Authors:G. Csiffáry, P. Nagy, A. Kiss and N. Adányi
An amperometric biosensor for the detection of organophosphorus and carbamate type pesticides was developed. Acetylcholinesterase enzyme (electric eel) was immobilized in a thin-layer enzyme cell, and acetylthiocholine chloride (AcTCh) was used as substrate. Amperometric detection with glassy carbon electrode was performed in a stopped-flow FIA system. The inhibition effect of dichlorvos (DDVP), carbofuran, methomyl, and pirimicarb were examined: the linear measuring ranges were 0.001–0.1 μmol l−1, 0.001–0.1 μmol l−1, 0.2-1 μmol l−1, and 0.1–10 μmol l−1, respectively. Soil extract and apple juice were measured with spiking method. It was concluded that the biosensor can be used for screening pesticide residues in food and environmental samples.
Authors:M. Nagy-Gasztonyi, Á. Kardos-Neumann and P. Á. Biacs
Blanching of vegetables before freezing has some advantages as well as a number of disadvantages. Process optimization involves measuring the rate of enzyme destruction, such that the blanching time is just long enough to destroy the indicator enzyme. Eventually, peroxidases were almost universally the enzymes of choice, as they are usually the most heat-stable enzymes found in vegetables and fruits, so by the time they are inactivated no other enzymes or micro-organisms remain. But there is no evidence that peroxidases are involved in deteriorative reactions in the food. The aim of this work was to improve blanching technology in Hungarian frozen food industry with special emphasis on broccoli treatment. Instead of peroxidases, lipoxygenases were chosen to determine the adequate blanching parameters. Usually, lipoxygenases accompany lipases, so lipase activity is measured, too. On the basis of model blanching experiments, the conclusion is that lipoxygenase could be used as indicator enzyme. Being less heat stable than peroxidase, this enzyme requires shorter heat treatment, hence its inactivation should result in minimum quality deterioration and economic loss.
Authors:L. Mesarčová, S. Marcinčák, J. Nagy, P. Popelka, M. Bača, P. Jevinová and D. Marcinčáková
Frozen fillets of Atlantic herrings (Clupea harengus) were used to evaluate the effect of glaze with or without addition of selected herbal extracts on lipid oxidation and sensory properties during 8 months of freezing storage under −14 °C. Fillets were divided into four groups: control non-glazed group, glazed group without addition of herbal extracts, and glazed groups with addition of hawthorn (Crataegus oxyacantha L.) extract (0.3%) and agrimony (Agrimonia eupatoria L.) extract (0.3%). The antioxidant activity and total phenolic content in hawthorn and agrimony extracts, and their effect on lipid deterioration expressed as thiobarbituric acid reactive substances were measured. The results showed that the herbal extracts of hawthorn and agrimony are effective antioxidants and good sources of total phenols. Significant influence of herbal extracts added into glaze on the extent of lipid oxidation changes has been obvious within 4 months storage of herring fillets under freezing conditions. Finally, positive influence of glaze and herbal extracts on organoleptic characteristics of fish fillets was found.
Authors:A. Szabo, A. Fonseca, L. P. Biro, Z. Konya, I. Kiricsi, A. Volodin, C. Van Hasendonck and J. B.Nagy
Some recent results on
the synthesis of coiled carbon nanotubes (CNTs) are summarized. Several
supported catalysts can lead to the formation of coiled CNTs. Interestingly,
certain domains of the coil pitch and coil diameter are favoured, and two
“stability islands”are found in the 3D representation of the number of coiled
CNTs as a function of both coil pitch and coil diameter. It is emphasized that
these nanotubes are formed either by introducing pairs of five-membered ring -
seven-membered ring or by forming haeckelite structures. The coiled CNTs could
be used in nanocomposite reinforcement as well as special sensors based on
their remarkable mechanical and electrical properties.