Semicarbazide: occurrence in food products and state-of-the-art in analytical methods used for its determination

A portable smartphone platform utilizing dual-sensing signals for visual determination of semicarbazide in food samples

Semicarbazide (SEM) is a metabolite of antibiotic nitrofurazone and a food contaminant in food production, showing potential carcinogenic, mutagenic, teratogenic, and toxic effects on human health. It is urgent to develop a highly efficient and sensitive assay for visual detection of SEM. In this paper, a pyrrolopyrrole cyanine fluorescent probe (PPCy-1) was reported for visualization and quantitative analysis of SEM through a chromophore reaction sensing mechanism for the first time. The probe towards SEM exhibited a fast response (10 min), a low detection limit (0.18 μM), high selectivity, and distinct dual ratiometric fluorescence turn-on and colorimetric modes. Its practicability was further verified by detecting SEM in meat, water, and honey samples with satisfactory recovery values. More importantly, a smartphone-assisted portable testing platform was constructed based on a PPCy-1-immobilized test paper or a polyamide thin film with a color scanning APP for real-time and on-site detection of SEM. This work provides low-cost, convenient, and rapid assays for visual SEM detection, which have potential applications in food safety monitoring.

Seventy-Day Toxicity Study in Juvenile Sprague-Dawley Rats with Semicarbazide (SEM) from Weaning to Sexual Maturity

The study was conducted to evaluate the toxicological effects, functional observation battery tests, and sexual maturity of semicarbazide oral gavage administration to juvenile Sprague-Dawley rats for 70 days at 0, 15, 30, and 60 mg/kg/day weaning to sexual maturity. At 60 mg/kg/day, there was a delay in mean age at acquisition of balano-preputial and vaginal patency and a decrease in body weight and food consumption in males. Treatment increased reticulocyte count, aspartate aminotransferase, and alanine aminotransferase levels in both sexes and decreased hematocrit and protein in males. Increased absolute and relative liver and spleen weight in both sexes were observed. Male rats had lower thymus and testes weights, whereas female rats had lower uterine weights. Semicarbazide caused significant changes in sperm motility, sperm count, and sperm abnormality. Histopathologically, semicarbazide caused cortical hypertrophy in adrenals and increased extramedullary hematopoiesis in the spleen; hepatocellular hypertrophy, follicular epithelial hypertrophy in the thyroid, and degeneration of seminiferous tubules in the testis were observed at 60 mg/kg/day when compared to control. Results suggest that 60 mg/kg/day of semicarbazide can exert systemic toxicity in juvenile rats. The no observed adverse effect level (NOAEL) of semicarbazide for juvenile Sprague-Dawley rats was estimated to be 30 mg/kg/day.

A colorimetric sensing platform for azodicarbonamide detection in flour based on MnO2 nanosheets oxidative system

Azodicarbonamide (ADA), as a dough conditioner food additive in flour, can be turned into toxic biurea and semicarbazide after high temperature processing. Hence, the using of ADA in food material should be strictly controlled, and the detection of ADA is very important for consumers' safety and health. Herein, a simple and fast colorimetric strategy has been developed for ADA detection based on the MnO₂ nanosheets-3,3',5,5'-tetramethylbenzidine (TMB)-glutathione (GSH) as oxidative sensing system (MnO₂-TMB-GSH). Since the ADA can selectively react with GSH via oxidizing the sulfydryl (-SH) group of GSH to disulfide bond (S-S), which makes GSH unable to reduce MnO₂ nanosheets and restore its oxidase-like activity. The absorbance changes of the TMB solution depended on ADA content. The MnO₂-TMB-GSH colorimetric platform can detect the ADA with a linear range of 10 μmol L^-1 (11.6 ppm) to 400 μmol L^-1 (464 ppm), and the limit of detection (LOD) is 3.3 μmol L^-1 (3.51 ppm). Some potential interferences in real sample were tested and did not affect the MnO₂-TMB-GSH colorimetric platform for ADA detection. Furthermore, the sensing platform was applied for detecting ADA in real flour sample with a recovery of 96%-105% (RSD < 5%). This colorimetric method can effectively and rapidly detect ADA additives in flour less than the prescribed standard (45 mg kg^-1), which shows a great potential for visualization analysis and on-site detection of ADA in flour. A simple and fast colorimetric strategy has been developed for azodicarbonamide (ADA) detection based on the MnO₂ nanosheets-3,3',5,5'-tetramethylbenzidine (TMB)-glutathione (GSH) as oxidative sensing system (MnO₂-TMB-GSH).

Stabilization of Azapeptides by Namide···H-Namide Hydrogen Bonds

An unusual N_amide···H-N_amide hydrogen bond (HB) was previously proposed to stabilize the azapeptide β-turns. Herein we provide experimental evidence for the N_amide···H-N_amide HB and show that this HB endows a stabilization of 1-3 kcal·mol^-1 and enforces the trans-cis-trans (t-c-t) and cis-cis-trans (c-c-t) amide bond conformations in azapeptides and N-methyl-azapeptides, respectively. Our results indicate that these N_amide···H-N_amide HBs can have stabilizing contributions even in short azapeptides that cannot fold to form β-turns.

The effect of redox agents on conformation and structure characterization of gluten protein: An extensive review

Gluten protein as one of the plant resources is affected by redox agent. Chemical modifications by redox agent have myriad advantages mainly short reaction times, no requirement for specialized equipment, low cost, and highly clear modification impacts. The gluten network properties could be influenced through redox agents (oxidative and reducing agents) which are able to alter the strength of dough via different mechanisms for various purposes. The present review examined the impact of different redox compounds on gluten and its subunits based on their effects on their bonds and conformations and thus with their impacts on the physico-chemical, morphological, and rheological properties of gluten and their subunits. This allows for the use of gluten for different of purposes in the food and nonfood industry.

Wheat protein disulfide isomerase improves bread properties via different mechanisms

Gluten network formation by the oxidation of glutenin sulfhydryl group majorly impacts the subsequent dough and bread properties, and an evolutionary list of chemical oxidants has been used as improvers in bread making. A systematic comparison between azodicarbonamide (ADA), Vc, wheat protein disulfide isomerase (wPDI) and disulfide bond formation protein C (DsbC) of their effects on the alveographic characters of dough and texture properties of subsequent bread was performed. Results show that wPDI improves dough alveographic characters and bread texture properties better in most aspects than other reagents. Free sulfhydryl analysis finds that addition of wPDI increased the free sulfhydryl content in both dough and bread. Compare with inorganic reagents and its bacterial homologue, improving the dough and bread properties with less oxidation of sulfhydryl lead to the proposal that wPDI acts by catalyzing the formation of rheologically active disulfide and reduction of inactive ones in a substrate specific manner.

Complete validation according to current international criteria of a confirmatory quantitative method for the determination of nitrofuran metabolites in seafood by liquid chromatography isotope dilution tandem mass spectrometry

Despite the ban of nitrofurans (NFs) for use in food production in many countries in the 1990s, NF metabolites in food are still regularly detected during import control testing. We have developed a confirmatory routine method for the detection and quantification of NF metabolites in seafood using LC-MS/MS and validated the method according to the strict criteria in European legislation and Codex Alimentarius. Method characteristics were found to fulfill the criteria. We report for the first time a new false positive for 1-amino-2,4-imidazolidinedione (AHD), the metabolite of Nitrofurantoin (NFT). By using optimized washing procedures, the non tissue bound false positives can be minimized. The results from the validation on both lean and fatty fish and crustaceans, results from proficiency tests and routine use over many years, demonstrates that the method is fit for purpose to determine NF metabolites in the seafood category.

Automated In-Injector Derivatization Combined with High-Performance Liquid Chromatography-Fluorescence Detection for the Determination of Semicarbazide in Fish and Bread Samples

Semicarbazide (1) is a widespread genotoxic food contaminant originating as a metabolic byproduct of the antibiotic nitrofurazone used in fish farming or as a thermal degradation product of the common flour additive azodicarbonamide. The goal of this study is to develop a simple and sensitive high-performance liquid chromatography coupled with fluorescence detection (HPLC-FLD) method for the detection of compound 1 in food products. In comparison to existing methods for the determination of compound 1, the reported method combining online precolumn derivatization and HPLC-FLD is less labor-intensive, produces higher sample throughput, and does not require the use of expensive analytical instruments. After validation of accuracy and precision, this method was applied to determine the amount of compound 1 in fish and bread samples. Comparative studies using an established liquid chromatography coupled with tandem mass spectrometry method did not yield systematically different results, indicating that the developed HPLC-FLD method is accurate and suitable for the determination of compound 1 in fish and bread samples.

Identification and occurrence of endogenous semicarbazide in prawns and crabs from Zhejiang Province, China

Semicarbazide (SEM) is a side-chain metabolite of the antibiotic drug nitrofurazone (NFZ) and is employed as a conclusive marker for the use of banned NFZ. Recent studies have shown that SEM in aquatic crustaceans can be derived natively or from other sources. The presence and distribution of endogenous SEM within aquatic crustaceans is examined in this paper, which finds that the SEM content varies amongst the muscle, shell, and viscera of various prawn and crab species within the range of 0.35-26.62 ng g(-1). The effects of heating and hypochlorite treatment on SEM levels were examined. The results indicate that thermal processing introduced a more significant impact, resulting in a maximum SEM value of 15.48 ng g(-1) in a sample of shell of Portunus trituberculatus crab, while SEM levels in muscle samples were not affected by the duration of heating. Though 6% active chlorine treatment led to SEM production ranging between 39.9 and 196.4 ng g(-1) in muscle samples from various crustaceans, SEM is unlikely to originate from hypochlorite or chlorine in practice where there are limits to actual chlorine in sanitation water and facilities. 5-Nitro-2-furaldehyde (NF) was proposed as a selective marker to differentiate between endogenous SEM and NFZ-derived SEM in seafood.

Semicarbazide in Selected Bird's Nest Products

Currently, a number of food producers use hypochlorite to bleach food and inhibit the growth of bacteria, preserving the food. Because the presence of high amounts of nitrogen could result in the formation of semicarbazide (SEM), the bleaching process could be one of the predominant sources of SEM in food. To investigate this, we selected instant bottled bird's nest as an example of a food that is bleached in its production. SEM was detected in 27 of 28 instant bottled bird's nest samples. The levels of SEM detected mostly fell in the range of 5 to 50 μg/kg, which accounted for 75% of all samples measured. The SEM detected in the instant bottled bird's nest was found to have originated neither from the use of the antimicrobial agent nitrofurazone nor from azodicarbonamide, which is used as a blowing agent in gaskets used to seal the metal lid of the bottle. Instead, it could have originated from the bleaching process used in the preparation of the nests. Additionally, human exposure to SEM via consumption of instant bottled bird's nest for five subgroups of the population was estimated. Sensitivity analysis suggested that concentration of SEM in food is the most significant parameter governing human exposure via consumption of SEM-containing food.

Assessment of the determination of azodicarbonamide and its decomposition product semicarbazide: investigation of variation in flour and flour products

Azodicarbonamide, as a bleaching agent and improving agent, is a permitted food additive in certain countries and can be determined by high-performance liquid chromatography. However, it partially degrades with the heat of processing to form trace amounts of semicarbazide, which shows carcinogenicity and also has been shown to cause tumors. The concentration of semicarbazide in azodicarbonamide-treated flour was determined by isotope dilution ((13)C, (15)N(2)-semicarbazide) liquid chromatography electrospray tandem mass spectrometry (LC-MS/MS). The quantification was obtained utilizing the homologous internal standard. The limits of detection were 1 mg/kg for azodicarbonamide and 0.5 × 10(-3) mg/kg for semicarbazide. The rates of recovery were 82.3-103.1% for azodicarbonamide and 72.4-116.5% for semicarbazide. This study prepared four different types of flour products to investigate the variation of semicarbazide. The concentration of semicarbazide in all types of flour products is higher than that in flour, and the concentration of semicarbazide in outside of flour products is slightly higher than that in the inside. As the problem of food safety hazard aggravates daily, we should be more concerned about food security and human health.

Age-related Susceptibility to Induction of Osteochondral and Vascular Lesions by Semicarbazide Hydrochloride in Rats

To compare the susceptibility to toxicity of semicarbazide hydrochloride (SEM-HCl) between young and adult rats, 3- and 20-week-old female SD rats were given a diet containing SEM-HCl at 0, 500, or 1,000 ppm and 0 or 1,000 ppm, respectively, for 4 weeks. Half of the animals were then maintained on basal diet for a further 2 weeks as recovery groups. Only in young rats was deformation of the knee joints as well as thorax and tail observed at 500 and 1,000 ppm. Histopathologically, severe osteochondral lesions, such as disarrangement and thickening of the epiphyseal cartilage and deformation of articular cartilage, were observed, but the severity of these lesions became reduced during the recovery period. In adult rats, osteochondral lesions were relatively mild. Fissures in the cartilage matrix of the tibia were characteristic of adult rats, and in these, reduction of severity was not obvious in the recovery group. In the thoracic aorta, the appearance of elastic laminae was altered only in young rats in both the 4-week treatment and recovery groups. These results suggest that growing animals are more susceptible to toxicity of SEM-HCl than adults are. Effects and the induced lesions link to the developing stage of the target organs.

Rapid identification of additives in poly(vinyl chloride) lid gaskets by direct analysis in real time ionisation and single-quadrupole mass spectrometry

Gaskets for lids of glass jars usually consist of poly(vinyl chloride) (PVC) containing plasticisers and additional additives, which may migrate into packed foodstuffs. To conform to legal regulations, any such migration has to be determined analytically, which is a big challenge due to the huge chemical variety of additives in use. Therefore, a rapid screening method by means of direct analysis in real time mass spectrometry (DART-MS), using a single-quadrupole mass spectrometer, was developed. On introducing a plastisol sample into the DART interface, protonated molecules and ammonium adducts were obtained as the typical ionisation products of any additives present, and cleavages of ester bonds as typical fragmentation processes. Generally, additives present in the 1% range could be directly and easily identified if ion suppressive effects deriving from specific molecules did not occur. These effects could be avoided by analysing toluene extracts of plastisol samples, and this also improved the sensitivity. Using this method, it was possible to identify phthalates, fatty acid amides, tributyl O-acetylcitrate, dibutyl sebacate, bis(2-ethylhexyl) adipate, 1,2-diisononyl 1,2-cyclohexanedicarboxylate, and even more complex additives like acetylated mono- and diacylglycerides, epoxidised soybean oil, and polyadipates, with a limit of detection of < or = 1% in PVC plastisols. Only in the case of epoxidised linseed oil were levels of > or = 5% required for identification. The detection of azodicarbonamide, used as a foaming agent within the manufacturing process, was possible in principle, but was not highly reproducible due to the very low concentrations in plastisols.

A ninety-day toxicity study of semicarbazide hydrochloride in Wistar Hannover GALAS rats

A ninety-day toxicity study of semicarbazide hydrochloride (SEM-HCl) was conducted in male and female Wistar Hannover GALAS rats fed diet containing the compound at concentration of 0, 250, 500 and 1000 ppm. Suppression of body weight gain and food consumption was found in both sexes at 1000 ppm throughout the study. Enlargement and deformation of knee joints were obvious at 500 and 1000 ppm from week 3, together with deformation of the thorax and tail. Histopathologically, disarrangement of chondrocytes and fissures in the cartilage matrix were apparent at all doses tested in epiphyseal and articular cartilage. The severity of these lesions increased dose-dependently, accompanied by increased connective tissues and bone deformation at high doses. Additionally, compact bones at 1000 ppm became thin, suggesting loss of bone mass. In the thoracic aorta, the edges of elastic laminae became rough and the interlaminar spaces were altered from a fibrillar to a rod or globular appearance. No abnormalities were detected in any other organs. Taken together, toxicological effects of subchronic exposure to SEM-HCI were mainly observed in bone, cartilage and the aorta, with the no-observed-adverse-effect-level estimated from the present histopathological examination of less than 250 ppm in both sexes.

Effects of the food contaminant semicarbazide following oral administration in juvenile Sprague-Dawley rats

Semicarbazide (SEM) is an azodicarbonamide by-product present in glass jar packaged foods including babyfoods, in bleaching steps and flour treatment. Experimental data showed SEM acting as osteolathyrogen agent, but few toxicological data are available in susceptible life-stages. This study aimed to evaluate effects of SEM oral administration for 28 days at 0, 40, 75, 140 mg/kg bw day during the juvenile period in Sprague-Dawley rats. Histopatological examinations of: epiphyseal cartilage - potential target of SEM lathyrogen action - testes, ovary, uterus, thyroid, thymus, spleen, adrenals, representative of the main developing organs relevant to juvenile toxicity, and neurobehavioural tests in males, were performed. Mortality at high and mid dose levels and significantly decreased body weight gain were observed in males even at the lowest dose. Lack of mineralization in cartilage at all dose levels was present. Marked alterations of spontaneous motor and exploratory behaviours were evident even at 40 mg/kg. Histological alterations were observed in all tissues; thyroid and ovary effects were present also at 40 mg/kg. The present study indicate that the NOAEL in juvenile rats is lower than 40 mg/kg for SEM oral administration. SEM administration during juvenile period exerted pleiotropic effects and further studies are suggested to elucidate mechanisms.

Development and validation of an analytical method for the determination of semicarbazide in fresh egg and in egg powder based on the use of liquid chromatography tandem mass spectrometry

In this work the development of a method to determine semicarbazide (SEM) in fresh whole egg and in whole egg and egg white powders as those used in the food industry, by using LC-MS/MS is described. The method is based on a recently validated one for the determination of SEM in baby food. SEM is extracted from egg with 0.2 mol L(-1) hydrochloric acid and derivatised with 2-nitrobenzaldehyde. The extract is neutralised and purified by passing through a solid phase extraction (SPE) cartridge. The 2-nitrobenzaldehyde derivative is eluted with ethyl acetate. The eluate is evaporated to dryness and the residue re-dissolved in methanol:water mobile phase. SEM is determined by reversed-phase LC-MS/MS. The "in-house" validation of this method has been performed taking into account the "Harmonized guidelines for single-laboratory validation of methods of analysis" (IUPAC Technical report) and the Commission Decision (2002/657/EC). The performance characteristics of the method were established by in-house validation procedures employing assays with standard solutions, sample blanks and spiked samples. Linearity, matrix effect, trueness, precision, selectivity, limits of detection and of quantification were determined. The fitness for purpose of this method was assessed based on its performance characteristics. LOD's of 0.15 and 0.4 microg kg(-1) for whole fresh egg and industrial egg powders, respectively, were obtained. The LOQ for fresh whole egg was 0.2 microg kg(-1) and for industrial egg powders 0.8 microg kg(-1). Linear calibration curves were obtained in the ranges 1-100 and 0.8-400 microg kg(-1) for fresh whole egg and the egg powders, respectively.

Semicarbazide in Canadian bakery products

Levels of semicarbazide were determined by liquid chromatography-tandem mass spectrometry using isotope dilution ((13)C(15)N(2)-semicarbazide) methodology, and they were measured, after hydrolysis in 0.125 M hydrochloric acid and derivatization with 2-nitrobenzaldehyde, as a sum of free and bound semicarbazide. Levels of semicarbazide in 11 bakery products, which were sampled at three time intervals from the same source, varied from not detected (<1ng g(-1)) to 560 ng g(-1). In some instances, concentrations of semicarbazide varied between batches of the same product, at times more than tenfold, suggesting that the addition of azodicarbonamide to the same product is not standardized in many baking establishments.