Chromatic Sensor to Determine Oxygen Presence for Applications in Intelligent Packaging.

A chromatic sensor has been designed for the detection of oxygen in package headspace. The sensor is based on the redox change of methylene blue (MB) to its leuco form. Its formulation includes the pigment, glycerol, as a sacrificial electron donor, TiO2, as a photocatalyst and ethylene-vinyl alcohol copolymer (EVOH), as a structural polymer matrix. The final sensor design that allows its manufacture by conventional printing and laminating technologies consists of the sensing polymer matrix (MB-EVOH) sandwiched in a suitable transparent multilayer structure. The outer layers protect the sensor from the external atmosphere and allow visualization of the colour. The inner layer is sufficiently opaque to facilitate sensor reading from the outside, is thick enough to avoid direct contact with food (functional barrier), and is oxygen-permeable to expose the sensing material to the internal package atmosphere. In the absence of oxygen, the sensor becomes white by irradiation with halogen lamps in less than 60 s. All components are substances permitted for food contact except the pigment, but specific migration analysis showed no trace of migration thanks to the functional barrier included in the design.

Development and optimization of antifungal packaging for sliced pan loaf based on garlic as active agent and bread aroma as aroma corrector.

The aim of the present work was the development of antimicrobial films containing garlic extract to be applied as active packaging for preservative-free sliced pan loaf, with the goal of extending its shelf-life. First, the antimicrobial capacity of garlic extract, a compound used as active agent, was tested against Penicillium expansum by the disc diffusion method. The extract showed high antimicrobial activity, 0.1 µL per Petri dish being the minimum inhibitory amount, and 0.25 µL the minimum fungicidal amount. Bread aroma was also used to mask the pungent odour of garlic and it was confirmed to have no antimicrobial activity. Subsequently, polyethylene (PE) aqueous emulsion and ethylene-vinyl alcohol copolymer (EVOH) and zein hydroalcoholic solutions containing 0.25 and 0.5% (w/w per dry polymer) of garlic extract and bread aroma were used to coat PE films, producing PE/PE, PE/EVOH and PE/zein active films. The antimicrobial capacity of the films was studied in vitro against Penicillium expansum, and in vivo with natural sliced bread. The results showed that all the films presented some antimicrobial activity, PE film coated with zein containing 0.5% of garlic extract and bread aroma being the film presenting the best results, maintaining bread free of mould infection for 30 days. Sensory tests showed that the addition of 1% of bread aroma improved the sensory experience of consumers and also revealed good purchase intention.

Anchoring Gated Mesoporous Silica Particles to Ethylene Vinyl Alcohol Films for Smart Packaging Applications.

This work is a proof of concept for the design of active packaging materials based on the anchorage of gated mesoporous silica particles with a pH triggering mechanism to a packaging film surface. Mesoporous silica micro- and nanoparticles were loaded with rhodamine B and functionalized with N-(3-trimethoxysilylpropyl)diethylenetriamine. This simple system allows regulation of cargo delivery as a function of the pH of the environment. In parallel, poly(ethylene-co-vinyl alcohol) films, EVOH 32 and EVOH 44, were ultraviolet (UV) irradiated to convert hydroxyl moieties of the polymer chains into ⁻COOH functional groups. The highest COOH surface concentration was obtained for EVOH 32 after 15 min of UV irradiation. Anchoring of the gated mesoporous particles to the films was carried out successfully at pH 3 and pH 5. Mesoporous particles were distributed homogeneously throughout the film surface and in greater concentration for the EVOH 32 films. Films with the anchored particles were exposed to two liquid media simulating acidic food and neutral food. The films released the cargo at neutral pH but kept the dye locked at acidic pH. The best results were obtained for EVOH 32 irradiated for 15 min, treated for particle attachment at pH 3, and with mesoporous silica nanoparticles. This opens the possibility of designing active materials loaded with antimicrobials, antioxidants, or aromatic compounds, which are released when the pH of the product approaches neutrality, as occurs, for instance, with the release of biogenic amines from fresh food products.

Antimicrobial food packaging film based on the release of LAE from EVOH.

The aim of this work was to develop antimicrobial films for active packaging applications containing the natural antimicrobial compound LAE (lauramide arginine ethyl ester) in EVOH copolymers with different mol % ethylene contents (i.e. EVOH-29 and EVOH-44). EVOH-29 and EVOH-44 films were made by casting and incorporating 0.25%, 1%, 5%, and 10% LAE in the film forming solution (w/w with respect to polymer weight). Previously, the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) of LAE against Listeria monocytogenes, Escherichia coli, and Salmonella enterica were determined by a microdilution assay. The antimicrobial activity of the resulting films was tested in vitro against these microorganisms in liquid culture media. The activity of the films was also evaluated over time. The results showed that films containing 5% and 10% LAE produced total growth inhibition and viable counts decreased with 0.25% and 1% LAE. Finally, the effectiveness of the films was tested by applying them to an infant formula milk inoculated with L. monocytogenes and S. enterica and stored for 6 days at 4°C. The application of films with LAE to infant formula milk inoculated with L. monocytogenes reduced at the end of storage period about 4 log in case of 10% LAE and with S. enterica reduced 3.74 log and 3.95 log with EVOH 29 5% and 10%, respectively, and EVOH-44 5% and 10% LAE reduced 1 log and 3.27 log, respectively, at the end of storage. The antimicrobial capacity of EVOH-29 films was greater than that of EVOH-44 films in all the cases tested. In general, the films were more effective in inhibiting the growth of L. monocytogenes than S. enterica, this inhibition being more acute at the end of the storage time.

Development of antimicrobial films for microbiological control of packaged salad.

The aim of the present work was to characterize the antimicrobial efficiency of films consisting of PP/EVOH structures with oregano essential oil and citral. Both substances are known for their antimicrobial activity based on their interaction with the cell membrane. The films developed were used to pack minimally processed salads, combining modified atmosphere technology to extend shelf-life and active packaging technology to reduce possible microbiological risks. The antimicrobial activity of the films against the pathogenic microorganisms Escherichia coli, Salmonella enterica and Listeria monocytogenes and natural microflora was investigated "in vitro" and also on the food itself. The effect of release of the antimicrobial agent on the sensory characteristics of the salad was also studied. The results showed that antimicrobial activity reduced spoilage flora on the salad as well as inhibited the growth of pathogens in contaminated salads. This effect was greater against Gram-negative bacteria. Sensory studies showed that the package that was most effective and most accepted by customers was the one containing 5% oregano essential oil.