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Home , Food packaging, Shelf life

Considerations for the Application of Time-

Integrators in Distribution

by

Bin Fu Graduate Assistant Department of and University of Minnesota St. Paul, MN

Theodore P, Labuza Professor Department of Food Science and Nutrition University of Minnesota St. Paul, MN

Introduction the maximum temperature was 59.7 -62°F and 4- 16 percent of their products exceeded 55°F during Today, consumers demand safe, natural, distribution. That led Kraft to install its own healthy and convenient food products. Fresh and/ cooler cases at retailer locations (36 ~ 4°F) for or minimally-processed using controlled/ their CAP/MAP line (Rice, 1989). Temperature modified atmospheric packaging (CAP/MAP) with abuse may exist at any point in the perishable are developing rapidly, The safety food distribution chain and jeopardize the product, and of foods depends on ingredient selec- such as loadinghmloading, temperature cycling in tion, control of processing conditions and main- walk-in coolers, storage displays and home trans- tenance of distribution conditions. The current port, The International Institute of Refrigeration U.S. distribution system cannot adequately meet (IIR, 1985) estimated current losses of perishable the requirements for the safety and quality main- foods of at least 10 percent due to physical dam- tenance of extended refrigerated (ESLR) age and inadequate temperature control; and the products. For example, the Fresh Chef line of National Academy of Sciences (NAS, 1987) and the soups and sauces of Campbell Soup reported that 1-16 percent of food losses (l-3% in Co. was pulled out of the market in 1987 due to , 1-4% in products, 10-16% in lack of temperature control and subsequent abuse. fresh produce) occurred during distribution. Culinary Brands used Federal Express to deliver its fresh products to overcome this problem. Legally, food manufacturers are considered Krafi did a survey, the result of which showed responsible for the ultimate quality and product that although the average temperature was 45”F, safety even when they have no control of the

Journal of Food DistributionResearch February 921page9 distribution chain based on the Food, Drug and (1976), Singh and Wells (1985), Taoukis (1989) Cosmetic (FD&C) Act. In addition, loss of qual- and Taoukis et al. (1991). ity leads to loss of sales and thereby loss of profit. A cost effective system to monitor the temperature Among all of those patented, only three conditions of individual products throughout dis- types of non-electronic, individual package ‘ITIs tribution and to indicate their remaining shelf life have ever been commercialized and evaluated and any potentially unsafe condition would be the extensively. l’TI type I is the 3M Monitor use of time-temperature integrators/indicators Mark~(Manske, 1983). It is based on a time- ~Is). The proper use of a ‘ITI tag could facili- temperature dependent diffusion of a blue dyed tate scheduling of distribution so that products fatty acid ester through a porous wick made of a approaching the end of their shelf life are moved high quality blotting . The measurable first at the warehouse and level; a TIT tag response is the distance of the advancing easily could indicate problem areas in the distribution visible dii%sion front of the blue dye from the system so that they could be resolved; and, by origin, much like reading a thermometer. A replacing and/or complementing open date - scanner could be used to record and calculate the ing at the point of purchase, it could reduce food distance traversed. Before use, the dye/ester waste and ensure that a consistent quality food mixture is separated from the wick by a barrier product reaches the consumer (’Taoukis and film so that no diffusion occurs. To activate the Lubuza, 1989a,b). indicator, the barrier is pulled off and diffusion starts if the temperature is above the melting point This paper will mainly present the kinetic of the ester. The melting point of the fatty acid basis for correlation of TTIs with foods and con- ester used in a particular MonitorMark tag deter- siderations for applying a TTI tag as well as mines its response temperature. MonitorMark several application examples. tags are available with response ranging from -17 “C to 48 “C and maximum run- Time-Temperature Integrators ning time of up to one year (Manske, 1983; 1985). Broadly speaking, a time-temperature inte- grater/indicator is a device or tag that can keep ‘ITI type II is the I-point? l’TI @lixt, track of an accumulated time-temperature distribu- 1983). It is based on a color change caused by a tion fimction to which a perishable product is pH decrease, due to a controlled enzymatic hydro- subjected, from the point of manufacture to the lysis of a substrate. Before activation the display shelf of the retail outlet, or even to the lipase and the lipid substrate are in two separate consumer. The operation of a ‘lTI is based on compartments, one of which has a visible win- mechanical, chemical or enzymatic systems that dow. At activation, the barrier that separates change irreversibly from the time of their activa- them is broken, and substrate are mixed, tion. The rate increases at higher temperatures in the pH drops and the color change starts as shown a manner similar to most chemical reactions. The by the presence of an added pH indicator. The change is usually expressed as a visible response, ‘lTI is triggered with a special activating device in the form of a mechanical deformation, color and can be applied manually or mechanically, development and/or color movement. Technical depending on the packaging line. The color and practical requirements for an ideal TTI have change can be visually recognized and compared been discussed in detail (Renier and Morin, 1962; to a color band surrounding the window (e.g. Sanderson-Walker, 1975; Taoukis, 1989). green-good, yellow-caution, reddon’t use). The change can also be measured continuously using TITs come in various sizes and shapes. an electronic color scanner and compared to an They vary in cost from a few pennies for a TTI internal standard. tag to more than several hundred dollars for an electronic device. A variety of ‘lTIs based on TTI type III is the Lifelines~ Fresh-Scan different physiochemical principles were and Fresh-Check systems (Fields, 1985). It is described by Schoen and Byrne (1972), Byrne based on the solid state polymerization of thinly

February 921page 10 Journal of Food Distribution Research coated colorless acetylenic monomer that changes quality follows either a simple constant rate of to a highly colored opaque . The measur- change at constant temperatures (zero order) or an able change is the reflectance which is measured exponential change (first order) as follows: with a laser optic wand with the information stored in a hand held computer. The indicator tag f(A) = AO- At = Q zero order (2a) has two bar codes, one for identification of the product and the other for identification of the and indicator model. The indicators are active from the time of production and have to be stored in the f(A) = lnAO- lnA, = k# first order (2b) freezer before use. It should be noted that most chemical reac- Another type of ‘IT is a consumer readable tions leading to quality loss in food systems are TI’I or consumer tag. It is a simple circular much more complex. However, the reaction device that reflects the product’s time-temperature kinetics can be simplified into either pseudo-zero history by producing a color change in the inner order or pseudo-first order (Benson, 1960; Frost circle. When the center is darker than the outer and Pearson, 1961; Connors, 1990). In the circle printed color, the product has passed end of of complex reaction kinetics with respect to reac- shelf life. Two types of consumer readable ‘ITIs tants, an intermediate or a final product (e.g. have been studied more extensively (Sherlock et peroxides or hexanal in lipid oxidation) could be al., 1991). used as a quality index,

Kinetic Basis for TTI Applications Sometimes, there is an induction period or lag time (tk~ before the quality deterioration Food Kinetics begins (e.g. amino acid and reducing deple- tion or browning pigment formation in the Usually, a distribution expert considers food Maillard reaction, microbial growth lag), The shelf life as the storage period at 73 “F and 50 length of th depends on many factors, but temper- percent RH for shelf stable foods, 5°F for frozen ature is the predominant factor. Given this, mod- foods and 40”F for refrigerated foods (Labuza, eling of both the induction or lag period and 1982), within which the product remains at an deterioration phase are necessary for accurate acceptable sensory, nutritional and microbial predictiomof quality loss and/or shelf life remain- quality level. However, in real life, variable ing. An example of such work has been demon- distribution and storage conditions may result in strated by Fu et al, (1991). lesser or greater shelf life for a particular food product. With respect to the temperature dependence of the reaction, the rate constant usually follows Loss of shelf life in a food or an individual the Arrhenius relationship, as shown below: ingredient is usually evaluated by the measurement E of a characteristic quality index, “A.” The quality kA = &d exp [-J@#] (3) index for foods includes , color, nutrients level, texture, and sensory quality as well as microbial load and production. The change where k~ is the pre-exponential faCtOr,EA(f@ is of quality index A with time t can usually be the activation energy (temperature sensitivity) of expressed as: the reaction that controls loss, R is the universal gas constant and T is the absolute f(A) = kAt (1) temperature (K), which may be constant or vari- able. ‘I%is says that the rate is an exponential where f(A) is the food quality function and kA is function of absolute temperature. It should be the rate constant for the food quality loss reaction. noted that the rate constant may be modeled by The form of a food quality function depends on other temperature sensitivity models, such as the the reaction order. In general, the change in square root model for microbial growth

Journal of Food Distribution Research February 921page 11 (Ratkowsky et al., 1982). The QIOapproach is The rate constant for a TTI response also also used sometimes, in which the rate is assumed follows the Arrhenius theory, to be increased by a constant factor, e.g. 2 to 3 times, for every 10°C increase in temperatures. E (7) It should be noted that the higher the temperature k, = kO,exp[-+#] sensitivity (Ed of the reaction, the faster the reaction goes when temperature is increased. where kl, kol and EAmlJare the rate constant, tie The change of a food quality function f(A), pre-exponential factor and the activation energy of for a known variable temperature exposure, T(t), TTIs, respectively. can be calculated through Eqs. (1) and (3) where: Table 1 summarizes the kinetic results of the three types of TTI and consumer tags studied by Taoukis and Labuza (1989a) and Sherlock et al. (1991). As noted, the EAWOvalues of tie indicators cover the range of the most important deteriorative reactions in foods. Wells and Singh The integral can be calculated analytically for (1988b) found similar activation energies for the simple T(t) fimctions or numerically for more tags they studied. complex ones, such as a sine wave temperature function. The concept of an effective temperature For an indicator exposed to the same vari- (Te~~)is also introduced to calculate the quality able temperature distribution, T(t), as the food change under a variable time-temperature condi- product, the response function can be expressed tion. T.~~is defined as the constant temperature by the following equations: that results in the same quality change as the variable temperature distribution over the same time period. Thus, f(A)t can be expressed as: j(X)t=fk#t = (8)

‘ITI Kbetics With the concept of an effective temperature, then: The same kinetic approach can be used to model the measurable change, x, of TTIs. Simi- larly, a l’TI response function f(x) can be defined (9) as:

f(x) = k,t (6) TINIS, Te~~mOcan be calculated from tie nI response: where k, is the rate constant for the lTI response.

EA(miR Different forms off(x) for each type of TTI T (lo) are shown in Table 1. It can be seen that TTI Mm = ln[kO,t/fix)] type I and the consumer tags follow a pseudo-zero order and type III follows pseudo-first order kinet- ics. TTI type 11 is a complex one, which was modeled by a first order kinetics by Wells and Singh (1988a).

February 921page 12 Journal of Food Distribution Research Table 1. Kinetics Parameters for Several ‘ITIs

Type Model f(x)* k (k;:~ol)

I 4P x’ 9.8 2.03x 108mm2/hr IL 4021 [lnl/(1-x)]”2 33.7 6.70x 10Zhr-l 11~ 4007 [lnl/(1-x)]”2 32.7 2.62x 10nhr-1 11~ 18 ln(x~x) 27.0 1.63x101%r-1 111~ 41 ln(x~x) 20.5 2.57x 1013hr-1 1110 68 ln(xO/x) 19.7 9.42x 101%r-1 Consumer tags A20 X. - x, 19.4 2.63x 101%.mits/hr A40 X. - x, 19.5 9.68x 101%nits/hr 3014 X. - x’ 11.4 5.40x 10%nits/hr 4014 X. - x’ 24.3 5. 80x101%nits/hr

* f(x) form for type 11was derived from Gaussian function (Taoukis, 1989).

Figure 1

Correlation Scheme of TIT With Food

? I ‘————————— Shelf life

v T I lTI kinetics baa

Assumption v ~1, Teff(~) = TeMfood)

Joumsl of Food Distribution Research Febrwy 92/page 13 Correlation of Food Shelf Life modes will occur in the same product at the same With ‘lTI Response time with equal importance. It is worthwhile to note that the mode or mechanism for food deterio- A kinetically based correlation scheme has ration may change, depending on the process been developed by Taoukis and Labuza (1989a) to treatments, package used, and storage and allow prediction of the shelf life of a product environmental conditions. The food processor based on the lTI response. The simplified form and/or distributor must know their products very is shown in Figure 1. well and must know the effects of various storage conditions on quality and shelf life. From the measured response of the tag and the tag kinetics (left side of the scheme), one can (2) Quality index: Generally, single chemi- predict an effective temperature for a variable cal indices are preferable as they can usually be time-temperature distribution. This value is then measured more easily and accurately. For exam- used on the right side of the scheme, with the ple, the criteria for selecting an appropriate qual- food kinetics, to predict the quality loss or shelf ity index out of the volatile components compris- life remaining. This scheme assumes that the ing a food flavor could be based either on their effective temperature response of the tag is equal importance to the organoleptic quality of the to that of the food, In many cases this may not be flavor or on their relative prominence and ease of true since it also assumes that the activation ener- quantitation and kinetic characterization. Thus, gies of the food and tag are equal. This can then one could follow the decrease of an important lead to large prediction errors (Taoukis et al., desirable component (e.g. citral) or the increase of 1990). Thus, there is a need to have a tag with a a developing off flavor (e.g. p-cymene). The temperature sensitivity close to that of the reaction initial level of a quality attribute (and its variation) resulting in quality loss. in a food must be known for modeling purposes. The final level (~) corresponding to the end of Considerations for Applying a TTI shelf life of a product is determined by legal requirements, consumer preference and/or market- Successful application of a TTI depends ing requirements as well as cost. The error in upon many factors, such as the knowledge of the food quality measurement becomes more impor- food product, the type of monitoring required and tant when the measured change causing shelf life the potential benefits as well as relative costs and is small (Benson, 1960). Improvement in analyti- reliability of the system at the temperatures to be cal procedures and better understanding of food encountered. In more detail, the following points quality factors as related to their organoleptic have to be considered when employing a TTI: characteristics, defined by sensory evaluation, may minimize this error. For some products, (1) Deterioration mode: In general, foods such as fresh shrimp, the shelf life differs depend- deteriorate through several modes: (i) biological ing on the quality of either ‘prime’ or ‘mediocre’ respiration, e.g. fresh fruits and vegetables; (ii) grade (Haard, 1991). To meet these require- microbial growth, e.g. many semi-processed and ments, the TIT may have to have multi-end points unprocessed food products; (iii) enzymatic degra- or multi-grade makers on a continuous scale. dation, e.g. polyphenol oxidase, peroxidase, lipoxidase and lipase in some raw and semi-pro- (3) Kinetic study: After determining the cessed products; (iv) chemical degradation, which critical deterioration mode of a and includes nutrient loss (e.g. C), color its limit quality index. A kinetic experimental change, lipid oxidation, non-enzymatic browning, study needs to be done to determine the order, flavor (loss or generation); (v) physical degrada- rate constant and temperature sensitivity. Data for tion, e.g. staling or hardening of bread, softening some foods may be found in the literature, such as of a cereal product, melting of a chocolate bar, the book “Shelf Life Dating of Foods” by Labuza package ice in a frozen product, cracking of a (1982). Methodology for “Accelerated Shelf Life textured product, and caking of a cake mix; and Testing” (ASLT) may be used in collecting the (vi) a combination of the above. Usually several

February 921page 14 Journal of Food Distribution Research kinetic data of foods experimentally (Labuza and pared foods, and fresh prepared sous vide meals Schmidl, 1985). by several different companies (Fields, 1991).

(4) TTI reliability, applicability and cost: Current applications are few but important Just like everything else, a TI’I has its own prob- in that they demonstrate the TIT potential as well lems and limitations. The reliability for ‘ITI as highlight the area of existing problems that applications includes its variability in responses need to be solved for wider application or other within the temperature range encountered, the types of applications to be successful. As a matter confidence on the determined kinetic parameters of fact, TT’Iapplications may be extended to other and the difference between EA(f@and EAmo. The products, such as health care products, horticul- applicability problem involves deviations from the tural products, etc. For example, one of the first Arrhenius relationship for both the TTI and food, and most significant applications was the use of the heat transfer problem since a T1’I tag is usu- the diffusion type TTI (3M) by the World Health ally applied on a package surface and does not Organization (WHO) to monitor refrigerated reflect the temperature response in the center of a vaccine shipments (Manske, 1985). load, and the chemical and light sensitivity of TIls. The cost of a ‘IT also depends on the In addition, with the use of ‘lXs, a new quantity required. All of these aspects and their inventory policy has been proposed to replace the potential solutions have been discussed in detail by traditional first-in first-out (FIFO) issue policy, Taoukis et al. (1991). which is called least shelf life first-out (LSFO) (Taoukis and Labuza, 1989a) or shortest-remain- Examplm of TTI Applications ing shelf-life (SRSL) (Wells and Singh, 1989) issue policy. The advantage of this policy is to Evaluations of T’TIs for a variety of food reduce food waste and to provide more consistent products have been done by several researchers quality at time of issue for food items which have (Fields and Prusik, 1986; Wells and Singh, been exposed to fluctuating temperature condi- 1988a,b,c), However, most studies reported in tions. the literature did not use the above kinetic analysis but relied more on correlation. Such a non-kinetic Summary approach is very limited in its application since the results cannot be extrapolated to other temper- The use of ‘ITIs is currently being consid- ature conditions. ered by many manufacturers and the USDA as a means to monitor or predict and shelf Examples of where TTIs have been applied life based on the temperature history of the food. in the past were a chain that used With the principles and methodology discussed in ‘Ills to monitor shipments of perishable refriger- this paper, one should be able to decide whether ated products and for inventory management one should employ a TTI tag for a particular (Mohel, 1988) and a Massachusetts com- food, how to choose a ‘ITI tag properly, how to pany who used the enzymatic based lTI on ship- calculate the effective temperature for a variable ping (Densford, 1983). Another large time-temperature distribution, how to correlate the food company has thoroughly tested the use of ‘ITI response with food quality or shelf life, and lTIs on their refrigerated fresh cut salads and how to calculate the quality loss or shelf life sauces and a large soft company tested them remaining correctly. for their drink lines (Anonymous, 1986). Others (Tyson Foods, Yoplait USA) have used the Acknowledgment system mainly for profiling the temperature during distribution or for trouble-shooting temperature This research was supported in part by 3M control problems (Fields, 1991). Other recent Co., St. Paul, Minn., the Minnesota-South Dakota applications of FreshCheck include fresh prepared Dairy Research Center, and the Minnesota Agri- meals, meat products and cultured dairy products, cultural Experimental Station Project 18-78. refrigerated salads, cream-based dips, fresh pre- University of Minnesota Agricultural Experiment

Journal of Food Distribution Research February 921page 15 Station paper No. . B. Fu was the recipi- spoilage of dairy products with time tem- ent of 1991 Applebaum Scholarship of Food perature indicators. J. Food Sci. 56:1209- Distribution Research Society upon which this 1215. research was based. Haard, N. F. 1991. Extending prime quality of References seafood. Presented at the 1991 Annual Meeting of the Institute of Food Anonymous. 1986. “Smart” : tracking Technologists, Dallas, TX. products and freshness. Modern Materials Handling. 2-5. IIR. 1985. Recommendations for the processing and handling of frozen foods. IntL Inst. Benson, S. W. 1960. l%e Foundations of Chem- Rej?igeration, Paris. ical Kinetics. McGraw-Hill, New York. Labuza, T. P. 1982. ShelfLije Dating of Foods. Blixt, K. G. 1983 The I-poin@ lTM - a versatile Food and Nutrition Press. Westport, CT. biochemical time-temperature integrator, IIR Commission C2 Preprints, Proceedings Labuza, T. P. and Schmidl, M. K. 1985. Accel- 16th Intl. Cong. Refrig. 629-631. erated shelf-life testing of foods. Food Technol. 19(9): 57-62,64. Byrne, C. H. 1976. Temperature indicators--the state of the art. Food Technol. June. 66- Manske, W. J. 1983. The application of con- 68. trolled fluid migration to temperature limit & time temperature integrators. Zntl. Inst. Connors, K. A. Chemical Kinetics: the study of Re@ig. C2 Preprints 16 Intl. Cong. Refrig. reaction rates in solution. VCH Publish- pp. 797-803. ers, Inc. New York. Manske, W. J. 1985. MonitorMark indicators as Densford, L. E. 1983. A capital idea for protect- management tools in the storage and distri- ing perishables. Progressive Grocer, Aug. bution of perishable products. Presented at pp. 17-18. 1985 AICHE meeting, Chicago, 11/10-15.

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