Maria Smolander

Monitoring of the quality of modified atmosphere packaged broiler chicken cuts stored in different temperature conditions. A. Time–temperature indicators as quality-indicating tools

Abstract The applicability of time–temperature indicators (TTIs) for the quality control of modified atmosphere packaged broiler chicken cuts was evaluated at various constant and variable temperature conditions. It was found that microbiological shelf-life could be considerably improved when the cold-chain was carefully maintained. Temperature had a critical effect on the amount of Enterobacteriaceae, proteolytic bacteria, hydrogen sulphide producing bacteria and clostridia, the microbial groups most likely to have an effect on the sensory quality. The results also indicate that TTIs seemed to be useful tools for evaluation of the quality of broiler chicken cuts.

Leak indicators for modified-atmosphere packages

Package integrity is an essential requirement for the high quality of modified-atmosphere packaged (MAP) food. The most effective method of detecting a leakage non-destructively throughout the whole distribution chain from the manufacturer to the consumer is to use a visual leak indicator that is permanently attached to the package. This article reviews visual leak indicators that are based on the detection of oxygen and carbon dioxide. The limitations and benefits of the current indicator technologies are discussed. Commercial indicators and the problems associated with their adoption, as well as the safety aspects of indicators, are also introduced.

Myoglobin-based indicators for the evaluation of freshness of unmarinated broiler cuts

Abstract A principle for a novel intelligent packaging concept, which indicates specifically the spoilage or the lack of freshness of a food product, is described. This freshness indicator for modified atmosphere packed poultry meat is based on the indication of the presence of hydrogen sulphide (H2S), which is produced in considerable amounts during the ageing of packed poultry during storage. In the preliminary evaluation of the indicator principle promising results were obtained for H2S-sensitive indicators based on a visually detectable colour change of agarose immobilised myoglobin. The colour change of the indicators attached into the packages containing unmarinated broiler correlated with the microbiological and sensory quality of broiler samples and the onset of the colour change took place concurrently with the sensory rejection of the odour.

A comparison of glucose oxidase and aldose dehydrogenase as mediated anodes in printed glucose/oxygen enzymatic fuel cells using ABTS/laccase cathodes

Current generation by mediated enzyme electron transfer at electrode surfaces can be harnessed to provide biosensors and redox reactions in enzymatic fuel cells. A glucose/oxygen enzymatic fuel cell can provide power for portable and implantable electronic devices. High volume production of enzymatic fuel cell prototypes will likely require printing of electrode and catalytic materials. Here we report on preparation and performance of, completely enzymatic, printed glucose/oxygen biofuel cells. The cells are based on filter paper coated with conducting carbon inks, enzyme and mediator. A comparison of cell performance using a range of mediators for either glucose oxidase (GOx) or aldose dehydrogenase (ALDH) oxidation of glucose at the anode and ABTS and a fungal laccase, for reduction of oxygen at the cathode, is reported. Highest power output, although of limited stability, is observed for ALDH anodes mediated by an osmium complex, providing a maximum power density of 3.5 μW cm(-2) at 0.34 V, when coupled to a laccase/ABTS cathode. The stability of cell voltage in a biobattery format, above a threshold of 200 mV under a moderate 75 kΩ load, is used to benchmark printed fuel cell performance. Highest stability is obtained for printed fuel cells using ALDH, providing cell voltages over the threshold for up to 74 h, compared to only 2 h for cells with anodes using GOx. These results provide promising directions for further development of mass-producible, completely enzymatic, printed biofuel cells.

Printing of polymer microcapsules for enzyme immobilization on paper substrate.

Poly(ethyleneimine) (PEI) microcapsules containing laccase from Trametes hirsuta (ThL) and Trametes versicolor (TvL) were printed onto paper substrate by three different methods: screen printing, rod coating, and flexo printing. Microcapsules were fabricated via interfacial polycondensation of PEI with the cross-linker sebacoyl chloride, incorporated into an ink, and printed or coated on the paper substrate. The same ink components were used for three printing methods, and it was found that laccase microcapsules were compatible with the ink. Enzymatic activity of microencapsulated TvL was maintained constant in polymer-based ink for at least eight weeks. Thick layers with high enzymatic activity were obtained when laccase-containing microcapsules were screen printed on paper substrate. Flexo printed bioactive paper showed very low activity, since by using this printing method the paper surface was not fully covered by enzyme microcapsules. Finally, screen printing provided a bioactive paper with high water-resistance and the highest enzyme lifetime.

A mediated glucose/oxygen enzymatic fuel cell based on printed carbon inks containing aldose dehydrogenase and laccase as anode and cathode

Enzyme electrodes show great potential for many applications, as biosensors and more recently as anodes and cathodes in biocatalytic fuel cells for power generation. Enzymes have advantages over metal catalysts, as they provide high specificity and reaction rates, while operating under mild conditions. Here we report on studies related to development of mass-producible, completely enzymatic printed glucose/oxygen biofuel cells. The cells are based on filter paper coated with conducting carbon inks containing mediators and laccase, for reduction of oxygen, or aldose dehydrogenase, for oxidation of glucose. Mediator performance in these printed formats is compared to relative rate constants for the enzyme-mediator reaction in solution, for a range of anode and cathode mediators. The power output and stability of fuels cells using an acidophilic laccase isolated from Trametes hirsuta is greater, at pH 5, than that for cells based on Melanocarpus albomyces laccase, that shows optimal activity closer to neutral pH, at pH 6. Highest power output, although of limited stability, was observed for ThL/ABTS cathodes, providing a maximum power density of 3.5 μWcm(-2) at 0.34 V, when coupled to an ALDH glucose anode mediated by an osmium complex. The stability of cell voltage above a threshold of 200 mV under a moderate 75 kΩ load is used to benchmark printed fuel cell performance. Highest stability was obtained for a printed fuel cell using osmium complexes as mediators of glucose oxidation by aldose dehydrogenase, and oxygen reduction by T. hirsuta laccase, maintaining cell voltage above 200 mV for 137 h at pH 5. These results provide promising directions for further development of mass-producible, completely enzymatic, printed biofuel cells.

Aldose dehydrogenase-modified carbon paste electrodes as amperometric aldose sensors

A biosensor using pyrroloquinoline quinone-dependent aldose dehydrogenase (ALDH) as a biological component was developed and used for the measurement of the aldose sugars xylose and glucose. Different immobilization methods for ALDH in carbon paste were studied. The best electrode performance was obtained when ALDH was adsorbed on the surface of a carbon paste electrode. Several mediator compounds were mixed into the carbon paste. The lowest working potential and highest catalytic current were obtained with dimethylferrocene as a mediator. Both storage and operational stability of the ALDH electrodes could be improved by the application of a membrane consisting of a poly(ester-sulfonic acid) cation-exchanger, Eastman AQ-29D. Application of the membrane reduced the non-specific oxidation of fermentation samples on the electrode surface.

Large-scale applicable purification and characterization of a membrane-bound PQQ-dependent aldose dehydrogenase

A membrane-bound xylose oxidizing PQQ-dependent dehydrogenase from Gluconobacter oxydans was purified with a simple large-scale applicable purification procedure. The activity recovery from membrane extract was 33% with 130-fold purification. Important characteristic with respect to the application of the dehydrogenase in biosensor technology were studied. The purified enzyme was most stable in the pH range 3.5-6.5. The pH optimum for xylose oxidation was in the range 7.5-8 for the solubilized enzyme. Optimal pH for the electrochemical detection of xylose oxidation was 6.5. Dimethyl and carboxylic acid derivatives of ferrocene were able to mediate electrons transferred in xylose oxidation from the enzyme immobilized on graphite electrode to the electrode. Hence the purified enzyme appeared to be suitable for biosensor applications.

Fully inkjet-printed parallel-plate capacitive gas sensors on flexible substrate

Small fully inkjet-printed gas sensors based on capacitive parallel-plate (PP) structures have been realized on flexible plastic foil and characterized. A gas sensing layer was inkjet-printed between inkjet-printed bottom and top silver electrodes. Compared with comb electrode (CE) geometries, PP structures drastically reduce the developing complexity of gas sensors on polymeric foil, avoiding the substrate parasitic signal. Furthermore, the use of porous inkjet-printed metal makes the patterning of complex grids on the top electrode unnecessary, since such porosity permits the analyte to flow into the sensing layer. This low demanding patterning resolution facilitates the miniaturization of the inkjet-printed sensors, introducing significant improvements in their sensing performances, such as sensitivity or response time. The printed sensing devices were characterized against pulses of relative humidity (R.H.) and their performances were analyzed.

Printed electronic switch on flexible substrates using printed microcapsules

Printed electronics, the manufacturing of electronic components on large, flexible, and low-cost substrates by printing techniques, can facilitate widespread, very low-cost electronics for consumer applications and disposable devices. New technologies are needed to create functional components in this field. This paper introduces a new method to create an all-additive printed switch on flexible substrate materials, such as polymer foils and paper substrates. The active layer of the switch component consists of neutral polyaniline (PANI), which can be doped by acid to induce a shift from a non-conductive to a conductive oxidation state. Monodisperse core–shell microcapsules containing an acidic aqueous core liquid were produced by a novel inkjet-based encapsulation technology. It was shown that unfavorable water evaporation from the microcapsules could be reduced by the addition of calcium chloride to the core liquid. A switch component was prepared, consisting of inkjet-printed interdigitated silver electrodes, PANI active layer and printed microcapsules. If an external pressure was applied, for instance with a finger, then the switch component changed its state from non-conductive to conductive with a simultaneous distinct color change. The results clearly demonstrate the feasibility of the presented approach to create either a visual or electronic signal for use in printed electronic applications.