Time temperature indicator with distinct end point
First Claim
1. A method for making an indicator for indicating time-temperature histories in conjunction with the storage of sensitive products and compositions, comprising admixing a first specific reaction pair for generating acid, a second specific reaction pair for generating base and at least one pH sensitive dye to form an aqueous solution, said first specific reaction pair having a first substrate present in a stoichiometric excess amount over the amount of a specific substrate provide in said second specific reaction pair.
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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 integratin 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.
79 Citations
6 Claims
- 1. A method for making an indicator for indicating time-temperature histories in conjunction with the storage of sensitive products and compositions, comprising admixing a first specific reaction pair for generating acid, a second specific reaction pair for generating base and at least one pH sensitive dye to form an aqueous solution, said first specific reaction pair having a first substrate present in a stoichiometric excess amount over the amount of a specific substrate provide in said second specific reaction pair.
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4. An improved packaging for room temperature and refrigerated storage of a foodstuff including a label incorporating an indicator composition, said indicator composition being a time temperature integrating indicator comprising:
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a first specific reaction pair including an active reagent and a substrate specific to said active reagent, said first specific reaction pair being reactive to form a first reaction product, said first reaction product tending to cause the pH value to change in an acidic or a basic first direction away from neutrality; a second specific reaction pair including an active reagent and a substrate specific to said active reagent, said second specific reaction pair being reactive to form a second reaction product, said second reaction product tending to cause the pH value of the indicator to change in a second direction opposite said first direction and beyond neutrality; said first reaction product and said second reaction product in turn being reactive to form a third reaction product including a stable pH buffer which maintains the pH of the indicator at a stable value on the second direction side of neutrality until said second reaction product is no longer produced, said substrate in said first specific reaction pair being present in a stoichiometric excess amount over the amount of the substrate in said second specific reaction pair; and at least one pH-sensitive dye exhibiting one color for a pH in a basic pH range and a second different color in an acidic pH range, whereby said time-temperature integrating indicator exhibits a rapid and distinct color change from one to the other of said first and second colors after a pre-determined amount of time has elapsed upon exposure to relatively constant temperatures, or after a relatively shorter period of time has elapsed, upon exposure to elevated temperatures.
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5. An indicator pouch for use in monitoring the time and temperature histories of an adjacent packaged food product to which said pouch is affixed, said pouch comprising a thermoplastic pouch envelope having an indicator solution-receiving cavity with a visually observable amount of a time temperature integrating indicator composition in said cavity, said indicator composition including:
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a first specific reaction pair including an active reagent and a substrate specific to said active reagent, said first specific reaction pair being reactive to form a first reaction product, said first reaction product tending to cause the pH value to change in an acidic or a basic first direction away from neutrality; a second specific reaction pair including an active reagent and a substrate specific to said active reagent, said second specific reaction pair being reactive to form a second reaction product, said second reaction product tending to cause the pH value of the indicator to change in a second direction opposite said first direction and beyond neutrality; said first reaction product and said second reaction product in turn being reactive to form a third reaction product including a stable pH buffer which maintains the pH of the indicator at a stable value on the second direction side of neutrality until said second reaction product is no longer produced, said substrate in said first specific reaction pair being present in a stoichiometric excess amount over the amount of the substrate in said second specific reaction pair; and at least one pH-sensitive dye exhibiting one color for a pH in a basic pH range and a second different color in an acidic pH range, whereby said time-temperature integrating indicator exhibits a rapid and distinct color change from one to the other of said first and second colors after a pre-determined amount of time has elapsed upon exposure to relatively constant temperatures, or after a relatively shorter period of time has elapsed, upon exposure to elevated temperatures. - View Dependent Claims (6)
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Specification