涡旋辅助分散液液微萃取分光光度法测定饮用水中的亚硝酸根

目的建立涡旋辅助分散液液微萃取分光光度法检测饮用水中亚硝酸根的含量。方法在酸性条件下,亚硝酸根与对硝基苯胺和二苯胺反应生成红色偶氮化合物,通过测定红色偶氮化合物间接测定亚硝酸根的含量,以分光光度法检测,外标法定量。确定萃取剂种类,利用正交试验对萃取剂的用量、酸浓度和涡旋时间进行优化。结果在浓度10～200μg/L范围内线性关系良好(r2=0.9912),检出限为2.0μg/L,富集倍数为14。加标回收率为87.3%～106.3%,相对标准偏差0.8%～4.4%。结论该方法具有简单、快速、灵敏度高、准确性好,适用于饮用水中亚硝酸根的日常监测。     

Effect of cooking or handling conditions on the furan levels of processed foods

The aim of this study was to investigate the possible effects of cooking or handling conditions on the concentration of furan in processed foods. The analytical method used to analyse furan levels in foods was optimized based on solid-phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS). In baby soups, the concentration of furan decreased by up to 22% after opening a lid for 10 min. In the baby food in retort packaging, the level of furan was reduced by 15–33% after heating the foods at 50°C without a lid. Furan in rice seasonings was evaporated completely after heating the foods at 60°C. Regarding powered milk, the levels of furan were too low to be compared under various conditions. The levels of furan decreased to 58% in beverage products for babies, after storing them at 4°C for 1 day without a lid. The levels of furan in canned foods such as cereal and vegetable were reduced by zero to 52% when they were stored without stirring in a refrigerator at 4°C for 1 day. When we boiled canned fish, the furan present was almost completely evaporated. It is recommended that canned meats be heated up to 50–70°C for the reduction (26–46%) of furan levels. The levels of furan in instant and brewed coffee samples were significantly reduced after storing for 11 to 20 min at room temperature without a lid (p < 0.05).     

Determination of nine preservatives in processed foods using a modified QuEChERS extraction and quantified by HPLC-PDA

ABSTRACT

In this study, a new method was developed for simultaneously determining nine preservatives, that is, benzoic acid (BA), sorbic acid (SOA), dehydroacetic acid (DHA) and PHBAs (methyl p-hydroxybenzoate [PHBA-me], ethyl p-hydroxybenzoate [PHBA-et], isopropyl p-hydroxybenzoate [PHBA-ipro], propyl p-hydroxybenzoate [PHBA-npro]), isobutyl p-hydroxybenzoate [PHBA-ibut] and butyl p-hydroxybenzoate [PHBA-nbut]), in processed foods, employing liquid chromatography (LC). This procedure accelerated sample preparation and improved efficiency by employing modified quick, easy, cheap, effective, rugged and safe (QuEChERS) extraction without clean-up. Samples were prepared with 20 mL of acetonitrile/water (1:1) with the assistance of a ceramic stone. The extract solutions were diluted 10 times or according to the detection amount and then injected into an LC-PDA. This method showed good linearity, and the LOQs were 10 mg/kg for BA, SOA and DHA and 5?mg/kg for the PHBAs. When validating this method, the recoveries of the nine preservatives were in the range 77.0–99.6%, RSD_r values were in the range 0.7–5.3% and those of RSD_wr were in the range 2.3–8.4%. These results suggest that this new method is highly reproducible.     

Simple and fast spectrophotometric determination of low levels of thiabendazole residues in fruit and vegetables after pre-concentration with ionic liquid phase microextraction

There is a great importance of monitoring thiabendazole (TBZ) residues in fruits and vegetables to ensure food safety. Therefore, a new ionic liquid (IL) phase microextraction method using IL, 1-butyl-3-methylimidazoliumhexafluorophosphate [C₄mim][PF₆], as extracting solvent is proposed for simple and fast determination of low levels of TBZ in fruits and vegetables by spectrophotometry. The method is based on selective complex formation of TBZ with Cu(II) ions in presence of PF₆^– as counter ion at pH 5.5, and then microextraction of the complex into the fine micro-drops of IL phase. After optimisation of variables affecting microextraction efficiency, the analytical parameters of the method were determined by calibration curves. The method exhibits a linear relationship (0.3–280 μg L^?1), low detection limit (0.1 μg L^?1), good intra- and inter-day precision (2.4–4.5% as RSD_r%, 2.1–5.6% as RSD_R%), good recovery (≥95.1–98.2%) and high sensitivity enhancement factor (150) by solvent-based calibration curve. It allows a detection limit of 0.24 μg L^?1 and a range of 0.8–250 μg L^?1 by the matrix-matched calibration curve. After validation, the method was successfully applied to the determination of TBZ residues with method quantification limits in fruit and vegetables of 2.0 and 2.5 µg kg^?1 with and without adding polyvinylpyrrolidone (PVP-15) solution. Recoveries range from 85.5% to 98.2% after spiking (10, 50 and 100 µg kg^?1, n: 3).     

Quantitative determination of thermally derived off-flavor compounds in milk using solid-phase microextraction and gas chromatography

Many volatile compounds generated during the thermal processing of milk have been associated with cooked, stale, and sulfurous notes in milk and are considered as off-flavor by most consumers. A headspace solid-phase microextraction (HS-SPME)/gas chromatographic technique for the quantitative analysis of thermally derived off-flavor compounds was developed in this study. The extraction temperature, time, and sample amount were optimized using a randomized 2³ central composite rotatable design with 2 central replicates and 2 replicates in each factorial point along with response surface methodology. Calibration curves were constructed in milk using the standard addition technique, and then used to quantify 20 off-flavor compounds in raw, pasteurized, and UHT milk samples with various fat contents. The concentrations of these volatiles in raw and pasteurized milk samples were not significantly different. However, dimethyl sulfide, 2-hexanone, 2-heptanone, 2-nonanone, 2-undecanone, 2-methylpropanal, 3-methylbutanal, heptanal, and decanal were found at higher concentrations in UHT milk as compared with raw and pasteurized milk samples. In addition, the concentration of methyl ketones was greater in UHT milk with higher fat content. The calculated odor activity values suggested that 2,3-butanedione, 2-heptanone, 2-nonanone, 2-methylpropanal, 3-methylbutanal, nonanal, decanal, and dimethyl sulfide could be important contributors to the off-flavor of UHT milk. The HS-SPME technique developed in this study is accurate and relatively simple, and can be used for the quantification of thermally derived off-flavor compounds in milk.     

Application of the standard addition method for the determination of acrylamide in heat-processed starchy foods by gas chromatography with electron capture detector

A gas chromatography electron capture detector (GC-ECD) using the standard addition method was developed for the determination of acrylamide in heat-processed foods. The method entails extraction of acrylamide with water, filtration, defatting with n-hexane, derivatization with hydrobromic acid and saturated bromine-water, and liquid–liquid extraction with ethyl acetate. The sample pretreatment required no SPE clean-up and concentration steps prior to injection. The final extract was analyzed by GC-ECD. The chromatographic analysis was performed on polar columns, e.g. Supelcowax-10 capillary column, and good retention and peak response of the analyte were achieved under the optimal conditions. The qualification of the analyte was by identifying the peak with same retention time as standard compound 2,3-DBPA and confirmed by GC–MS. GC–MS analysis confirmed that 2,3-DBPA was converted to 2-BPA nearly completely on the polar capillary column, whether or not treated with triethylamine. A four-point standard addition protocol was used to quantify acrylamide in food samples. The limit of detection (LOD) was estimated to be 0.6 μg/kg on the basis of ECD technique. Validation and quantification results demonstrated that the method should be regarded as a low-cost, convenient, and reliable alternative for conventional investigation of acrylamide.     

Microbiological and mycotoxicological analyses of processed cereal-based complementary foods for infants and young children from the German market

This study investigated several food safety criteria in 38 different commercial products of processed cereal-based foods (PCF) from the German market. Microbiological assessment, followed by 16S RNA gene sequencing of suspect colonies, included aerobic mesophilic bacteria, moulds, Enterobacteriaceae, Cronobacter spp., and presumptive Bacillus cereus. Mycotoxin analyses were performed by enzyme immunoassays for deoxynivalenol (DON), zearalenone (ZEN), T-2/HT-2 toxins (T-2/HT-2; oat containing products only), ergot alkaloids (EA), and alternariol (AOH). No violative result above existing European Union regulations or international guidelines was obtained. Most samples had very low aerobic mesophilic cell counts (<2.0 × 10¹ CFU/g), the maximum was 9.6 × 10² CFU/g. A few samples contained low numbers of opportunistic pathogens, most notably Cronobacter sakazakii, Acinetobacter spp., Pantoea spp., and enterotoxigenic Bacillus wiedmannii. Levels of mycotoxin contamination were very low, well below European Union maximum limits. DON was found in 10 samples, at levels of 9–35 µg/kg. T-2/HT-2 were found in all 15 oat-based products (1–8 µg/kg). All samples were negative for ZEN and EA. A high number (n = 25) of samples yielded weakly positive results for the nonregulated AOH (0.4–2 µg/kg), but just three samples exceeded a level of 1 µg/kg. No relationship between cereal composition and analytical findings for microbiological parameters and mycotoxins could be found. As long as PCF meals are freshly prepared and consumed immediately after preparation, the risk from sporadically occurring opportunistic bacteria appears to be minimal.     

Rapid determination of benzo(a)pyrene in processed meat and fish samples by second-derivative constant-energy synchronous fluorescence spectrometry

A simple, rapid and cost-effective method has been established for the determination of the quantity of benzo(a)pyrene (BaP), one of the most carcinogenic polycyclic aromatic hydrocarbons (PAHs), in roasted, smoked and charcoal grilled foods. Second-derivative constant-energy synchronous fluorescence spectrometry (DCESFS) improves the spectral resolution and selectivity of the fluorescence method. By using this method, processed meat, fish and some other food samples were analysed without resorting to complex pre-separation and purification procedures. The method was found to have a recovery of 97.7%?±?4.3%. The limit of detection (LOD) for BaP was 0.14?µg?kg^–1, far below the regulatory limit (1.0?µg?kg^–1) for BaP in food samples specified by the European Union. A certified reference material (Coconut oil, BCR®-458) was used to confirm the validity of the proposed method. The results suggest that the measurements are in a good agreement with the certified BaP concentrations (5.4% deviation). The results obtained by the proposed method for analysing BaP in food samples correlated well with those obtained by GC/MS.     

Extraction and quantification of major carotenoids in processed foods and supplements by liquid chromatography

A simple, fast and robust method with minimum steps, small sample size and amounts of solvents was developed to determine major carotenoids contents in processed foods, tablets and gel capsules. The method involves dispersion of the sample in hot water (60 °C) with added butylated hydroxytoluene (BHT) in ethanol to minimize oxidation, followed by extraction with chloroform and analysis by liquid chromatography. Chromatographic parameters were: a C30 column protected with a C18 guard cartridge; gradient elution at the rate of 1.0 mL/min starting with 100% methanol (A) and ending with 40:60 (v/v) methanol/isopropanol (B); detection set at 450 nm for carotenoids, and 325 nm for retinol, retinyl acetate and retinol palmitate. The method exhibited: (i) high degree of repeatability (%rsd); (ii) linear calibration curves (r² ? 0.9998); (iii) low detection; and quantification limits. The method was validated with standard reference material 2383 for trans-β-carotene; and tested for α-, and β-carotenes, lutein, zeaxanthin, cryptoxanthin, trans-retinol in processed foods, tablets and gel supplements.     

Sweet processed foods in Brazil: use of sugar and sweeteners,inclusion of sugar claims and impact on nutritional profile

This study characterised the main sweet beverages and food products marketed in Brazil regarding (i) the addition of sugar/sweeteners, (ii) nutritional profile and (iii) sugar claims. Results revealed that most of the beverages had added sweeteners, while food products were mainly sweetened with sugar. Moreover, >90% of the powdered products had added sweeteners. ‘Zero sugar’ (46%) and ‘light’ (55%) were the most common sugar claims in sugar-free and reduced-sugar products, respectively. Powdered products, soya drinks and baked products included claims less frequently. Regarding the nutritional profile, beverages with sugar substitution had a proportionally greater reduction in the content of carbohydrates and calories (up to 99%, for both) in relation to food (<82% and <85%, respectively). The results suggest that reducing sugar in solid foods remains a greater challenge than in beverages and that this reduction has less impact on the final energy density of foods.     

Colorimetric assay for determination of trimethylamine-nitrogen (TMA-N) in fish by combining headspace-single-drop microextraction and microvolume UV–vis spectrophotometry

In this work, headspace-single-drop microextraction has been used in combination with microvolume UV–vis spectrophotometry to enhance the determination of trimethylamine-nitrogen (TMA-N) in fish samples. TMA-N is often used for monitoring fish freshness, but due to the low analytical sensitivity usually achieved, its determination must be performed after certain time of storage in some fish species. The proposed methodology, based on the extraction and subsequent complexation of volatile TMA-N onto a picric acid-containing xylene microdrop exposed to the headspace, involves an important improvement of sensitivity (detection limit 6 × 10⁻⁴ mg TMA-N per 100 g of fish), a miniaturization of the AOAC Official Method (971.14) and a simple approach for routine labs. This method is well suited to determination of TMA-N in different species of frozen and fresh fish samples from markets and to study the evolution of TMA-N concentration in farmed turbot at the earliest stages of deterioration.     

Migration of melamine from can coatings cross-linked with melamine-based resins,into food simulants and foods

Resins based on melamine-formaldehyde and related analogues such as methylolated melamine are used to cross-link coatings used inside food cans and on the metal closures of glass jars. Thirteen commercially coated cans and closures representing 80% of the European market were tested using simulants under realistic industrial heat-processing conditions for canned and jarred foods. The food simulants and the retort conditions used were 3% acetic acid for 1?h at 100°C and 10% ethanol for 1?h at 130°C. The highest migration level seen for melamine into simulant was 332?µg?kg^?1. There was no detectable migration of the melamine analogues cyanuric acid (<1?µg?kg^?1) or ammelide (<5?µg?kg^?1) from any sample. Twelve of the thirteen samples released no detectable ammeline (<5?µg?kg^?1) but the coating giving the highest release of melamine did also release ammeline at 8?µg?kg^?1 with the higher of the two process temperatures used. Migration experiments into food simulant and foods themselves were then conducted using two experimental coatings made using amino-based cross-linking resins. Coated metal panels were exposed to the food simulant 10% (v/v) aqueous ethanol and to three foodstuffs under a range of time and temperature conditions both in the laboratory and in a commercial food canning facility using proprietary time and temperature conditions. The highest migration into a food was 152?µg?kg^?1 from the first coating processed for a long time at a moderate sterilisation temperature. The highest migration into simulant was also from this coating at 220?µg?kg^?1 when processed at 134°C for 60?min, dropping to 190?µg?kg^?1 when processed at 123°C for 70?min. Migration from the second coating was quite uniformly two to three times lower under all tests. These migration results were significantly higher than the levels of melamine extractable using 95% ethanol at room temperature. The experiments show that commercial canning and retorting can be mimicked in an acceptable way using laboratory tests with an autoclave or a simple pressure cooker. The results overall show there is hydrolytic degradation of the melamine cross-linked resins to release additional melamine. There is a strong influence of the temperature of heat treatment applied with foods or simulants but only a minor influence of time of heating and only a minor influence, if any, of food/simulant acidity.     

食用菌中甲醛的提取和乙酰丙酮分光光度法分析

目的建立适用于多种食用菌的甲醛提取技术和甲醛含量的乙酰丙酮分光光度法测定技术。方法研究灭酶处理、浸泡时间和温度对食用菌样品中甲醛提取的影响,并用凯氏定氮仪蒸馏单元对处理后的食用菌样品进行水蒸汽蒸馏,替代了直接蒸馏法。结果食用菌鲜样和干样粉碎后直接用水蒸汽蒸馏提取,能快速提取样品中的甲醛,并能反映样品真实的甲醛含量;甲醛在1μg/ml浓度内呈线性相关,相对标准偏差(RSD)10%(n=5),回收率为82.10%~97.98%。结论本方法快速简便、准确度高、精密性好,适用于多种食用菌中甲醛含量的分析。     

离子液体单滴微萃取-超高效液相色谱联用测定食品塑料包装材料中5种邻苯二甲酸酯的研究

建立了一种基于离子液体单滴微萃取技术结合超高效液相色谱(IL-SDME-UPLC)对5种邻苯二甲酸酯类物质(PAEs)进行检测的方法,并成功应用于食品塑料包装材料中PAEs的分析。实验分别考察了离子液体种类、离子液体用量、萃取时间、萃取温度及盐效应对PAEs萃取效果的影响。结果表明,以30 uL 1-辛基-3-甲基咪唑六氟磷酸盐([C₈MIM][PF₆])为萃取剂,在25 ℃恒温水浴振荡5 min,不加入NaCl的条件下萃取效果最佳。在此优化条件下,结合UPLC测定了油桶及饮料瓶中的五种PAEs。结果显示,五种PAEs在2~100 μg/mL浓度范围内线性良好,相关系数R²>0.999,方法的检出限为0.3~0.92 μg/mL(S/N=3)。在10、20、30 μg/mL三个浓度水平下的加标回收率DMP为37.42%~43.50%;DBzP为65.04%~76.90%;DBP为67.22%~79.88%;DCHP为77.60%~89.82%;DOP为81.07%~87.62%,相对标准偏差(RSD)为0.01%~6.66%(n=3)。该方法绿色、简便、快捷、可操作性强,适用于食品塑料包装材料中邻苯二甲酸酯类的分析检测。     

葛根淀粉提取及直链、支链淀粉的双波长测定

以淀粉提取率为指标,采用正交实验研究了葛根淀粉的加工工艺,并确定了最佳工艺参数为:料水比为2:17,浸泡液的pH为8.5,浸泡时间为1h;同时采用双波长分光光度法对葛根中直链淀粉和支链淀粉的显色反应和光度测定的最佳条件进行了详细的考察,根据吸收光谱,确定直链淀粉的测定波长为617nm和476nm,支链淀粉的测定波长为415nm和532nm,建立回归方程并求得葛根淀粉中直链淀粉的含量为18.29%,支链淀粉的含量为77.24%。      

Survey of furan in foods and coffees from five European Union countries

Canned and jarred baby foods (74), canned and jarred adult foods (63) and 70 coffees sold in Belgium, Italy, Portugal, Spain and The Netherlands were analysed for their furan content using a validated automated headspace GC–MS procedure. Seven balsamic vinegars from Italy and Spain were also analysed. All 74 baby food samples contained detectable furan, with an average level of 37 ng/g. A total of 54 of 63 canned and jarred foods contained detectable furan with an average level of 24 ng/g. Levels of furan in coffee as consumed were very variable and reflected different preparation methods and coffee strengths. Over 50% of Italian samples contained more than 200 ng/g, whereas over 20% of Belgian coffees contained less than 21 ng/g furan. Some brews made from fine grained coffee contained much more furan than did brews made from normal or coarse grained coffee. Although furan was low in most instant coffees, two Italian products “instant espresso” and “instant mocha” contained about 150 ng/g furan. Balsamic vinegars from Spain contained 159–662 ng/g of furan; however, other samples from Spain and Italy contained only 6–25 ng/g.     

Interference-free determination of acrylamide in potato and cereal-based foods by a laboratory validated liquid chromatography–mass spectrometry method

A simple and rapid method was developed and validated for the determination of acrylamide in potato and cereal-based foods by using a single quadrupole liquid chromatography–mass spectrometry (LC–MS) interfaced with positive atmospheric pressure chemical ionization (APCI+). Acrylamide was simply extracted with 0.01 mM acetic acid in a vortex mixer prior to LC–MS analysis. The applicability of validated method was shown for a wide range of processed foods including chips, fries, crisps, breads, biscuits and cookies. The mean recovery was found to be 99.7 with a repeatability of 1.8% in the range 100–1000 ng/g. During LC–MS analyses, the major interfering co-extractive was identified as valine which yields characteristic [M + H]⁺ and compound specific product ions having m/z of 118 and 72, respectively. Valine increased the baseline signal preventing accurate and precise quantitation, and resulted in poorer sensitivity in selected ion monitoring mode. The adverse effect of valine could be limited by instrumentally adjusted delay time or by solid-phase extraction with strong cation-exchanger sorbent.     

Combined application of essential oils from Origanum vulgare L. and Rosmarinus officinalis L. to inhibit bacteria and autochthonous microflora associated with minimally processed vegetables

This study assessed the occurrence of an enhancing inhibitory effect of the combined application of Origanum vulgare (OV) and Rosmarinus officinalis (RO) essential oils against bacteria associated to minimally processed vegetables using the determination of Fractional Inhibitory Concentration (FIC) index, kill-time assay in vegetal broth and application in vegetable matrices. Moreover, it was determined chemical composition of the essential oils and their effects alone and in mixture on sensory characteristics of minimally processed vegetables. Carvacrol (66.9 g/100 g) was the most prevalent compound in OV essential oil, while for RO was 1.8-cineole (32.2 g/100 g). OV and RO essential oil showed MIC in a range of 1.25-5 and 20-40 ??L/mL, respectively. FIC indices of the combined application of the essential oils were 0.5 against Listeria monocytogenes, Yersinia enterocolitica and Aeromonas hydrophilla suggesting a synergic interaction. Only for Pseudomonas fluorescens FIC index was 0.75 purposing additive effect. Application of the essential oils alone (MIC) or in mixture (¼ MIC + ¼ MIC or ¼ MIC + ½ MIC) in vegetable broth caused significant decrease (p < 0.05) in bacterial count over 24 h. Mixture of essential oils reduced (p < 0.05) the inocula of all bacteria in vegetable broth and in experimentally inoculated fresh-cut vegetables. Similar efficacy was found to reduce the autochthonous microflora in vegetables. Sensory evaluation of vegetables sanitized with essential oils revealed that the scores of the most evaluated attributes fell between like slightly and neither like nor dislike. The combination of essential oils at sub-inhibitory concentrations could mean an interesting approach to sanitize minimally processed vegetables.