Mariusz Tichoniuk

Electrochemical detection of foodborne pathogen Aeromonas hydrophila by DNA hybridization biosensor.

The paper describes an electrochemical DNA biosensor used for the detection of Aeromonas hydrophila. This opportunistic pathogen is recognized as an emerging foodborne hazard and is associated with a variety of virulence factors including production of cytotoxic enterotoxin aerolysin. The genosensor recognition layer was prepared using mixed self-assembled monolayer (SAM) consisting of thiolated single-stranded DNA probe (ssDNA) and diluent molecules--mercaptoalcohol: mercaptoethanol (MCE) or mercaptohexanol (MCH) or mercaptononanol (MCN). The voltammetric examination of double-layer capacitance of biosensor recognition interface supported by chronocoulometric quantitation of DNA present on the electrode surface showed that mixed ssDNA and MCH monolayer revealed the lowest defectiveness. Its double-layer capacitance equaled 4.0 μF cm(-2) and ssDNA probe surface coverage reached 8.5×10(11) molecules cm(-2) of gold electrode surface. Chronocoulometric quantitation of DNA and square wave voltammetry (SWV) measurements of electroactive indicator, methylene blue (MB) were performed to investigate the influence of hybridization reaction time, concentration of target DNA fragments, and presence of non-complementary DNA on the electrochemical response of genosensor recognition interface. The biosensor enabled distinction between the DNA samples isolated from A. hydrophila (present at the concentration of 2.5 μg cm(-3)) and other microbial DNA.

The Application of Natural Dyes in Food Freshness Indicators Designed for Intelligent Packaging

Th e paper presents natural dyes i.e. curcumin, grape peel and beetroot extract which were incorporated into the compositions of food freshness indicators. Th e obtained indicators were assessed and compared with an artifi cial dye, methyl red, in relation to their capability of volatile amine monitoring. Additionally, a model of volatile amine release based on the evaporation of ammonia solution was applied in the fi rst stage of the presented research. Th e response of freshness indicators was estimated by the colorimetric analyses of colour alteration and the calculation of Total Colour Diff erence (TCD) index values. Comparing to the methyl red dye, the grape peel extract gave a similar response with the TCD value equalled ca. 30 units. Beetroot extract did not provide a desirable colour change and the most promising composition was the indicator containing the curcumin addition. Further research was made on the freshness indicators containing only curcumin, grape peel extract or methyl red. Th e indicators were evaluated in relation to their response to the spoilage of raw cod fl esh both in the model system (chamber with evaluated indicators) and in food packaging (plastic box). Although all examined natural dyes were able to detect food spoilage, the response comparable to the methyl red was obtained for grape peel extract in the model system and for curcumin in a real package. Both natural dyes and methyl red provided the colour changes correlated with cod fl esh spoilage and characterized with TCD values equal to ca. 30 units.