Eduspace

SENSOR         A sensor is defined as a device used to detect, locate or quantify energy or matter, giving a signal for the detection or measurement of a physical or chemical property to which the device responds (Kress-Rogers, 1998a). To qualify as a sensor, a device must be able to provide continuous output of a signal. Most sensors contain two basic functional units a receptor and a transducer. The transducer is a device capable of transforming the energy carrying the physical or chemical information about the sample into a useful analytical signal.         Chemical sensor and biosensor technology has developed rapidly in recent years. The main types of transducers with potential use in packaging systems include electrical, optical, thermal or chemical signal domains. Sensors can be applied as the determinant of a primary measurable variable or, using the marker concept, as the determinant of another physical,...

FRESHNESS INDICATOR            The idea of freshness indicators is that they monitor the quality of the packed food by reacting in one way or another to changes taking place in the fresh food product as a result of microbiological growth and metabolism ( Smolander, 2008 ). Freshness indicators are designed to respond to chemicals released by food as a result of spoilage; usually an oxidative process is effected by bacteria, yeasts and fungi, which break down food carbohydrates, proteins, and fats to a wide variety of low-molecular-weight molecules, such as CO2 ( Mattila et al ., 1990 ), lactic and acetic acids ( Kakouri et al ., 1997 ), aldehydes, alcohols (ethanol) ( Cameron and Tasila, 1995; Randell et al ., 1995 ), sulfurcontaining species (hydrogen sulphide) ( Smolander et al ., 1998 ) and nitrogen containing molecules, such as ammonia ( Pacquit, 2007; Horan, 1998 ) and amines ( Wallach and Novikov, 1998; Okuma et al ., 2000). ...

CO2 INDICATORS These indicators provide fast colour reaction, demonstrating that the correct CO2 level has been put in every package. The indicators display the desired concentrations of carbon dioxide inside the package (Ahvenainen, Hurme, 1997). This allows incorrectly packaged product to be immediately repacked        The chemistry that is usually employed to sense CO2 is based on its ability to acidify water.        The detection of the protons released by carbonic acid, H 2 CO 3 , is easily achieved using a pH-indicating dye, such as meta -cresol purple, which is blue when deprotonated (MCP - ) and yellow when acidified (MCPH). Thus, an aqueous solution containing MCP - is blue in the absence of CO 2 , but yellow when saturated with CO2. ideally, a solvent-based (i.e., largely hydrophobic), intelligent ink for CO2 is desired. This is achieved by coupling the a...