Time-temperature Indicators Research Articles

Development and characterization of a prototype of a lactic acid–based time–temperature indicator for monitoring food product quality

Temperature is a crucial factor affecting the quality and safety of food products during both distribution and storage. The difficulty in controlling and monitoring the temperature history of food products makes it difficult to precisely predict shelf life. Time–temperature indicators (TTIs) provide a visual summary of a product’s accumulated chill-chain history, recording the effects of both time and temperature. Attempts have been made to develop a prototype of a time–temperature indicator based on the diffusion of lactic acid, which is temperature-dependent. Four lactic acid-based TTIs were made in different substrate concentrations. Color changes associated with the diffusion of lactic acid were monitored. In the vapor diffusion of lactic acid, an irreversible color change of a chemical chromatic indicator (from green to red) clearly and progressively occurred due to the pH reduction. The temperature dependence of these TTIs kinetics was characterized isothermally in the range of 4–45 °C, yielding activation energy ( E a) of, approximately, 50 kJ mol −1. The mathematical models of each TTI were established according to the relationships between color changes and time and temperature. The differences between the E a values of the TTIs and the E a associated with food quality losses – including enzymatic loss, hydrolysis, lipid oxidation, nutrient loss and microbial growth – were less than 40 kJ mol −1, and therefore these TTIs could be considered as good candidates to monitor food quality losses. Although these TTIs do not cover the whole range of food quality losses, they could be applied to show the time–temperature history of some foods, especially fruits and vegetables, and to indicate food quality associated with time–temperature exposure.

A novel photochromic time–temperature indicator to support cold chain management

SummaryA detailed investigation of the behaviour of a new printable photochromic time–temperature indicator (TTI) was conducted to characterise its properties under specific temperature conditions and to analyse the influence of ultra violet (UV) light irradiation (activation) on the discolouration process. The reproducibility of the charging process and the discolouration process of the TTI were analysed. For different charging times the calculated activation energies based on the Arrhenius model ranged from 23.2 to 25.3 kcal mol−1 depending on the UV light irradiation (charging time). A quality contour diagram was established to define the appropriate charging time for different kinds of products. Due to the possibility of defining the shelf life of a TTI by different charging times, this novel TTI constitutes a reliable tool to monitor the cold chains of a broad range of food products on their way from production to consumption.

El frágil inicio de la cadena de frío vacunal en España

Two studies aiming to analyze the vaccine cold chain throughout Spain, performed from 1988-89, sparked interest in vaccine logistics among public health authorities. The studies were performed using evaluation methodology based on cold chain monitor cards with a time-temperature indicator (Battersby's report) and cross-sectional surveys on the conditions of the cold chain (Ferrando's report) in the second and third levels (provincial and local stores). The technical reports revealed the precariousness of the situation, identified the weak points that were jeopardizing the vaccines’ efficiency, and favored awareness of an activity that constitutes the vertebral column of any immunization program. The improvements proposed were gradually implemented by regional governments. More funds for equipment and personnel training were provided and specific management protocols were established.

Nutritional Quality of Commercial Fruit Baby Food

Commercial fruit baby food is a preserved fruit product usually made with fruit purees, sugar, water and variable additives (thickening agents, antioxidants, etc.). As the foodstuffs intended for particular nutritional uses, baby foods for infants and young children conforms to a set of strict guidelines e.g. maximum levels for pesticide residues, microbiological contamination, addition of additives, labelling, etc. However, being an important supplement to children diet and/or for their progressive adaptation to ordinary food, the nutritional quality of commercial fruit baby food in very important. Ten samples of commercial fruit baby food from the market were analysed for the fruit content, ascorbic acid and total polyphenols content and total antioxidant capacity determined by DPPH method. Hydroxymethylfurfural (HMF) and furfural content were followed as the time-temperature effort indicators. The method for the estimation of fruit content in products was based on the concentration of glucose, fructose, sorbitol, potassium, formol number, malic and citric acid, phosphorus, ash and refractive index and the results were compared with the Code of practice of AIJN and literature sources. The study indicates that there are big differences in composition and quality of commercial fruit baby food, whereas some samples contain fruits only, another products are diluted with significant amount of sugar, water and starchy fillers.

Applicability of a microbial Time Temperature Indicator (TTI) for monitoring spoilage of modified atmosphere packed minced meat

The applicability of a microbial Time Temperature Indicator (TTI) prototype, based on the growth and metabolic activity of a Lactobacillus sakei strain developed in a previous study, in monitoring quality of modified atmosphere packed (MAP) minced beef was evaluated at conditions simulating the chill chain. At all storage temperatures examined (0, 5, 10, 15 °C), the results showed that lactic acid bacteria (LAB) were the dominant bacteria and can be used as a good spoilage index of MAP minced beef. The end of product's shelf life as revealed by the sensory evaluation coincided with a LAB population level of 7 log 10 CFU/g. For all temperatures tested, the growth of L. sakei in the TTI resembled closely the growth of LAB in the meat product, with similar temperature dependence of the μ max and thus similar activation energy values calculated as 111.90 and 106.90 kJ/mol, for the two systems, respectively. In addition, the end point of TTI colour change coincided with the time of sensory rejection point of the beef product during its storage under isothermal chilled temperature conditions. The estimated activation energy, E α, values obtained for parameters related to the response of Δ E (total colour change of the TTI) describing the kinetics of colour change of the TTI during isothermal storage (i.e. the maximum specific rate of Δ Ε evolution curve, μ Δ Ε , and also the reciprocal of t i, time at which half of the maximum Δ Ε is reached), were 112.77 and 127.28 kJ/mol, respectively. Finally, the application of the microbial TTI in monitoring the quality deterioration of MAP minced beef due to spoilage was further evaluated under dynamic conditions of storage, using two separate low temperature periodic changing scenarios, resembling the actual conditions occurring in the distribution chill chain. The results showed that the end point of TTI, after storage at those fluctuating temperature conditions, was noted very close to the end of product's sensorial shelf life. This finding points to the applicability of the developed microbial TTI as a valuable tool for monitoring the quality status during distribution and storage of chilled meat products, which are spoiled by lactic acid bacteria or other bacteria exhibiting similar kinetic responses and spoilage potential.

Time–temperature indicators for high temperature applications

New thermochromic materials are reported, which are useful for application as time–temperature indicators (TTIs) in temperature regimes that are complementary to those accessible with existing technologies. The design approach involves incorporating small amounts (0.3–2.9 wt.-%) of the excimer-forming, photoluminescent chromophores 4,4′-bis(2-benzoxazolyl)stilbene or a cyano-substituted oligo(p-phenylene vinylene) derivative into ethylene/norbornene copolymers with glass transition temperatures (Tg) between 131 and 149 °C. These dye/polymer blends were melt-processed and quenched from homogeneous melts to below their Tg to kinetically trap the dyes in dispersed states, which exhibit monomer fluorescence. Upon annealing the materials above Tg, self-assembly of the dye molecules into aggregates that allow for excimer formation occurs, concomitant with permanent and pronounced fluorescence color changes. This approach yielded TTI materials that demonstrate a predictable, Arrhenius-type behavior and which are useful in a temperature regime from ∼130 to 200 °C. The kinetics of the color change were tunable on time scales between seconds and days by changing dye concentration, dye structure, or host polymerTg.

Neurobiology of social attachment: A comparative approach to behavioral, neuroanatomical, and neurochemical studies

A new strategy to prevent food deterioration is the use of intelligent-active food packaging. Intelligent-active packaging is defined as a barrier film which prevents or delays the spoilage of food or reveals the deterioration process in food by different mechanisms. In this study, the intelligent-active property was imbedded into food packaging films made of ethylene-vinyl acetate copolymer an abundant, flexible, and non-toxic polymer blend by incorporation of different additives. Anthocyanin extracted from red cabbage was stabilized on montmorillonite and added to the film as a time-temperature indicator. Other materials such as ZnO nanoparticles, rosemary extract, and modified montmorillonite were used to achieve antimicrobial, antioxidant, and air barrier activity. The additives and prepared films were characterized by FTIR, XRD, FESEM, TGA, and mechanical analysis. The performance of the prepared films was investigated by antioxidant capacity test by DPPH, in vitro test, minimum bactericidal concentration (MBC), minimum inhibition concentration (MIC), antibacterial test and capacity of oxygen absorbance. Results showed that films which contain rosemary extract, ZnO, and modified montmorillonite exhibited remarkable antibacterial and antioxidant activity compared to pristine EVA film.

Modelling pH evolution and lactic acid production in the growth medium of a lactic acid bacterium: Application to set a biological TTI

Time temperature integrators or indicators (TTIs) are effective tools making the continuous monitoring of the time temperature history of chilled products possible throughout the cold chain. Their correct setting is of critical importance to ensure food quality. The objective of this study was to develop a model to facilitate accurate settings of the CRYOLOG biological TTI, TRACEO ®. Experimental designs were used to investigate and model the effects of the temperature, the TTI inoculum size, pH, and water activity on its response time. The modelling process went through several steps addressing growth, acidification and inhibition phenomena in dynamic conditions. The model showed satisfactory results and validations in industrial conditions gave clear evidence that such a model is a valuable tool, not only to predict accurate response times of TRACEO ®, but also to propose precise settings to manufacture the appropriate TTI to trace a particular food according to a given time temperature scenario.

Fadable ink for time–temperature control of food freshness: Novel new time–temperature indicator

A novel new colorimetric time–temperature indicator, based on fadable ink has been developed. The printed sign is able to disappear in a defined time period. The color fading is based on the red-ox properties of anthraquinone derivative. Beige anthraquinone β-sulfonate can be easily reduced by sodium hydrosulfite and become red color. By contacting with oxygen, the red color turns back into beige. The time–temperature indicator comprises three thin layers materials either on paper or plastic substrate. The rate of color change is varied by the chemical composition of the polyacrylate. This multilayer structure time–temperature indicator can be easily made by knife coater and screen printing. The made indicator should be very useful to monitor freshness of food.

Validation of Thermal Processing Using Time-Temperature Indicators as Process Probes

1.1 Thermal processing Thermal processing is the basis for the majority of the operations of the food industry, with processes such as canning being the basis for large industry sectors. The aim of thermal processing is to reduce the bacterial load in the food to a level that allows it to be safe over the proposed shelf life of the material. In addition, reactions that lead to the creation of acceptable taste and flavour (such as the gelatinisation of starch, the denaturation of proteins, and Maillard reactions) should be promoted, whilst those which lower quality (such as, for example, the loss of vitamins or the creation of carcinogens such as acrylamide) minimised. The practical problem is that the need for process safety is paramount – the damage done to a brand by the need to recall product, or a food poisoning outbreak, is so severe that processes are routinely overdesigned. The result is lowered product quality, which in turn makes the material less attractive to the consumer. The job of the food engineer is to ensure that the quality of the food is maximised while maintaining safety. In part this is an optimisation process and can be highly mathematical [1-3]; however in practice the critical issue is in validating the process. Such validation requires that there is an effective measurement method which can show the level of thermal treatment which the material has received. In some cases, it is possible to measure the temperature-time profile of the food accurately, and thus infer the amount of processing it has received using equations such as:

Development of a microbial time/temperature indicator prototype for monitoring the microbiological quality of chilled foods.

A time/temperature indicator (TTI) system based on the growth and metabolic activity of a Lactobacillus sakei strain was developed for monitoring food quality throughout the chilled-food chain. In the designed system, an irreversible color change of a chemical chromatic indicator (from red to yellow) progressively occurs due to the pH decline that results from microbial growth and metabolism in a selected medium. The relation of the TTI response (color change) to the growth and metabolic activity (glucose consumption, lactic acid production, pH decrease) of L. sakei was studied. In addition, the temperature dependence of the TTI kinetics was investigated isothermally in the range of 0 to 16 degrees C and modeled with a system of differential equations. At all temperatures tested, the pH and color changes of the TTI system followed closely the growth of L. sakei, with the endpoint (the time at which a distinct visual color change to the final yellow was observed) of the TTI coinciding with a population level of 10(7) to 10(8) CFU/ml. The endpoint decreased from 27 days at 0 degrees C to 2.5 days at 16 degrees C, yielding an activation energy of 97.7 kJ/mol, which was very close to the activation energy of the L. sakei growth rate in the TTI substrate (103.2 kJ/mol). Furthermore, experiments conducted on the effect of the inoculum level showed a negative linear relationship between the level of L. sakei inoculated in the system medium and the endpoint of the TTI. For example, the endpoint at 8 degrees C ranged from 6 to 2 days for inoculum levels of 10(1) and 10(6) CFU/ml, respectively. This relationship allows the easy adjustment of the TTI endpoint at a certain temperature according to the shelf life of the food product of concern by using an appropriate inoculum level of L. sakei. The microbial TTI prototype developed in the present study could be used as an effective tool for monitoring shelf life during the distribution and storage of food products that are spoiled primarily by lactic acid bacteria or other bacteria exhibiting similar kinetic responses and spoilage potentials. Apart from the low cost, the main advantage of the proposed TTI is that its response closely matches the loss of the quality of a food product by simulating the microbial spoilage process in particular environments.

Development and characterization of a new amylase type time–temperature indicator

Time–temperature indicators (TTIs) are effective on realization of cold chain throughout food processing and distribution. In this paper, a new amylase type TTI based on the reaction between amylase and starch was developed. Four amylase type TTIs were made in four different substrate concentrations. The mathematical models of each TTI were drawn up, which showed the relationships between the changes of indicator’s color and time and temperature. The activation energies ( E a), which were 109.63, 114.59, 112.98 and 102.74 kJ/mol of each TTI, could be changed to match the E a of food product, by modifying the proportion of the amylase and starch. The results present that this new amylase type TTI could be applied to show the time–temperature history of foodstuffs, and to indicate the food quality, which is associated with the undergoing of the time–temperature exposure.

Thermal Inactivation kinetics of acid phosphatase (ACP) in cod (Gadus morhua)

Thermal inactivation of acid phosphatase (ACP) in muscle extracts of farmed cod was measured in the range of 55–67.5 °C obtaining D60=6.78±0.10 min and z=6.37±0.09 °C. These data show that ACP is less thermo-stable than heat-resistant pathogen micro-organisms (e.g. Listeria monocytogenes) and therefore could be inactivated in heat-preserved fish products. As a consequence, residual ACP activity is not recommended as a quantitative intrinsic time temperature indicator (TTI) relative to pathogenic micro-organisms, based on these preliminary studies. Hence, ACP residual activity is probably not a shelf life limiting factor of cod products but might have its potential as an indirect monitor of quality parameters during thermal processing.

Advances in vaccine stability monitoring technology

Electronic time–temperature indicator (eTTI) monitors can be programmed to exactly follow the stability characteristics of vaccines with a high degree of realism. The monitors have a visual output, enabling vaccine status to be assessed at a glance, and can also output more detailed statistical data. When packaged with vaccine vials in groups of about 10 vials per box, the eTTI can remain with a vaccine throughout most of the vaccine's lifetime. The monitors can detect essentially all cold-chain breaks, and can detect issues, such as inadvertent freezing, that are presently not detected by other vaccine stability monitors such as Vaccine Vial Monitors (VVM).

Past, current and potential utilisation of active and intelligent packaging systems for meat and muscle-based products: A review

Interest in the use of active and intelligent packaging systems for meat and meat products has increased in recent years. Active packaging refers to the incorporation of additives into packaging systems with the aim of maintaining or extending meat product quality and shelf-life. Active packaging systems discussed include oxygen scavengers, carbon dioxide scavengers and emitters, moisture control agents and anti-microbial packaging technologies. Intelligent packaging systems are those that monitor the condition of packaged foods to give information regarding the quality of the packaged food during transport and storage. The potential of sensor technologies, indicators (including integrity, freshness and time-temperature (TTI) indicators) and radio frequency identification (RFID) are evaluated for potential use in meat and meat products. Recognition of the benefits of active and intelligent packaging technologies by the food industry, development of economically viable packaging systems and increased consumer acceptance is necessary for commercial realisation of these packaging technologies.

Kinetic study of a purified anionic peroxidase isolated from Eupatorium odoratum and its novel application as time temperature indicator for food materials

An anionic peroxidase isoenzyme having a pI of 3.5 was purified from Eupatorium odoratum, commonly called, ‘siam weed’, belonging to family, Asteraceae. The molecular weight of the enzyme was identified as 55kD. The specific activity of the crude extract was increased to 647U/mg from 62U/mg by ammonium sulfate precipitation. The enzyme was 114-fold purified by ion exchange chromatography and had a specific activity of 7094IU/mg. The specificity constant (kcat/Km) of the isozyme was 8.75×105s−1M−1 with ABTS and 6.9×105s−1M−1 with H2O2 as substrates. The enzyme was found to be very stable at room temperature (30±2°C) and retained more than 90% activity even after a period of 2months and was stable for more than 6months at 4±1°C without any additive, stabilizer or preservative. The activation energy for inactivation (Ea) of the isozyme was 120.14kJmol−1 and the half-life was found to be around 34h at 50°C. The purified Eupatorium peroxidase has an optimum pH of 4.5 and optimum temperature of 55°C. This isozyme was stable in metal ionic solutions and showed increased activity in presence of Hg2+, K+ and Ca2+. The enzyme can also be used as a low cost time-temperature indicator strip for which the preliminary works have already been carried out satisfactorily.

Microbiological aspects of thermally processed foods

The knowledge requirements of the food microbiologist working with thermally processed products are very challenging; particularly in relation to minimally processed foods. In the past, the minimum criteria for sterilized canned foods was very well-defined, however, the diversity of food products, packages and related heat processes are now very difficult to summarize in terms of minimum requirements. The overall heating characteristics of these products can be complex, particularly for mixed particulate products or multicompartment packages. Similarly, the death kinetics of the contaminating micro-organisms can be markedly different dependent on the composition of the food product. These factors combined with the consumer demands for 'fresher' foods has resulted in product, process and package development and innovation progressing at a much faster rate than in the past. While food safety is the most important factor, there are also other issues such as shelf-life and visual quality that have strong market influences and must therefore also be considered by the microbiologist.

Intelligent Packaging: Concepts and Applications

ABSTRACT: Intelligent packaging is an emerging technology that uses the communication function of the package to facilitate decision making to achieve the benefits of enhanced food quality and safety. In this paper, the term intelligent packaging is defined based on a proposed model of packaging functions, which is consistent with the historical development of food packaging. A conceptual framework is also developed to provide more precise meaning to the definition and to elucidate the anatomy of the intelligent packaging system. The latest advances in smart package devices including barcode labels, radio frequency identification tags, time-temperature indicators, gas indicators, and biosensors are reviewed. The applications of the conceptual framework to Hazard Analysis Critical Control Points and microwave ovens are illustrated. A research roadmap for intelligent packaging is also suggested.

The impact of pressure, temperature and treatment time on starches: pressure-induced starch gelatinisation as pressure time temperature indicator for high hydrostatic pressure processing

The applicability of pressure-induced starch gelatinisation as a pressure time temperature indicator (PTTI) was investigated by examining the impact of pressure, temperature and treatment time on starches of A-type, B-type and C-type crystallinity. Pressure-induced starch gelatinisation was highly sensitive to changes of temperature, pressure and treatment time. At constant temperature and treatment time, the degree of gelatinisation increased with increasing pressure. The higher the temperature, the lower was the pressure of complete gelatinisation at the temperatures investigated. At constant temperature and pressure, the degree of gelatinisation increased with increasing treatment time. However, the degree of gelatinisation of potato starch suspensions remained unchanged after treatments above 60 min. The velocity rate of gelatinisation increased, the higher the constant pressure, indicating that pressure-induced gelatinisation is a time-dependant process. Hence, an application of starches as PTTIs seems possible. However, the starches have to be carefully selected regarding maximum gelatinisation at the temperature and treatment time applied in the high hydrostatic pressure process that reflects the pressure range desirable for processing.

Formation kinetics and application of 5-hydroxymethylfurfural as a time–temperature indicator of lethality for continuous pasteurization of apple cider

The formation kinetics for HMF were determined to validate the total lethality of a continuous flow microwave pasteurization system for apple cider. Kinetics parameters for the formation of 5-hydroxymethyl furfural (HMF) were determined for a model apple cider solution (10 °brix and pH of 3.8) at 25, 40, 60, and 80 °C and asparagine concentrations of 5 and 10 mM using a bioreactor with temperature and pH control. The kinetics for HMF formation was shown to follow an apparent zero-order reaction with an activation energy of 27.3 kJ/mol. These kinetic parameters were then used to estimate the formation of HMF concentrations in apple cider based on time–temperature profiles needed to achieve a 5-log reduction of Escherichia coli 0157:H7. Calculated HMF formation, 1.56 ppm for the microwave pasteurization system and 1.19 ppm for the conventional system, compared well with measured HMF formation, 1.57 ppm for the microwave pasteurization system and 1.2 ppm for the conventional pasteurization system.