Low temperature thaw indicator

摘要

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 expose has not been detected. An irreversible sensor would draw attention to any food packages which had been exposed to conditions likely to cause deterioration of food. This paper 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 is octanol, which has a reported melting point of -16.3℃. The octanol is contained in microcapsules prior to freezing of the packaging. The indicator is 6-amino MGL. It is bonded to microgranular cellulose to prevent migration into the packaging. 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 octanol are broken using mild physical pressure. If thawing occurs, the octanol melts and desorbs the salt from the 6-amino MGL, closing the lactone ring thus causing a colour change.