty acids, totox value, thiobarbituric acid‐reactive substances and p‐anisidine value. RESULTS: Films containing antioxidants isolated from barley husks were effective in slowing down lipid hydrolysis and primary and secondary lipid oxidation processes. Secondary lipid oxidation reached maximum values in the 12th month of storage in control samples and samples packaged with antioxidant‐containing film. Maximum lipid hydrolysis and lipid oxidation values for control cod samples were significantly higher than the maximum values found in samples packaged with antioxidant‐containing film. CONCLUSION: The results confirm the efficacy of natural antioxidants derived from barley husks in slowing down lipid hydrolysis and increasing the oxidative stability of cod flesh. They also demonstrate the potential usefulness of natural antioxidants extracted from barley husks in the development of active packaging films for food preservation. Copyright © 2011 Society of Chemical Industry     

Development and Application of a Method for the Analysis of 9 Mycotoxins in Maize by HPLC‐MS/MS

A reliable and sensitive liquid chromatography/tandem mass spectrometry (LC‐MS/MS) method was developed for the simultaneous determination of aflatoxins (AFB₁, AFB₂, AFG₁, and AFG₂), ochratoxin A (OTA), deoxynivalenol (DON), zearalenone (ZEA), fumonisin B₁ (FB₁), and T2‐toxin in maize. The samples were first extracted using acetonitrile: water: acetic acid (79 : 20 : 1), and then further cleaned‐up using OASIS HLB cartridge. Optimum conditions for the extraction and chromatographic separation were investigated. The mean recoveries of mycotoxins in spiked maize ranged from 68.3% to 94.3%. Limits of detection and quantification ranged from 0.01 to 0.64 μg/kg and from 0.03 to 2.12 μg/kg, respectively. The LC‐MS/MS method has also been successfully applied to 60 maize samples, which were collected from Shaanxi Province of China. Twenty‐four of the total 60 samples (40%) were contaminated with at least 1 of these 9 mycotoxins. Occurrence of mycotoxins were 6.7%, 1.7%, 3.3%, 6.7%, 1.7%, 23.3%, and 3.3% for AFB₁, AFB₂, OTA, ZEA, DON, FB₁, and T2‐toxin, respectively. The results demonstrated that the procedure was suitable for the simultaneous determination of these mycotoxins in maize matrix.     

Isolation and Characterization of Virgin Olive Oil Phenolic Compounds by HPLC/UV and GC-MS

ABSTRACT This research examined the phenolic fraction of extra virgin olive oil samples from Lianolia variety olives grown in the region of Preveza, Greece. Phenolic compounds were extracted from oil samples, separated by reversed‐phase high‐performance liquid chromatography (HPLC), and characterized by gas chromatography‐mass spectrometry (GC‐MS). Both simple and complex phenols were detected with the latter being the most abundant. 3–4‐Dihydroxyphenyl ethanol (hydroxytyrosol) and p‐hydroxyphenylethanol (tyrosol) predominated among the simple phenols. Complex phenolic compounds were further separated by preparative HPLC and analyzed by GC‐MS before and after hydrolysis. The presence of hydroxytyrosol and tyrosol derivatives was confirmed. Both derivatives were always present in greater quantities and made up an average exceeding 70% in all samples analyzed.     

Co-occurrence of Fusarium mycotoxins in mouldy and healthy corn from Korea

A total of 71 samples consisting of 36 mouldy and 35 visibly healthy corn were collected from Kangwon province of Korea and analysed for 8-ketotrichothecenes, zearalenone (ZEA), and fumonisins, including fumonisin B1 (FB1), fumonisin B2 (FB2), and fumonisin B3 (FB3). Five 8-ketotrichothecenes, namely deoxynivalenol (DON), 15-acetyldeoxynivalenol (15-ADON), 3-acetyldeoxynivalenol (3-ADON), nivalenol (NIV), and 4-acetylnivalenol (4-ANIV), ZEA, FB1, FB2, and FB3 were detected in corn samples. DON, 15-ADON, 3-ADON, NIV, 4-ANIV, ZEA, FB1, FB2, and FB3 were detected in mouldy corn with mean values of 4.0, 0.9, 0.2, 1.7, 0.4, 0.6, 23.2, 7.5, and 6.3mug/g, respectively. Visibly healthy corn samples were contaminated with lower levels of 8-ketotrichothecenes, ZEA, and fumonisins than mouldy corn samples. However, 5 of 35 healthy corn samples analysed were contaminated with fumonisins at high levels up to 12.5mug/g for FB1, 5.4mug/g for FB2, and 0.5mug/g for FB3. This is the first report on the simultaneous occurrence of trichothecenes, ZEA, and fumonisins in corn from Korea.     

Effect of steam treatment on soluble phenolic content and antioxidant activity of the Chaga mushroom (Inonotus obliquus)

The effect of steam treatment on free phenolic acids in Chaga mushrooms (Inonotus obliquus) was investigated. Untreated and steam-treated (120 °C, 3 h) samples of I. obliquus were extracted with organic solvents and free phenolic acid-containing fractions were isolated. Free phenolic acids were determined by LC/PDA (liquid chromatography/photodiode array), ESI LC/MS (electrospray ionisation liquid chromatography/mass spectrometry), and GC/MS (gas chromatography/mass spectrometry). After the steam treatment, the soluble phenolic content determined by modified Folin–Ciocalteu method was increased and antioxidant activity was enhanced, as confirmed by a DPPH (1,1-diphenyl-2-picrylhydrazyl) radical scavenging activity assay. The amounts of vanillic acid, protocatechuic acid, syringic acid, and 2,5-dihydroxyterephthalic acid were increased significantly as the result of the steam treatment, suggesting that the liberation of low molecular weight free phenolics was enhanced by the steaming process. Consequently, the radical scavenging activity was also significantly enhanced by free phenolics produced using this method.     

Evaluation of three commercial ELISA kits for rapid screening of deoxynivalenol in unpolished wheat

Evaluation of commercial ELISA kits for the screening of deoxynivalenol (DON) was carried out. Three kinds of commercial kits supplied by different companies were used. Three lots of naturally contaminated wheat and DON-free wheat (<0.05 microg/g) were used as samples. The values obtained from ELISA were compared with those of the HPLC-UV method. In the results obtained from 14 institutions using ELISA, the CV values were less than 17.6% for all the commercial kits. The DON-free sample was not detected as positive with any commercial kits. Also there was no negative finding among the naturally contaminated samples used in this experiment. Coefficients of determination in ELISA and HPLC analysis were 0.979-0.999. These results indicate that ELISA using any of the three commercial kits is efficient for the screening of DON in wheat.     

Hepatic steatosis by dietary-conjugated linoleic acid is accompanied by accumulation of diacylglycerol and increased membrane-associated protein kinase C ε in mice

Scope : Conjugated linoleic acid reduces weight gain and adipose mass while inducing liver enlargement, hepatic steatosis, and insulin resistance in mice. The objective of this study was to determine if hepatic steatosis induced by conjugated linoleic acid would predict for hepatic diacylglycerol accumulation, increased membrane‐associated protein kinase C ε, and hyperglycemia. Methods and results : Six‐wk‐old C57Bl/6 male mice were fed a high‐saturated fat diet for 3 wk and were then randomized to high‐saturated fat diet with or without conjugated linoleic acid (1.5% wt). Following a 6‐wk intervention, hepatic triacylglycerol, diacylglycerol, membrane‐associated protein kinase C ε, and gluconeogenic gene expression were determined. Fasting glucose was determined at baseline and at the end of the study. Conjugated linoleic acid increased hepatic triacylglycerol and diacylglycerol concentration in association with increased membrane‐associated protein kinase C ε. Diacylglycerol concentration proved to be a better predictor than triacylglycerol concentration for the change from baseline in fasting glucose concentration and final insulin concentration. The increase in diacylglycerol concentration was also associated with increased hepatic gluconeogenic gene expression in conjugated linoleic acid‐treated animals. Conclusion : Our data suggest that conjugated linoleic acid can initiate the pathophysiology responsible for hepatic insulin resistance. Additional studies are needed to determine if the accumulation of hepatic diacylglycerol by conjugated linoleic acid leads to hepatic insulin resistance.     

Effectiveness of density segregation and sodium carbonate treatment on the detoxification of Fusarium-contaminated corn fed to growing pigs

The effectiveness of using rinsing, density segregation or 0.1 M sodium carbonate treatments of Fusarium-contaminated corn containing deoxynivalenol (DON) and zearalenone were tested both chemically and by feeding the material to growing pigs. Uninfected and Fusarium graminearum-inoculated corn (containing 40.3 mg DON and 0.94 mg zearalenone kg^?1cor) were subjected to various treatments: no treatment (control), rinsed, rinsed and all floating material removed, soaked in 0.1 M sodium carbonate for 24 h or soaked in 0.1 M sodium carbonate for 24 h after removal of the floating material. All corn samples were analysed for DON and zearalenone. Rinsing the contaminated corn reduced the concentrations of both mycotoxins by 44% while soaking in 0.1 M sodium carbonate reduced the toxin concentrations an additional 35%. In both cases, removal of the floating material decreased concentrations another 8 and 4%, respectively. In the feeding study, 10-week-old barrows were fed diets containing 17.5% of the treated corn samples over a 21 day period. Daily feed consumption and weight gains were significantly improved in pigs fed the rinsed-minus-floating corn and the sodium carbonate-soaked corn with and without floating material compared to the untreated contaminated corn. The chemical and biological data demonstrated that rinsing combined with the removal of floating material or soaking in 0.1 M sodium carbonate with or without removal of floating material were effective in reducing the toxicity of the contaminated corn. Due to a higher energy requirement needed to dry the corn soaked in sodium carbonate, the combination of rinsing and removal of the floating material is recommended as a more general and practical method of detoxification of contaminated grain.     

Interlaboratory study of LC-UV and LC-MS methods for the simultaneous determination of deoxynivalenol and nivalenol in wheat

To evaluate LC methods with UV or MS detection for simultaneous analysis of deoxynivalenol (DON) and nivalenol (NIV) in wheat, an interlaboratory study was conducted in 11 laboratories. DON and NIV were purified using a multifunctional column, and their concentrations were determined using LC-UV or LC-MS(/MS). No internal standards were used. Three fortified wheat samples (0.1, 0.5 and 1 mg/kg), one naturally contaminated wheat sample, and one blank wheat sample were used. The recoveries ranged from 90% to 110% for DON and from 76% to 83% for NIV. For DON, the relative standard deviations for repeatability (RSDr) ranged from 1.1% to 7.6%. The relative standard deviations for reproducibility (RSDr) ranged from 7.2% to 25.2%. For NIV, the RSDr ranged from 2.0% to 10.7%, and the RSDr ranged from 7.0% to 31.4%. Regardless of sample and detector, the HorRat values for DON and NIV ranged from 0.4 to 1.4. Both LC-UV and LC-MS(/MS) methods were considered to be suitable for application as an official method.     

Occurrence and distribution of Fusarium graminearum and deoxynivalenol in sweet corn ears

Unusual wet and cool weather conditions during the 1994 growing season in Maryland and Delaware resulted in a severe outbreak of Fusarium graminearum on sweet corn ears ('Moore' variety) prior to harvesting and canning. The number of ears visibly infected with Fusarium spp. ranged from less than 5% to 25% in some fields. Infection typically occurred at the tassel end of the ears. Fusarium graminearum was isolated from surface disinfected kernels, both those which were visibly infected and those kernels which appeared disease-free in an area up to 5cm from the edge of the visibly moulded areas. Infected ears were cut into four sections and the kernels only were analysed for deoxynivalenol (DON) using liquid chromatography (LC)and mass spectrometry/gas chromatography (GC/MS). Kernels from the visibly mouldy area of the ears contained DON at levels of approximately 446mg/g DON on average; whereas in the nonvisibly infected portion of the ears adjacent to the mouldy tips, DON levels averaged approximately 10mg/g. Sections of ears closest to the base contained no detectable DON or less than 1 μg/g. This is the first reported natural occurrence of the mycotoxin DON in sweet corn prior to harvest and canning.