Abstract: An enzymatic substrate adsorbed on a solid carrier with a large specific surface area of over 50 m.sup.2 /g. The enzymatic substrate shall be stable in the absence of the corresponding enzyme and essentially non-soluble in water. The substrate containing layer surrounding the carrier may also comprise diluents and thickeners. The substrate-carrier together with an enzyme and a pH indicating substance is also useful as a time-temperature indicating device.

Abstract: PH indicator composition has controlled change of color at a selected sub-freezing temperature. The composition comprises at least one pH indicator, a buffer solution containing at least one inorganic ion in solution and a control agent or a precursor of a control agent. The buffer solution has a pH capable of changing when the temperature of the buffer solution is lowered to below freezing. The control agent is capable of effecting a change in ionic strength and proton composition of the frozen pH indicator composition to thereby control the temperature at which the color change occurs. A method of using the composition comprises lowering the temperature from a first temperature above freezing to a second temperature at which the pH indicator composition is in a substantially frozen state. The composition is particularly useful in a color change thermometer.

Abstract: An enzymatic substrate adsorbed on a solid carrier with a large specific surface area of over 50 m.sup.2 /g. The enzymatic substrate shall be stable in the absence of the corresponding enzyme and essentially non-soluble in water. The substrate containing layer surrounding the carrier may also comprise diluents and thickeners. The substrate-carrier together with an enzyme and a pH indicating substance is also useful as a time-temperature indicating device.