Synthesis, characterisation and behavioural studies of novel thaw indicator systems

Many food products are kept at temperatures well below the freezing point of water for long-term preservation. If food is exposed to higher temperatures for a certain time there is a risk that it will deteriorate leading to loss of quality or a risk to the health of the subsequent consumer. The latter is more likely if the exposure has not been detected. An irreversible sensor would draw attention to any food packages which had been exposed to conditions likely to cause deterioration offood. This thesis describes the development of a chemical sensor for use as a thaw indicator which can be applied to food packaging. The thaw indicator consists of a temperature sensor which is activated when the temperature rises above a certain level, and an indicator which draws attention to any sensor that has been activated. The temperature sensor discussed in this paper contains an alcohol, either octanol or nonanol, which have melting points of-16°C and -6°C respectively. The alcohol is contained in microcapsules prior to freezing of the packaging. DSC analysis showed depressed melting and freezing points of encapsulated nonanol and octanol. The indicator is 6-amino MGL. It is bonded to microgranular cellulose using epoxide chemistry to prevent migration of the dye into the packaging. Further studies into the immobilization of 6-amino MGL were undertaken and discussed using an alternative dye, 3’,3”-diaminophenolphthalein, bonded onto three substrates, cellulose, PVOH and Sepharose. A third component, a salt-LiBr, is added to the 6-amino MGL so it is initially in the ring open state. Colour change as a function of salt concentration is discussed. The system is printed onto packaging. After freezing, the capsules of alcohol are broken using mild physical pressure. If thawing occurs, the alcohol melts and desorbs the salt from the 6-amino MGL, closing the lactone ring thus causing a colour change. Behavioural studies of the assembled thaw indicators is discussed with cumulative AE* for the octanol thaw indicator system ranging from 21.96 at -10°C to 22.07 at -20°C, and the nonanol thaw indicator system ranging from 25.38 at -8°C to 29.82 at -18°C.