Determination of Seven <Emphasis Type="Italic">N</Emphasis>-nitrosamines in Agricultural Food Matrices Using GC-PCI-MS/MS

The quantitative analytical methods for seven N-nitrosamines including N-nitrosodimethylamine (NDMA), N-nitrosomethylethylamine (NMEA), N-nitrosodiethylamine (NDEA), N-nitrosodibutylamine (NDBA), N-nitrosopiperidine (NPIP), N-nitrosopyrrolidine (NPYR), and N-nitrosomorpholine (NMOR) were established for agricultural food matrices. Four food matrices were used for the method development: rice soup as a fatless solid matrix, apple juice as a fatless liquid matrix, corn oil as a fat-rich liquid matrix, and 20 % alcohol as an alcohol matrix. A combination of solid-supported liquid-liquid extraction (SLLE) using Extrelut NT and a solid phase extraction (SPE) using Florisil was employed for fatless matrices. For an alcohol matrix, only SLLE was used without SPE, and liquid-liquid extraction (LLE) was established for a fat-rich matrix. The extract was analyzed by gas chromatography-positive chemical ionization-tandem mass spectrometry (GC-PCI-MS/MS) using ammonia gas as an ion source. Linearity, recovery, repeatability, inter-day precision, reproducibility, and uncertainty were evaluated for method validation using four matrices. Method detection limits for all of the investigated N-nitrosamines were ranged from 0.10 to 0.18 μg/kg for the rice soup, from 0.10 to 0.19 μg/kg for the apple juice, 0.10 μg/kg for the corn oil, and from 0.10 to 0.25 μg/kg for 20 % alcohol, depending on N-nitrosamines. Established methods were applied to determine seven N-nitrosamines in some agricultural food products.     

Simultaneous Determination of Five Neonicotinoid Insecticides in Edible Fungi Using Ultrahigh-Performance Liquid Chromatography-Tandem Mass Spectrometry (UHPLC-MS/MS)

A robust analytical method for simultaneously determining five neonicotinoid insecticides (clothianidin, dinotefuran, imidacloprid, thiacloprid, and thiamethoxam) in commonly consumed edible fungi (Agaricus bisporus, Flammulina velutipes, Hypsizygus marmoreus, Lentinus edodes, and Pleurotus eryngii) was provided in the present study. Samples were pretreated using a modified QuEChERS (quick, easy, cheap, efficient, rugged, and safe) method with the detection of neonicotinoids by ultrahigh-performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS). A number of optimizations performed to sample pretreatment and detection conditions were discussed. Limits of detection (LODs) for all analytes in edible fungi were between 0.03 and 0.7 μg kg^?1, while limits of quantitation (LOQs) ranged from 0.1 to 2 μg kg^?1. Mean recoveries for clothianidin, dinotefuran, imidacloprid, thiacloprid, and thiamethoxam were in the range of 100.5–118.0, 73.9–89.5, 88.6–117.8, 72.9–121.8, and 98.9–117.2%, respectively, with RSDs less than 8.1%. This method could be used for fast screen of the five neonicotinoid insecticides in edible fungi for risk assessing aims.     

Rapid Determination of Free Amino Acids,Nucleosides, and Nucleobases in Commercial Clam Species Harvested at Different Seasons in Jiangsu,China, Using UFLC-MS/MS

In this study, a sensitive and rapid method for the simultaneous quantification of 17 nucleosides and nucleobases and 23 free amino acids in clam samples using ultra-fast liquid chromatography coupled with tandem mass spectrometry (UFLC-MS/MS) was developed. Sufficient separation of 40 analytes was achieved on an Acquity BEH Amide column (2.1 mm?×?100 mm, 1.7 μm) in a single run of 15 min. The overall limits of detection (LODs) and limits of quantification (LOQs) were between 0.05~38.8 and 0.15~128 ng/mL for the 40 analytes, respectively. The newly developed method was validated and subsequently applied for the analysis of the content variation of 40 analytes in four commercial clam species (Mactra veneriformis, Ruditapes philippinarum, Meretrix meretrix, and Cyclina sinensis) collected monthly from January to December 2014 at the coast of Jiangsu, China. Significant seasonal variation was observed for most analytes. Major nucleosides and nucleobases were at their highest contents in June or July, the contents of free amino acids showed the same pattern. Thus, if high concentrations of these functional small molecules are desired, Jiangsu native clams should be harvested in early summer. The results suggest that the present UFLC-MS/MS method could be employed as a useful tool for quality assessment of the clam samples as well as other food samples using nucleobases, nucleosides, and free amino acids as markers.     

A New Chemical Marker-Model Food System for Heating Pattern Determination of Microwave-Assisted Pasteurization Processes

New chemical marker-model food systems with d-ribose and NaOH precursors as color indicators and gellan gels as chemical marker carrier were explored for the assessment of the heating pattern of in packaged foods processed in microwave-assisted pasteurization system (MAPS). In determining appropriate precursor concentrations, a solution of 2% (w/w) d-ribose and 60 mM NaOH was heated at 60–90 °C for 0–20 min. The solution absorbance at 420 nm increased linearly, while the color parameters L* decreased linearly with heating time at all processing temperatures. In storage, the produced brown color was stable at 4 and 22 °C within 7 days. The new chemical marker-model foods were prepared by mixing 2% (w/w) d-ribose and 60 mM NaOH with 1% (w/v) low-acyl gellan gum and 20 mM CaCl₂·2H₂O solution. The dielectric constant of the model food samples decreased with the addition of sucrose, and the loss factors increased with the addition of salt. After processing in the pilot MAPS, the heating pattern and cold and hot spots in the new chemical marker-model food system could be clearly recognized and precisely located through a computer vision method. This is the first time that the caramelization reaction was used as a time-temperature indicator in gellan gel model food. This study shows the possibility of using the new chemical marker-model food system for heating pattern determination of the MAPS.     

Preparation of Acryloyl <Emphasis Type="Italic">β</Emphasis>-Cyclodextrin Organic Polymer Monolithic Column and Its Application in Solid-Phase Microextraction and HPLC Analysis for Carbofuran and Carbaryl in Rice

An acryloyl β-cyclodextrin (A-β-CD) monolithic column for solid-phase microextraction (SPME) and determination of carbofuran and carbaryl by high-performance liquid chromatography (HPLC) have been prepared through a “one-step” polymerization method. The synthesis conditions, including the volume of cross-linker, the ratio and volume of mixed porogenic solvent consisted of methanol and N,N-dimethylformamide were optimized. The prepared monolithic column was characterized by thermogravimeteric analysis (TGA), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and Brunner-Emmet-Teller (BET) measurement. The eluent type, volume and flow rate, sample volume, flow rate, acidity, and ionic strength were optimized in detail. Under the optimized conditions, a simple, rapid, and sensitive SPME-HPLC method was developed for determination of carbofuran and carbaryl in rice samples. The method yielded a linear calibration curve in the concentration ranges of 1.5–200 μg/kg for carbofuran and 0.3–200 μg/kg for carbaryl with correlation coefficients (R ²) of above 0.9955. Limits of detection (S/N = 3) were 0.5 μg/kg for carbofuran and 0.1 μg/kg for carbaryl, respectively. The recoveries of this method ranged from 88.1 to 105.8%. The relative standard deviations were less than 8.1%.     

Simultaneous Determination of Aflatoxin B1, Bisphenol A,and 4-Nonylphenol in Peanut Oils by Liquid-Liquid Extraction Combined with Solid-Phase Extraction and Ultra-High Performance Liquid Chromatography-Tandem Mass Spectrometry

An analytical method based on liquid-liquid extraction combined with solid-phase extraction and isotope dilution-ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was well developed for simultaneous determination of aflatoxin B1 (AFB1), bisphenol A (BPA), and 4-nonylphenol (4-NP) in peanut oil. After adding isotope internal standards, the samples were firstly diluted by normal hexane and then extracted by acetonitrile and Carb/PSA solid-phase extraction cartridge in sequence to obtain the extracted solution. All the extracted solution was merged and was subsequently dried to near dryness by a mild nitrogen stream. Three target analytes were separated on a Phenomenex Luna C18 chromatographic column, quantified by an internal standard method and detected by ESI positive (ESI⁺) and negative (ESI^?) subsection acquisition modes under multi-reaction monitoring (MRM) conditions. Results demonstrated that the three target analytes exhibited excellent linearity in their corresponding concentration ranges of 0.1–100.0 μg/L with correlation coefficients all greater than 0.998. The corresponding method limits of quantitation (MLOQ, S/N?=?10) of AFB1, BPA, and 4-NP were 0.2, 1.0, and 2.0 μg/kg, respectively. Moreover, the mean recoveries for negative samples spiked at three concentration levels were calculated between 87.7 and 105.1% with relative standard deviation (RSD, n?=?6) ranging from 2.2 to 7.9% and the interday precision (n?=?5) ranging from 5.0 to 8.7%. Finally, the method was successfully applied to analyze 52 peanut oil samples, and AFB1 and 4-NP were detected in 43 samples with the concentrations in the ranges of 0.5–69.4 and 9.3–77.8 μg/kg, respectively. None of BPA was detected in any samples.     

Reusable 2-(Dimethylamino)ethyl Methacrylate Polymers On-line Solid-Phase Extraction Coupled to Liquid Chromatography Tandem Mass Spectrometry for Rapid Determination of Acidic Pesticides in Foods

A rapid and easy method was developed for the sensitive determination of six acidic pesticides (2,4,5-trichlorophenoxyacetic acid, acifluorfen, methyl-4-chlorophenoxyacetic acid, fluroxypyr, haloxyfop, and bispyribac-sodium) in pear, apple, cucumber, and rice samples. This method was a full automatic platform using a novel polymeric monolith-based on-line solid-phase extraction (SPE) coupled to liquid chromatography-tandem mass spectrometry (LC-MS/MS). A poly(2-(dimethylamino)ethyl methacrylate-co-ethylene dimethacrylate) monolith was fabricated as the sorbent, and the morphology, surface area, and extraction performance of the polymers were characterized. With the addition of 10.0 mL of acetonitrile and 1.0 to 5.0 g of anhydrous NaCl, the food samples were homogenized and centrifuged. The extracted samples were directly loaded and cleaned on the polymers using a 5 mmol L^?1 ammonium acetate solution and subsequently eluted into the analytical column for next separation with an acetonitrile-1.5% formic acid solution as eluting solvent. The detection limit (S/N?=?3) was 0.2 to 2.0 μg kg^?1 for the analytes, and the intra- and inter-day recoveries in pear, apple, cucumber, and rice samples ranged from 80 to 104%, and 83 to 115% with relative standard deviations of less than 13.5%. The developed on-line SPE LC-MS/MS protocol permits an automated and high-throughput determination in only 15 min. Moreover, the intra-batch (n?=?5) and inter-batch precisions (n?=?3) for the preparation of the polymers were lower than 11.6% and the sorbent was sufficiently stable for 500 extraction cycles without a significant loss in the extraction efficiency. The developed method was successfully applied to monitor six acidic pesticides in vegetable, fruit, and cereal samples.     

Development and characterization of reconstituted hydrogel from <Emphasis Type="Italic">Aloe vera</Emphasis> (<Emphasis Type="Italic">Aloe barbadensis</Emphasis> Miller) powder

Structural and rheological characterization of reconstituted hydrogels developed from A. vera non-fibrous alcohol insoluble residue (NFAIR) powder using different methods [viz., shaking (S), heating-shaking (HS), and heating (H)] and concentrations (viz., 0.2–1.6 %, w/v) was carried out. Functional group distribution by FTIR spectroscopy and Congo red (CR) method revealed the presence of acetylated acemannan in A. vera powder. Dynamic oscillation studies of A. vera (NFAIR) fluids at all concentrations of 0.2–1.6 %, w/v, showed gel strength in the order of H > HS > S method. However, in H method, increase in concentration from 0.2 to 1.6 %, w/v showed the conformational transition from semi-diluted solution to weak gel nature. Rheological models described the effect of heating temperatures (HT); 30–90 °C, and times (Ht); 15–60 min on viscoelastic behavior in reconstituted A. vera fluids. The reconstituted A. vera hydrogel prepared with a concentration of 1.6 %, w/v using 50 °C (HT) and 30 min (Ht) condition showed a good agreement with the Power law (storage modulus, G′) and Weak gel model (complex modulus, G*) fitted data (R² > 0.94) resulting higher viscoelastic moduli intercepts; G′₀ (71.5 Pa s ^n′), G″₀ (33.5 Pa s ^n″), lower slopes; n′ (0.22), n″ (0.06), higher network strength (A _F , 121.3 Pa s^1/z ) and number of network (z, 5.3) values. The obtained results suggested that heating at 50 °C/30 min can develop aqueous weak gel networks of A. vera with enhanced gel strength which may be utilized as a novel gelling agent for wide variety of targeted applications in food and pharmaceutical sectors.     

Rapid Screening and Determination of the Residues of Hormones and Sedatives in Milk Powder Using the UHPLC-MS/MS and SPE

A method based on the ultra-high-performance liquid chromatography tandem mass spectrometry for determination of the residues of sex hormones, glucocorticoids, and sedatives in milk powder was developed. The sample was extracted with the acetic acid-acetonitrile (1:99, v/v) twice, purified by the PRiME hydrophilic-lipophilic balance (HLB) cartridges and analyzed by the ultra-high-performance liquid chromatography-tandem mass spectrometry. The analytes were separated by the Waters Acquity UPLC? BEH C18 column (50 mm?×?2.1 mm, 1.7 μm) and determined using the electrospray ionization in the positive mode with the multiple reaction monitoring (MRM). The developed method was validated with the specificity, linearity and range, matrix effects, recovery, and precision. The results showed that the analytes were linear with the correlation of determinations (R²) higher than 0.991 in the corresponding ranges. The limits of detection (LODs) and limits of quantification (LOQs) were in the range of 0.1–1.1 μg kg^?1 and 0.3–3.8 μg kg^?1, respectively. The average recoveries of the analytes ranged from 78.5 to 107.0% with the relative standard deviations lower than 15%. The practical applicability was tested by analyzing real samples and the progesterone was observed in two samples.     

Simple and Fast Determination of Acrylamide and Metabolites in Potato Chips and Grilled Asparagus by Liquid Chromatography Coupled to Mass Spectrometry

The purpose of this study was to evaluate an analytical procedure for the determination of acrylamide in different starchy foods such as potato chips and grilled asparagus. The method is based on high-performance liquid chromatography coupled to triple quadrupole tandem mass spectrometry (HPLC-QqQ-MS/MS). A solid–liquid extraction procedure, using water as extraction solvent, has been developed followed by a cleanup procedure based on solid-phase extraction (SPE) or dispersive solid-phase extraction (d-SPE). Polymeric cartridges (Oasis HLB) and aluminum oxide (Al₂O₃) were used for potato and asparagus matrices, respectively. The optimized procedures were validated, and limits of detection and quantitation were 4 and 12 μg/kg for potato chips and 2 and 5 μg/kg for grilled asparagus, respectively. Recoveries were evaluated, and good values were obtained, ranging from 90 to 117 % for potato chips and from 90 to 116 % for grilled asparagus. The method was applied to real samples, and concentrations ranged from 105 to 860 μg/kg in potato chips, whereas higher values were detected in grilled asparagus (from 292 to 1469 μg/kg). Furthermore, single-stage Orbitrap high-resolution mass spectrometry has been used for the putative identification of acrylamide-N-acetyl-S-(2-carbamoylethyl)-l-cysteine (AAMA) in urine.     

A Gompertz Model Approach to Microbial Inactivation Kinetics by High-Pressure Processing Incorporating the Initial Counts,Microbial Quantification Limit,and Come-Up Time Effects

During come-up time (CUT), the time to reach a desired processing pressure, isobaric-isothermal conditions cannot be assumed in the estimation of kinetic parameters for the design of commercial high-pressure processing (HPP) treatments. Since CUT effects on microbial population, enzyme activity, and chemical concentration are often ignored, kinetic models incorporating the non-isobaric and non-isothermal conditions prevailing during CUT were the objective of this work. The analysis of peer-reviewed data on the HPP inactivation of bacteria (counts observations n = 919, 60 survival curves) and bacterial spores (n = 273, 12 curves) showed that a Gompertz model (GMPZ) approach is an effective alternative. The GMPZ parameter A was fixed as the difference between the initial population (log₁₀ N _o ) and the lower quantification limit of microbial counts (log₁₀ N _lim), while exponential equations were used to describe pressure effects on the lag time (λ) and the maximum inactivation rate (μ_max). In low-acid media (pH > 4.5), λ decreased exponentially with pressure, allowing the identification of a theoretical pressure level (P _λ) sufficient to initiate microbial inactivation during CUT. The parameter μ_max exponentially increased with pressure for all evaluated datasets. Dynamic pressure effects during CUT were simplified by assuming isobaric conditions during CUT (t _CUT), allowing to obtain GMPZ parameter estimates using only nonlinear regression (R ² ～ 0.938, σ ² = 0.030–0.604). The proposed approach is a simpler, promising tool for a more informative analysis of the kinetics of microbial inactivation by HPP and should be further validated with additional experimental data.     

Optimization of Extraction Parameters of Total Phenolics from <Emphasis Type="Italic">Annona crassiflora</Emphasis> Mart. (Araticum) Fruits Using Response Surface Methodology

In this study, response surface methodology was used to optimize the extraction temperature (25–75 °C) and ethanol concentration (0–70 %, ethanol/water, v/v) to maximize the extraction of total phenolic compounds (TPC) from araticum pulp. The efficiency of the extraction process was monitored over time, and equilibrium conditions were reached between 60–90 min. A second-order polynomial model was adequately fit to the experimental data with an adjusted R ² of 0.9793 (p < 0.0001) showing that the model could efficiently predict the TPC content. Optimum extraction conditions were ethanol concentration of 46 % (v/v), extraction temperature of 75 °C and extraction time of 90 min. Under the optimum conditions, the araticum pulp showed high TPC content (4.67 g GAE/100 g dw) and also high antioxidant activity in the different assays used (46.56 μg/mL, 683.65 μmol TE/g and 1593.72 μmol TE/g for DPPH IC₅₀, TEAC and T-ORAC_FL, respectively). From our extraction procedure, we successfully recovered a significantly higher amount of TPC compared to other studies in the literature to date (1.5–22-fold higher). Furthermore, TPC and antioxidant activity were present in the fruit in levels that are difficult to find in other common fruits. These results expose a potential approach for improving human health through consumption of araticum fruit.     

Characterization and evaluation of antimicrobial activity of actinonin against foodborne pathogens

This study revealed the antimicrobial properties of actinonin against major foodborne pathogens, Escherichia coli O157:H7, Listeria monocytogenes, Salmonella Typhimurium, Staphylococcus aureus, and Vibrio vulnificus. Among them, actinonin caused growth defect in S. Typhimurium and V. vulnificus. Minimal inhibitory concentration (MIC) values of actinonin were determined by broth microdilution methods. The MICs of actinonin were ≤0.768 μg/ml for S. Typhimurium and ≤0.192 μg/ml for V. vulnificus. Susceptibility to actinonin in both pathogens was measured by colony-forming ability and disc diffusion test. The results showed actinonin had antimicrobial activity against S. Typhimurium and V. vulnificus in a dose-dependent manner. The inhibitory effects on swarming motility were determined, and cytotoxicity of each pathogen against HeLa cells was decreased significantly by actinonin treatment. Furthermore, actinonin showed an antimicrobial efficacy in food models infected with these pathogens. These results demonstrate that actinonin is potentially an effective agent for food sanitization or preservation.     

Application of Vacuum Frying as a Furan and Acrylamide Mitigation Technology in Potato Chips

Consumers like fried snacks, and taste, color, and texture are key aspects in their preference. However, during frying of foods some toxic compounds, such as furan and acrylamide, are produced. The objective of this work was to mitigate furan and acrylamide formation in potato chips, without affecting their main quality attributes, by using vacuum frying. To accomplish this purpose, potato slices were fried at atmospheric (P _abs 29.92 inHg) and vacuum conditions (P _abs 3.00 inHg), using equivalent thermal driving forces (T _{water boiling point} ? T _oil = 50, 60, or 70 °C). Furan and acrylamide concentration, oil content, and texture of both atmospheric and vacuum-fried samples were determined. Vacuum-fried potato chips showed reductions of about 81, 58, and 28% of furan, acrylamide, and oil content, respectively, when compared to their atmospheric counterparts. Additionally, the texture was not affected (p > 0.05) by changes in the pressure during frying. Results clearly showed that vacuum frying is an effective technology for furan and acrylamide mitigation in potato chips, since it reduces the content of both contaminants and preserves the quality attributes of fried snacks.     

Extraction and in vitro antioxidant capacity evaluation of phenolic compounds from pigmented aromatic rice (<Emphasis Type="Italic">Oryzae sativa</Emphasis> L.) cultivars

The aroma generating volatile components profile and in vitro antioxidant capacities of different aromatic rice cultivars was determined by GC–MS analysis and in terms of DPPH scavenging activity, lipid peroxidation inhibition, phosphomolybdenum reduction and reducing power assay. The total phenolic content including both free and bound forms in the analyzed aromatic rice cultivars, Mushki budgi (1.62 mg GAE/g), Mushki kandi (1.63 mg GAE/g) and Kamad (1.60 mg GAE/g) were found double the amount as compared to non-aromatic Koshkari (0.86 mg GAE/g) cultivar. The aromatic rice cultivars had also shown higher total flavonoid content and antioxidant activity than non-aromatic rice cultivar (Koshkari). The GC–MS results indicated 21-aromatic compounds present in sufficient quantities in aromatic cultivars and some of them were unique to these cultivars. Among the compounds identified, aldehydes were found in higher quantity followed by alkanes, ketones and esters. Among the aromatic rice cultivars, Mushki budgi and Mushki kandi were found possessing higher quantity of flavoring components such as benzaldehyde, a carcinostatic agent. The cultivars Mushki budgi and Mushki kandi indicated positive correlation of TPC, TFC and the in vitro antioxidant components largely, while the less aromatic Kamad, correlate with only two components viz DPPH and lipid peroxidation.     

A New and Simple Approach for Decontamination of Food Contact Surfaces with Gliding Arc Discharge Atmospheric Non-Thermal Plasma

In this study, a gliding arc discharge (GAD) microplasma system was designed, and its decontamination effect was investigated on stainless steel (SS), silicone (Si), and polyethylene terephthalate (PET) surfaces artificially contaminated with 8.15 ± 0.28 log cfu/mL of Escherichia coli and 6.18 ± 0.21 log cfu/mL of Staphylococcus epidermidis. Each of the contaminated surfaces was treated with high purity air (79% nitrogen and 21% oxygen) or nitrogen plasmas for 1–10 min at varying rates of gas flow. Significant reductions of 3.76 ± 0.28, 3.19 ± 0.31, and 2.95 ± 0.94 log cfu/mL in S. epidermidis, and 2.72 ± 0.82, 4.43 ± 0.14, and 3.18 ± 0.96 log cfu/mL in E. coli on SS, Si, and PET surfaces, respectively, were achieved after 5 min of plasma treatment by using nitrogen as the plasma forming gas (p < 0.05). The temperature changes of each surface during plasma generation were lower than 35 °C and were not affected by the type of plasma forming gas. Additionally, morphological changes in the structure of E. coli and S. epidermidis after GAD plasma treatments were demonstrated using scanning electron microscopy (SEM).     

Steady- and Unsteady-State Determination of the Water Vapor Permeance (<Emphasis Type="Italic">WVP</Emphasis>) of Polyethylene Film to Estimate the Moisture Gain of Packed Dry Mango

The water vapor permeance (WVP; g m^?2 d^?1 Pa^?1) of packaging films quantifying the water vapor transfer rate between foods and its surroundings is usually determined in units operating under steady-state conditions that do not necessarily reflect food handling scenarios. This study evaluated the determination of the WVP of a polyethylene (PE) film by steady-state method ASTM F1249-06 using a permeability cell and unsteady-state method ASTM E96/E96M in which 102 vacuum-sealed PE bags containing silica gel were stored (37.8 °C, 75% relative humidity) and weighed over 25 days. Average steady-state WVP (2.935 ± 0.365 × 10^?3, n = 4) fell within the 95% quantiles of unsteady-state WVP values (1.818–3.183 × 10^?3, n = 2142). Moisture uptake of dehydrated mango stored at 37.8 °C and 75% relative humidity was predicted with WVP values obtained by both methods. Predictions were validated by monitoring over 25 days the weight gain of 100 PE bags with dry mango. Experimental moisture averages during storage fell within one standard deviation of predictions using the unsteady-state WVP (R ² = 0.974). The same was observed only until day 15 for predictions obtained with the steady-state WVP. Calculations for days 20–25 overestimated the moisture uptake by 6.0–7.2%, resulting in registered R ² = 0.924. The unsteady-state WVP determination is low-cost, uses large numbers of film samples, and allowed more accurate predictions of dry mango moisture uptake. Knowledge of the moisture uptake controlled by the film WVP is essential when predicting the safety and quality changes limiting the shelf-life of foods.     

Verification of 5-Methyltetrahydrofolic Acid in Nutritional Products

A simple method for the verification of supplemental (6R,S)-5-methyl-5,6,7,8-tetrahydrofolic acid, “5-MTHF,” in nutritional products is described. Nutritional product samples are prepared for the liquid chromatographic/fluorescence detection (LC/FLD) determination of 5-MTHF by buffer dilution, 10-min centrifugation, and syringe filtration. Method performance has been defined by assessments of 5-MTHF linearity (r ² averaged 0.9999 ± 0.0001, and all relative calibration errors averaged ≤0.6%, for ten consecutive six-point standard curves), intermediate precision (rsd = 1.1%, n = 9, for three products fortified at ～1.73 μmol/kg = ～795 μg/kg, tested on each of 3 days), accuracy (spike recovery average = 92.8 ± 1.0%, n = 9, for nutritional products spiked with 5-MTHF at ～1.73 μmol/kg, or ～795 μg/kg), and selectivity (absence of interference from reagent blanks, and from four compounds structurally related to 5-MTHF). The 5-MTHF recovery, as % of unheated controls, from a simulated heat treatment (20 min at 120 °C) averaged 99.1 ± 0.6%, n = 4. The limits of 5-MTHF detection (S/N = 3) and quantification (S/N = 10) were experimentally determined to be 10 μg/kg (～0.020 μmol/kg) and 30 μg/kg (～0.060 μmol/kg), respectively (<10× the expected fortification rate). The method provides a simple and inexpensive means for verifying proper fortification, and for assessing the stability to processing and storage conditions, of free 5-MTHF in nutritional products. A finding of interest is the indication that liquid nutritional products may comprise a stable matrix for 5-MTHF fortification.     

Saltatory Rolling Circle Amplification (SRCA): a Novel Nucleic Acid Isothermal Amplification Technique Applied for Rapid Detection of <Emphasis Type="Italic">Shigella</Emphasis> Spp. in Vegetable Salad

Shigella spp. are enteric pathogens that pose a serious threat to public health worldwide. A novel saltatory rolling circle amplification (SRCA) assay was developed to detect Shigella spp. in food targeting the ipaH gene. SRCA as an isothermal amplification method requires no expensive thermocycle instrument and could avoid electrophoresis as visualization results was successfully applied for SRCA. In order to confirm the specificity of this assay, 34 strains including 11 strains belonging to different Shigella species and 23 non-Shigella bacteria were detected with pure cultures. The sensitivity of Shigella flexneri by SRCA was evaluated using agarose gel electrophoresis, which was 7.3 × 10¹ fg/μL. In addition, the amplification results were also determined by adding the fluorochrome, SYBR Green I (1 μL of 1000×), allowing naked eye visualization of results, and the sensitivity was 7.3 × 10⁰ fg/μL. Moreover, the sensitivity of PCR was 7.3 × 10² fg/μL, showing that the sensitivity of SRCA by electrophoresis and SYBR Green I fluorescence were 10- and 100-fold higher than that of PCR, respectively. The detection limit of SRCA was also evaluated with artificially inoculated vegetable salad without enrichment, and it was 4.7 × 10² and 4.7 × 10¹ CFU/g by electrophoresis and fluorescence, respectively. The detection limit by PCR was 4.7 × 10³ CFU/g, which was 10- and 100-fold higher than that of SRCA. Therefore, SRCA is a potentially reliable tool for rapid and specific detection of Shigella in food and could be useful in underdeveloped countries with limited resources.     

Determination of Six Paraben Residues in Fresh-cut Vegetables Using QuEChERS with Multi-walled Carbon Nanotubes and High-Performance Liquid Chromatography–Tandem Mass Spectrometry

In this study, an optimized QuEChERS sample preparation method was developed to analyze residues of six parabens: methyl-, ethyl-, n-propyl-, isopropyl-, n-butyl-, and isobutylparaben in five fresh-cut vegetables (potato, broccoli, carrot, celery, and cabbage) with high-performance liquid chromatography–tandem mass spectrometry (HPLC–MS/MS). Homogenized samples were extracted using acetonitrile, and the extracts were cleaned with the novel sorbent multi-walled carbon nanotubes (MWCNTs). MWCNTs provided 84–94% removal of chlorophyll and lower matrix effects (MEs) compared to commonly used primary-secondary-amine (PSA) sorbent. Selected parabens were separated by HPLC with isocratic elution using acetonitrile and 0.1% (v/v) formic acid solution and determined by triple quadrupole MS/MS. The method validation results showed that recoveries were at 70–120% with RSDs <20%. Calibration curves showed linear responses of six parabens with R ² > 0.99. Fifty fresh-cut vegetable samples from different farmer markets in Beijing, China were collected to measure the paraben residues, and only one sample was tested positive with methylparaben concentration at 81 μg/kg.