For the first time, alginate polymer has been applied to prevent dyes from leaching out of colorimetric oxygen indicator films, which enable people to notice the presence of oxygen in the package in an economic and simple manner. The dye-based oxygen indicator film suffers from dye leaching upon contact with water. In this work, UV-activated visual oxygen indicator films were fabricated using thionine, glycerol, P25 TiO2, and zein as a redox dye, a sacrificial electron donor, UV-absorbing semiconducting photocatalyst, and an encapsulation polymer, respectively. When this zein-coated film was immersed in water for 24h, the dye leakage was as high as 80.80±0.45%. However, introduction of alginate (1.25%) as the coating polymer considerably diminished the dye leaching to only 5.80±0.06%. This is because the ion-binding ability of alginate could prevent the cation dye from leaching into water. This novel water-resistant UV-activated oxygen indicator was also successfully photo-bleached and regained colour fast in the presence of oxygen.

A rapid planar chromatographic method for identification and quantification of 25 water-soluble dyes in food was developed. In a horizontal developing chamber, the chromatographic separation on silica gel 60F(254) high-performance thin-layer chromatography plates took 12 min for 40 runs in parallel, using 8 mL ethyl acetate-methanol-water-acetic acid (65 + 23 + 11 + 1, v/v/v/v) mobile phase up to a migration distance of 50 mm. However, the total analysis time, inclusive of application and evaluation, took 60 min for 40 runs. Thus, the overall time/run can be calculated as 1.5 min with a solvent consumption of 200 μL. A sample throughput of 1000 runs/8 h day can be reached by switching between the working stations (application, development, and evaluation) in a 20 min interval, which triples the analysis throughput. Densitometry was performed by absorption measurement using the multiwavelength scan mode in the UV and visible ranges. Repeatabilities [relative standard deviation (RSD), 4 determinations] at the first or second calibration level showed precisions of mostly <or=2.7%, ranging between 0.2 and 5.2%. Correlation coefficient values (R >= 0.9987) and RSD values (<or=4.2%) of the calibration curves were highly satisfactory using classical quantification. However, digital evaluation of the plate image was also used for quantification, which resulted in RSD values of the calibration curves of mostly <or=3.0%, except for two <or=6.0%. The method was applied for the analysis of some energy drinks and bakery ink formulations, directly applied after dilution. By recording of absorbance spectra in the visible range, the identities of the dyes found in the samples were ascertained by comparison with the respective standard bands (correlation coefficients >or= 0.9996). If necessary for confirmation, online mass spectra were recorded within a minute.

In the present study, a new ultrasound assisted extraction (UAE) method was developed for preconcentration of selenite, Se(iv), from sample matrices prior to analysis. The method is based on complex formation between phenoxazine dye, resazurin, and triiodide, I₃⁻, which is produced by oxidation of iodide with Se(iv) in the presence of cetylpyridinium chloride (CPC) at pH 5.0, and then the extraction of the complex into the micellar phase of the extracting agent. The proposed process offers good sensitivity, ease of use and short analysis time. The variables affecting complex formation and extraction efficiency were studied and optimized in detail. Under optimal conditions, a good linear relationship was obtained in the range of 2.5–120 μg L⁻¹ with a detection limit of 0.76 μg L⁻¹. The precision was found to be 3.5% (n: 5, 10 and 40 μg L⁻¹). After preconcentration of a 15 mL sample, a sensitivity enhancement factor of 34.1 was obtained. The method offers good sensitivity, ease of use and short analysis time. Total inorganic Se was determined after the reduction of Se(vi) to Se(iv) using hydrochloric acid. The validation was evaluated by analysis of two standard reference materials (SRMs) and the recovery test. Finally, the method was successfully applied to the determination of inorganic Se in selected samples, and recoveries higher than 93.7% to 103% were obtained.

AIM: To improve the efficacy of intercalating dyes to distinguishing between infectious and inactivated hepatitis A virus (HAV) in food. METHODS AND RESULTS: Different intercalating dyes were evaluated for the discrimination between infectious and thermally inactivated HAV suspensions combining with the RT‐qPCR proposed in the ISO 15216. Among them, PMAxx was the best dye in removing the RT‐qPCR signal from inactivated HAV. Applied to lettuce and spinach, PMAxx–Triton pretreatment resulted in complete removal of the RT‐qPCR signal from inactivated HAV. Likewise, this study demonstrates that this pretreatment is suitable for the discrimination of inactivated HAV in shellfish without further sample dilution. In mussels and oysters, the developed viability RT‐qPCR method reduced the signal of inactivated HAV between 1·7 and 2·2 logs at high inoculation level, and signal was completely removed at low inoculation level. CONCLUSIONS: This study showed that the use of PMAxx is an important improvement to assess HAV infectivity by RT‐qPCR. It was shown that PMAxx–Triton pretreatment is suitable for the analysis of infectious HAV in complex food samples such as vegetables and shellfish. SIGNIFICANCE AND IMPACT OF THE STUDY: The PMAxx–Triton pretreatment can be easily incorporated to the ISO norm for infectious virus detection.

A simple and inexpensive liquid chromatography diode array detector (LC-DAD) procedure has been developed to analyse food dyes in beverages, candies, jams, salted fish, Chinese sausage, and cake. A reverse stationary phase provided sufficient selectivity and chromatographic performance for the separation of 11 water-soluble dyes (tartrazine, amaranth, indigo carmine, ponceau 4R, sunset yellow, allura red, carmoisine, fast green FCF (Food green 3), brilliant blue, quinoline yellow, and indocyanine green). The samples were extracted with 1% ammonium solutions and acetonitrile, purified, and concentrated using a C₁₈ solid-phase extraction (SPE) cartridge for beverages, and weak anion exchange SPE cartridge for solid samples. They were determined using a reverse-phase C₁₈ column with gradient elution of 0.2% ammonium acetate buffer, and acetonitrile as the mobile phase. Multiple-specific wavelengths were used to monitor the dyes in the visible range to provide higher sensitivity and an expanded scope for a large number of analytes. The limit of detection and limit of quantification of the dyes were in the range of 0.2 - 0.5 and 0.5 - 1.0 µg/mL, respectively. The precision of the method ranged from 2.71 to 6.31%, while recovery ranged from 90.8 to 105.6%. The validated method was successfully applied to the quantitative analysis of 11 water-soluble dyes in 36 commercial products obtained from the local supermarket. Application to the analysis of beverages and food samples available to consumers proved that the described methods are suitable for the routine analysis of dyes in food products containing a broad range of dyes.