Distribution of deoxynivalenol in wheat,wheat flour,bran, and gluten,and variability associated with the test procedure

Analytical data obtained on deoxynivalenol (DON) concentration in naturally contaminated wheat during processing in an industrial mill were statistically analyzed, and the distribution functions of DON concentration in lots of wheat, bran, wheat flour, and gluten were estimated. The analytical method had acceptable precision (HORRAT 0.25-0.32) for each test sample. The total variance combined sampling, sample preparation, and analytical variances were 0.188, 0.033, 0.42, and 0.0014 ppm2 for wheat, 1.93; flour, 0.99; bran, 4.68; and gluten, 0.29, respectively. The distribution function of DON contamination presented an asymmetric tail for high values of concentration in wheat grains and wheat flour; in bran it seemed to be bimodal with 2 separated peaks of different concentrations; in gluten the normal distribution function gave a reasonably good fit to empirical data. The function eta(c) = -In(-Inp), where p (c) is the cumulative distribution function was linear with c in the so-called extreme-value type I distribution and could be fitted by a cubic polynomial in c in the distributions determined for all the products. This variability and distributional information contributes to the design of better sampling plans in order to reduce the total variability and to estimate errors in the evaluation of DON concentration in lots of wheat and wheat products.     

Phenolic compounds and the antioxidant activity of the bran,flour and whole grain of different wheat varieties

Total phenolic content and DPPH radical scavenging capability of the bran layer, flour made from endosperm and whole grain of wheat were determined. Fifteen different wheat samples of ten spring and five winter wheat varieties were analyzed. The spring wheat varieties were grown in both conventional and organic conditions. The total phenolic content of the bran layer found to be the highest (1258-3157 μg/g), followed by that of grains (168 - 459 μg/g) and the lowest of flour (44 - 140 μg/g). The bound phenolic acids were quantified by CE-DAD analysis after alkaline hydrolysis. Ferulic acid was a major compound among phenolic acids found in wheat varieties.     

高效液相色谱-二极管阵列检测法测定小麦粉及面粉改良剂中福美双

福美双是重要的二硫代氨基甲酸酯(DTC)杀菌剂,在小麦中使用限量以1 mg/kg二硫化碳(CS2)计.目前我国相关检测方法是针对二硫代氨基甲酸酯一类的化合物,二硫代氨基甲酸酯通过与酸反应生成CS2,采用光谱法或色谱法测定CS2,间接实现二硫代氨基甲酸酯测定.该方法无法特异性实现对福美双的检测,因此开展小麦粉中福美双检测...     

Multielement determination in wheat and bran

Instrumental neutron activation analysis was employed to measure 26 elements in three wheat varieties and in bran retained on U.S. standard sieve#e40. It was observed that the mineral content of bran was much higher than whole wheat and more than 90% of the elemental content was retained in the bran. The concentrations of As, Ce, Cr, Cs, Eu, Hf, Hg, La, Sb, Sc, Sr, Th and V in whole wheat and bran were below the detection limit.     

Experience with wheat and wheat flour CRMs

The Chemical Section of OHM [1–2] embarked on the preparation of a wheat sample series as CRMs in 1992. The certification process has been carried out according to the recommendations of ISO. Since then a series of wheat flour samples has been developed as well. The investigations of the long-term stability and the application of wheat and flour CRMs are presented. Received: 23 May 1997 / Revised 8 September 1997 / Accepted: 16 September 1997     

Determination of deoxynivalenol and nivalenol in corn and wheat by liquid chromatography with electrospray mass spectrometry

The fungus Fusarium graminearum is a pathogen of both wheat and corn. Strains of the fungus from the United States produce a toxin, deoxynivalenol (DON); strains of the fungus from Asia and Europe produce DON or a related toxin, nivalenol. These toxins can cause disease in livestock, and their potential presence in feed and foods is a concern for animal and human health. A method was developed to detect both toxins in corn and wheat by liquid chromatography/mass spectrometry of an extract of ground grain. The method requires no sample cleanup and can detect the toxins at 0.05 microg/g.     

偶合反应化学发光法测定过氧化苯甲酰

基于过氧化苯甲酰可以氧化K4Fe(CN)6生成K3Fe(CN)6,生成的K3Fe(CN)6在碱性溶液氧化鲁米诺可产生强的化学发光的特性,建立了测定过氧化苯甲酰的偶合反应化学发光新方法.该方法测定过氧化苯甲酰的线性范围为1.0×10-8～4.0×10-6 g/mL, 检出限为5×10-9 g/mL,相对标准偏差为3.0% (1.0×10-7 g/mL过氧化苯甲酰溶液,n=11).该方法已用于市售面粉中过氧化苯甲酰的测定.     

抑制褪色光度法测定油炸面制食品中痕量铝

建立抑制褪色光度法快速测定食品中痕量铝的方法。在硫酸介质中,一定量的铝离子对溴酸钾氧化罗丹明B褪色有抑制作用,据此建立了抑制褪色光度法快速测定食品中痕量铝的新体系,最大吸收波长为550 nm。在1 mol/L硫酸介质中,铝含量在0.07~0.4μg/mL范围内与吸光度具有良好的线性关系,相关系数r=0.9995,检出限为0.02μg/mL。用该方法测定油炸面制食品中痕量铝,测定结果的相对标准偏差为1.3%~3.1%(n=11),加标回收率为99.3%~103.5%。该方法测定结果准确可靠,可用于食品中痕量铝的测定。     

Determination of deoxynivalenol in processed foods

Deoxynivalenol (DON), commonly referred to as vomitoxin, belongs to a class of naturally occurring mycotoxins produced by Fusarium fungi. The presence of DON in foods is a human health concern. The frequency of occurrence of DON in wheat is high, although cleaning prior to milling can reduce DON concentration in final products, and food processing can partially degrade the toxin. This paper describes a method for the determination of DON in some major wheat food products, including bread, breakfast cereals, pasta, pretzels, and crackers. Test samples containing 5% polyethylene glycol were extracted with water. After blending and centrifuging, the supernatant was diluted with water and filtered through glass microfiber filter paper. The filtrate was then passed through an immunoaffinity column and the toxins eluted with methanol. The toxins were then subjected to RPLC separation and UV detection. The accuracy and repeatability characteristics of the method were determined. Recoveries of DON spiked at levels from 0.5 to 1.5 microg/g in the five processed foods were >70%. SD and RSD values ranged from 2.0 to 23.5% and from 2.0 to 23.2%, respectively. HorRat values were <2 for all of the matrixes examined. The method was found to be acceptable for the matrixes examined. LC/MS/MS with multiple-reaction monitoring was used to confirm the identity of DON in naturally contaminated test samples.     

面粉中增白剂过氧化苯甲酰的示差脉冲伏安法测定

研究了以二氯甲烷作为萃取剂,二氯甲烷-乙酸(1.5×10-2mol/L)为底液,四丁基高氯酸铵(0.01mol/L)为支持电解质,玻碳电极作为工作电极,采用示差脉冲伏安法测定过氧化苯甲酰。过氧化苯甲酰的阴极峰电位为-0.045V(vs.Ag/AgCl),峰电流与过氧化苯甲酰浓度在2.5×10-6～1.0×10-4mol/L范围内呈良好的线性关系,检出限为2.5×10-7mol/L。本法可直接用于小麦面粉中增白剂过氧化苯甲酰的测定。     

Determination of nivalenol and deoxynivalenol in wheat using liquid chromatography-mass spectrometry with negative ion atmospheric pressure chemical ionisation.

A new, rapid and sensitive method has been developed for the determination of nivalenol (NIV) and deoxynivalenol (DON) by using HPLC in combination with an atmospheric pressure chemical ionization (APCI)-interface and a single quadrupole mass spectrometer. Different LC and MS parameters have been optimized prior to this in order to obtain better results and sensitivity. The effect of nebulizing temperature on the sensitivity and fragmentation of NIV and DON in an APCI interface was investigated. Also, the influence of the cone voltage on the fragmentation pattern was studied, which was shown to have a tremendous effect. Furthermore, the effect of modifiers such as ammonium acetate, acetic acid and ammonia on the ionisation yield of the above substances have been investigated. The extraction was carried out using acetonitrile-water. A two step purification was then applied on two different Mycosep clean up columns. We have used a modified, rapid and isocratic HPLC method combined with a negative ion APCI-MS for the separation and quantitative determination of NIV and DON in wheat extract. An RP C18 column was used for the separation of selected compounds in wheat extract with water-acetonitrile-methanol (82:9:9, v/v/v) at a flow-rate of 1 ml/min without a split. Calibration curves show good linearity and reproducibility. The detection limit and precision were determined for NIV and DON. Both compounds could be detected down to microg/kg level in wheat using selected ion monitoring of the [M-H]- ions and the main fragments.     

Simultaneous and rapid determination of deoxynivalenol and its acetylate derivatives in wheat flour and rice by ultra high performance liquid chromatography with photo diode array detection

A simple and reliable method of ultra high performance liquid chromatography coupled with photo‐diode array detection has been proposed for the simultaneous determination of deoxynivalenol and its acetylated derivatives in wheat flour and rice, especially focusing on the optimization of sample extraction, cleanup, and chromatographic separation conditions. Sample pretreatment consisted of a first step using a quick, easy, cheap, effective, rugged, and safe based extraction procedure and a subsequent cleanup step based on solid‐phase extraction. The method was extensively validated in wheat flour and rice, obtaining satisfactory analytical performance with good linearity (R² ≥ 0.999), acceptable recoveries (80.0–104.4%), and repeatability (RSDs 1.3–10.7%). The limits of detection (21.7–57.4 μg/kg) and quantitation (72.3–191.4 μg/kg) for deoxynivalenols were lower than those usually permitted by various countries’ legislation in these food matrices. The method was applied to 34 wheat and rice samples. The results were further compared with results of ultra high performance liquid chromatography with electrospray ionization tandem mass spectrometry.     

Determination of niacin in infant formula and wheat flour by anion-exchange liquid chromatography with solid-phase extraction cleanup

Niacin content must be included on food labels of infant formula products and bakery products containing enriched flour. Liquid chromatographic (LC) determination of niacin in complex food matrixes is complicated by the presence of endogenous compounds that absorb at the commonly used wave-length of 260 nm. Also, the presence of particulate matter in the standard sulfuric acid extraction procedure results in reduced life of LC columns and precolumns. A simple, rapid, solid-phase extraction (SPE) procedure for separation and cleanup of niacin from a complex food matrix digest has been developed. By using a vacuum manifold with the SPE column system, multiple samples can be processed quickly and efficiently for LC analysis, compared with gravimetric column cleanup. Sulfuric acid sample digest is passed over an aromatic sulfonic acid cation-exchange (ArSCX-SPE) or a sulfonated Florisil SPE column. Niacin is eluted with 0.25M sodium acetate-acetic acid, pH 5.6 buffer in vacuo. LC chromatograms of the resulting eluate are free of interference from other components absorbing at 260 nm at the retention time of niacin. Validation of the method was obtained from agreement of analytical results on available reference materials. For both SPE methods, values for niacin in SRM 1846 Infant Formula (milk-based powder) were within uncertainty ranges of the certified value. Use of several calibration procedures (the LC computer program, a peak area response graphic standard curve, or the method of standard additions) with both SPE procedures resulted in niacin values for 3 RM-Wheat Flours (not certified for niacin) in agreement (90-105%) with their respective values reported in the literature. Several commercial wheat flours showed a broad 260 nm interference, resulting in high niacin values. Niacin recoveries from spiked soy-based liquid infant formulas ranged from 95-107% with the ArSCX-SPE column. Calibration curves of niacin were linear up to 400 micrograms/mL, with a detection limit of 0.2 microgram/mL.     

Determination of nickel, chromium and cobalt in wheat flour using slurry sampling electrothermal atomic absorption spectrometry

The slurry technique was applied to the determination of Ni, Cr and Co in wheat flour by electrothermal atomic absorption spectrometry (ETAAS). The influence of the graphite furnace temperature programme was optimized. Optimum sensitivity was obtained by using a mixture of 15% HNO₃–10% H₂O₂ as suspended medium for a 3% w/v slurry in the determination of Ni; lower concentrations of HNO₃ were necessary for the determination of Co and Cr (viz. 5 and 10%). The precision of direct analyses of the slurries was improved by using mechanical agitation between measurements; thus, the RSD of the measurements was ca. 5% for repeatability. The direct slurry sampling (SS) technique is suitable for the determination of Ni and Cr in wheat flour samples at levels of 150–450 and 30–72 ng g⁻¹, respectively, as it provides results similar to those obtained by ashing the sample. However, the typically low level of Co in these samples precluded its determination by the proposed method (the study was made in an SRM spiked wholemeal flour), at least in those samples that were contaminated with elevated concentrations of the metal (viz. more than 90 ng of Co per g of flour). The method provides a relative standard deviation of 6, 8, and 4% for Ni, Cr, and Co, respectively.     

Quantification of deoxynivalenol in wheat using an immunoaffinity column and liquid chromatography

A simple and accurate method to quantify the mycotoxin deoxynivalenol (DON) in wheat is described. The method uses immunoaffinity chromatography for DON isolation and liquid chromatography (LC) for toxin detection and quantification. Wheat samples are extracted in water, filtered twice and applied to an immunoaffinity column. Following a water wash, DON is eluted from the column with methanol and injected onto an LC system with a UV detector for quantification. Test performance was evaluated in terms of antibody specificity, limit of detection, percentage recovery, precision, column capacity, assay linearity and comparison with the GC-electron-capture detection (ECD) method of Tacke and Casper. Specificity of the immunoaffinity column cleanup procedure was confirmed with only DON (>80%) and its 15-C derivatives (40-50%) being recognized by the antibody while 3-C DON derivatives, nivalenol, T-2 and fusarenon-X did not bind. The limit of detection is at least 0.10 microg/g. Percentage recovery for the entire assay range averages 90% with an average relative standard deviation of 8.3%. Naturally contaminated samples showed comparable precision. Column capacity was determined to be 3.3 microg. The assay showed a high degree of linearity (r2=0.999) and an optimum assay range of 0.10 to 10.0 microg/g. Comparative analysis of 28 naturally or artificially contaminated wheat samples using DONtest-HPLC and the GC-ECD method of Tacke and Casper showed that DONtest-HPLC is a statistically significant predictor of the GC-ECD method (r2=0.982).     

Experience with wheat flour reference material

The Chemical Section of the National Office of Measures, Hungary (OMH) [1] embarked on the preparation of a wheat sample series as a Certified Reference Material [2] (CRM) in 1992. The practical implementation of the wheat sample series has shown that test- ing laboratories are in great need of easy-to-use flour reference samples to objectively and independently qualify wheat. To fill this need, we have developed a three-term flour reference sample series. The certification process was car-ried out according to ISO recommendations. Investigations of the long-term stability [3] and the application of wheat and flour CRMs are continuing. Wheat is one of the most widely grown crops in Hun- gary and it is one of the major determinative factors in the economy. Its uniform and objective qualification is of outstanding importance. There are well-equipped laborato-ries with sufficient experience to assess wheat flour quality, howev- er, proficiency testing has shown that certified samples need to be used to achieve exact and uniform measuring results. Received: 12 November 1999 Accepted: 16 August 2000     

Rapid detection of nivalenol and deoxynivalenol in wheat using surface plasmon resonance immunoassay

A surface plasmon resonance (SPR) immunoassay using a monoclonal antibody was developed to measure nivalenol (NIV) and deoxynivalenol (DON) contamination in wheat. A highly sensitive and stable DON-immobilized sensor chip was prepared, and an SPR detection procedure was developed. The competitive inhibition assay used a monoclonal antibody that cross-reacts with NIV and DON. The half maximal inhibitory concentration (IC₅₀) values of the SPR assay were 28.8 and 14.9 ng mL⁻¹ for NIV and DON, respectively. The combined responses of NIV and DON in wheat were obtained using a simultaneous detection assay in a one-step cleanup procedure. NIV and DON were separated using a commercial DON-specific immunoaffinity column (IAC) and their responses were obtained using an independent detection assay. Spiked tests using these toxins revealed that recoveries were in the range 91.5-107% with good relative standard deviations (RSDs) (0.40-4.1%) and that detection limits were 0.1 and 0.05 mg kg⁻¹ for NIV and DON, respectively. The independent detection using IAC showed detection limits of 0.2 and 0.1 mg kg⁻¹ for NIV and DON, respectively. SPR analysis results were correlated with those obtained using a conventional LC/MS/MS method for wheat co-contaminated with NIV and DON. These results suggested that the developed SPR assay is a practical method to rapidly screen the NIV and DON co-contamination of wheat and one of a very few immunoassays to detect NIV directly.     

Shear stress relaxation of wheat flour dough and gluten

Measurements of shear stress relaxation of wheat flour dough and its corresponding gluten in cone-plate geometry are reported. The range of shear strains used is 0.1–1.0. It is found that the relaxation function is separable into a function of strain and a function of time for shear strains up to 0.4 for dough and 1.0 for gluten. The strain function is non-linear for both dough and gluten. Typically the observed half relaxation time is 1.5 seconds for both dough and gluten. The data suggest the existence of two separate flow processes. The observed time-dependence of the relaxation function has been analysed in terms of a theory of flow as a cooperative phenomenon. In this analysis the process which occurs at short times (0.1–10 s), is characterized by a four-fold coordination of flow units. This process is similar in dough and gluten. The second process, occurring at longer times (10–10⁴ s), is different for dough and gluten and the coordination numbers found are two and one, respectively. This second flow process has to our knowledge not been reported previously.     

Determination of arsenic in wheat flour by electrothermal atomic absorption spectrometry using a continuous precipitation-dissolution flow system

A precise, accurate automatic preconcentration method for the determination of total arsenic at the ng g(-1) level in wheat flour is proposed. The sensitivity of the method can be increased by a factor of 20 by precipitating As(V) from 10 ml of digested sample using a weakly acid silver solution. The Ag(3)AsO(4) precipitate is dissolved with 0.5 ml of 6 M ammonia and the resulting solution is collected in an autosampler cup of the ETAAS instrument. The limit of detection achieved in the determination of total arsenic using Pd(NO(3))(2) as modifier is 0.3 ng ml(-1). The proposed method avoids spectral interferences from cations as they do not precipitate with silver cation; anions, which are coprecipitated with silver, are tolerated at concentrations up to about 10 000 times that of As(V). The need to determine As at very low levels in wheat samples, where chloride and phosphate can occur at concentrations 50 000 and 300 000 times higher, respectively, that of arsenic, requires additional steps to suppress the interference of both anions.     

ESR detection of wheat flour before and after irradiation

We revealed free radicals in wheat flour before and after gamma-ray irradiation and their thermal behavior during heat-treatment using electron spin resonance (ESR) spectroscopy. The ESR spectrum of wheat flour before irradiation consists of a sextet centered at g = 2.0 and a singlet signal at the same g-value position. The first one is attributable to a signal with hyperfine (hf) interactions of Mn2+ ion (hf constant: 7.4 mT). The second is originated from carbon-centered radical. Upon gamma-ray irradiation, however, a new signal with two triplet lines at the low and high field ends was detected in wheat flour on top of the Mn2+ sextet lines. We analyzed the triplet ESR lines as powder spectra (rhombic g-tensor symmetry) with nitrogen (14N) hyperfine interactions. This indicates that a new organic radical was induced in the conjugated protein portion of wheat flour by the gamma-ray irradiation. Intensity of the organic free radical at g = 2.0 detected in irradiated wheat flour increased monotonically by the thermal treatment. The analysis of the time-dependent evolution and decay process based on the theory of transient phenomena as well as the nonlinear least-squares numerical method provided a unique time constant for the radical evolution and decay in wheat flour during the heat-treatment.