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.

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.