Sulfites in foods: uses, analytical methods, residues, fate, exposure assessment, metabolism, toxicity, and hypersensitivity

Gastric mucosal irritation following oral exposure to sodium metabisulphite: A reproducible effect?

Sulphiting agents, such as sodium metabisulphite (SM), are used in food as bleaching agents and to prevent browning reactions. A 1972 repeat dose study in rats found that dietary sulphites caused irritation of the stomach with inflammation, hyperplasia and bleeding. We conducted a 7-day dietary study in rats to confirm that stomach lesions were the most sensitive toxicological endpoint. Rat feed was prepared daily with 0%, 0.25%, 0.5%, 1% or 4% (w/w) SM. Parameters included clinical signs, feed and water intake, bodyweight gain, haematology, serum protein chemistry, necropsy findings and gastrointestinal histopathology. There were no treatment-related clinical signs or gastrointestinal lesions. Mean bodyweight gain was markedly decreased in the 4% (w/w) SM group although feed consumption was marginally depressed. Slightly lower mean values for RBC, Hb, Hct, total WBC and lymphocyte count were observed in the 4% SM group with no evidence of compensatory haematopoiesis. The gastric lesions in rats observed in a 1972 study of dietary SM for 10-56 days could not be replicated. These findings create uncertainty around the most relevant toxicological endpoint to establish a suitable health based guidance value, which can only be overcome if a robust long-term dietary study is undertaken.

The effect of sulfite and chronic restraint stress on brain lipid peroxidation and anti-oxidant enzyme activities

Sulfites are used as anti-microbial and anti-oxidant agents in a variety of drugs, and function as a preservative in many food preparations. In addition to these effects, sulfites oxidize to sulfite radicals initiating lipid peroxidation. The objective of our study was to investigate the effect of restraint stress and sulfite on brain lipid peroxidation and anti-oxidant enzyme activities. Forty male Wistar rats, aged three months, were randomized to one of the following groups: control, restraint stress, sulfite-treated and restraint stress-/sulfite-treated. Chronic restraint stress was applied for 21 days (1 h/day) and sodium metabisulfite (520 mg/kg per day) was given by gavage for the same period. Lipid peroxidation was measured using the thiobarbituric acid (TBA) fluorometric assay. TBA-reactive substances (TBARS) were found increased in all treatment groups when compared to the control group. Spectrophotometric measurement of copper/zinc superoxide dismutase (Cu/Zn SOD) and catalase (CAT) revealed decreased enzyme activities in rats exposed to restraint stress compared to control and sulfite-treated rats. GSH-Px activities were significantly decreased in the restraint stress and sulfite-treated rats compared with the control rats. GSH-Px activity measured in restraint stress-/sulfite-treated rats was significantly lower than in the other groups. The presented data confirms the pro-oxidant activity of restraint stress and establishes that decreased anti-oxidant enzyme activities in restraint stress-treated rats enhances brain lipid peroxidation caused via the ingestion of sulfites.

Food safety risk assessment for estimating dietary intake of sulfites in the Taiwanese population

The purpose of this study was to assess the health risk associated with dietary intake of sulfites for Taiwanese general consumers by conducting a total diet study (TDS). We evaluated the exposure of Taiwanese to sulfites in the diet and its associated health risk. This study used a list of 128 food items representing 83% of the total daily diet. Among the 128 food items, 59 items may contain sulfites. Samples of the 59 food items were collected and subjected to chemical analysis to determine the sulfur dioxide concentration. Health risk was assessed by calculating the ratio of exposure level to the acceptable daily intake (ADI) level of the analyte. For high-intake consumers, the HI of sulfites was 19.7% ADI for males over the age of three years at the 95th percentile; whereas for females over the age of 66, the HI was 17.8% ADI. The HI for high-intake consumers was above 10% ADI. This suggests that regulatory actions must be continued and that consumers should be advised to be aware of processed foods with relatively high contamination to avoid excessive exposure.

Sulfur Dioxide Contributes to the Cardiac and Mitochondrial Dysfunction in Rats

Epidemiological studies have demonstrated an association between sulfur dioxide (SO2) and an increase of morbidity and mortality of cardiovascular diseases, such as ischemic heart disease, heart failure, and arrhythmia. Mitochondrion is the most sensitive organelle in myocardium of animals exposed to SO2 Here we study the molecular characterization of mitochondrial dysfunction in cardiac muscles of rat after SO2 exposure. We found that the cytochrome c oxidase (COX) activity, mitochondrial membrane potential (ΔΨm), ATP contents, mitochondrial DNA (mtDNA) contents, and mRNA expression of complexes IV and V subunits encoded by mtDNA were decreased after NaHSO3 treatment in vitro or SO2 inhalation in vivo The mitochondrial dysfunctions were accompanied by depressions of co-activator of peroxisome proliferator activated receptor gamma (PGC-1α), nuclear respiratory factor 1, and mitochondrial transcription factor A (TFAM) mRNA and protein. We observed swollen mitochondria and lower amounts of cristae in hearts of rats after 3.5 mg/m(3) SO2 inhalation for 30 days. Interestingly, NaHSO3 induced mitochondrial dysfunctions marked by ΔΨm and ATP reduction could be inhibited by an antioxidant N-acetyl-L-cysteine (NALC), accompanied by the restoration of transcriptional factors expressions. The cardiac mitochondrial dysfunctions could also be alleviated by overexpression of TFAM. SO2 induced abnormal left ventricular function was restored by NALC in vivo Our findings demonstrate that SO2 induces cardiac and mitochondrial dysfunction. And inhibition of reactive oxygen species and enhancing the transcriptional network controlling mitochondrial biogenesis can mitigate the SO2-induced mitochondrial dysfunction.

An A–π–A′ structural ratiometric fluorescent probe based on benzo[e]indolium for bisulfite and its application in sugar samples and living cells

An A–π–A′ structural ratiometric fluorescent probe 1 bearing a benzo[e]indolium moiety was developed for the detection of HSO₃⁻ in PBS buffer solution.

A single fluorescent probe for multiple analyte sensing: efficient and selective detection of CN−, HSO3− and extremely alkaline pH

A water-soluble broadly emitting (500–650 nm) fluorescent probe (IECBT) for the selective and sensitive detection of multiple analytes, including CN⁻, HSO₃⁻ and extremely alkaline pH, is designed and synthesized.

A solo fluorogenic probe for the real-time sensing of SO32−and SO42−/HSO4−in aqueous medium and live cells by distinct turn-on emission signals

A fluorogenic probe (L) rendered rapid and differential turn-on responses to SO₃²⁻and SO₄²⁻/HSO₄⁻in aqueous medium.

Investigation of the effects of a sulfite molecule on human neuroblastoma cells via a novel oncogene URG4/URGCP

AIM

The aim of this study is to determine the anticancer effect of sulfite on SH-SY5Y neuroblastoma cells in vitro conditions and elucidate underlying molecular mechanism of sulfite and explore its therapeutic activity.

MAIN METHODS

In this study, cytotoxic effects of sulfite in SH-SY5Y cels were detected over time in a dose dependent manner with the IC50 doses ranging from 0.5 to 10 mM. Genotoxic effect of sulfite was shown by comet assay. IC50 doses in the SH-SY5Y cells were detected as 5 mM. Expression profiles of the target genes related to apoptosis and cell cycle control were determined by quantitative RT-PCR. Protein changes were determined by western blot analysis.

KEY FINDINGS

URG4/URGCP, CCND1, CCND2, CDK4, CDK6, E2F4 and BCL-2 gene expression levels were significantly reduced and RB1, TP53, BAX, BID, CASP2, CASP3, CASP9 and DIABLO gene expressions were significantly increased in dose group cells. The mechanism of this result may be related to sulfite dependent inhibition of cell cycle at the G1 phase by down-regulating URG4/URGCP or CCND1, CDK4, CDK6 gene expression and stimulating apoptosis via the intrinsic pathway. Sulfite suppressed invasion and colony formation in SH-SY5Y cell line using matrigel invasion chamber and colony formation assay, respectively.

SIGNIFICANCE

It is thought that sulfite demonstrates anticarcinogenesis activity by affecting cell cycle arrest, apoptosis s, invasion, and colony formation on SH-SY5Y cells. Sulfite may be an effective agent for treatment of neuroblastoma as a single agent or in combination with other agents.

Interaction of polyphenol oxidase of Solanum tuberosum with β-cyclodextrin: Process details and applications

Polysaccharides differing in structure and chemical nature were screened for their ability to bind non-covalently with polyphenol oxidase (PPO) from potato (as a model) and their effect on enzyme activity. All the polysaccharides selected inhibited the PPO but β-cyclodextrin showed maximum inhibition under optimum conditions. Process details for the inhibition of PPO were studied with respect to concentration of β-cyclodextrin, temperature, pH, and time. Higher inhibition constant and lower half life was obtained at 40 °C than at 30 °C in the presence of inhibitor. β-Cyclodextrin showed mixed type of inhibition of PPO. β-Cyclodextrin was further exploited as anti-browning agent in selected fruit juices. It not only showed a significant anti-browning effect on freshly prepared potato juice but was also effective in other fruit juices. Better effect was seen in pineapple, apple and pear as compared to banana, sugarcane and guava fruit juices.

Development of a liquid chromatography-tandem mass spectrometry method for the determination of sulfite in food

Sulfites are widely used food preservatives that can cause severe reactions in sensitive individuals. As a result, the U.S. FDA requires that sulfites be listed on the label of any food product containing >10 mg/kg (ppm) sulfite (measured as sulfur dioxide). Currently, the optimized Monier-Williams (MW) method (AOAC Official Method 990.28) is the most common approach for determining sulfite concentrations in food samples. However, this method is time-consuming and lacks specificity in certain matrices. An improved rapid, sensitive, and selective method has been developed using electrospray ionization (ESI) high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) for the determination of sulfite in various food matrices. A total of 12 different types of foods were evaluated. These included dried fruits and vegetables, frozen seafood, sweeteners, and juices. The matrix is extracted with a buffered formaldehyde solution, converting free and reversibly bound sulfite to the stable formaldehyde adduct, hydroxymethylsulfonate (HMS). Extracts are prepared for injection using a C18 SPE cartridge to remove any lipophilic compounds. HMS is then separated from other matrix components using hydrophilic interaction chromatography (HILIC) and detected using multiple reaction monitoring (MRM). The method was validated at 5 concentrations in 12 food matrices. Accuracy data showed spiked recoveries ranging from 84 to 115% in representative foods. Six commercially available sulfited products were analyzed using the LC-MS/MS method, as well as the MW method, to determine if differences exist.

Induction of omega 6 inflammatory pathway by sodium metabisulfite in rat liver and its attenuation by ghrelin

Background

Sodium metabisulfite is commonly used as preservative in foods but can oxidize to sulfite radicals initiating molecular oxidation. Ghrelin is a peptide hormone primarily produced in the stomach and has anti-inflammatory effects in many organs. This study aimed to assess endogenous omega-3 (n-3) and omega-6 (n-6) polyunsaturated fatty acids (PUFAs) in rat peripheral organs following sodium metabisulfite treatment and determine the possible effect of ghrelin on changes in n-6 inflammatory pathway.

Methods

Male Wistar rats included in the study were allowed free access to standard rat chow. Sodium metabisulfite was given by gastric gavage and ghrelin was administered intraperitoneally for 5 weeks. Levels of arachidonic acid (AA, C20:4n-6), dihomo-gamma-linolenic acid (DGLA, C20:3n-6), eicosapentaenoic acid (EPA, C20:5n-3) and docosahexaenoic acid (DHA, C22:6n-3) in liver, heart and kidney tissues were determined by an optimized multiple reaction monitoring (MRM) method using ultra fast-liquid chromatography (UFLC) coupled with tandem mass spectrometry (MS/MS). Cyclooxygenase (COX) and prostaglandin E2 (PGE2) were measured in tissue samples to evaluate changes in n-6 inflammatory pathway.

Results

Omega-6 PUFA levels, AA/DHA and AA/EPA ratio were significantly increased in liver tissue following sodium metabisulfite treatment compared to controls. No significant change was observed in heart and kidney PUFA levels. Tissue activity of COX and PGE2 levels were also significantly increased in liver tissue of sodium metabisulfite treated rats compared to controls. Ghrelin treatment decreased n-6 PUFA levels and reduced COX and PGE2 levels in liver tissue of sodium metabisulfite treated rats.

Conclusion

Current results suggest that ghrelin exerts anti-inflammatory action through modulation of n-6 PUFA levels in hepatic tissue.

BODIPY-based colorimetric/ratiometric fluorescence probes for sulfite in aqueous solution and in living cells

Two colorimetric/ratiomrtric fluorescence probes for sulfite utilizing the Michael-addition mechanism were designed. BSP1 could be applied in the imaging of sulfite in living cells.

A reversible fluorescent-colorimetric imino-pyridyl bis-Schiff base sensor for expeditious detection of Al3+ and HSO3− in aqueous media

A reversible fluorescent-colorimetric imino-pyridyl bis-Schiff base receptor (N¹E,N⁴E)-N¹,N⁴-bis(pyridine-4-ylmethylene)benzene-1,4-diamine (L) for easy, convenient, rapid and sensitive detection of both Al³⁺ and HSO₃⁻ in aqueous medium has been developed.

A twisted intramolecular charge transfer probe for rapid and specific detection of trace biological SO2 derivatives and bio-imaging applications

A highly “reactive” probe showed a ratiometric fluorescence response to HSO₃⁻ with fast response and low detection limit (3.0 nM).

A highly sensitive and selective turn-on fluorescent probe for sulfite and its application in biological imaging

A new fluorescein-based probe (1) has been developed for the highly sensitive and selective detection of sulfite.

Transcriptome structure variability in Saccharomyces cerevisiae strains determined with a newly developed assembly software

Background

RNA-seq studies have an important role for both large-scale analysis of gene expression and for transcriptome reconstruction. However, the lack of software specifically developed for the analysis of the transcriptome structure in lower eukaryotes, has so far limited the comparative studies among different species and strains.

Results

In order to fill this gap, an innovative software called ORA (Overlapped Reads Assembler) was developed. This software allows a simple and reliable analysis of the transcriptome structure in organisms with a low number of introns. It can also determine the size and the position of the untranslated regions (UTR) and of polycistronic transcripts. As a case study, we analyzed the transcriptional landscape of six S. cerevisiae strains in two different key steps of the fermentation process. This comparative analysis revealed differences in the UTR regions of transcripts. By extending the transcriptome analysis to yeast species belonging to the Saccharomyces genus, it was possible to examine the conservation level of unknown non-coding RNAs and their putative functional role.

Conclusions

By comparing the results obtained using ORA with previous studies and with the transcriptome structure determined with other software, it was proven that ORA has a remarkable reliability. The results obtained from the training set made it possible to detect the presence of transcripts with variable UTRs between S. cerevisiae strains. Finally, we propose a regulatory role for some non-coding transcripts conserved within the Saccharomyces genus and localized in the antisense strand to genes involved in meiosis and cell wall biosynthesis.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-1045) contains supplementary material, which is available to authorized users.

The effect of ingested sulfite on visual evoked potentials, lipid peroxidation, and antioxidant status of brain in normal and sulfite oxidase-deficient aged rats

Sulfite, commonly used as a preservative in foods, beverages, and pharmaceuticals, is a very reactive and potentially toxic molecule which is detoxified by sulfite oxidase (SOX). Changes induced by aging may be exacerbated by exogenous chemicals like sulfite. The aim of this study was to investigate the effects of ingested sulfite on visual evoked potentials (VEPs) and brain antioxidant statuses by measuring superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) activities. Brain lipid oxidation status was also determined via thiobarbituric acid reactive substances (TBARS) in normal- and SOX-deficient aged rats. Rats do not mimic the sulfite responses seen in humans because of their relatively high SOX activity level. Therefore this study used SOX-deficient rats since they are more appropriate models for studying sulfite toxicity. Forty male Wistar rats aged 24 months were randomly assigned to four groups: control (C), sulfite (S), SOX-deficient (D) and SOX-deficient + sulfite (DS). SOX deficiency was established by feeding rats with low molybdenum (Mo) diet and adding 200 ppm tungsten (W) to their drinking water. Sulfite in the form of sodium metabisulfite (25 mg kg(-1) day(-1)) was given by gavage. Treatment continued for 6 weeks. At the end of the experimental period, flash VEPs were recorded. Hepatic SOX activity was measured to confirm SOX deficiency. SOX-deficient rats had an approximately 10-fold decrease in hepatic SOX activity compared with the normal rats. The activity of SOX in deficient rats was thus in the range of humans. There was no significant difference between control and treated groups in either latence or amplitude of VEP components. Brain SOD, CAT, and GPx activities and brain TBARS levels were similar in all experimental groups compared with the control group. Our results indicate that exogenous administration of sulfite does not affect VEP components and the antioxidant/oxidant status of aged rat brains.

Non-enzymatic browning in citrus juice: chemical markers, their detection and ways to improve product quality

Citrus juices are widely consumed due to their nutritional benefits and variety of pharmacological properties. Non-enzymatic browning (NEB) is one of the most important chemical reactions responsible for quality and color changes during the heating or prolonged storage of citrus products. The present review covers various aspects of NEB in citrus juice viz. chemistry of NEB, identifiable markers of NEB, analytical methods to identify NEB markers and ways to improve the quality of citrus juice. 2,5-Dimethyl-4-hydroxy-3(2H)-furanone (DMHF) is one of the promising marker formed during browning process with number of analytical methods reported for its analysis; therefore it can be used as an indicator for NEB process. Amongst analytical methods reported, RP-HPLC is more sensitive and accurate method, which can be used as analytical tool. NEB can be prevented by removal of amino acids/ proteins (via ion exchange treatment) or by targeting NEB reactions (e.g. blockage of furfural/ HMF by sulphiting agent).

Loss of sulfur dioxide and changes in some chemical properties of Malatya apricots (Prunus armeniaca L.) during sulfuring and drying

BACKGROUND

This study was conducted to determine the differences in some analytical properties of four apricot cultivars and to determine the changes in these analytical properties during sulfuring and sun-drying.

RESULTS

There were significant differences in the contents of polyphenols, carotenoids and organic acids (OA) as well as antioxidant activities (AOAs) of the cultivars (P < 0.05). After sulfuring and drying, considerable reductions were detected in the contents of total polyphenols (TPCs, 11-26%), OAs (4-32%) and β-carotene (6-21%), and AOAs (2-21%) of the samples. Sun-drying resulted in 71-83% decreases in sulfur dioxide (SO2 ) contents of sulfured-dried apricots (SDAs) in comparison with apricots immediately after sulfuring. As the TPCs increased, the SO2 absorption by the samples also increased. In contrast, the OA contents had no effect on SO2 absorption, but an increase in OA content resulted in an increase in the browning values of the SDAs. As expected, increases in contents of ferulic acid (r = 0.932), chlorogenic acid (r = 0.850), epicatechin (r = 0.804) and quercetin (r = 0.750) led to an increase in browning values of the SDAs.

CONCLUSION

There were significant effects of cultivar and processing on the physico-chemical properties investigated in the study, and with the absorption of SO2 and the formation of a brown colour in the samples.

Decreased immunoglobulin E (IgE) binding to cashew allergens following sodium sulfite treatment and heating

Cashew nut and other nut allergies can result in serious and sometimes life-threatening reactions. Linear and conformational epitopes within food allergens are important for immunoglobulin E (IgE) binding. Methods that disrupt allergen structure can lower IgE binding and lessen the likelihood of food allergy reactions. Previous structural and biochemical data have indicated that 2S albumins from tree nuts and peanuts are potent allergens, and that their structures are sensitive to strong reducing agents such as dithiothreitol. This study demonstrates that the generally regarded as safe (GRAS) compound sodium sulfite effectively disrupted the structure of the cashew 2S albumin, Ana o 3, in a temperature-dependent manner. This study also showed that sulfite is effective at disrupting the disulfide bond within the cashew legumin, Ana o 2. Immunoblotting and ELISA demonstrated that the binding of cashew proteins by rabbit IgG or IgE from cashew-allergic patients was markedly lowered following treatment with sodium sulfite and heating. The results indicate that incorporation of sodium sulfite, or other food grade reagents with similar redox potential, may be useful processing methods to lower or eliminate IgE binding to food allergens.

Colorimetric Detection of Sulfite in Foods by a TMB-O2-Co3O4 Nanoparticles Detection System

In this paper, we first discovered that Co3O4 nanoparticles (NPs) possess intrinsic oxidase-like activity and can catalytically oxidize peroxidase substrates, such as 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) and 3,3',5,5'-tetramethylbenzidine (TMB), to form colored products, in the absence of exogenously added H2O2. The presence of sulfite inhibited the TMB-O2-Co3O4 NPs reaction system and caused a change in color of the reaction system. On the basis of this phenomenon, a colormetric approach to detect sulfite was established with a good linear relationship ranging from 0.2×10(-6) to 1.6×10(-5) M and a detection limit of 5.3×10(-8) M. The method was used to detect sulfite in foods. Good recoveries ranging from 93.8% to 100.5% were obtained. Furthermore, the mechanism was studied and results showed that the oxidase-like activity of the Co3O4 NPs was not from •OH or O2•- radical generated. It may probably originate from their ability to transfer an electron between the peroxidase substrate and oxygen absorbed on the surface of the Co3O4 NPs.

Sulfite disrupts brain mitochondrial energy homeostasis and induces mitochondrial permeability transition pore opening via thiol group modification

Sulfite oxidase (SO) deficiency is biochemically characterized by the accumulation of sulfite, thiosulfate and S-sulfocysteine in tissues and biological fluids of the affected patients. The main clinical symptoms include severe neurological dysfunction and brain abnormalities, whose pathophysiology is still unknown. The present study investigated the in vitro effects of sulfite and thiosulfate on mitochondrial homeostasis in rat brain mitochondria. It was verified that sulfite per se, but not thiosulfate, decreased state 3, CCCP-stimulated state and respiratory control ratio in mitochondria respiring with glutamate plus malate. In line with this, we found that sulfite inhibited the activities of glutamate and malate (MDH) dehydrogenases. In addition, sulfite decreased the activity of a commercial solution of MDH, that was prevented by antioxidants and dithiothreitol. Sulfite also induced mitochondrial swelling and reduced mitochondrial membrane potential, Ca(2+) retention capacity, NAD(P)H pool and cytochrome c immunocontent when Ca(2+) was present in the medium. These alterations were prevented by ruthenium red, cyclosporine A (CsA) and ADP, supporting the involvement of mitochondrial permeability transition (MPT) in these effects. We further observed that N-ethylmaleimide prevented the sulfite-elicited swelling and that sulfite decreased free thiol group content in brain mitochondria. These findings indicate that sulfite acts directly on MPT pore containing thiol groups. Finally, we verified that sulfite reduced cell viability in cerebral cortex slices and that this effect was prevented by CsA. Therefore, it may be presumed that disturbance of mitochondrial energy homeostasis and MPT induced by sulfite could be involved in the neuronal damage characteristic of SO deficiency.

Curcumin can prevent the changes in cerebellar structure and function induced by sodium metabisulfite in rat

Sulfites are used as anti-microbial and anti-oxidant agents in the food and pharmaceutical industries. Curcumin, a flavonoid, is an Asian spice that shows neuroprotective activities. The current study aimed to stereologically assess the rats' cerebellar cortex and rotarod performance following sulfite exposure and determine the possible neuroprotective potential of curcumin. The rats were divided into five groups: distilled water, olive oil, curcumin (100 mg/kg/day), sodium metabisulfite (25 mg/kg/day), and sodium metabisulfite+curcumin. At 56 days after treatment, rotarod performance was tested, and then the cerebellum was removed for stereological analysis. The study results revealed 31%, 36%, 19% and 24% decrease in the total volume of the cerebellum, cortex, the total number of the Purkinje cells and length of the nerve fibers in the cortex per Purkinje, respectively in the sodium metabisulfite-treated rats compared to the distilled water group (p<0.01). The pre-trained animals on the rotarod apparatus were tested first on the fixed speed rotarod protocol followed by the accelerating rotarod protocol two days later. The results showed a significant decrease in the latency to fall in both test in sulfite-treated rats. The sulfite effects on the structural parameters and rotarod performance were significantly protected by the concomitant curcumin treatment (p<0.001). Sulfite can induce structural and functional changes in the rats' cerebellum and concomitant curcumin prescription plays a neuroprotective role.

Comparison of four different methods for the determination of sulfites in foods marketed in South Korea

Sulfites in foods were analysed using four methods: optimised Monier-Williams (official method), modified Rankine, HPLC and ion-exchange chromatography (IEC). The modified Rankine and HPLC methods were performed according to the previously reported methods but with some modifications. The IEC method was carried out through a combination of a modified Rankine apparatus and an anion-exchange column for the first time. In false-positive response tests, false-positive results with acetic acid and propionic acid were not observed in the modified Rankine, HPLC or IEC methods, unlike the optimised Monier-Williams method. All methods were evaluated for accuracy, precision and simple correlations. Modified Rankine, HPLC and IEC methods were determined to be suitable for foods with less than 10 mg kg(-1) of sulfur dioxide (SO₂). The modified Rankine and HPLC methods were suggested to be the most appropriate for the determination of sulfites in foods due to their high correlation coefficient with the optimised Monier-Williams method (R(2) = 0.9138 and 0.9011, respectively).

Monitoring of sulphites levels in shrimps samples collected in Puglia (Italy) by ion-exchange chromatography with conductivity detection

In shrimps the treatment with sulphiting agents is currently the best option for controlling Melanosis, which is a visual defect of the products that compromises marketability. However, sulphites may cause pseudo-allergic reactions in humans. In this study, 210 samples of shrimps were analysed in order to assess the residual levels of sulphiting agents. A quantifiable sulphites concentration was detected in 76 samples, and these concentrations were higher than the legal limits in eight samples. Considering the important pseudo-allergenic effects caused by these food additives, the non-negligible percentage of 3.8% and the high levels registered in non-compliant samples (up to 1174.1 mg kg(-1)), a strong contrast action based on permanent controls is necessary. Moreover, the levels measured in whole samples were up to four times higher than in the edible parts. These results suggest to consider the introduction of legal limits, related to sulphurous anhydride in the whole product.

Theoretical studies of sulfite – sulfur dioxide clusters, SO32−(SO2)n: structure and stability of SnO2n+1 anions, n = 1–5

Density functional calculations using the B3PW91 functional with the 6-311+G(3df) basis set were performed on the addition of n = 1–4 SO2 molecules to SO3− and SO32−. Geometry optimizations were performed for a large number of possible structures. At n = 4, the dianionic cluster becomes adiabatically more stable than the monoanionic one, with an adiabatic electron detachment energy of 0.30 eV. Monoanionic clusters are characterized by the O–S–O–SO3 moiety having long O–S bonds to SO2 molecules. Dianionic clusters, however, prefer S–S bonding of O3S–O–S(O) with SO2.

Sulfite-mediated oxidation of myeloperoxidase to a free radical: immuno-spin trapping detection in human neutrophils

Previous studies focused on catalyzed oxidation of (bi)sulfite, leading to the formation of the reactive sulfur trioxide ((•)SO3(-)), peroxymonosulfate ((-)O3SOO(•)), and sulfate (SO4(•-)) anion radicals, which can damage target proteins and oxidize them to protein radicals. It is known that these very reactive sulfur- and oxygen-centered radicals can be formed by oxidation of (bi)sulfite by peroxidases. Myeloperoxidase (MPO), an abundant heme protein secreted from activated neutrophils that play a central role in host defense mechanisms, allergic reactions, and asthma, is a likely candidate for initiating the respiratory damage caused by sulfur dioxide. The objective of this study was to examine the oxidative damage caused by (bi)sulfite-derived free radicals in human neutrophils through formation of protein radicals. We used immuno-spin trapping and confocal microscopy to study the protein oxidations driven by sulfite-derived radicals. We found that the presence of sulfite can cause MPO-catalyzed oxidation of MPO to a protein radical in phorbol 12-myristate 13-acetate-activated human neutrophils. We trapped the MPO-derived radicals in situ using the nitrone spin trap 5,5-dimethyl-1-pyrroline N-oxide and detected them immunologically as nitrone adducts in cells. Our present study demonstrates that myeloperoxidase initiates (bi)sulfite oxidation leading to MPO radical damage, possibly leading to (bi)sulfite-exacerbated allergic reactions.

Curcumin, the main part of turmeric, prevents learning and memory changes induced by sodium metabisulfite, a preservative agent, in rats

Sodium metabisulfite is used as a disinfectant, antioxidant, and preservative agent in the food, beverage, and drug industries. Neurons are highly sensitive to sulfite toxicity. Curcumin is the main part of turmeric and has neuroprotective effects on a variety of nervous system damages. The present study aimed to investigate the possible protective role of curcumin in learning and memory after exposure to sulfite in rats. The rats were divided into five groups receiving distilled water (solvent of the sulfite), olive oil (solvent of the curcumin), sodium metabisulfite (25 mg/kg/day), curcumin (100 mg/kg/day), and sulfite + curcumin. All the animals received daily gavages for 8 weeks. At the end of the 8(th) week, learning and memory were assessed in a partially-baited eight arm radial maze. The animals treated with sulfite showed fewer correct choices and more reference and working memory errors during the learning phase, at the end of the learning phase, and during the retention testing (p<0.001). The study results demonstrated that sulfite-exposure was associated with impaired learning and memory in rats. Adding curcumin to the rat nutrition plays a protective role in learning and memory after exposure to sulfite.

Ghrelin inhibits sodium metabisulfite induced oxidative stress and apoptosis in rat gastric mucosa

This study aimed to investigate the effect of ghrelin administration on sulfite induced oxidative and apoptotic changes in rat gastric mucosa. Forty male albino Wistar rats were randomized into control (C), sodium metabisulfite (Na2S2O5) treated (S), ghrelin treated (G) and, Na2S2O5+ghrelin treated (SG) groups. Sodium metabisulfite (100 mg/kg/day) was given by gastric gavage and, ghrelin (20 μg/kg/day) was given intraperitoneally for 5 weeks. Plasma-S-sulfonate level was increased in S and SG groups. Na2S2O5 administration significantly elevated total oxidant status (TOS) levels while depleting total antioxidant status (TAS) levels in gastric mucosa. Ghrelin significantly decreased gastric TOS levels in the SG group compared with the S group. Additionally, TAS levels were found to be higher in SG group in reference to S group. Na2S2O5 administration also markedly increased the number of apoptotic cells, cleaved caspase-3 and PAR expression (PARP activity indicator) and, decreased Ki67 expression (cell proliferation index) in gastric mucosal cells. Ghrelin treatment decreased the number apoptotic cells, cytochrome C release, PAR and, caspase-3 expressions while increasing Ki67 expression in gastric mucosa exposed to Na2S2O5. In conclusion, we suggest that ghrelin treatment might ameliorate ingested-Na2S2O5 induced gastric mucosal injury stemming from apoptosis and oxidative stress in rats.

Factors supporting cysteine tolerance and sulfite production in Candida albicans

The amino acid cysteine has long been known to be toxic at elevated levels for bacteria, fungi, and humans. However, mechanisms of cysteine tolerance in microbes remain largely obscure. Here we show that the human pathogenic yeast Candida albicans excretes sulfite when confronted with increasing cysteine concentrations. Mutant construction and phenotypic analysis revealed that sulfite formation from cysteine in C. albicans relies on cysteine dioxygenase Cdg1, an enzyme with similar functions in humans. Environmental cysteine induced not only the expression of the CDG1 gene in C. albicans, but also the expression of SSU1, encoding a putative sulfite efflux pump. Accordingly, the deletion of SSU1 resulted in enhanced sensitivity of the fungal cells to both cysteine and sulfite. To study the regulation of sulfite/cysteine tolerance in more detail, we screened a C. albicans library of transcription factor mutants in the presence of sulfite. This approach and subsequent independent mutant analysis identified the zinc cluster transcription factor Zcf2 to govern sulfite/cysteine tolerance, as well as cysteine-inducible SSU1 and CDG1 gene expression. cdg1Δ and ssu1Δ mutants displayed reduced hypha formation in the presence of cysteine, indicating a possible role of the newly proposed mechanisms of cysteine tolerance and sulfite secretion in the pathogenicity of C. albicans. Moreover, cdg1Δ mutants induced delayed mortality in a mouse model of disseminated infection. Since sulfite is toxic and a potent reducing agent, its production by C. albicans suggests diverse roles during host adaptation and pathogenicity.

Determination of sulfite with emphasis on biosensing methods: a review

Sulfite is used as a preservative in a variety of food and pharmaceutical industries to inhibit enzymatic and nonenzymatic browning and in brewing industries as an antibacterial and antioxidizing agent. Convenient and reproducible analytical methods employing sulfite oxidase are an attractive alternative to conventional detection methods. Sulfite biosensors are based on measurement of either O2 or electrons generated from splitting of H2O2 or heat released during oxidation of sulfite by immobilized sulfite oxidase. Sulfite biosensors can be grouped into 12 classes. They work optimally within 2 to 900 s, between pH 6.5 and 9.0, 25 and 40 °C, and in the range from 0 to 50,000 μM, with detection limit between 0.2 and 200 μM. Sulfite biosensors measure sulfite in food, beverages, and water and can be reused 100-300 times over a period of 1-240 days. The review presents the principles, merits, and demerits of various analytical methods for determination of sulfite, with special emphasis on sulfite biosensors.