Furfural Determination with Disposable Polymer Films and Smartphone-Based Colorimetry for Beer Freshness Assessment.

We have developed disposable color-changing polymeric films for quantification of furfural-a freshness indicator-in beer using a smartphone-based reader. The films are prepared by radical polymerization of 4-vinylaniline, as a furfural-sensitive indicator monomer, 2-hydroxymethyl methacrylate as a comonomer, and ethylene dimethyl methacrylate (EDMA) as a cross-linker. The sensing mechanism is based on the Stenhouse reaction in which aniline and furfural react in acidic media with the generation of a deep red cyanine derivative, absorbing at 537 nm, which is visible to the naked eye. The colorimetric response has been monitored using either a portable fiber-optic spectrophotometer or the built-in camera of a smartphone. Under the optimized conditions, a linear response to furfural in beer was obtained in the 39 to 500 µg L(-1) range, with a detection limit of 12 µg L(-1), thus improving the performance of other well-established colorimetric or chromatographic methods. The novel films are highly selective to furfural, and no cross-reactivity has been observed from other volatile compounds generated during beer aging. A smartphone application (app), developed for Android platforms, measures the RGB color coordinates of the sensing membranes after exposure to the analyte. Following data processing, the signals are converted into concentration values by preloaded calibration curves. The method has been applied to determination of furfural in pale lager beers with different storage times at room temperature. A linear correlation (r > 0.995) between the storage time and the furfural concentration in the samples has been confirmed; our results have been validated by HPLC with diode-array detection.

Molecularly Imprinted Polymer-Based Hybrid Materials for the Development of Optical Sensors.

We report on the development of new optical sensors using molecularly imprinted polymers (MIPs) combined with different materials and explore the novel strategies followed in order to overcome some of the limitations found during the last decade in terms of performance. This review pretends to offer a general overview, mainly focused on the last 3 years, on how the new fabrication procedures enable the synthesis of hybrid materials enhancing not only the recognition ability of the polymer but the optical signal. Introduction describes MIPs as biomimetic recognition elements, their properties and applications, emphasizing on each step of the fabrication/recognition procedure. The state of the art is presented and the change in the publication trend between electrochemical and optical sensor devices is thoroughly discussed according to the new fabrication and micro/nano-structuring techniques paving the way for a new generation of MIP-based optical sensors. We want to offer the reader a different perspective based on the materials science in contrast to other overviews. Different substrates for anchoring MIPs are considered and distributed in different sections according to the dimensionality and the nature of the composite, highlighting the synergetic effect obtained as a result of merging both materials to achieve the final goal.

Rapid determination of Alternaria mycotoxins in tomato samples by pressurised liquid extraction coupled to liquid chromatography with fluorescence detection.

A sensitive and reliable method using pressurised liquid extraction (PLE) followed by molecularly imprinted solid phase extraction (MISPE) and high performance liquid chromatography with fluorescence detection (HPLC-FLD) has been developed for the analysis of alternariol (AOH) and alternariol monomethyl ether (AME) in tomato samples. Influence of several extraction parameters that affect PLE efficiency were evaluated for the simultaneous extraction of both mycotoxins in the selected samples. AOH and AME were optimally extracted using MeOH/water (25:75, v/v) at 70°C as solvent, a pressure of 1000 psi and a single extraction cycle. The resulting PLE extracts were pre-concentrated by molecularly imprinted solid phase extraction (MISPE) cartridges followed of analysis by HPLC with fluorescence detection (λexc = 258, λem = 440 nm). The proposed method was applied to the analysis of AOH and AME in fortified tomato samples (20-72 µg· kg-1) with recoveries of 84-97% (RSD < 8%, n = 6) for AOH and 67-91% (RSD < 13%, n = 6) for AME. The detection limit for AOH and AME were 7 and 15 µg· kg-1, respectively. The ensuing PLE-MISPE-HPLC-FLD method was validated for the analysis of both mycotoxins in tomato samples in accordance with European Commission Decision 2002/657/EC.

Molecularly imprinted hydrogels as functional active packaging materials.

This paper describes the synthesis of novel molecularly imprinted hydrogels (MIHs) for the natural antioxidant ferulic acid (FA), and their application as packaging materials to prevent lipid oxidation of butter. A library of MIHs was synthesized using a synthetic surrogate of FA, 3-(4-hydroxy-3-methoxyphenyl)propionic acid (HFA), as template molecule, ethyleneglycol dimethacrylate (EDMA) as cross-linker, and 1-allylpiperazine (1-ALPP) or 2-(dimethylamino)ethyl methacrylate (DMAEMA), in combination with 2-hydroxyethyl methacrylate (HEMA) as functional monomers, at different molar concentrations. The DMAEMA/HEMA-based MIHs showed the greatest FA loading capacity, while the 1-ALLP/HEMA-based polymers exhibited the highest imprinting effect. During cold storage, FA-loaded MIHs protected butter from oxidation and led to TBARs values that were approximately half those of butter stored without protection and 25% less than those recorded for butter covered with hydrogels without FA, potentially extending the shelf life of butter. Active packaging is a new field of application for MIHs with great potential in the food industry.