| abstract |
A new and improved integrating indicator system operable to signal the attainment of one or more preselected time-temperature integrals which monitor the temperature and time history of a product utilizes a dual system of specific reaction pairs which simultaneously generate acid and alkali from two neutral substrates. One of the substrates is present in excess of the other. The preferred dynamic indicator system generates a constant pH buffer in the alkali range that is maintained until one of the substrates is depleted. At that time, a rapid pH change in the indicator solution to the acid range occurs, resulting in a very sharp visual color change in a pH-sensitive dye. In preferred embodiments, the specific reaction pairs are enzyme/substrate pairs, preferably urease/urea and yeast/triacetin. A preferred combination pH-sensitive dye package includes m-nitrophenol, p-nitrophenol and litmus to provide an indicator which changes from green to reddish pink upon the expiration of a given amount of time at constant temperature, or in a shorter period of time, upon exposure to elevated abuse temperatures. In especially preferred embodiments, one of the enzyme substrate pairs includes an enzyme component provided by a microorganism which has been shock treated prior to incorporation in the indicator to improve temperature sensitivity and provide extended half life. The new and improved integrating indicators are adapted for use with packaged foodstuffs intended for refrigerated and room temperature handling and storage at temperatures between about 20° F. to about 120° F. |