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The temperature abuse encountered by food products during storage due to deviations from the recommended storage conditions often leads to a considerable loss, especially for frozen and refrigerated foods. From a consumer perspective, the real history of time–temperature data is of interest so that the customer can get an idea about the remaining shelf-life. The time–temperature indicator or integrator (TTI), a small and inexpensive device, is attached to the packaging material and provides the time–temperature history of a food product during storage, thus estimating remaining shelf-life in a non-destructive manner. The enzymatic TTI is based on a thermo-sensitive reaction between enzyme and substrate. A suitable dye is mixed into this medium as an indicator, which changes its color depending on the variation in the pH of the reaction medium. In the recent past, several TTIs have been developed based on different enzymes, including lipase, amylase, phospholipase, urease, laccase, and others. The corresponding applied food matrices were fruits, vegetables, milk products, seafood, poultry, and meat products. Developing a new enzymatic TTI requires a systematic approach to correlate the response-TTI dependency. Such development needs a thorough understanding of the kinetics of food quality attributes and the activation energy. This review provides an overview of enzymatic TTI, theoretical considerations, and the systematic approach required to develop any enzymatic TTI. The integration of such information will simplify the design of novel enzymatic TTIs for a wide array of food products during frozen storage. [ABSTRACT FROM AUTHOR]

Time-temperature integrator/indicator (TTI) is a temperature monitoring tool that visually presents the temperature history of foods to easily and cost-effectively manage the temperature of food products in cold chain system. However, few TTIs exhibit suitable performance under chilled conditions over a long period, such as beyond 100 days, as in the storage and distribution of chilled beef across the world. This study aimed to visualize the temperature history of chilled vacuum-packed beef, during international distribution, using Maillard reaction–based TTIs to record the accumulated temperature under chilled conditions, for more than 100 days. The developed Maillard reaction–based TTI comprised of double-sealed large and small plastic pouches. While the small pouch contained 500 μL D-xylose solution, the large pouch contained 1000 μL glycine solution with disodium hydrogen phosphate solution. Both the solutions were mixed by breaking the small pouch into the large pouch, following which the Maillard reaction started, depending on the ambient temperature. We examined two different combinations of the solution concentrations of TTI that turned brown and yellow at − 0.5 °C after approximately 77 days and 100 days, respectively. The developed TTIs, along with Tasmanian chilled beef, were transported from Australia to Japan through commercial supply chains and stored at a constant temperature of − 0.5 °C. One of the TTIs (TTI-brown) turned pale brown after 77 days which is the current shelf life of Australian chilled beef in Japan. The color of TTI-yellow changed to clear yellow after 150 days, when the chilled beef developed an off-odor, as judged by sensory evaluation. The TTI-brown was functional until day 77 which is the current shelf life of Australian beef in Japan, while the TTI-yellow was functional until day 150 to indicate remaining shelf life of beef. The results collectively indicated the Maillard reaction–based TTIs to realize visualization of temperature history during long-term storage and distribution of chilled beef. [ABSTRACT FROM AUTHOR]

Food sterilisation, i.e. heating to above 120 °C for several min, still remains a primary method of food preservation. Current time-temperature integrators (TTIs), used to assess the thermal impact, only work at pasteurisation temperatures (below 100 °C). The aim of this work was to develop and validate a sterilisation TTI using an α-amylase from the hyperthermophile Pyrococcus furiosus. Previous experiments have found that this α-amylase has a z value similar to that of Clostridium botulinum spores and the enzyme is sufficiently heat resistant to show a measurable residual activity after 30 min at 121 °C. Analysis found a D value of 24 min and a slightly variable z value of around 11 °C. The decrease in enzymatic activity from thermal processing was found after a F process of 5 min to be 67 %, and for a F of 30 min it was 12 %, thus making P. furiosus α-amylase a strong and relevant candidate for a sterilisation TTI. Trials with canned water and mango chutney as test materials have confirmed the potential application of the enzyme within an industrially relevant setting of a model reel and spiral retort. The thermal data showed that at low or marginal F values, of less than 15 min, the correlation between the TTI and thermocouple data was closely comparable ( R = 0.96). The applicability of these TTIs over the range of industrial processes is also shown. [ABSTRACT FROM AUTHOR]